Glass catfish ( Kryptopterus vitreolus) are notable in the aquarium trade for their highly transparent body pattern. This transparency is due to the loss of most reflective iridophores and light-absorbing melanophores in the main body, although certain black and silver pigments remain in the face and head. To date, however, the molecular mechanisms underlying this transparent phenotype remain largely unknown. To explore the genetic basis of this transparency, we constructed a chromosome-level haplotypic genome assembly for the glass catfish, encompassing 32 chromosomes and 23 344 protein-coding genes, using PacBio and Hi-C sequencing technologies and standard assembly and annotation pipelines. Analysis revealed a premature stop codon in the putative albinism-related tyrp1b gene, encoding tyrosinase-related protein 1, rendering it a nonfunctional pseudogene. Notably, a synteny comparison with over 30 other fish species identified the loss of the endothelin-3 ( edn3b) gene in the glass catfish genome. To investigate the role of edn3b, we generated edn3b -/- mutant zebrafish, which exhibited a remarkable reduction in black pigments in body surface stripes compared to wild-type zebrafish. These findings indicate that edn3b loss contributes to the transparent phenotype of the glass catfish. Our high-quality chromosome-scale genome assembly and identification of key genes provide important molecular insights into the transparent phenotype of glass catfish. These findings not only enhance our understanding of the molecular mechanisms underlying transparency in glass catfish, but also offer a valuable genetic resource for further research on pigmentation in various animal species.
玻璃猫鱼（ Kryptopterus vitreolus）是一种值得大家关注的观赏鱼，因其身体极其透明而广受喜爱。虽然其面部和头部保留了些许黑色素和银色素，但其躯体绝大部分失去了大多数的反射性彩虹细胞和吸光性黑素细胞。然而迄今为止，这种透明表型的分子机制在很大程度上仍是未知的。为了解析导致这种迷人透明体型的潜在遗传线索，该研究通过整合PacBio和Hi-C测序技术，为玻璃猫鱼构建了包含32条染色体和23 344个蛋白编码基因的染色体级别单体型全基因组图谱。同时，在推测与白化病相关的 tyrp1b基因核苷酸序列中发现了一个提前终止密码子，从而导致其成为一个假基因。有趣的是，通过与30多种其它鱼类进行基因组共线性比较，在玻璃猫鱼基因组中发现存在内皮素-3（edn3b）基因的缺失。随后，实施基因敲除获得了edn3b−/−突变型斑马鱼，并观察到与野生型斑马鱼相比，其体表条纹的黑色色素显著减少。换言之，验证得出edn3b基因的缺失在一定程度上促成了玻璃猫鱼的透明表型。总之，该研究为玻璃猫鱼建立了高质量的染色体图谱，并确定了几个参与形成透明表型的重要基因。该研究结果不仅增强我们对玻璃猫鱼透明表型分子机制的理解，也为深入研究各类动物的体表色素沉着提供宝贵的遗传资源。
Keywords: Glass catfish; Transparent phenotype; Whole-genome sequencing; edn3b−/− mutant.