PIWIL4 (HIWI2) is a PIWI-clade Argonaute protein that in the mammalian male germline acts as the nuclear effector of the piRNA pathway. It is loaded with secondary, predominantly transposon-antisense piRNAs generated by PIWIL2-catalysed slicing in cytoplasmic nuage (piP-bodies), then enters the nucleus of fetal prospermatogonia, where it engages nascent transposon transcripts and directs de novo DNA methylation and heterochromatin formation at LINE1 and related elements. Unlike PIWIL1 and PIWIL2, its slicer activity is dispensable. Loss of the mouse ortholog Miwi2 causes transposon derepression and male sterility. PIWIL4 is also broadly expressed in somatic and cancer cells, where it is largely cytoplasmic and binds tRNA-derived small RNAs.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003676 nucleic acid binding | IEA GO_REF:0000002 | MODIFY | Summary: InterPro-based nucleic acid binding. Reason: Correct but too general. PIWIL4 is a PIWI-clade Argonaute whose defining nucleic-acid-binding activity is loading of piRNA guides; piRNA binding is the informative replacement. Proposed replacements: piRNA binding Supporting Evidence: PMID:25038252 Immunoprecipitation of Hiwi2 from MDAMB231 cancer cells enriches for piRNAs that are predominantly derived from processed tRNAs and expressed genes |
| GO:0003723 RNA binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-based RNA binding. Reason: General but correct; PIWIL4 (HIWI2) is a piRNA-binding Argonaute (RNA-binding PAZ/PIWI domains). piRNA binding (GO:0034584) is the more specific MF. Supporting Evidence: PMID:25038252 Immunoprecipitation of Hiwi2 from MDAMB231 cancer cells enriches for piRNAs that are predominantly derived from processed tRNAs and expressed genes |
| GO:0004521 RNA endonuclease activity | IBA GO_REF:0000033 | REMOVE | Summary: Ancestral PIWI slicer activity propagated to PIWIL4. Reason: PIWIL4/MIWI2 is the slicer-incompetent acceptor of the mammalian ping-pong cycle: Miwi2 catalytic-dead mice are fertile with normal secondary piRNA biogenesis, UniProt records no catalytic activity, and a curated NOT annotation exists. The family-level slicer node is right for the clade but the positive assertion contradicts the curated NOT annotation for PIWIL4 and should be removed. Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN008584027 SUPPORTS SOURCE BUT NOT TARGET Argonaute/PIWI slicer node grounded by slicer-competent members (MILI, MIWI, Aub, Ago3); the MIWI2/PIWIL4 lineage acts as a non-slicing nuclear effector. Supporting Evidence: PMID:22020280 Surprisingly, homozygous Miwi2(DAH) mice are fertile, transposon silencing is established normally and no defects in secondary piRNA biogenesis are observed. file:human/PIWIL4/PIWIL4-uniprot.txt In contrast to PIWIL1 and PIWIL2, does not show |
| GO:0004521 RNA endonuclease activity | ISS NOT GO_REF:0000024 | ACCEPT | Summary: NOT RNA endonuclease activity, transferred from mouse MIWI2. Reason: Negated annotation. Consistent with the mouse Miwi2 DAH knock-in (fertile, no silencing defect) and the UniProt statement that PIWIL4, unlike PIWIL1/PIWIL2, shows no endonuclease activity. Strictly, dispensability in vivo is not proof of absent catalysis, but the functional conclusion that PIWIL4 does not act as a slicer is sound. Supporting Evidence: PMID:22020280 Surprisingly, homozygous Miwi2(DAH) mice are fertile, transposon silencing is established normally and no defects in secondary piRNA biogenesis are observed. file:human/PIWIL4/PIWIL4-uniprot.txt In contrast to PIWIL1 and PIWIL2, does not show |
| GO:0005634 nucleus | EXP PMID:25038252 The human Piwi protein Hiwi2 associates with tRNA-derived pi... | ACCEPT | Summary: PIWIL4 is a nuclear PIWI protein. Reason: MIWI2 is the nuclear effector of the mammalian piRNA pathway in fetal prospermatogonia, where it targets nascent transposon transcripts and directs DNA methylation. Somatic human cell data show a mostly cytoplasmic pool, but nuclear localization is the defining site of action. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: PIWIL4 is a nuclear PIWI protein. Reason: MIWI2 is the nuclear effector of the mammalian piRNA pathway in fetal prospermatogonia, where it targets nascent transposon transcripts and directs DNA methylation. Somatic human cell data show a mostly cytoplasmic pool, but nuclear localization is the defining site of action. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0005634 nucleus | IDA PMID:28025795 Possible role of HIWI2 in modulating tight junction proteins... | ACCEPT | Summary: PIWIL4 is a nuclear PIWI protein. Reason: MIWI2 is the nuclear effector of the mammalian piRNA pathway in fetal prospermatogonia, where it targets nascent transposon transcripts and directs DNA methylation. Somatic human cell data show a mostly cytoplasmic pool, but nuclear localization is the defining site of action. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: PIWIL4 is a nuclear PIWI protein. Reason: MIWI2 is the nuclear effector of the mammalian piRNA pathway in fetal prospermatogonia, where it targets nascent transposon transcripts and directs DNA methylation. Somatic human cell data show a mostly cytoplasmic pool, but nuclear localization is the defining site of action. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0005634 nucleus | ISS GO_REF:0000024 | ACCEPT | Summary: PIWIL4 is a nuclear PIWI protein. Reason: MIWI2 is the nuclear effector of the mammalian piRNA pathway in fetal prospermatogonia, where it targets nascent transposon transcripts and directs DNA methylation. Somatic human cell data show a mostly cytoplasmic pool, but nuclear localization is the defining site of action. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0005654 nucleoplasm | IDA GO_REF:0000052 | ACCEPT | Summary: Nucleoplasm (HPA immunofluorescence). Reason: Consistent with the nuclear effector role. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0005737 cytoplasm | EXP PMID:15489334 The status, quality, and expansion of the NIH full-length cD... | KEEP AS NON CORE | Summary: Cytoplasmic PIWIL4. Reason: Cytoplasmic PIWIL4 is observed in somatic cancer cells and MIWI2 occupies cytoplasmic piP-body granules before nuclear import, but the effector function is nuclear. Supporting Evidence: PMID:25038252 the bulk of somatic Hiwi2 resides in the cytoplasm |
| GO:0005737 cytoplasm | EXP PMID:25038252 The human Piwi protein Hiwi2 associates with tRNA-derived pi... | KEEP AS NON CORE | Summary: Cytoplasmic PIWIL4. Reason: Cytoplasmic PIWIL4 is observed in somatic cancer cells and MIWI2 occupies cytoplasmic piP-body granules before nuclear import, but the effector function is nuclear. Supporting Evidence: PMID:25038252 the bulk of somatic Hiwi2 resides in the cytoplasm |
| GO:0005737 cytoplasm | IDA PMID:28025795 Possible role of HIWI2 in modulating tight junction proteins... | KEEP AS NON CORE | Summary: Cytoplasmic PIWIL4. Reason: Cytoplasmic PIWIL4 is observed in somatic cancer cells and MIWI2 occupies cytoplasmic piP-body granules before nuclear import, but the effector function is nuclear. Supporting Evidence: PMID:25038252 the bulk of somatic Hiwi2 resides in the cytoplasm |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Cytoplasmic PIWIL4. Reason: Cytoplasmic PIWIL4 is observed in somatic cancer cells and MIWI2 occupies cytoplasmic piP-body granules before nuclear import, but the effector function is nuclear. Supporting Evidence: PMID:25038252 the bulk of somatic Hiwi2 resides in the cytoplasm |
| GO:0005737 cytoplasm | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Cytoplasmic PIWIL4. Reason: Cytoplasmic PIWIL4 is observed in somatic cancer cells and MIWI2 occupies cytoplasmic piP-body granules before nuclear import, but the effector function is nuclear. Supporting Evidence: PMID:25038252 the bulk of somatic Hiwi2 resides in the cytoplasm |
| GO:0007283 spermatogenesis | IBA GO_REF:0000033 | ACCEPT | Summary: Spermatogenesis. Reason: Miwi2-null mice are male-sterile owing to transposon derepression; PIWIL4 variants are associated with human germ cell maturation arrest. Supporting Evidence: PMID:18381894 The loss of MILI (miwi-like) and MIWI2 (mouse piwi 2), two mouse homologs of Drosophila Piwi, activates retrotransposon gene expression |
| GO:0007283 spermatogenesis | ISS GO_REF:0000024 | ACCEPT | Summary: Spermatogenesis. Reason: Miwi2-null mice are male-sterile owing to transposon derepression; PIWIL4 variants are associated with human germ cell maturation arrest. Supporting Evidence: PMID:18381894 The loss of MILI (miwi-like) and MIWI2 (mouse piwi 2), two mouse homologs of Drosophila Piwi, activates retrotransposon gene expression |
| GO:0010669 epithelial structure maintenance | IMP PMID:28025795 Possible role of HIWI2 in modulating tight junction proteins... | KEEP AS NON CORE | Summary: HIWI2 knockdown in RPE cells disrupts tight junctions and honeycomb morphology. Reason: A somatic, single-study knockdown phenotype acting via Akt/GSK3 signaling; peripheral to the germline function and mechanism unclear. Supporting Evidence: PMID:28025795 When HIWI2 was knocked down in retinal pigment epithelial cells, the typical honeycomb morphology was affected. |
| GO:0031047 regulatory ncRNA-mediated gene silencing | IBA GO_REF:0000033 | ACCEPT | Summary: piRNA-guided gene silencing. Reason: PIWIL4 is the piRNA-guided nuclear effector of transposon silencing. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0034584 piRNA binding | IBA GO_REF:0000033 | ACCEPT | Summary: piRNA binding. Reason: Hiwi2 immunoprecipitates bind piRNAs in somatic cells; MIWI2 binds secondary antisense piRNAs in fetal germ cells. Core MF. Supporting Evidence: PMID:25038252 Immunoprecipitation of Hiwi2 from MDAMB231 cancer cells enriches for piRNAs that are predominantly derived from processed tRNAs and expressed genes PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. |
| GO:0034584 piRNA binding | IDA PMID:25038252 The human Piwi protein Hiwi2 associates with tRNA-derived pi... | ACCEPT | Summary: piRNA binding. Reason: Hiwi2 immunoprecipitates bind piRNAs in somatic cells; MIWI2 binds secondary antisense piRNAs in fetal germ cells. Core MF. Supporting Evidence: PMID:25038252 Immunoprecipitation of Hiwi2 from MDAMB231 cancer cells enriches for piRNAs that are predominantly derived from processed tRNAs and expressed genes PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. |
| GO:0034584 piRNA binding | ISS GO_REF:0000024 | ACCEPT | Summary: piRNA binding. Reason: Hiwi2 immunoprecipitates bind piRNAs in somatic cells; MIWI2 binds secondary antisense piRNAs in fetal germ cells. Core MF. Supporting Evidence: PMID:25038252 Immunoprecipitation of Hiwi2 from MDAMB231 cancer cells enriches for piRNAs that are predominantly derived from processed tRNAs and expressed genes PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. |
| GO:0034587 piRNA processing | IBA GO_REF:0000033 | ACCEPT | Summary: piRNA processing. Reason: PIWIL4 is the acceptor of MILI-generated secondary piRNAs; loading and 3 maturation occur on the PIWI protein. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. |
| GO:0043186 P granule | IBA GO_REF:0000033 | ACCEPT | Summary: Nuage (P granule). Reason: MIWI2 resides in piP-bodies, a nuage subtype, in fetal gonocytes. Supporting Evidence: PMID:20011505 The second type of granules, piP-bodies, harbors the MIWI2-TDRD9-MAEL module of the piRNA pathway |
| GO:0043186 P granule | ISS GO_REF:0000024 | ACCEPT | Summary: Nuage (P granule). Reason: MIWI2 resides in piP-bodies, a nuage subtype, in fetal gonocytes. Supporting Evidence: PMID:20011505 The second type of granules, piP-bodies, harbors the MIWI2-TDRD9-MAEL module of the piRNA pathway |
| GO:0071547 piP-body | ISS GO_REF:0000024 | ACCEPT | Summary: piP-body. Reason: piP-bodies are defined by the MIWI2-TDRD9-MAEL module. Supporting Evidence: PMID:20011505 The second type of granules, piP-bodies, harbors the MIWI2-TDRD9-MAEL module of the piRNA pathway |
| GO:0140965 secondary piRNA processing | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Secondary piRNA processing. Reason: PIWIL4/MIWI2 is the recipient of secondary piRNAs produced by MILI slicing; its own catalytic domain is not required. Participation as the loading acceptor is genuine but the processing steps are executed by MILI and the PET complex. Supporting Evidence: PMID:29437694 The putative MIWI2 catalytic domain for slicer activity is not required for secondary piRNA biogenesis and transposon suppression |
| GO:0141005 transposable element silencing by heterochromatin formation | ISS GO_REF:0000024 | ACCEPT | Summary: Transposable element silencing by heterochromatin formation. Reason: Nuclear MIWI2-piRNA complexes recruit silencing machinery to transposon loci. Supporting Evidence: PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. file:human/PIWIL4/PIWIL4-uniprot.txt nucleus and mediates silencing of active transposons: engages with |
| GO:0141196 transposable element silencing by piRNA-mediated DNA methylation | ISS GO_REF:0000024 | ACCEPT | Summary: TE silencing by piRNA-mediated DNA methylation. Reason: Core BP: MIWI2 directs de novo DNA methylation of LINE1/IAP during fetal germline reprogramming. Supporting Evidence: PMID:18381894 The loss of MILI (miwi-like) and MIWI2 (mouse piwi 2), two mouse homologs of Drosophila Piwi, activates retrotransposon gene expression by impairing DNA methylation in the regulatory regions of the retrotransposons. PMID:18922463 MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. |
Loading supporting content…
Download this section (compressed HTML)Q: Does human PIWIL4 execute nuclear transposon DNA methylation in fetal germ cells, and which adaptor (SPOCD1-like) links it to DNMT3?
Q: What is the function of tRNA-derived small RNAs bound to cytoplasmic PIWIL4 in somatic cells?
Experiment: CLIP or proximity ligation of PIWIL4 in human fetal testis or hPGCLCs combined with methylation profiling.
Hypothesis: PIWIL4-piRNA complexes bind nascent LINE1 transcripts in human fetal germ cells.
Type: Nascent-RNA crosslinking
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)