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。双态性别(卵子和精子)是多细胞生物体生殖成功的基本策略，然而关于两种不同性别是如何从具有形态相同交配类型的单细胞祖先进化而来的，人们几乎一无所知。Carteri Volvox carteri是一种两性二态的多细胞绿藻，与非二态单细胞莱茵衣藻(Chlamydomonas Rehardtii)亲缘关系密切。在这两种藻类中，性别分化是由一个多基因单倍体交配基因(MT)控制的。相对于衣藻属的MT，Volvox中的MT经历了显着的扩展，并获得了性染色体的特性。我们的数据表明，Volvox MT基因通过很大程度上非适应性过程的快速进化为性别选择和遗传创新提供了原材料。我们建议测试在Volvox MT中出现的这种创新的四个来源以及它们如何促进二态性别的进化：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蛋白是在转录后调控对性诱导剂的反应，还是在翻译后调控。我们将使用RNAi使vcMid失活，以确定它的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Volvox精子发生因子的关键变化。2.vcMid基因调控网络输出重构。表达vcMid转基因(Eve：：Mid-T)的雌性Volvox会产生精子。我们将使用来自雌性、雄性、Eve：：Mid-T系和vcMid敲除系的定量RNA-Seq数据来识别控制精子发生的vcMid调节的靶基因和控制卵子发生的雌性MT基因。3.共同的MT基因MAT3的共选和分化。我们将确定女性和男性等位基因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。性别调控的MAT3选择性剪接的机制将被研究。4.新基因的形成。HMG1和FSI1是新发现的女性MT基因，尚未发现同源基因。表位标记、RNAi敲除和错误表达将分别用于测试它们对雌卵识别和配子识别的预测贡献。其他新的男性和女性MT基因的保守性将在相关物种中进行调查。我们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，许多人类遗传病与性染色体有关或受到性别的影响，这项工作将有助于阐明支配这些疾病病因学的一般原理。好了！

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. !