Maria D. Vibranovski, Ph.D
Department of Genetics and Evolutionary Biology
University of São Paulo
Third Floor Lecture Hall, Jianzan Building (Phase I)
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.
与直觉相反，新基因能够迅速在保守的发育过程中发挥关键作用。一些研究表明它们在与性选择和认知行为相关的生物功能创新中具有重要作用。在众多已研究的物种中，无一例外，新基因在睾丸中富集表达，更具体地说是在雄性配子发生的后期阶段。我们的研究聚焦在精子发生过程 - 一个对物种的生存和演化非常重要的生物过程，并且在发育不同阶段扮演不同角色 – 从而了解新基因的功能和演化。具体而言，我们证实新基因在睾丸中的富集表达是雄性配子发生的后期阶段中单倍体选择的结果。新产生的表型在与二倍体相比，单倍体具有明显的优势去固定新兴的适应性突变。毫无疑问，在精子发育阶段，有利的新基因拥有更好的固定机会。我们还研究了果蝇减数分裂前性染色体失活（MSCI）对新基因起源与演化的影响。在减数分裂前，雄性生殖细胞中X染色体上基因的转录是否会被抑制， 长期存在争议。我们通过单细胞测序来探究MSCI是否在果蝇睾丸中发生，以及何时发生。在早期生殖细胞中，性染色体基因表达与常染色体基因表达的比例（X：A）是平衡的，活性RNA聚合酶II（Pol II）同时存在于X和常染色体上。当精母细胞成熟时，X：A比率降低，活性Pol II从X染色体上消失。我们的结果不仅表明MSCI确实发生在果蝇精子发生过程中，而且还阐明了X染色体失活的分子机制。综上所述，雄性生殖细胞的发育对新基因的起源具有重要影响，这揭示了新基因在生殖方面的潜在作用。例如，新基因在减数分裂时和减数分裂后的表达和适应性与精子的形态发生和运动直接相关。
Maria D. Vibranovski is an assistant professor of Department of Genetics and Evolutionary Biology at University of São 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 São 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.