Researchers identify oncogene linked to pigmentation patterns in mountain swordtail fish
Scientists studying the mountain swordtail fish (Xiphophorus nezahualcoyotl) have identified the xmrk oncogene as responsible for two distinct melanic pigmentation patterns, resolving a nearly century-old genetic mystery. The gene's location near the sex-determining region and its variable structure across sex chromosomes explains why these traits are sex-linked. The findings demonstrate how long-read sequencing can reveal the genetic basis of complex sex-linked traits and may inform understanding of similar traits in other species.
Researchers generated a complete, gapless assembly of the X. nezahualcoyotl genome and used genome-wide association studies (GWAS) to map two pigmentation phenotypes—'spotted side' and 'marmoratus'—to a region near the xmrk oncogene on sex chromosomes. The study found that xmrk haplotypes vary dramatically in gene content, structure, and repetitive element composition, and can be located on both X and Y chromosomes. This structural variability may affect chromosomal stability and recombination patterns between haplotypes associated with each pigmentation pattern. The work resolves a longstanding debate about the 'macromelanophore determining locus,' a region implicated in pigmentation control for nearly a century but whose causal gene remained controversial due to the technical difficulty of sequencing sex chromosomes. The findings showcase how modern long-read sequencing technology can illuminate the genetic architecture of complex, dynamic genomic regions underlying phenotypic variation.
What's missing
The study does not discuss potential implications for understanding cancer risk in swordtails or other species, despite identifying an oncogene. The functional mechanism by which xmrk variation produces distinct pigmentation patterns is not detailed. The evolutionary significance of the observed haplotype variation and its role in speciation or population divergence is not addressed.
What different sources said
- bioRxivCenter
Two melanic pigment patterns are associated with a sex chromosome-linked oncogene in the mountain swordtail Xiphophorus nezahualcoyotl
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