A gamete-specific, sex-limited homeodomain protein in Chlamydomonas

J Cell Biol. 1998 Dec 28;143(7):1971-80. doi: 10.1083/jcb.143.7.1971.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cell Adhesion
  • Cell Fusion
  • Chlamydomonas reinhardtii / metabolism*
  • DNA, Complementary / genetics
  • Fertilization
  • Gene Expression Regulation, Developmental
  • Germ Cells / metabolism*
  • Homeodomain Proteins / chemistry
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / physiology*
  • Models, Molecular
  • Molecular Sequence Data
  • Plant Proteins / physiology*
  • Protein Conformation
  • Protozoan Proteins / physiology*
  • Sequence Alignment
  • Sequence Homology, Amino Acid


  • DNA, Complementary
  • GSP1 protein, Chlamydomonas
  • Homeodomain Proteins
  • Plant Proteins
  • Protozoan Proteins

Associated data

  • GENBANK/AF108140