The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The requested identity is internally consistent and supported by the zebrafish literature. A0A8M1NAS7 corresponds to zebrafish elastin b, gene symbol elnb, historically also called eln2, in Danio rerio (formerly Brachydanio rerio). It is the teleost-duplicated paralog distinct from elna/eln1: elnb lies on chromosome 21 in a duplicated genomic neighborhood, whereas elna lies on chromosome 15. Both encode tropoelastins, but Elnb is the more divergent and functionally specialized paralog. No literature on an unrelated same-symbol gene was used. (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 2-4)
The best-supported primary annotation is: Elnb is a secreted, non-enzymatic extracellular-matrix precursor whose cross-linked elastin product supplies elastic compliance to the bulbus arteriosus and also helps specify or stabilize its smooth-muscle identity during development. Its role is therefore both structural and instructive; it is not an enzyme or transporter and has no substrate in the enzymatic sense. (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 8-9)
| Annotation aspect | Best-supported conclusion | Evidence type | Key quantitative result | Principal source/date |
|---|---|---|---|---|
| Identity and paralog | elnb, also called eln2, is the chromosome-21 elastin paralog in Danio rerio and is distinct from elna/eln1 on chromosome 15. The assignment to A0A8M1NAS7 is consistent with the supplied UniProt identity and the literature. | Direct zebrafish genomics | Two teleost elastin paralogs; reported elnb gene structure comprises 59 exons. | Moriyama et al., Jan. 2016; Hoareau et al., Feb. 2022 (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 2-4) |
| Molecular class | Elnb is a divergent, non-enzymatic tropoelastin precursor and structural extracellular-matrix protein with alternating hydrophobic and lysine-containing cross-linking regions. | Direct sequence annotation plus family inference | Predicted protein approximately 173 kDa; about 18% identity and 21% similarity to human tropoelastin. | Hoareau et al., Feb. 2022 (hoareau2022zebrafishasa pages 2-4) |
| Extracellular localization and processing | The precursor is expected to be secreted, deposited onto fibrillin-rich microfibrils, self-associated, and lysyl-oxidase-cross-linked into insoluble elastin. These processing steps are well established for the elastin family but have not all been demonstrated specifically for A0A8M1NAS7. | Family inference | No elnb-specific processing rate or cross-link density reported. | Bhanji/Miao zebrafish elastin work, 2007; Hoareau et al., Feb. 2022 (bhanji2007elastininzebrafish pages 23-29, hoareau2022zebrafishasa pages 2-4) |
| Bulbus arteriosus expression | elnb/eln2 is strongly associated with the developing bulbus arteriosus (BA), where it is the predominant elastin paralog; expression is also reported in the swim bladder during development. | Direct zebrafish expression | BA expression observed at 3–4 days post-fertilization; by 4 dpf, eln2 expression exceeded eln1 in level and extent in the BA and swim bladder. | Miao/Bhanji, 2007; Moriyama et al., Jan. 2016 (moriyama2016evolutionofthe pages 4-4, bhanji2007elastininzebrafish pages 23-29) |
| Developmental function | Elnb helps specify and maintain the smooth-muscle identity of the teleost BA. Loss produces ectopic cardiomyocytes and can cause BA hypoplasia; rescue by elnb, but not elna, supports paralog-specific neofunctionalization. | Direct zebrafish perturbation and rescue | Ectopic BA cardiomyocytes occurred in 67.9% of elnb morphants; elnb mRNA rescued the phenotype dose-dependently. | Moriyama et al., Jan. 2016 (moriyama2016evolutionofthe pages 4-4) |
| Mechanical role | Mature Elnb-rich matrix provides BA compliance and elastic recoil, enabling the BA to act as a Windkessel-like reservoir that smooths pulsatile cardiac output. elnb loss shortens BA contraction duration and reduces deformation. | Direct zebrafish functional assay; comparative physiology | No exact zebrafish deformation values available in the gathered excerpts; comparative teleost BA estimates include about 30-fold greater compliance than mammalian aorta, which should not be treated as a zebrafish-specific value. | Moriyama et al., Jan. 2016; Hoareau et al., Feb. 2022 (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 8-9) |
| TGF-β/Alk5–Fbln5 context | Endothelial TGF-β receptor Alk5 signaling acts upstream of OFT smooth-muscle and elastic-matrix organization. It supports fbln5 expression and uniform Eln2 coverage, but a direct Alk5-to-elnb transcriptional mechanism has not been established. | Direct zebrafish pathway perturbation | Uniform Eln2 surrounded 77.6% of control SMCs and 71.9% after endothelial Alk5 rescue; Fbln5 restoration partially rescued Eln2 coverage and OFT function. | Boezio et al., Sept. 2020 (boezio2020endothelialtgfβsignaling pages 11-13, boezio2020endothelialtgfβsignaling pages 15-16) |
| 2024 single-cell result | elnb, postnb, and fbln5 mark a BA cell cluster interpreted as smooth-muscle-rich. The BA population was more represented at 72 hpf, while proliferation was higher at 48 hpf. | Direct zebrafish scRNA-seq | 52,447 cells from four samples; 34,676 passed quality control; 18 cardiac populations resolved at 48 and 72 hpf. | Nahia et al., June 2024 (nahia2024scrnaseqrevealsthe pages 4-5) |
| Major uncertainty | Direct biochemical characterization of the A0A8M1NAS7 protein remains limited. Its exact mature proteoform, cross-links, binding partners, turnover, and any receptor-mediated signaling activity are mostly inferred from elastin-family biology; morpholino findings should be weighed alongside genetic evidence. | Evidence-gap assessment | No purified-protein substrate, catalytic reaction, or high-resolution structure is reported; Elnb is structural rather than enzymatic. | Moriyama et al., Jan. 2016; Hoareau et al., Feb. 2022 (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 8-9, hoareau2022zebrafishasa pages 2-4) |
Table: This table separates direct zebrafish findings from comparative evidence and elastin-family inference for A0A8M1NAS7. It highlights the strongest functional, localization, pathway, and quantitative evidence while making key uncertainties explicit.
Teleost whole-genome duplication generated two zebrafish elastin paralogs, now termed elna and elnb. Synteny places elna beside limk1a on chromosome 15 and elnb beside limk1b on chromosome 21, providing strong evidence that these are genuine duplicated loci rather than alternative names for one gene. Older publications use eln1/eln2 inconsistently; for this target, the relevant correspondence is Elnb = Eln2. Claims from elna mutants should therefore not be transferred automatically to Elnb. (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 2-4)
The supplied UniProt description—elastin/tropoelastin precursor, elastin family, Tropoelastin domain IPR003979—accords with the literature. The reported zebrafish elnb gene contains 59 exons and predicts an approximately 173-kDa protein. Elnb is unusually divergent: one review reports about 18% amino-acid identity and 21% similarity to human tropoelastin. Nevertheless, it retains the defining elastin architecture of alternating hydrophobic and lysine-rich cross-linking regions, as well as conserved C-terminal features implicated in elastin assembly and cell interaction. (hoareau2022zebrafishasa pages 2-4)
Elnb is a structural extracellular elastomer. Its soluble precursor, tropoelastin, is expected to be secreted and assembled into an insoluble elastic matrix. Hydrophobic sequence segments drive association and provide entropic recoil, whereas lysine-containing segments permit covalent cross-linking. The mature matrix can stretch under systolic pressure, store mechanical energy, and recoil during diastole. This converts pulsatile ventricular output into smoother downstream flow—the Windkessel function of the teleost bulbus arteriosus. (hoareau2022zebrafishasa pages 8-9, hoareau2022zebrafishasa pages 2-4)
Direct biochemical characterization of purified A0A8M1NAS7 is limited. Deposition on fibrillin-rich microfibrils, association with proteins such as fibulin-5, and lysyl-oxidase-mediated conversion into insoluble elastin are strongly supported by general elastin biology and zebrafish elastic-matrix studies, but not every processing step has been demonstrated specifically for this accession. These should therefore be treated as high-confidence family-based inference, not complete protein-specific biochemical validation. (bhanji2007elastininzebrafish pages 23-29, boezio2020endothelialtgfβsignaling pages 11-13, boezio2020endothelialtgfβsignaling pages 15-16)
Elnb has no known catalytic reaction or transported substrate. Its principal molecular output is a compliant extracellular matrix. However, genetic experiments show that its role is not merely passive: Elnb-rich matrix influences whether outflow-tract progenitors acquire smooth-muscle rather than myocardial identity. The likely mechanism is mechanochemical—matrix composition and stiffness alter cellular state—but a specific Elnb receptor or complete downstream signaling chain has not been established in the evidence reviewed here. (moriyama2016evolutionofthe pages 4-4, hoareau2022zebrafishasa pages 8-9)
The precursor enters the secretory pathway and functions outside the cell, ultimately in the extracellular elastic matrix. Its strongest documented site is the bulbus arteriosus (BA), the smooth-muscle-rich chamber immediately downstream of the zebrafish ventricle. Expression is detectable in the developing BA/outflow region at approximately 3–4 days post-fertilization, and Elnb is described as the predominant elastin paralog there. Developmental expression has also been reported in the swim bladder. (moriyama2016evolutionofthe pages 4-4, bhanji2007elastininzebrafish pages 23-29, hoareau2022zebrafishasa pages 8-9)
Recent single-cell evidence sharpens this localization. Nahia and colleagues profiled zebrafish hearts at 48 and 72 hours post-fertilization and identified a BA cluster marked jointly by elnb, postnb, and fbln5, consistent with a smooth-muscle/elastic-matrix-producing population. The BA population was more represented at 72 hpf, whereas its proliferative activity was higher at 48 hpf. This establishes elnb as a useful BA lineage marker but does not prove absolute lineage specificity. (nahia2024scrnaseqrevealsthe pages 4-5)
At the protein level, Eln2 immunostaining forms matrix around outflow-tract smooth-muscle cells. Thus, the most precise localization annotation is secreted extracellular matrix surrounding BA/OFT smooth-muscle cells, rather than cytosol, nucleus, or plasma membrane. (boezio2020endothelialtgfβsignaling pages 11-13)
Moriyama et al. provided the strongest direct functional evidence. elnb depletion or mutation caused cardiomyocytes to appear ectopically in the BA, where smooth-muscle cells normally predominate. Ectopic BA cardiomyocytes occurred in 67.9% of morpholino-treated embryos in the reported experiment and persisted into later life in some animals. Rescue was paralog-specific: elnb mRNA corrected the phenotype dose-dependently, whereas elna mRNA did not. This argues that Elnb acquired a specialized function after teleost genome duplication and that Elna cannot simply substitute for it. (moriyama2016evolutionofthe pages 4-4)
The evidence supports the interpretation that Elnb promotes smooth-muscle fate or suppresses myocardial differentiation in second-heart-field-derived BA precursors. Strong depletion can also produce BA hypoplasia. Thus, Elnb participates in the developmental emergence of a teleost-specific outflow organ, not only in its later mechanics. (hoareau2022zebrafishasa pages 8-9)
Both elastin paralogs contribute to BA deformation, but elnb loss strongly reduces contraction duration and deformation, identifying Elnb as a major determinant of BA elasticity. The mature BA acts as an elastic reservoir that expands during systole and recoils during diastole, reducing pressure fluctuations before blood reaches delicate gill vessels. (moriyama2016evolutionofthe pages 4-4)
Reviews cite teleost BA compliance approximately 30-fold greater than mammalian aorta and an elastin-to-collagen ratio roughly tenfold higher in rainbow trout BA. These values illustrate the organ's unusual material properties but are comparative teleost measurements, not direct quantitative measurements of zebrafish Elnb. (hoareau2022zebrafishasa pages 8-9)
Endothelial TGF-β receptor/Alk5 signaling is upstream of proper OFT smooth-muscle development and elastic-matrix organization. In alk5 mutants, smooth-muscle layers and Eln2 matrix become disorganized. Endothelial Alk5 re-expression restored uniform Eln2 surrounding 71.9% of smooth-muscle cells, close to 77.6% in controls, while also improving OFT morphology and function. These measurements concern Eln2 protein coverage and organization, not necessarily elnb transcription. (boezio2020endothelialtgfβsignaling pages 11-13)
Alk5 loss or inhibition reduces fbln5, encoding fibulin-5, an extracellular assembly factor for elastic laminae. Global or endothelial restoration of fibulin-5 partially rescues Eln2 coverage and OFT function. The defensible pathway model is therefore:
endothelial TGF-β/Alk5 signaling → fibulin-5 and endothelial–matrix organization → proper Elnb-containing elastic matrix and smooth-muscle wall formation.
A direct TGF-β/Alk5-to-elnb transcriptional connection has not been demonstrated. (boezio2020endothelialtgfβsignaling pages 11-13, boezio2020endothelialtgfβsignaling pages 15-16)
Ltbp3 depletion reportedly leaves elnb transcription and proto-Elnb production intact but impairs Elnb maturation or function. This places Ltbp3 at the assembly/maturation level rather than as a simple activator of elnb transcription. Because latent TGF-β-binding proteins can also participate structurally in elastic-fiber assembly, the phenotype should not be interpreted solely as proof of canonical TGF-β signaling through Elnb. (moriyama2016evolutionofthe pages 4-4)
The most informative direct 2024 advance is the peer-reviewed single-cell atlas by Nahia et al., published in iScience in June 2024 (DOI/URL). Four samples initially yielded 52,447 cells; 34,676 passed quality control, resolving 18 cardiac populations at 48 and 72 hpf. The elnb/postnb/fbln5 BA signature independently confirms Elnb's association with developing outflow-tract smooth muscle and supplies a cell-resolved context for future perturbation studies. (nahia2024scrnaseqrevealsthe pages 4-5)
A 2024 review of zebrafish duplicated genes emphasizes elna–elnb as an example of paralog divergence and highlights the elnb-specific rescue results. Its principal contribution is conceptual rather than new biochemical evidence: duplicated zebrafish genes should be annotated separately because one paralog may acquire a lineage- or organ-specific role that the other cannot replace.
No 2023–2024 study retrieved here supersedes the causal evidence from Moriyama et al. The recent literature mainly strengthens cell-type assignment, places Elnb within broader ECM gene programs, and reinforces zebrafish as a model for elastic-fiber and outflow-tract biology.
Elnb is currently most useful as:
There is no evidence that A0A8M1NAS7 itself is a clinical drug target or approved biomarker. Its present implementation is primarily in developmental biology, comparative evolution, disease modeling, microscopy, and genetic or chemical screening.
The functional assignment is strong at the organ and developmental levels but incomplete at the molecular level. Direct zebrafish evidence includes spatial expression, morpholino and genetic perturbation, paralog-specific rescue, functional BA measurements, immunostaining, and recent single-cell transcriptomics. In contrast, exact secretion kinetics, mature cross-link composition, binding partners, turnover, high-resolution structure, and receptor-mediated signaling remain poorly characterized for A0A8M1NAS7 itself. General tropoelastin assembly mechanisms should consequently be labeled as inference from the elastin family. (bhanji2007elastininzebrafish pages 23-29, hoareau2022zebrafishasa pages 2-4)
Morpholino phenotypes can have off-target or persistence-related limitations, but concordance with mutation data and the specific rescue by elnb mRNA substantially strengthens the conclusion. The evidence does not support treating elna and elnb as interchangeable, nor does it support assigning Elnb an enzymatic reaction. (moriyama2016evolutionofthe pages 4-4)
Recommended functional annotation: elnb encodes a secreted tropoelastin precursor that is assembled and covalently cross-linked into the extracellular elastic matrix of the zebrafish bulbus arteriosus. This Elnb-rich matrix provides compliance and elastic recoil for Windkessel-like damping of pulsatile blood flow and supplies a matrix-dependent developmental cue promoting smooth-muscle rather than myocardial identity in the teleost cardiac outflow tract. Its organization is supported by endothelial TGF-β/Alk5–fibulin-5 signaling and other elastic-fiber maturation machinery. (moriyama2016evolutionofthe pages 4-4, boezio2020endothelialtgfβsignaling pages 11-13, boezio2020endothelialtgfβsignaling pages 15-16)
References
(moriyama2016evolutionofthe pages 4-4): Yuuta Moriyama, Fumihiro Ito, Hiroyuki Takeda, Tohru Yano, Masataka Okabe, Shigehiro Kuraku, Fred W. Keeley, and Kazuko Koshiba-Takeuchi. Evolution of the fish heart by sub/neofunctionalization of an elastin gene. Nature Communications, Jan 2016. URL: https://doi.org/10.1038/ncomms10397, doi:10.1038/ncomms10397. This article has 109 citations and is from a highest quality peer-reviewed journal.
(hoareau2022zebrafishasa pages 2-4): Marie Hoareau, Naïma El Kholti, Romain Debret, and Elise Lambert. Zebrafish as a model to study vascular elastic fibers and associated pathologies. International Journal of Molecular Sciences, 23:2102, Feb 2022. URL: https://doi.org/10.3390/ijms23042102, doi:10.3390/ijms23042102. This article has 38 citations.
(hoareau2022zebrafishasa pages 8-9): Marie Hoareau, Naïma El Kholti, Romain Debret, and Elise Lambert. Zebrafish as a model to study vascular elastic fibers and associated pathologies. International Journal of Molecular Sciences, 23:2102, Feb 2022. URL: https://doi.org/10.3390/ijms23042102, doi:10.3390/ijms23042102. This article has 38 citations.
(bhanji2007elastininzebrafish pages 23-29): T Bhanji. Elastin in zebrafish and mice. Unknown journal, 2007.
(boezio2020endothelialtgfβsignaling pages 11-13): Giulia LM Boezio, Anabela Bensimon-Brito, Janett Piesker, Stefan Guenther, Christian SM Helker, and Didier YR Stainier. Endothelial tgf-β signaling instructs smooth muscle cell development in the cardiac outflow tract. eLife, Sep 2020. URL: https://doi.org/10.7554/elife.57603, doi:10.7554/elife.57603. This article has 52 citations and is from a domain leading peer-reviewed journal.
(boezio2020endothelialtgfβsignaling pages 15-16): Giulia LM Boezio, Anabela Bensimon-Brito, Janett Piesker, Stefan Guenther, Christian SM Helker, and Didier YR Stainier. Endothelial tgf-β signaling instructs smooth muscle cell development in the cardiac outflow tract. eLife, Sep 2020. URL: https://doi.org/10.7554/elife.57603, doi:10.7554/elife.57603. This article has 52 citations and is from a domain leading peer-reviewed journal.
(nahia2024scrnaseqrevealsthe pages 4-5): Karim Abu Nahia, Agata Sulej, Maciej Migdał, Natalia Ochocka, Richard Ho, Bożena Kamińska, Marcin Zagorski, and Cecilia Lanny Winata. Scrna-seq reveals the diversity of the developing cardiac cell lineage and molecular players in heart rhythm regulation. Jun 2024. URL: https://doi.org/10.1016/j.isci.2024.110083, doi:10.1016/j.isci.2024.110083. This article has 24 citations and is from a peer-reviewed journal.