Origins and functional evolution of Y chromosomes across mammals.
Diego Cortez, Ray Marin, Deborah Toledo-Flores, Laure Froidevaux, Angélica Liechti, Paul D Waters, Frank Grützner, Henrik Kaessmann
Author Information
Diego Cortez: 1] Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland [2] Swiss Institute of Bioinformatics, 1015 Lausanne, Switzerland.
Ray Marin: 1] Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland [2] Swiss Institute of Bioinformatics, 1015 Lausanne, Switzerland.
Deborah Toledo-Flores: The Robinson Research Institute, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia.
Laure Froidevaux: Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland.
Angélica Liechti: Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland.
Paul D Waters: School of Biotechnology and Biomolecular Sciences, UNSW Australia, Sydney, New South Wales 2052, Australia.
Frank Grützner: The Robinson Research Institute, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia.
Henrik Kaessmann: 1] Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland [2] Swiss Institute of Bioinformatics, 1015 Lausanne, Switzerland.
Y chromosomes underlie sex determination in mammals, but their repeat-rich nature has hampered sequencing and associated evolutionary studies. Here we trace Y evolution across 15 representative mammals on the basis of high-throughput genome and transcriptome sequencing. We uncover three independent sex chromosome originations in mammals and birds (the outgroup). The original placental and marsupial (therian) Y, containing the sex-determining gene SRY, emerged in the therian ancestor approximately 180 million years ago, in parallel with the first of five monotreme Y chromosomes, carrying the probable sex-determining gene AMH. The avian W chromosome arose approximately 140 million years ago in the bird ancestor. The small Y/W gene repertoires, enriched in regulatory functions, were rapidly defined following stratification (recombination arrest) and erosion events and have remained considerably stable. Despite expression decreases in therians, Y/W genes show notable conservation of proto-sex chromosome expression patterns, although various Y genes evolved testis-specificities through differential regulatory decay. Thus, although some genes evolved novel functions through spatial/temporal expression shifts, most Y genes probably endured, at least initially, because of dosage constraints.
