2007 Fiscal Year Final Research Report Summary
Evolutionary Biological Studies of Morphological Bipolarization in Conjugating Gametes
| Project/Area Number |
17370087
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Evolutionary biology
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| Research Institution | The University of Tokyo |
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Principal Investigator |
NOZAKI Hisayoshi The University of Tokyo, Graduate School of Science, Associate Professor (40250104)
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| Co-Investigator(Kenkyū-buntansha) |
SEKIMOTO Hiroyuki Japan Women's University, Faculty of Science, Associate Professor (20281652)
NISHII Ichiro Initiative Research Unit, Riken, Initiative Research Scientist, 独立主幹研究員 (80392059)
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| Project Period (FY) |
2005 – 2007
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| Keywords | evolution / gamete / isogamy / colonial Volvocales / mating type / male-specific gene / oogamy / minus dominace gene |
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| Research Abstract |
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.
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Research Products
(198 results)
