title: A gamete-specific, sex-limited homeodomain protein in Chlamydomonas.
abstract: During fertilization in Chlamydomonas, gametes of opposite mating types interact with each other through sex-specific adhesion molecules on their flagellar surfaces. Flagellar adhesion brings the cell bodies of the gametes into close contact and initiates a signal transduction pathway in preparation for cell-cell fusion. We have identified a cDNA, gsp1, whose transcript levels are upregulated during flagellar adhesion. The GSP1 polypeptide is a novel, gamete-specific homeodomain protein, the first to be identified in an alga. Its homeodomain shows significant identity with several higher plant homeodomain proteins. Although encoded by a single copy gene present in cells of both mating types, immunoblot analysis showed that GSP1 was expressed in mating type (mt)+ gametes, but was not detectable in mt- gametes or in vegetative cells of either mating type. Moreover, GSP1 appeared late during gametogenesis, suggesting that it may function during adhesion with mt- gametes or after zygote formation. GSP1 is expressed in imp11, mt- mutant gametes, which have a lesion in the mid gene involved in sex determination and exhibit many phenotypic characteristics of mt+ gametes. Thus, gsp1 is negatively regulated by mid and is the first molecule to be identified in Chlamydomonas that shows sex-limited expression.
authors.affiliation: Department of Cell Biology and Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
authors.forename: V
authors.initials: V
authors.lastname: Kurvari
authors.forename: N V
authors.initials: NV
authors.lastname: Grishin
authors.forename: W J
authors.initials: WJ
authors.lastname: Snell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002448:Cell Adhesion; D002459:Cell Fusion; D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D005306:Fertilization; D018507:Gene Expression Regulation, Developmental; D005854:Germ Cells / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000502:physiology*; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000502:physiology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; C116848:GSP1 protein, Chlamydomonas; D018398:Homeodomain Proteins; D010940:Plant Proteins; D015800:Protozoan Proteins