Department of Genetics and Evolutionary Biology
University of S?o Paulo
Chinese Institute for Brain Research, Beijing
10:00-11:00 Friday，August 23th, 2019
Dr. Li Zhang
Spermatogenesis role on the evolution of new genes
New genes can quickly assume critical roles in developmental pathways by producing essential structures. Several studies have pointed their important role in the formation of different novel traits related to sexual selection and cognitive behavior, among others. In different groups of species, new genes are majorly expressed in testis, more specifically in later phases of male gametogenesis. Our group study the role and impact of spermatogenesis - a system of great importance for survival and evolution of species that varies temporally with the development - to understand function and evolution of new genes. More specifically, we have discovered that their enhanced expression in testis is a consequence of haploid selection during the latter stages of male gametogenesis. Because emerging adaptive mutations will be fixed faster if their phenotypes are expressed by haploid rather than diploid genotypes, new genes with advantageous functions arising during this unique stage of development have a better chance to become fixed. In Drosophila, our group also investigate the impact of Meiotic Sex Chromosome Inactivation (MSCI) on the evolution and origin of new genes. The phenomenon, known as the transcriptional silencing of genes on the X chromosome in the male germline prior to meiosis, has long been hypothesized to occur in Drosophila testes. We have combined cytological data and single-cell expression profile to ask if and when MSCI occurs. In early germ cells, the ratio of sex-linked to autosomal (X:A) gene expression is balanced, and active RNA Polymerase II (Pol II) is present on the X and autosomes. As spermatocytes mature, the X:A ratio decreases and active Pol II is depleted from the X chromosome. Our results not only show that MSCI does occur in Drosophila spermatogenesis, but also elucidate the molecular mechanism responsible for the X chromosome regulation. Together, male germline development has important implications on the origin of new genes revealing their potential role in fertility and fecundity, as new gene meiotic and post-meiotic expression and fitness can be directly related to sperm morphogenesis and motility.
與直覺相反，新基因能夠迅速在保守的發育過程中發揮關鍵作用。一些研究表明它們在與性選擇和認知行為相關的生物功能創新中具有重要作用。在眾多已研究的物種中，無一例外，新基因在睪丸中富集表達，更具體地說是在雄性配子發生的后期階段。我們的研究聚焦在精子發生過程 - 一個對物種的生存和演化非常重要的生物過程，并且在發育不同階段扮演不同角色 – 從而了解新基因的功能和演化。具體而言，我們證實新基因在睪丸中的富集表達是雄性配子發生的后期階段中單倍體選擇的結果。新產生的表型在與二倍體相比，單倍體具有明顯的優勢去固定新興的適應性突變。毫無疑問，在精子發育階段，有利的新基因擁有更好的固定機會。我們還研究了果蠅減數分裂前性染色體失活（MSCI）對新基因起源與演化的影響。在減數分裂前，雄性生殖細胞中X染色體上基因的轉錄是否會被抑制， 長期存在爭議。我們通過單細胞測序來探究MSCI是否在果蠅睪丸中發生，以及何時發生。在早期生殖細胞中，性染色體基因表達與常染色體基因表達的比例（X：A）是平衡的，活性RNA聚合酶II（Pol II）同時存在于X和常染色體上。當精母細胞成熟時，X：A比率降低，活性Pol II從X染色體上消失。我們的結果不僅表明MSCI確實發生在果蠅精子發生過程中，而且還闡明了X染色體失活的分子機制。綜上所述，雄性生殖細胞的發育對新基因的起源具有重要影響，這揭示了新基因在生殖方面的潛在作用。例如，新基因在減數分裂時和減數分裂后的表達和適應性與精子的形態發生和運動直接相關。
Maria D. Vibranovski is an assistant professor of Department of Genetics and Evolutionary Biology at University of S?o Paulo. She received trainings for genetics for her master’s degree and trainings for biochemistry and molecular biology for her Ph.D. degree in Brazil. Then She worked as a postdoctoral researcher in University of Chicago before she returned University of S?o Paulo. Maria’s major interest is centered on sexual selection especially the testes-biased expression of new genes. Her studies have elucidated the impact of Meiotic Sex Chromosome Inactivation on the evolution of new genes. More importantly, her recent work shows that haploid selection during the latter stages of spermatogenesis play an important role of new gene evolution. Maris’s research is fundamentally important to understand how sexual selection and sex chromosome work together to fix genetic novelties, which naturally is very closely connected to the creation of functional novelties related to sexual differences.