id: B3DH22 gene_symbol: samsn1a product_type: PROTEIN status: COMPLETE taxon: id: NCBITaxon:7955 label: Danio rerio description: samsn1a (SAM domain, SH3 domain and nuclear localization signals 1a) is one of two zebrafish co-orthologs of vertebrate SAMSN1 (HACS1, SLy2, NASH1); its paralog is samsn1b. It encodes an intracellular adaptor of the SLy/SASH1 family with an N-terminal disordered region, a central SH3 domain and a C-terminal SAM domain. In mammals SAMSN1 is expressed mainly in hematopoietic cells, is found in cytoplasm and nucleus, is induced by B-cell activation signals, binds tyrosine-phosphorylated proteins and, through its SH3 domain, the inhibitory receptor PIRB, and acts as an inhibitory adaptor that dampens B-cell activation (mouse knockout B cells are hyper-responsive). The zebrafish protein keeps a highly conserved SH3 domain but is much longer than human SAMSN1 and only 38% identical to samsn1b overall. samsn1a is zygotically expressed; in situ hybridization detects it in blood and macrophages of the early embryo, bulk RNA-seq places it highest in granulocytes, spleen and head kidney, and single-cell studies use it as a marker of retinal bipolar cells. No functional study of the zebrafish gene has been published. existing_annotations: - term: id: GO:0050869 label: negative regulation of B cell activation evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: involved_in supporting_entities: - MGI:MGI:1914992 - PANTHER:PTN002642349 review: summary: Negative regulation of B cell activation, propagated from the SAMSN1 node PTN002642349, whose experimental seed is the mouse Hacs1 (Samsn1) knockout. action: ACCEPT reason: The IBA places the function at a node that contains both zebrafish SAMSN1 co-orthologs. The seed evidence is sound (Hacs1-/- B cells hyper-proliferate on BCR stimulation and show increased tyrosine phosphorylation), and the SH3 domain that mediates the PIRB interaction is 82% identical between samsn1a and human SAMSN1. samsn1a is expressed in blood, macrophages, granulocytes, spleen and head kidney, so there is no expression-based argument that it sits outside immune cells. The function has not been tested in zebrafish; the annotation is accepted as a phylogenetic inference, and the same call is made for samsn1b. supported_by: - reference_id: PMID:19923443 supporting_text: Purified splenic B cells from Hacs1(-/-) mice showed increased cell proliferation on BCR (B-cell receptor) stimulation. - reference_id: PMID:19923443 supporting_text: This study suggests that Hacs1 is an immunoinhibitory adaptor that might be a useful target for immune suppression therapy. - reference_id: file:DANRE/samsn1a/samsn1a-bioinformatics/RESULTS.md supporting_text: The SH3 domain is the best-conserved part of both copies - term: id: GO:1902531 label: regulation of intracellular signal transduction evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: involved_in supporting_entities: - PANTHER:PTN000266438 - UniProtKB:O94885 review: summary: Regulation of intracellular signal transduction, propagated from the SLy/SASH1 family node PTN000266438 (seeded by human SASH1). action: ACCEPT reason: A broad but appropriate process for an SH3-SAM adaptor of the SLy/SASH1 family. The mammalian family members act as intracellular signalling adaptors, and SAMSN1 itself associates with tyrosine-phosphorylated proteins after B-cell receptor stimulation. samsn1a keeps the SH3 and SAM domains that define the family. The term is general, but no more specific process is established across the family. supported_by: - reference_id: PMID:33710696 supporting_text: Intracellular adaptor proteins are indispensable for the transduction of receptor-derived signals, as they recruit and connect essential downstream effectors. - reference_id: PMID:15381729 supporting_text: HACS1 associates with tyrosine-phosphorylated proteins after B cell activation and binds in vitro to the inhibitory molecule paired Ig-like receptor B. core_functions: - description: SH3-SAM intracellular signalling adaptor of the SLy/SASH1 family, expressed in myeloid cells, hematopoietic organs and retinal bipolar cells; by homology with mammalian SAMSN1 an inhibitory adaptor in immune-receptor signalling. No activity has been measured for the zebrafish protein, so no molecular function term is asserted. directly_involved_in: - id: GO:1902531 label: regulation of intracellular signal transduction - id: GO:0050869 label: negative regulation of B cell activation supported_by: - reference_id: PMID:33188360 supporting_text: Here, we describe the interaction between the HACS1 SH3 domain and a sequence near the third immunoreceptor tyrosine-based inhibition motif (ITIM3) of the paired immunoglobulin receptor B (PIRB). - reference_id: PMID:11536050 supporting_text: Immunostaining and cellular fractionation studies localized the HACS1 protein predominantly to the cytoplasm. - reference_id: file:DANRE/samsn1a/samsn1a-bioinformatics/RESULTS.md supporting_text: The SH3 domain is the best-conserved part of both copies references: - id: GO_REF:0000033 title: Annotation inferences using phylogenetic trees findings: [] - id: PMID:11536050 title: HACS1 encodes a novel SH3-SAM adaptor protein differentially expressed in normal and malignant hematopoietic cells. findings: [] reference_review: relevance: HIGH correctness: VERIFIED review_notes: Abstract only; human HACS1 (SAMSN1) cloning, hematopoietic expression, cytoplasmic protein. - id: PMID:11594764 title: Identification of Nash1, a novel protein containing a nuclear localization signal, a sterile alpha motif, and an SH3 domain preferentially expressed in mast cells. findings: [] reference_review: relevance: MEDIUM correctness: VERIFIED review_notes: Abstract only; human NASH1 (SAMSN1) in mast cells, nuclear localization. - id: PMID:15381729 title: The SH3-SAM adaptor HACS1 is up-regulated in B cell activation signaling cascades. findings: [] reference_review: relevance: HIGH correctness: VERIFIED review_notes: Full text; induction in B-cell activation, phosphotyrosine protein association, PIR-B binding, cytoplasmic and nuclear staining. - id: PMID:19923443 title: Enhanced adaptive immunity in mice lacking the immunoinhibitory adaptor Hacs1. findings: [] reference_review: relevance: HIGH correctness: VERIFIED review_notes: Abstract only; mouse knockout, the experimental seed of the B-cell IBA (MGI:1914992). - id: PMID:33188360 title: HACS1 signaling adaptor protein recognizes a motif in the paired immunoglobulin receptor B cytoplasmic domain. findings: [] reference_review: relevance: MEDIUM correctness: VERIFIED review_notes: SH3 domain NMR structure and PIRB ITIM3 binding. - id: PMID:33710696 title: The emerging and diverse roles of the SLy/SASH1-protein family in health and disease-Overview of three multifunctional proteins. findings: [] reference_review: relevance: MEDIUM correctness: VERIFIED review_notes: Abstract only; family review (SASH3, SAMSN1, SASH1). - id: PMID:37988404 title: Single-cell RNA sequencing unravels the transcriptional network underlying zebrafish retina regeneration. findings: [] reference_review: relevance: LOW correctness: VERIFIED review_notes: Zebrafish retina scRNA-seq; samsn1a used as a bipolar-cell marker. - id: PMID:36047082 title: Jag2b-Notch3/1b-mediated neuron-to-glia crosstalk controls retinal gliogenesis. findings: [] reference_review: relevance: LOW correctness: VERIFIED review_notes: Zebrafish retina scRNA-seq; samsn1a listed among bipolar-cell markers. - id: PMID:39325796 title: Single-nuclei transcriptome analysis of channel catfish spleen provides insight into the immunome of an aquaculture-relevant species. findings: [] reference_review: relevance: LOW correctness: VERIFIED review_notes: Channel catfish (not zebrafish) spleen snRNA-seq; samsn1a among myeloid cluster markers. - id: file:DANRE/samsn1a/samsn1a-bioinformatics/RESULTS.md title: samsn1a / samsn1b protein, expression and synteny comparison reference_review: relevance: HIGH correctness: VERIFIED review_notes: Manual audit verified the sidecar supports both teleost SAMSN1 ohnologs retaining the SH3 domain, SAM domain and 14-3-3 motif region; it reports partial expression differences with overlapping hematopoietic calls. findings: [] suggested_questions: - question: Which zebrafish blood cell types express samsn1a and samsn1b (macrophages, neutrophils, B cells, dendritic-like cells), and do the two copies overlap in any of them? - question: Is the retinal expression split between the copies (samsn1a in bipolar cells, samsn1b in photoreceptors and pineal) a zebrafish-specific partition, and is gar SAMSN1 expressed in retina? - question: Does the long N-terminal region shared by the fish and gar proteins but absent from human SAMSN1 carry functional motifs (for example 14-3-3 or phosphotyrosine docking sites)? suggested_experiments: - hypothesis: samsn1a restrains activation of zebrafish B cells or myeloid cells, as Hacs1 does in mouse. description: Generate samsn1a mutants (ideally promoter-less or RNA-less alleles to avoid transcriptional adaptation) alone and with samsn1b; measure adult B-cell responses to immunization and larval macrophage and neutrophil responses to infection or wounding. experiment_type: genetic interaction - hypothesis: samsn1a and samsn1b have complementary cell-type expression. description: Double fluorescent in situ (HCR) or reanalysis of zebrafish single-cell atlases for the two copies in blood, kidney marrow, retina and pineal, with gar SAMSN1 as an outgroup. experiment_type: expression analysis