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特征进化中的作用。两性异形（卵子和精子）是多细胞生物繁殖成功的基本策略，但几乎没有人知道两种不同的性别是如何从一个形态上相同的交配类型的单细胞祖先进化而来的。团藻是一种多细胞的绿色藻类，性二型，与非二型单细胞的莱茵衣藻密切相关。在这两种藻类的性别分化是由一个多基因的单倍体交配位点（MT）。团藻中的MT相对于衣原体的MT经历了显著的扩增，并获得了性染色体的特性。我们的数据表明团藻MT基因的快速进化主要是通过非适应性过程提供了性选择和遗传创新的原材料。我们建议测试团藻MT中出现的这种创新的四个来源，以及它们如何促进两性异形的进化：1。男性性别决定基因vcMid的基因调控网络输入的重塑。我们将测试vcMid蛋白是响应于性诱导物而在转录后调节还是在转录后调节。我们将使用RNAi来检测vcMid，以确定其缺失是否足以诱导卵子发生。我们将使用跨物种互补来确定使vcMid成为团藻精子发生因子的关键变化。2. vcMid的基因调控网络输出的重塑。表达vcMid转基因（Eve：：Mid-T）的雌性团藻产生精子。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数据来鉴定控制精子发生的vcMid调节的靶基因和控制卵子发生的雌性MT基因。3. MT基因MAT 3的共选择和分化。我们将确定女性和男性等位基因MAT 3-f和MAT 3-m是否通过相互敲低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MAT 3剪接的机制将进行研究。4.新基因的形成。HMG 1和FSI 1是新发现的女性MT基因，目前还没有同源基因。表位标记、RNAi敲除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。其他新的男性和女性MT基因的保护将在相关物种中进行调查。 我们的研究结果如何在volvocine藻类的二型性进化可能有一般意义的性染色体的起源和它们的贡献，大规模的进化变化的理解。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这些疾病的病因学的一般原则。!

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. !