Many organisms have a global mechanism for dosage compensation (DC) operating along the entire male X chromosome, which equalizes gene expression on the male X with that on the two Xs in females and/or on autosomes. At the initial stage of sex chromosome evolution, however, gene-by-gene (or localized) DC may also be necessary because the degeneration of Y-linked genes occurs independently at different times. We therefore tested whether the up-regulation of X-linked genes depends on the status of their Y-linked homologs, using the young sex chromosomes, neo-X and neo-Y, in Drosophila miranda. In support of the presence of gene-by-gene DC, the extent of up-regulation in males was indeed higher for neo-X-linked genes with pseudogenized neo-Y-linked homologs than for neo-X-linked genes with functional neo-Y-linked homologs. Further molecular evolutionary analysis also supports the idea that many individual neo-X-linked genes first acquired the potential for up-regulation, which then enabled the pseudogenization of neo-Y-linked homologs, without serious deleterious effects on male fitness.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We thank the editor and the reviewers for their constructive comments on our manuscript. We also thank Mai Fujimi, Chie Iwamoto, Miu Kubota, Kanako Onizuka, and Yasuko Urabe for their help in conducting experiments and Masanori Toda for species identification. We are also grateful to Yosuke Seto, Aya Takahashi, Koichiro Tamura, Kentaro M. Tanaka, and Ryo Yamaguchi for their comments on earlier versions of the manuscript. This work was supported by grants from Tokyo Metropolitan University and Japan Society for the Promotion of Science (Grant numbers 25711023, 15K14585, and 17H05015) to M.N.