ACRV1 encodes SP-10, an intra-acrosomal protein of mammalian spermatids and spermatozoa. It is made as a 265-residue precursor with an N-terminal signal peptide, enters the secretory pathway and accumulates in the nascent acrosomal vesicle of Golgi-phase round spermatids; expression is confined to the testis. Structurally it has two parts - a long serine/glutamate/glycine-rich block of three interleaved short repeats that is intrinsically disordered, and a C-terminal Ly-6/uPAR ("three-finger") domain with ten cysteines, the same fold used by CD59, the urokinase receptor and the secreted Ly-6 proteins. Alternative splicing produces at least eleven mRNAs encoding 81-265 residues, all by in-frame deletions inside the repeat block, and intra-acrosomal endoproteolysis - including a trypsin-like activity, possibly acrosin - cleaves the precursor into a ladder of 18-32 kDa peptides during testicular and early epididymal maturation; together these give the heterogeneous SP-10 banding pattern seen on blots of human sperm. In the intact acrosome SP-10 is a hydrophilic peripheral protein of the acrosomal matrix, layered against the inner face of the outer acrosomal membrane and the outer face of the inner acrosomal membrane, and inaccessible from the sperm surface. After the acrosome reaction it remains on the sperm head, concentrated on the inner acrosomal membrane of the equatorial segment, where antibody-blocking experiments implicate it in binding of acrosome-reacted sperm to the oolemma, independently of beta-1 integrins, rather than in binding to the zona pellucida. Mice lacking Acrv1 are nonetheless fertile, with testis appearance, testis histology and sperm motility all examined and reported normal, so the contribution is dispensable at least individually. Because SP-10 is abundant, testis-restricted and displayed only after the acrosome reaction, it has long been used as a marker of acrosome status and staging, and was designated a candidate contraceptive-vaccine antigen.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | MODIFY | Summary: Correct but three levels vaguer than the evidence it was drawn from; modified to acrosomal vesicle. Resolving the WITH/FROM field settles this row. MGI:MGI:104590 is mouse Acrv1, UniProtKB P50289 - the true one-to-one orthologue, not a paralogue. Asking what that donor itself carries for this term (QuickGO, geneProductId=UniProtKB:P50289, goId=GO:0005737, goUsage=descendants) returns five hits, and two of them are the donor's own IDA annotations to GO:0001669 acrosomal vesicle (PMID:1591350, PMID:16093322), with an ISO and an IEA to the same term alongside. GO:0001669 is a confirmed descendant of GO:0005737. So the donor's experimental evidence is specifically acrosomal, and the propagated statement threw that away. Two further facts make the loss of precision gratuitous rather than cautious. First, human ACRV1 already carries its own IDA to GO:0001669 from HPA, so as written this row adds nothing. Second, the WITH/FROM list is short - the mouse orthologue, one PANTHER node, and the gene itself - so there is no wide, functionally heterogeneous clade forcing a conservative ancestral term. The qualifier should change with the term. is_active_in asserts the protein is active where it sits, which presupposes a molecular activity ACRV1 does not have; the two existing GO:0001669 rows both use located_in, and the replacement should match them. This is a recommendation, not an aside: the proposed annotation is located_in GO:0001669, not is_active_in GO:0001669. Hence MODIFY rather than REMOVE: the assertion is true, the propagation machinery worked, and the constructive fix is to state what the donor's IDA states. Reason: The sole protein donor in WITH/FROM, mouse Acrv1 (P50289), carries two IDA annotations to GO:0001669 acrosomal vesicle, a descendant of GO:0005737; the human gene has its own IDA to the same specific term. Replacing the vague ancestor with the term the evidence supports, and with it the qualifier: the replacement should be located_in GO:0001669, matching the two existing rows for that term, rather than is_active_in, which presupposes a molecular activity ACRV1 has not been shown to have. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: MGI:MGI:104590 · mouse Acrv1 (UniProtKB P50289, ASPX_MOUSE) SUPPORTS TRANSFER True orthologue, resolved through UniProt xref:mgi-104590 using the bare numeric id (the doubled MGI:MGI: form returns HTTP 400). It carries its own IDA annotations to GO:0001669 acrosomal vesicle from PMID:1591350 and PMID:16093322, so it supports a far more specific term than the one propagated. PANTHER:PTN008565525 · PANTHER internal tree node in PTHR17571 SUPPORTS TRANSFER An ancestral tree node, not a protein. PTHR17571 contains no other reviewed human member, so a functionally heterogeneous clade cannot be the reason a broad ancestral term was chosen. The remaining explanation may be pipeline policy rather than curator judgement - PAN-GO annotates from a deliberately restricted term set - in which case the TERM_SCOPING_PROBLEM root cause describes where the annotation sits relative to its evidence, not a mistake by the curator. Either way the specific term is the one the evidence supports, which is why this is put to GO Central as a question. UniProtKB:P26436 · human ACRV1 (the gene being annotated) SUPPORTS TRANSFER Self-referential token. In PAN-GO WITH/FROM this records the curator treating the human protein as an annotated member of the node rather than a circular inference, so it is not a defect; it simply adds no independent support. Proposed replacements: acrosomal vesicle Supporting Evidence: file:human/ACRV1/ACRV1-uniprot.txt CC -!- SUBCELLULAR LOCATION: Cytoplasmic vesicle, secretory vesicle, acrosome. PMID:2310816 Light and electron microscopic immunocytochemistry localized SP-10 throughout the acrosome, and electron microscopic evidence demonstrated a bilaminar array in association with the inner aspect of the outer acrosomal membrane and the outer aspect of the inner acrosomal membrane. |
| GO:0031982 vesicle | IBA GO_REF:0000033 | MODIFY | Summary: Same propagation as the cytoplasm row, same conclusion: modify to acrosomal vesicle. This is the second of the two PAN-GO annotations for ACRV1, from the identical WITH/FROM triple. GO:0001669 acrosomal vesicle is a descendant of GO:0031982 as well as of GO:0005737 (both appear in the QuickGO ancestor list for GO:0001669), and the same QuickGO query against the mouse donor P50289 restricted to descendants of GO:0031982 returns the same two IDA annotations to GO:0001669. There is nothing wrong with the inference; ACRV1 genuinely is a vesicle protein. But "vesicle" for a protein whose compartment has been established by electron-microscopic immunocytochemistry in human sperm since 1990 is an under-annotation, and the specific term is already present on the same gene with better evidence. Modified for the same reason as the previous row. Reason: Redundant, less precise ancestor of GO:0001669, which the same WITH/FROM donor supports by IDA and which is already annotated to human ACRV1 by IDA. As on the cytoplasm row, the proposed replacement is located_in GO:0001669 rather than is_active_in. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: MGI:MGI:104590 · mouse Acrv1 (UniProtKB P50289, ASPX_MOUSE) SUPPORTS TRANSFER Orthologous donor whose own evidence for anything under GO:0031982 is two IDA annotations to GO:0001669 acrosomal vesicle, so it licenses the specific term rather than this one. PANTHER:PTN008565525 · PANTHER internal tree node in PTHR17571 SUPPORTS TRANSFER Internal node identifier rather than a gene product; reported as such rather than as unresolvable. UniProtKB:P26436 · human ACRV1 (the gene being annotated) SUPPORTS TRANSFER Self-reference; valid in PAN-GO but contributes no evidence beyond the annotation itself. Proposed replacements: acrosomal vesicle Supporting Evidence: file:human/ACRV1/ACRV1-uniprot.txt CC Note=Nascent acrosomal vesicle of Golgi phase spermatids. PMID:7888499 After a follicular fluid-induced acrosome reaction, SP-10 was detected on the inner acrosomal membrane in the equatorial segment and was associated with hybrid vesicles. |
| GO:0001669 acrosomal vesicle | IEA GO_REF:0000044 | ACCEPT | Summary: Accepted. This is the keyword pipeline working exactly as intended. GO_REF:0000044 maps UniProt subcellular-location vocabulary terms to GO, and here it maps SL-0007 (acrosome) from the UniProt line "Cytoplasmic vesicle, secretory vesicle, acrosome". The mapping is faithful and the underlying UniProt statement is itself well founded: SP-10 has been localised to the acrosome of human spermatids and spermatozoa by light and electron microscopic immunocytochemistry since 1990, and the same conclusion is reached independently by the HPA immunofluorescence annotation on this gene and by two IDA annotations on the mouse orthologue. The only reservation is that the human evidence is finer than any keyword can express. Immunogold EM places SP-10 in the acrosomal matrix layered against both acrosomal membranes, and phase partitioning shows it is a peripheral rather than integral membrane protein. GO:0043159 acrosomal matrix and GO:0002079 inner acrosomal membrane are the terms that evidence supports, and neither is annotated. That is an argument for adding annotations, not for changing this one, so it is proposed additively below rather than folded into a MODIFY here. Reason: Faithful mapping of UniProt SL-0007 acrosome, corroborated by independent human IDA (HPA) and by mouse orthologue IDA; the compartment assignment is not in doubt. Supporting Evidence: file:human/ACRV1/ACRV1-uniprot.txt CC -!- SUBCELLULAR LOCATION: Cytoplasmic vesicle, secretory vesicle, acrosome. PMID:2310816 Light and electron microscopic immunocytochemistry localized SP-10 throughout the acrosome, and electron microscopic evidence demonstrated a bilaminar array in association with the inner aspect of the outer acrosomal membrane and the outer aspect of the inner acrosomal membrane. |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | MARK AS OVER ANNOTATED | Summary: Over-annotated. A single yeast two-hybrid screen hit between a lysosomal thioesterase and an intra-acrosomal protein, on opposite sides of a membrane. Partner P50897 is PPT1, palmitoyl-protein thioesterase 1, whose UniProt localisations are lysosome, secreted, Golgi and endoplasmic reticulum and whose function is hydrolysis of palmitoyl thioesters including palmitoylated proteins. Nothing in the PPT1 or the SP-10 literature connects them; PPT1 deficiency causes infantile neuronal ceroid lipofuscinosis, and ACRV1 expression is restricted to testis. The evidence is thinner than the record suggests. Querying IntAct directly for P26436 shows this interaction recorded three times from the one publication - as "two hybrid array", "two hybrid pooling" and "validated two hybrid" - with both partners over-expressed and an MI-score of 0.56. So the NbExp=3 in the UniProt INTERACTION block counts three yeast two-hybrid variants inside a single screen, not three independent methods, and there is no orthogonal confirmation for this pair anywhere in IntAct. There is also a topological problem that applies to all five of these rows. ACRV1 has a signal peptide and resides in the lumen of a secretory organelle, so in a spermatid it is never in the compartment where PPT1's cytosolic face or any cytosolic protein could reach it; the two-hybrid assay expressed a signal-peptide-bearing open reading frame in a yeast nucleus, where that peptide is inert. Add the 166-residue disordered, serine- and glutamate-rich low-complexity region that makes up the middle of ACRV1 - a classic sticky-prey feature - and the set behaves like screen background. Marked as over-annotated rather than removed: a two-hybrid hit is a real observation and may yet mean something, but bare protein binding conveys no function, and this pair does not license a functional claim. Reason: Unreplicated yeast two-hybrid hit from a neurodegeneration-focused screen, recorded three times as three Y2H variants of one experiment; no orthogonal assay, no biological connection to acrosome biology, and the two proteins occupy opposite sides of a membrane in vivo. Supporting Evidence: PMID:32814053 connects ∼5,000 human proteins via ∼30,000 candidate interactions and is generated by systematic yeast two-hybrid interaction screening of ∼500 ND-related proteins PMID:2310816 Immunofluorescence showed that SP-10 was not associated with the surface of acrosome-intact, ejaculated sperm. file:human/ACRV1/ACRV1-bioinformatics/RESULTS.md The 166-residue linker is composed almost entirely of a few residue types (S 18.7%, E 17.5%, G 13.3%, Q 7.8%, A 7.2%, H 7.2%). Knowledge gap: No physiological binding partner of SP-10 inside the acrosome has been identified; the acrosomal-matrix anchor that retains it against detergent extraction is an inferred, uncharacterised entity. OPEN BIOLOGY MF_DARK Resolve: Crosslinking or affinity capture from purified human acrosomal matrix under chaotrope elution, followed by mass spectrometry. "Together the results suggest that SP-10 is a hydrophilic peripheral acrosomal membrane protein that may be associated with a TX-114-resistant "anchor."" — PMID:1591355 |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | MARK AS OVER ANNOTATED | Summary: Over-annotated, on the same grounds as the other four rows from this screen. Partner Q7Z699 is SPRED1, a Sprouty-related EVH1-domain protein that suppresses growth-factor-driven MAP kinase signalling and localises to the cell membrane, caveolae and nucleus. SPRED1 loss causes Legius syndrome; it has no reported role in spermatogenesis or fertilisation, and no SP-10 paper mentions RAS/MAPK signalling. As a membrane-associated cytoplasmic adaptor it is also on the wrong side of the acrosomal membrane from SP-10. IntAct records this pair only from PMID:32814053, again under the three two-hybrid method labels with both partners over-expressed, MI-score 0.56. No co-immunoprecipitation, no co-localisation, no reciprocal pulldown. This is the pattern the curation guidelines warn about: bare protein binding tells us nothing about activity, and there is no informative term to modify it to, because the interaction itself is unsupported beyond one screen. Marked over-annotated. Reason: Single-screen Y2H hit with a cytoplasmic MAPK-pathway suppressor; no orthogonal evidence, no functional or tissue overlap with an intra-acrosomal spermatid protein. Supporting Evidence: PMID:32814053 connects ∼5,000 human proteins via ∼30,000 candidate interactions and is generated by systematic yeast two-hybrid interaction screening of ∼500 ND-related proteins file:human/ACRV1/ACRV1-bioinformatics/RESULTS.md ACRV1's own experimental molecular-function annotations are GO:0005515, of which informative: **none**. |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | MARK AS OVER ANNOTATED | Summary: Over-annotated, and this row has an additional defect worth recording: the partner accession is not the canonical protein it is labelled with. Q86WV8 is an unreviewed TrEMBL entry of 366 residues, submitted from cDNA clone AAH47772 under the name "Tuberous sclerosis 1". Canonical human TSC1 is Q92574, 1164 residues. So the interaction is with a partial ORFeome clone covering less than a third of TSC1, and the IntAct alias field records it as clone CCSB_14153 - a Center for Cancer Systems Biology ORFeome construct. Whatever the two-hybrid signal represents, it is not an interaction with full-length TSC1, and the GOA row inherits an accession that no other TSC1 annotation uses. The generic objections apply as well: recorded only from PMID:32814053 under the three two-hybrid method labels with both partners over-expressed, MI-score 0.56; TSC1 is a cytosolic component of the TSC1-TSC2 complex regulating mTORC1, with no reported acrosomal or spermatid role; and ACRV1 is lumenal, so the pair cannot meet in vivo. Marked over-annotated rather than removed - the observation stands, but neither its interpretation nor even its partner identity is secure. Reason: Y2H hit from one screen, and the WITH/FROM accession Q86WV8 is an unreviewed 366-residue TrEMBL fragment rather than canonical TSC1 (Q92574, 1164 aa), so the partner identity in the record is itself a partial clone. Supporting Evidence: PMID:32814053 connects ∼5,000 human proteins via ∼30,000 candidate interactions and is generated by systematic yeast two-hybrid interaction screening of ∼500 ND-related proteins |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | MARK AS OVER ANNOTATED | Summary: Over-annotated. Partner Q8N5K1 is CISD2 (NAF-1), an iron-sulfur protein of the endoplasmic reticulum and mitochondrial outer membranes that antagonises BECN1-dependent autophagy and whose loss causes Wolfram syndrome 2. Both of CISD2's membranes present its functional domain to the cytosol, and ACRV1 sits in the lumen of a secretory vesicle, so the two are separated by a bilayer wherever they are co-expressed. There is no autophagy or mitochondrial thread anywhere in the SP-10 literature, and no acrosomal thread in the CISD2 literature. Evidentially this row is identical to the other four: IntAct holds it only from PMID:32814053, three times under "two hybrid array", "two hybrid pooling" and "validated two hybrid", both partners over-expressed, MI-score 0.56. Marked over-annotated. Reason: Single-screen Y2H hit with an ER/mitochondrial outer-membrane protein whose domain faces the cytosol; no orthogonal support and a compartment mismatch with a secretory-vesicle lumenal protein. Supporting Evidence: PMID:32814053 connects ∼5,000 human proteins via ∼30,000 candidate interactions and is generated by systematic yeast two-hybrid interaction screening of ∼500 ND-related proteins |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | MARK AS OVER ANNOTATED | Summary: Over-annotated. Partner Q9BZ23-2 is a cytoplasmic isoform of PANK2, pantothenate kinase 2, which catalyses the rate-determining step of coenzyme A synthesis. UniProt assigns the mitochondrial location to isoform 1 only and places the remaining isoforms, this one among them, in the cytoplasm - note that the accession suffix and the isoform name do not run in step, Q9BZ23-2 being UniProt's named isoform 3. A pantothenate kinase and an acrosomal matrix protein have no shared pathway, no shared compartment and no shared literature. PANK2 mutations cause pantothenate kinase-associated neurodegeneration, which is presumably why PANK2 was in the bait set of a neurodegeneration-focused interactome screen - the same reason the other four partners are there. That the five partners of ACRV1 form a coherent set only with respect to the screen's disease focus, and not with respect to any biology of ACRV1, is itself informative about their status. IntAct records the pair from PMID:32814053 alone, three times under the three two-hybrid labels, both partners over-expressed, MI-score 0.56. Marked over-annotated. Reason: Single-screen Y2H hit with a cytosolic CoA-biosynthesis enzyme; the five ACRV1 partners cohere only as a neurodegeneration bait panel, not as acrosomal biology, and none has orthogonal support. Supporting Evidence: PMID:32814053 connects ∼5,000 human proteins via ∼30,000 candidate interactions and is generated by systematic yeast two-hybrid interaction screening of ∼500 ND-related proteins file:human/ACRV1/ACRV1-bioinformatics/RESULTS.md its compartment is the lumen of a secretory organelle, topologically separate from the cytosol -- which is why its cytosolic yeast-two-hybrid partners cannot meet it in vivo |
| GO:0001669 acrosomal vesicle | IDA GO_REF:0000052 | ACCEPT | Summary: Accepted, and this is the best-supported annotation on the gene. GO_REF:0000052 records Human Protein Atlas immunofluorescence curation. The call is independently corroborated by three decades of human sperm work: immunocytochemistry on human testis sections localised SP-10 to round spermatids and spermatozoa in the adluminal compartment and, by light and electron microscopy, throughout the acrosome; immunogold EM on epididymal, ejaculated and capacitated human sperm concentrated the label in the equatorial segment; and after the acrosome reaction the protein remains on the inner acrosomal membrane. The mouse orthologue carries two independent IDA annotations to the same term. Kept as core. Given how sparse the rest of the record is, this compartment assignment plus the acrosome-reaction-dependent redistribution is essentially what is known about ACRV1 with confidence, and the finer terms it licenses (acrosomal matrix, inner acrosomal membrane) are proposed additively rather than as replacements. Reason: Immunofluorescence localisation confirmed by independent light- and electron-microscopic immunocytochemistry on human testis and sperm, and by two IDA annotations on the mouse orthologue. Supporting Evidence: PMID:2310816 Immunocytochemistry on testis sections indicated that SP-10 was localized to round spermatids and spermatozoa within the adluminal compartment of the seminiferous epithelium. PMID:7888499 Electron microscopic immunocytochemical observations of epididymal, ejaculated, and capacitated sperm revealed that colloidal gold labeling of SP-10 was most abundant within the principal segment and posterior bulb of the equatorial segment of the acrosome PMID:2310816 After induction of the acrosome reaction with the ionophore A23187, SP-10 remained displayed on the sperm head in association with the inner acrosomal membrane and equatorial segment. |
| GO:0007283 spermatogenesis | NAS PMID:21252238 TDP-43 is a transcriptional repressor: the testis-specific m... | MARK AS OVER ANNOTATED | Summary: Over-annotated. The gene is regulated during spermatogenesis; it has not been shown to participate in it, and the mouse knockout argues that it does not. Read the cited paper and the direction of the relationship inverts. PMID:21252238 is a study of TDP-43, which represses the mouse acrv1 promoter through GTGTGT motifs and is associated with paused RNA polymerase II there in spermatocytes; its conclusion is about TDP-43 regulating acrv1, and it contains no assay of ACRV1 protein function at all. acrv1 is the transcriptional target. The defensible content of that paper for this gene is a statement about expression timing - round-spermatid-specific transcription - which is not a biological-process annotation. NAS is also the weakest available evidence code, so nothing here rests on a curator having read data we cannot see. The independent evidence points the same way. CRISPR knockout of mouse Acrv1 leaves males fertile, with litter sizes indistinguishable from wild type; testis appearance, testis histology and sperm motility were examined for all twelve knockouts in that study and only Gm17266, not Acrv1, showed an abnormality. The same report notes that immunising male rodents against SP-10 did not arrest spermiogenesis. A protein whose loss perturbs neither the process nor its output is a poor candidate for involved_in that process. Why stop at MARK_AS_OVER_ANNOTATED when the citation is wrong and the null is fertile? Because the two objections attack the evidence, not the proposition. SP-10 is a spermatid-specific product and a constituent of the acrosome, an organelle assembled during spermiogenesis, so a curator with an assembly assay could plausibly earn this term; and a fertile knockout demonstrates dispensability, which is not the same as non-participation. What is established is that the term rests on nothing at present. MARK_AS_OVER_ANNOTATED says exactly that and leaves the term available to better evidence, whereas REMOVE would assert the stronger claim that ACRV1 takes no part in building the acrosome, which no experiment has tested. The sole documented function of ACRV1 is at fertilisation, after spermatogenesis is over, and that role is proposed additively below rather than substituted here, since it is a different process and not a different level of the same one. Reason: The cited reference studies TDP-43 repressing the mouse acrv1 promoter and assays no ACRV1 protein function, so the annotation is an expression-timing statement recast as process participation; Acrv1-null male mice are fertile and anti-SP-10 immunisation does not arrest spermiogenesis. Supporting Evidence: PMID:21252238 our study shows that TDP-43 is a transcriptional repressor and that it regulates spatiotemporal expression of the acrv1 gene during spermatogenesis PMID:38697008 we generated knockout mice for 12 genes (Acrv1, Adgrf3, Atp8b5, Cfap90, Cfap276, Fbxw5, Gm17266, Lrrd1, Mroh7, Nemp1, Spata45, and Trim36) that are expressed predominantly in the testis and examined the appearance and histological morphology of testes, sperm motility, and male fertility. PMID:38697008 We found that the average number of pups sired by each KO male was 7 to 10 pups per litter during the mating period, comparable to the WT control (about 9 pups per litter), suggesting that there was no significant difference between the fecundity of KO and WT males. PMID:38697008 Furthermore, the immunization with anti-human SP-10 antibody in male rodents did not induce the arrest of spermiogenesis (Sehgal et al., 1996). |
| GO:0007342 fusion of sperm to egg plasma membrane involved in single fertilization | IMP PMID:10775167 A monoclonal antibody to human SP-10 inhibits in vitro the b... | NEW | Summary: Proposed as a new annotation. This is the only functional role ever demonstrated for SP-10, and GOA currently carries no fertilisation term for ACRV1 at all. A monoclonal antibody raised against human SP-10 residues 135-149 inhibited binding of human sperm to zona-free hamster oolemma in the sperm penetration assay, while the same antibody did not inhibit sperm-zona binding in the hemizona assay; the authors further excluded beta-1 integrins as the oolemmal ligand using F9 cells and beta-1-null derivatives. The evidence code is IMP: a function-blocking antibody is a specific inhibitor, and the inference runs from a perturbation phenotype (block the protein, watch binding fall) rather than from direct observation of the protein doing anything, which is what IDA requires. GO:0007342 is defined as the binding and fusion of a sperm with the plasma membrane of the oocyte as part of single fertilization, and explicitly covers the binding step, which is what was measured; the localisation fits, since SP-10 becomes displayed on the equatorial segment after the acrosome reaction and the equatorial segment is where oolemma fusion begins. An apparent conflict resolves in favour of the annotation. Anti-SP-10 antibodies reduced bovine in vitro fertilisation by reducing sperm-zona SECONDARY binding, which reads as contradicting the negative hemizona result. It does not: the hemizona assay scores primary binding by acrosome-intact sperm, whereas secondary binding is attachment of the inner acrosomal membrane after the acrosome reaction. SP-10 is inaccessible on acrosome-intact sperm, so a role confined to post-acrosome-reaction steps is consistent with both papers, and the shared conclusion across two species is that SP-10 contributes after the acrosome reaction. One further result in the bovine paper is deliberately not annotated. The same antibodies reduced the ability of capacitated spermatozoa to complete the acrosome reaction, which would suggest GO:0007340 acrosome reaction. Three things argue against taking it: the antibodies are anti-human reagents used on bovine sperm, the same abstract reports that they also reduced the motility of capacitated spermatozoa, so a general effect on capacitated cells is not excluded as the cause, and SP-10 becoming accessible only after the acrosome reaction makes a role in triggering that reaction hard to place mechanistically. The sperm-oolemma result does not share the second problem, because it was obtained on human sperm with a defined-epitope monoclonal in an assay that scores binding rather than progression. The caveat that must travel with this annotation: Acrv1-null male mice are fertile, so the contribution is dispensable, at least when no other acrosomal gene is disrupted. GO annotates participation rather than requirement, so a fertile knockout does not veto the term, but a curator preferring maximum caution could annotate the parent GO:0007338 single fertilization instead, or hold the annotation pending a direct SP-10-oolemma binding assay. The heterologous hamster oolemma is a second, milder caveat. Reason: Antibody inhibition of native human SP-10 blocks sperm-oolemma binding but not sperm-zona binding, with the protein displayed on the equatorial segment of acrosome-reacted sperm; corroborated in a second species by reduced sperm-zona secondary binding and impaired acrosome reaction. No fertilisation term is currently annotated to ACRV1. Supporting Evidence: PMID:10775167 Monoclonal Ab pep-SP10 inhibited sperm-oolemma binding in the zona-free hamster egg penetration test, but it did not inhibit sperm-zona binding in the hemizona assay. PMID:10775167 human SP-10, expressed on the equatorial region of acrosome-reacted sperm, indeed mediates sperm-oolemma binding in a beta(1) integrin-independent manner, but not sperm-zona binding PMID:8882296 SP-10 antibodies exerted their anti-fertilization effect by reducing sperm-zona secondary binding. PMID:8882296 Consistent with the accessibility of the SP-10 antigen following capacitation, SP-10 antibodies also reduced the ability of capacitated spermatozoa to complete the acrosome reaction. PMID:8882296 Furthermore, SP-10 antibodies affected the motility of capacitated spermatozoa, while not affecting the motility of noncapacitated spermatozoa. file:human/ACRV1/ACRV1-deep-research-affinage.md SP-10 expressed on the equatorial region of acrosome-reacted sperm mediates sperm-oolemma binding in a beta-1 integrin-independent manner, but does not mediate sperm-zona binding. Knowledge gap: The oolemmal ligand that SP-10 engages is unidentified; beta-1 integrins have been excluded but no positive candidate has been proposed or tested. OPEN BIOLOGY MF_DARK Resolve: Affinity or crosslinking capture of oolemmal proteins using recombinant SP-10 or its 135-149 epitope region, with validation by loss of sperm binding on ligand-depleted oocytes. "While the molecular characterization of the SP-10 protein has been clarified, little is yet known of its functional role in fertilization." — PMID:10775167 "we demonstrated that the oolemmal ligands of human SP-10 did not include beta(1) integrins, the most promising candidates for oocyte ligands involved in sperm-oolemma binding" — PMID:10775167 |
| GO:0002079 inner acrosomal membrane | IDA PMID:7888499 Human SP-10: acrosomal distribution, processing, and fate af... | NEW | Summary: Proposed as a new annotation. The existing acrosomal vesicle terms cannot express which acrosomal membrane SP-10 sits on, and that detail is the whole basis of the proposed fertilisation role. Three human observations converge. Immunogold electron microscopy on acrosome-reacted sperm detects SP-10 on the inner acrosomal membrane of the equatorial segment; ionophore-induced acrosome reaction leaves it displayed on the sperm head in association with the inner acrosomal membrane and equatorial segment; and in intact sperm the detergent-resistant pool is associated with the acrosomal matrix and the inner acrosomal membrane. GO:0002079 is defined as the acrosomal membrane region underlying the acrosomal vesicle and facing the sperm nucleus, which is the region responsible for the interactions that let sperm reach and fuse with the egg plasma membrane - exactly the location the antibody-blocking result implicates. SP-10 is peripherally associated rather than integral, which is compatible with located_in for a membrane-associated protein and is stated explicitly in the acrosomal matrix annotation alongside this one. Reason: Two independent electron-microscopic immunocytochemical studies of human sperm place SP-10 on the inner acrosomal membrane after the acrosome reaction, and the detergent-resistant pool is associated with that membrane in intact sperm; the compartment is currently annotated only at the level of the whole acrosomal vesicle. Supporting Evidence: PMID:7888499 After a follicular fluid-induced acrosome reaction, SP-10 was detected on the inner acrosomal membrane in the equatorial segment and was associated with hybrid vesicles. PMID:2310816 After induction of the acrosome reaction with the ionophore A23187, SP-10 remained displayed on the sperm head in association with the inner acrosomal membrane and equatorial segment. PMID:1591355 TX-114-resistant SP-10 was associated with the equatorial segment and with TX-114-resistant portions of the acrosomal matrix and the inner acrosomal membrane. |
| GO:0043159 acrosomal matrix | IDA PMID:1591355 Interactions of human sperm acrosomal protein SP-10 with the... | NEW | Summary: Proposed as a new annotation, to record the sub-acrosomal localisation that the existing acrosomal vesicle terms cannot express. Two independent human experiments support it. Triton X-114 phase partitioning of human sperm resolves a detergent-resistant SP-10 pool associated with the acrosomal matrix and the inner acrosomal membrane, and shows both pools to be hydrophilic - so SP-10 is peripheral to, not integral in, the acrosomal membranes; that resistant pool is released by 150 mM sodium thiocyanate or by pH extremes but not by repeated detergent or 1.5 M NaCl, the classic signature of a matrix-associated protein. Independently, electron-microscopic immunocytochemistry places SP-10 in a bilaminar array against the inner face of the outer acrosomal membrane and the outer face of the inner acrosomal membrane, which is the matrix compartment. GO:0043159 acrosomal matrix is defined as the structural framework or dense core at the interior of an acrosome, which is exactly this. Proposed rather than substituted for the existing GO:0001669 rows, since those are separately sourced and correct. Reason: Detergent-resistant, chaotrope-releasable, hydrophilic partitioning of native human sperm SP-10 plus EM immunolocalisation to a bilaminar array between the two acrosomal membranes identify the acrosomal matrix specifically, a term absent from the current record. Supporting Evidence: PMID:1591355 TX-114-resistant SP-10 was associated with the equatorial segment and with TX-114-resistant portions of the acrosomal matrix and the inner acrosomal membrane. PMID:1591355 Together the results suggest that SP-10 is a hydrophilic peripheral acrosomal membrane protein that may be associated with a TX-114-resistant "anchor." PMID:2310816 Light and electron microscopic immunocytochemistry localized SP-10 throughout the acrosome, and electron microscopic evidence demonstrated a bilaminar array in association with the inner aspect of the outer acrosomal membrane and the outer aspect of the inner acrosomal membrane. PMID:38697008 Acrv1 is an evolutionarily conserved gene encoding the sperm protein SP-10, which abundantly exists in the acrosomal matrix and the inner acrosomal membrane in mammals (Reddi, 2023). |
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Download this section (compressed HTML)Q: Should the two PAN-GO annotations for ACRV1 be tightened from cytoplasm and vesicle to acrosomal vesicle? The mouse orthologue that supplies the WITH/FROM evidence carries two IDA annotations to GO:0001669, and the human protein has its own IDA to the same term, so the propagated terms are strictly less precise than their source.
Suggested experts: GO Central / PAN-GO curators
Q: Is the negative hemizona result of PMID:10775167 and the reduced sperm-zona secondary binding of PMID:8882296 reconcilable as primary versus secondary binding, as proposed in this review, or do the two studies genuinely disagree? The answer decides whether GO:0007339 binding of sperm to zona pellucida should also be considered.
Suggested experts: sperm-egg interaction specialists
Q: Given that Acrv1-null male mice are fertile, is the antibody-inhibition evidence for a role in sperm-oolemma binding strong enough to annotate, and if so at what level - GO:0007342 or the more cautious parent GO:0007338?
Suggested experts: GO biological-process curators, reproductive biologists
Q: What is the acrosomal-matrix anchor that retains SP-10 against detergent extraction but releases it with thiocyanate? Identifying it would give ACRV1 its first physiological binding partner.
Suggested experts: acrosome biochemistry laboratories
Q: Does the Ly-6/uPAR domain of SP-10 have a ligand-binding activity analogous to its relatives, or has the fold been repurposed purely as a stable scaffold in a proteolytically hostile compartment?
Suggested experts: three-finger-protein structural biologists
Q: ACRV1 is aberrantly expressed in ovarian cancer, where its knockdown attenuates ZNF280A-driven AKT phosphorylation and glycolysis (PMID:41338461). Should any GO annotation follow from a testis-restricted protein acting in a tissue that never normally expresses it, or is this strictly an ectopic-expression phenotype?
Suggested experts: GO Consortium, cancer biologists
Q: UniProt records eleven splice isoforms but no functional distinction among them. Since all isoforms with measurable abundance retain the complete Ly-6/uPAR domain and differ only in the length of the disordered spacer, is there any evidence that the spacer length is functionally relevant?
Suggested experts: spermatid gene expression laboratories
Experiment: Identify the oolemmal ligand of SP-10. Use recombinant SP-10, its isolated Ly-6/uPAR domain, and the 135-149 epitope peptide as affinity baits against detergent extracts of human or hamster oocyte plasma membrane, with photo-crosslinking to capture low-affinity contacts, and validate hits by testing whether depleting the candidate from the oolemma reduces binding of acrosome-reacted sperm.
Hypothesis: SP-10 displayed on the equatorial segment engages a specific, non-integrin oolemmal protein that mediates the binding step it is required for.
Type: affinity capture and crosslinking
Experiment: Capture the acrosomal-matrix anchor. Crosslink intact human or bovine acrosomes, then elute with 150 mM sodium thiocyanate under the conditions that release the detergent-resistant SP-10 pool, and identify co-eluting proteins by mass spectrometry; compare against a detergent-only elution to separate matrix partners from bulk lumenal content.
Hypothesis: The detergent-resistant, chaotrope-releasable SP-10 pool is held by one or a few specific acrosomal matrix proteins rather than by nonspecific aggregation.
Type: crosslinking mass spectrometry
Experiment: Test redundancy behind the fertile Acrv1-null phenotype. Compare Acrv1-null and wild-type males in competitive and sequential mating, in in vitro fertilisation with zona-intact and zona-free oocytes, and in sperm-oolemma binding assays; then generate combinatorial knockouts of Acrv1 with other acrosomal matrix genes.
Hypothesis: SP-10 makes a real but redundant contribution to sperm-oolemma binding that is revealed only under competition or in vitro, and is masked in a standard fertility test.
Type: mouse genetics and in vitro fertilisation
Experiment: Determine the structure of the SP-10 Ly-6/uPAR domain (residues 185-265) by NMR or crystallography, and map its surface conservation across mammalian orthologues, to ask whether it retains a ligand-binding groove comparable to CD59 or uPAR or presents a featureless scaffold.
Hypothesis: The three-finger fold of SP-10 retains a conserved ligand-binding surface, which would predict a molecular function and identify residues to mutate.
Type: structural biology
Experiment: Ask whether the disordered spacer length matters, by expressing the four abundant isoforms (81-265 residues, differing only in spacer length) in a spermatid or heterologous secretory system and comparing acrosomal targeting, proteolytic processing rate, and matrix association under the detergent and chaotrope fractionation used on native sperm.
Hypothesis: The alternatively spliced spacer tunes proteolytic processing or matrix retention rather than conferring distinct molecular functions.
Type: isoform comparison and cell fractionation
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: ACRV1 has no assignable molecular function. Neither its own experimental record nor its protein family supplies a candidate activity, and the gap is a genuine absence of biochemistry rather than a curation backlog.
OPEN BIOLOGY MF_DARK
What is known: Its compartment, its topology within the acrosome, its proteolytic maturation, its splice-isoform repertoire and its post-acrosome-reaction redistribution are all established by direct experiment on human material.
Significance: SP-10 is one of the most abundant acrosomal proteins and a long-standing contraceptive-vaccine candidate, yet what it does molecularly is unknown, which limits both mechanistic understanding of the equatorial segment and rational vaccine design.
What would resolve it: A binding assay for the LU domain against oolemmal and acrosomal-matrix candidates, plus a structure of the domain, would type the activity; alternatively, a defensible molecular-function term may only become available once the ligand is known.
Provenance (the field's own admissions):
Gap: Why an abundant, conserved, testis-specific acrosomal protein is dispensable for mouse fertility is unresolved; whether the null phenotype is masked by redundancy among acrosomal matrix proteins, or whether SP-10's contribution is only measurable under competitive or in vitro conditions, has not been tested.
OPEN BIOLOGY BP_DARK
What is known: Individual CRISPR disruption of mouse Acrv1 gives litter sizes indistinguishable from wild type, alongside antibody-inhibition evidence in two species that SP-10 contributes to gamete binding.
Significance: The answer determines whether the fertilisation annotation describes a genuine but redundant contribution or an in vitro artefact of antibody blocking, and whether SP-10 is a viable contraceptive target.
What would resolve it: Competitive mating and sequential-mating assays with Acrv1-null males, in vitro fertilisation with zona-intact and zona-free oocytes, and combinatorial knockouts with other acrosomal matrix genes.
Provenance (the field's own admissions):
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