Origins and functional evolution of Y chromosomes across mammals

Wednesday, 23 April, 2014
Nature maagzine_25 April 2014_cover_Ychromosome

 

Nature 508, 488–493 (24 April 2014) doi:10.1038/nature13151

Diego Cortez, Ray Marin, Deborah Toledo-Flores, Laure Froidevaux, Angélica Liechti, Paul D. Waters, Frank Grützner & Henrik Kaessmann

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Received 20 August 2013  Accepted 17 February 2014  Published online 23 April 2014

 

Abstract: 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 180million 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 140million 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.

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