Diversity of reptile sex chromosome evolution revealed by cytogenetic and linked-read sequencing
Zexian Zhu, 浙江大学生命科学研究院生命系统稳态与保护教育部重点实验室, 浙江省肿瘤分子细胞生物学重点实验室, 浙江 杭州 310058, 中国, Kazumi Matsubara, Foyez Shams, Jason Dobry, Erik Wapstra, Tony Gamble, Stephen D. Sarre, Arthur Georges, Jennifer A. Marshall Graves, Qi Zhou, Tariq Ezaz, 堪培拉大学应用生态研究所, 堪培拉 2601, 澳大利亚, 塔斯马尼亚大学生物科学学院, 塔斯马尼亚 7001, 澳大利亚, 马凯特大学生物科学系, 威斯康星州密尔沃基市 52322, 美国, 拉筹伯大学生命科学学院, 墨尔本 3168 澳大利亚, 维也纳大学神经科学与发育生物学学系, 维也纳 1030, 奥地利, 浙江大学医学院附属第二医院生殖医学中心, 浙江 杭州 310009, 中国
Abstract
Reptile sex determination is attracting much attention because the great diversity of sex-determination and dosage compensation mechanisms permits us to approach fundamental questions about mechanisms of sex chromosome turnover. Recent studies have made significant progress in better understanding diversity and conservation of reptile sex chromosomes, with however no reptile master sex determination genes identified. Here we describe an integrated genomics and cytogenetics pipeline, combining probes generated from the microdissected sex chromosomes with transcriptome and genome sequencing to explore the sex chromosome diversity in non-model Australian reptiles. We tested our pipeline on a turtle, two species of geckos, and a monitor lizard. Genes identified on sex chromosomes were compared to the chicken genome to identify homologous regions among the four species. We identified candidate sex determining genes within these regions, including conserved vertebrate sex-determining genes <i>pdgfa, pdgfra</i> <i>amh</i> and <i>wt1</i>, and demonstrated their testis or ovary-specific expression. All four species showed gene-by-gene rather than chromosome-wide dosage compensation. Our results imply that reptile sex chromosomes originated by independent acquisition of sex-determining genes on different autosomes, as well as translocations between different ancestral macro- and microchromosomes. We discuss the evolutionary drivers of the slow differentiation and turnover of reptile sex chromosomes.