The pellicle is formed by the zygote-specific wall (Cavalier-Smith 1976), which is constructed to replace the vegetative cell wall shed before mating (Claes 1971). The zygotic cell wall is composed of a fibrous material, which contains hydroxyproline as a major amino acid, glucose as the most abundant sugar residue, and a (1-3) β-D-glucan as the major structural polysaccharide (Grief
et al. 1987). At least six zygote specific peptides with molecular masses of 76 kDa, 120 kDa, 150 kDa and >200 kDa (A, B and C) have been identified as components of zygotic walls (Minami and Goodenough 1978).
Zygote-specific cDNA clones, which encoded the extensin-like proteins ZSP-1 and ZSP-2 (Woessner and Goodenough 1989), have also been obtained in previous studies (Ferris and Goodenough 1987). However, no gene was characterized that played a role in cell adhesion for pellicle formation, in
Chlamydomonas.
To elucidate the relationships between the pellicle and these peptides and genes, a detailed time schedule of gene expression in pellicle formation needs to be constructed. The aims of this study are to clarify when the pellicle is formed, and to estimate when mRNA and proteins involved in pellicle formation are synthesized, by using transcription and translation inhibitors administered at various times after mating.
The pellicle, filmy aggregate of zygotic cells formed in the green alga
Chlamydomonas reinhardtii, was characterized as a model of inter-cellular adhesion. Pellicle formation was observed following treatment with inhibitors of transcription and translation in the gamate and at various times after mating. The pellicle forms between 2.5 and 3.5 hr after gamete mixing and is sensitive to cytoplasmic inhibitors of transcription and translation, when they are mixed with gametes or zygotes soon after mating. This indicates that the pellicle formation related gene (s) is (are) one of the early zygote-specific genes, and that transcription occurs within the first 20 min after gamete mixing. The protein (s) required for pellicle formation is (are) synthesized predominantly between 1 and 2 hr after mating, just before pellicle formation.
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