Deciphering neo-sex and B chromosome evolution by the draft genome of Drosophila albomicans

• Published in: BMC genomics 2012-03, Vol.13 (1), p.109-109, Article 109
• Main Authors: Zhou, Qi, Zhu, Hong-mei, Huang, Quan-fei, Zhao, Li, Zhang, Guo-jie, Roy, Scott W, Vicoso, Beatriz, Xuan, Zhao-lin, Ruan, Jue, Zhang, Yue, Zhao, Ruo-ping, Ye, Chen, Zhang, Xiu-qing, Wang, Jun, Wang, Wen, Bachtrog, Doris
• Format: Article
• Language: English
• Subjects: Animals; B chromosome; Biology; Birth; Chromosome Duplication - genetics; Chromosomes; Chromosomes, Insect - genetics; Degeneration; Drosophila; Drosophila - genetics; Drosophila albomicans; Evolution; Evolution, Molecular; Female; Females; Fertility; Genetic aspects; Genome, Insect - genetics; Genomes; Genomics; Heredity; Inbreeding; Insects; Male; Males; Molecular evolution; Molecular Sequence Annotation; Natural history; neo-sex chromosome; Nucleotide sequence; Phylogeny; Planck, Max; Recombination, Genetic - genetics; scaffolds; Science; Sex chromosomes; X Chromosome - genetics; Y chromosome; Y Chromosome - genetics
• ISSN: 1471-2164; 1471-2164
• DOI: 10.1186/1471-2164-13-109

Drosophila albomicans is a unique model organism for studying both sex chromosome and B chromosome evolution. A pair of its autosomes comprising roughly 40% of the whole genome has fused to the ancient X and Y chromosomes only about 0.12 million years ago, thereby creating the youngest and most gene-rich neo-sex system reported to date. This species also possesses recently derived B chromosomes that show non-Mendelian inheritance and significantly influence fertility. We sequenced male flies with B chromosomes at 124.5-fold genome coverage using next-generation sequencing. To characterize neo-Y specific changes and B chromosome sequences, we also sequenced inbred female flies derived from the same strain but without B's at 28.5-fold. We assembled a female genome and placed 53% of the sequence and 85% of the annotated proteins into specific chromosomes, by comparison with the 12 Drosophila genomes. Despite its very recent origin, the non-recombining neo-Y chromosome shows various signs of degeneration, including a significant enrichment of non-functional genes compared to the neo-X, and an excess of tandem duplications relative to other chromosomes. We also characterized a B-chromosome linked scaffold that contains an actively transcribed unit and shows sequence similarity to the subcentromeric regions of both the ancient X and the neo-X chromosome. Our results provide novel insights into the very early stages of sex chromosome evolution and B chromosome origination, and suggest an unprecedented connection between the births of these two systems in D. albomicans.