title: The Xmrk oncogene can escape nonfunctionalization in a highly unstable subtelomeric region of the genome of the fish Xiphophorus.
abstract: The Xmrk oncogene involved in melanoma formation in the fish Xiphophorus was formed relatively recently by duplication of the epidermal growth factor co-orthologue egfrb. In the platyfish X. maculatus, Xmrk is located close to the major sex-determining locus in a subtelomeric region of the X and Y sex chromosomes that frequently undergoes duplications and other rearrangements. This region accumulates repetitive sequences: more than 80% of the 33-kb region 3' of Xmrk is constituted by retrotransposable elements. The high degree of nucleotide identity between X- and Y-linked sequences and the rarity of gonosome-specific rearrangements indicated that the instability observed was not a manifestation of gonosome-specific degeneration. Seven other duplicated genes were found, all corresponding, in contrast to Xmrk, to pseudogenes (nonfunctionalization). Functional persistence of Xmrk in a highly unstable region in divergent Xiphophorus species suggests a beneficial function under certain conditions for this dispensable and potentially injurious gene.
mesh_terms: D000818:Animals; D001483:Base Sequence; D003532:Cyprinodontiformes / Q000235:genetics*; D004251:DNA Transposable Elements; D005260:Female; D029941:Fish Proteins / Q000235:genetics*; D020440:Gene Duplication; D015698:Genomic Library; D006824:Hybridization, Genetic; D008297:Male; D008969:Molecular Sequence Data; D009857:Oncogenes; D011401:Promoter Regions, Genetic; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D014960:X Chromosome / Q000235:genetics; D014998:Y Chromosome / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D029941:Fish Proteins; D020794:Receptor Protein-Tyrosine Kinases; C077101:Xmrk protein, Xiphophorus