| Aspect | Key finding | Species/system | Evidence type | Source (author year journal) | URL | Citation context id |
|---|---|---|---|---|---|---|
| Identity | The target corresponds to zebrafish **Glce-B / glce-b (glceb)**, one of two zebrafish paralogs of the single human **GLCE** gene; zebrafish **Glce-A** and **Glce-B** encode 585-aa proteins with ~67% and ~73% homology to human GLCE, respectively, and both map as orthologous counterparts of human GLCE. | *Danio rerio* embryos/genome comparison | Gene cloning, sequence comparison, chromosomal mapping | Ghiselli & Farber 2005, *BMC Developmental Biology* | https://doi.org/10.1186/1471-213x-5-19 | (pqac-00000000, pqac-00000001) |
| Enzymatic reaction | Glce/GLCE is a **D-glucuronyl C5-epimerase (EC 5.1.3.17)** that catalyzes conversion of **D-glucuronic acid (GlcA) to L-iduronic acid (IdoA)** in heparan sulfate/heparin chains, increasing chain flexibility and ligand-binding capacity. | Zebrafish Glce; vertebrate HS biosynthesis | Biochemical assay, structural biology, review synthesis | Qin et al. 2015, *J Biol Chem*; Li 2010, *Prog Mol Biol Transl Sci* | https://doi.org/10.1074/jbc.m114.602201 ; https://doi.org/10.1016/S1877-1173(10)93004-4 | (pqac-00000003, pqac-00000004, pqac-00000006) |
| Substrate specificity | Substrate recognition requires **N-sulfated glucosamine adjacent to the epimerization site**; Glce recognizes motifs such as **(GlcA-GlcNS)n** and binds/inverts uronic acid within HS precursor chains. O-sulfated heparin-like products behave as inhibitors rather than optimal substrates. | Human/zebrafish GLCE systems; HS/heparin oligosaccharides | Structural biology, biochemical mechanism, review synthesis | Debarnot et al. 2019, *PNAS*; Qin et al. 2015, *J Biol Chem*; Li 2010, *Prog Mol Biol Transl Sci* | https://doi.org/10.1073/pnas.1818333116 ; https://doi.org/10.1074/jbc.m114.602201 ; https://doi.org/10.1016/S1877-1173(10)93004-4 | (pqac-00000003, pqac-00000006) |
| Reversibility / in vivo directionality | The catalytic step is **reversible in vitro** (GlcA ↔ IdoA), but HS biosynthesis appears effectively **irreversible in vivo**, because subsequent O-sulfation/product formation disfavors reversal and helps lock in IdoA-containing products. | Vertebrate GLCE/HS biosynthesis | Structural biology, biochemical review | Qin et al. 2015, *J Biol Chem*; Li 2010, *Prog Mol Biol Transl Sci* | https://doi.org/10.1074/jbc.m114.602201 ; https://doi.org/10.1016/S1877-1173(10)93004-4 | (pqac-00000003, pqac-00000004, pqac-00000006) |
| Localization | GLCE is a **type II transmembrane Golgi enzyme** in the HS biosynthetic machinery; zebrafish Glce proteins are predicted to contain an N-terminal hydrophobic segment consistent with Golgi localization. HS products act at the **cell surface and extracellular matrix** after biosynthesis. | Zebrafish and vertebrate cells | Sequence-based inference, cell biology review, pathway context | Ghiselli & Farber 2005, *BMC Developmental Biology*; Li 2010, *Prog Mol Biol Transl Sci* | https://doi.org/10.1186/1471-213x-5-19 ; https://doi.org/10.1016/S1877-1173(10)93004-4 | (pqac-00000000, pqac-00000006) |
| Expression pattern | **glce-A and glce-B transcripts are maternally supplied**, broadly expressed during gastrulation, and become more restricted by **24 hpf**, with enrichment in the **hindbrain/around the fourth ventricle**; no major expression difference between the two paralogs was detected in the original zebrafish study. | *Danio rerio* embryos | RT-PCR, whole-mount in situ hybridization | Ghiselli & Farber 2005, *BMC Developmental Biology* | https://doi.org/10.1186/1471-213x-5-19 | (pqac-00000000, pqac-00000001) |
| Developmental phenotype | Overexpression of zebrafish Glce causes **dose-dependent ventralization** (smaller head, expanded blood islands, abnormal somites), while morpholino knockdown causes **dorsalization** (reduced ventral tail fin, kinked/coiled tail, enlarged heart cavity), establishing an essential role in **dorso-ventral axis formation**. | *Danio rerio* embryos | Gain-of-function and loss-of-function embryology | Ghiselli & Farber 2005, *BMC Developmental Biology* | https://doi.org/10.1186/1471-213x-5-19 | (pqac-00000000, pqac-00000001, pqac-00000002) |
| Pathway links | Glce functions in the **heparan sulfate biosynthesis pathway**, after N-sulfation and before/with O-sulfation steps; it modulates HS-dependent morphogen systems including **BMP**, and is discussed in the context of **Wnt, FGF, and Hedgehog** signaling. Zebrafish experiments directly showed that Glce **enhances Bmp2b ventralizing activity**, while knockdown impairs it. | Zebrafish embryos; vertebrate HS pathway | Developmental genetics, pathway review, protein interaction/structure | Ghiselli & Farber 2005, *BMC Developmental Biology*; Li 2010, *Prog Mol Biol Transl Sci*; Qin et al. 2015, *J Biol Chem* | https://doi.org/10.1186/1471-213x-5-19 ; https://doi.org/10.1016/S1877-1173(10)93004-4 ; https://doi.org/10.1074/jbc.m114.602201 | (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000003, pqac-00000006) |
| Quantitative data | Zebrafish embryonic epimerase activity at **10 hpf was ~2×** that at the **64-cell stage**; overexpression increased activity at 10 hpf by **~73%**; morpholino knockdown reduced activity to **~34% of control**. | *Danio rerio* embryos | Enzyme assay during development and perturbation | Ghiselli & Farber 2005, *BMC Developmental Biology* | https://doi.org/10.1186/1471-213x-5-19 | (pqac-00000001, pqac-00000002) |
| Quantitative data | Product/inhibitor analysis in structural-biochemical work showed **heparin IC50 ≈ 225 µg/mL** and **N-sulfated heparin IC50 ≈ 10 µg/mL**, supporting strong inhibition by highly sulfated products/analogs and explaining how downstream sulfation can constrain reversal. | Zebrafish Glce with heparin/HS analogs | In vitro inhibition assay, structural interpretation | Qin et al. 2015, *J Biol Chem* | https://doi.org/10.1074/jbc.m114.602201 | (pqac-00000003, pqac-00000008, pqac-00000009, pqac-00000010) |
| Quantitative data | Zebrafish and human GLCE proteins form **stable dimers with two catalytic sites per dimer**; active-site tyrosines **Tyr468, Tyr528, Tyr546** are required for activity, providing mechanistic support for annotation of F1QR43 as a functional Glce-family epimerase. | Zebrafish structural construct; conserved vertebrate GLCE | X-ray crystallography, mutagenesis | Qin et al. 2015, *J Biol Chem* | https://doi.org/10.1074/jbc.m114.602201 | (pqac-00000003, pqac-00000004, pqac-00000008) |


*Table: This table summarizes the key functional annotation evidence for zebrafish glceb/Glce-B (UniProt F1QR43), including enzyme function, localization, developmental roles, pathway context, and quantitative measurements. It is useful as a compact evidence map linking the zebrafish gene to the broader GLCE/heparan sulfate biosynthesis literature.*