Evolution of sexually dimorphic germ cells in Volvox carteri

描述（由申请人提供）：我们工作的长期目标是了解性染色体在复杂发育性状进化中的作用。两性二态性（卵子和精子）是多细胞生物繁殖成功的基本策略，然而几乎没有人知道两个不同的性别是如何从一个具有相同交配类型的单细胞祖先进化而来的。carteri Volvox carteri是一种两性二态的多细胞绿藻，与非二态单细胞的reinhardchlamydomonas有密切的关系。在这两种藻类的性分化是由一个多基因单倍体交配位点（MT）控制的。相对于衣藻的MT，团藻的MT经历了显著的扩展，并获得了性染色体的特性。我们的数据表明，通过非适应性过程的快速进化，为性选择和遗传创新提供了原材料。我们建议测试四个在Volvox MT中出现的这种创新的来源，以及它们是如何促进两性进化的：男性性别决定基因vcMid基因调控网络输入的重塑。我们将测试vcMid蛋白是在转录后受到性诱导剂的调控还是在翻译后受到调控。我们将使用RNAi灭活vcMid，以确定其缺失是否足以诱导卵子发生。我们将使用跨种互补来确定使vcMid成为Volvox精子发生因子的关键变化。vcMid基因调控网络输出的重塑。表达vcMid转基因的雌性团藻（Eve::Mid-T）产生精子。我们将使用来自雌性、雄性、Eve: Mid-T系和vcMid敲低系的定量RNA-seq数据来鉴定vcMid调控的控制精子发生的靶基因和控制卵子发生的雌性MT基因。3. 共享MT基因MAT3的合作和分化。我们将确定雌性和雄性等位基因MAT3-f和MAT3-m是否通过相互敲除和替换来控制早期胚胎生殖细胞周期模式。性别调节的选择性MAT3剪接机制将被研究。4. 新基因的形成。HMG1和FSI1是新的女性MT基因，没有已知的同源基因。表位标记、RNAi敲低和错误表达将分别用于测试它们对雌性卵子身份和配子识别的预测贡献。其他新的雄性和雌性MT基因的保护将在相关物种中进行研究。我们关于藻藻二态进化的发现可能对理解性染色体的起源及其对大规模进化变化的贡献具有普遍意义。此外，许多人类遗传疾病与性染色体有关或受性别影响，这项工作将有助于阐明控制此类疾病病因的一般原则。！

DESCRIPTION (provided by applicant): The long-term goal of our work is to understand the role of sex chromosomes in the evolution of complex developmental traits. Dimorphic sexes (eggs and sperm) are a fundamental strategy for reproductive success in multicellular organisms, yet almost nothing is known about how two different sexes evolved from a proposed unicellular ancestor with morphologically identical mating types. Volvox carteri is a multicellular green alga that is sexually dimorphic and is closely related to Chlamydomonas reinhardtii, a non-dimorphic unicell. In both algal species sexual differentiation is controlled by a multigenic haploid mating locus (MT). MT in Volvox has undergone a remarkable expansion relative to MT from Chlamydomonas and acquired the properties of a sex chromosome. Our data suggest that rapid evolution of Volvox MT genes through largely non-adaptive processes provided raw material for sexual selection and genetic innovation. We propose to test four sources of such innovation that arose in Volvox MT and how they contributed to the evolution of dimorphic sexes: 1. Remodeling of gene regulatory network inputs for a male sex determination gene, vcMid. We will test whether vcMid protein is regulated post-transcriptionally in response to sex inducer or is regulated post- translationally. We will inactivate vcMid using RNAi to determine whether its absence is sufficient to induce oogenesis. We will use trans-species complementation to determine the key changes that allowed vcMid to become a spermatogenesis factor in Volvox. 2. Remodeling of gene regulatory network outputs for vcMid. Female Volvox that express a vcMid transgene (Eve::Mid-T) produce sperm. We will use quantitative RNA-seq data from females, males, Eve::Mid-T lines, and vcMid knockdown lines to identify the vcMid-regulated target genes that control spermatogenesis and female MT genes that control oogenesis. 3. The cooption and divergence of a shared MT gene, MAT3. We will determine whether the female and male alleles, MAT3-f and MAT3-m, control early embryonic germ cell cycle patterning by reciprocal knockdowns and replacements. The mechanism of sex-regulated alternative MAT3 splicing will be investigated. 4. Formation of new genes. HMG1 and FSI1 are new female MT genes with no known homologs. Epitope tagging, RNAi knockdowns and mis-expression will be used to test their predicted contributions to female egg identity and gamete recognition, respectively. Conservation of other novel male and female MT genes will be investigated in related species. Our findings on how dimorphism evolved in volvocine algae are likely to have general significance for understanding the origin of sex chromosomes and their contribution to large-scale evolutionary changes. In addition, many human genetic diseases are linked to sex chromosomes or are impacted by gender, and this work will help elucidate the general principles that govern the etiology of such diseases. ! PUBLIC HEALTH RELEVANCE: Many human diseases are linked to sex chromosomes or have etiologies that are significantly affected by gender. This proposal investigates the origins of gender and sex chromosomes in a model organism, Volvox carteri, whose development and evolution has many parallels with humans and other animals. The knowledge obtained from our studies will provide fundamental information on sex chromosome biology that may lead to a better understanding of human sex-linked diseases.