Evolutionary Biological Studies of Morphological Bipolarization in Conjugating Gametes

真核生物的有性生殖最初是同性配子的，并认为异性配子/受精在动物、陆地植物和绿藻等许多谱系中独立进化。导致卵子配子从同配子进化而来的确切进化机制还知之甚少。在本研究中，我们介绍了分子遗传学数据的使用，以阐明在集群草类动物Pleodorina starrii(Nozaki等人)中卵配子和同配子的进化起源。2006年，卡夫。生物学)。在近亲莱茵衣藻中，有性繁殖是同配型的，交配型为正负。交配型负性代表了一种“显性”，因为莱茵哈蒂亚的MID(“负显性”)基因是使细胞分化为负交配型的同源配子的必要条件和充分条件。直到我们成功地克隆了星星藻的MID基因，才在绿藻中鉴定出性别特异的基因。这种“OTOKOGI”(PlestMID)基因只存在于男性基因组中，编码一种蛋白质，大量定位于成熟精子的细胞核中。因此，星斑潜蝇的雄性是由其同配子祖先的显性(交配型减去)进化而来的。在这项研究中首次发现的雄性特有基因“OTOKOGI”，为克隆雄性交配型基因座并确定其基因组成提供了强有力的第一步。通过比较衣藻属和Pleodorina属的其他交配类型连锁基因，可能会发现还有哪些基因在蜘蛛类“雄性”的进化过程中起着重要作用。对这种进化基因的研究应该能揭示雄配子和雌配子进化的潜在机制，这些配子在大小和运动性上存在差异。

Eukaryotic sex was initially isogametic and it is assumed that anisogamy/oogamy evolved independently in many lineages including animals, land plants and volvocine green algae. The exact evolutionary mechanisms that were responsible for the evolution of oogamy from isogamy were poorly understood. In the present study, we introduced the use of molecular-genetic data in elucidating the evolutionary origin of oogamy from isogamy in the colonial volvocacean Pleodorina starrii (Nozaki et al. 2006, Cuff. Biology). In the close relative Chlamydomonas reinhardtii, sexual reproduction is isogametic with mating-types plus and minus. Mating type minus represents a "dominant sex" because the MID ("minus-dominance") gene of C. reinhardtii is both necessary and sufficient to cause the cells to differentiate as isogametes of the minus mating type. No sex-specific genes had been identified in the volvocine green algae until we successfully cloned the MID gene of P. starrii. This "OTOKOGI" (PlestMID) gene is present only in the male genome, and encodes a protein localized abundantly in the nuclei of mature sperm. Thus, P. starrii maleness evolved from the dominant sex (mating type minus) of its isogamous ancestor. The male-specific gene "OTOKOGI", first identified in this study, provides a powerful first step toward cloning the male mating type locus and determining its gene composition. Comparison of other mating type-linked loci between Chlamydomonas and Pleodorina may reveal which other genes have been important in the evolution of volvocacean "maleness." Studies of such evolved genes should shed light on the mechanisms underlying the evolution of male and female gametes that are differentiated in size and motility.