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Regulation of secretory protein gene expression in Paramecium: Role of the cortical exocytotic sites
- Galvani, AngÃ©lique, Sperling, Linda
- European journal of biochemistry 2000 v.267 no.11 pp. 3226-3234
- Paramecium, biogenesis, calcium, exocytosis, gene activation, gene expression, messenger RNA, multigene family, mutants, polypeptides, secretion, secretory granules, stored products, transcriptional activation
- In cells that possess a regulated secretory pathway, exocytosis can lead to transcriptional activation of genes encoding products stored in secretory granules as well as genes required for granule biogenesis. With the objective of understanding this response, we have examined the expression of Paramecium secretory protein genes in different physiological and genetic contexts. The genes belong to the trichocyst matrix protein (TMP) multigene family, encoding polypeptides that form the crystalline matrix of the secretory granules, known as trichocysts. Approximately 1000 trichocysts per cell are docked at preâformed cortical exocytotic sites. Their rapid and synchronous exocytosis can be triggered by vital secretagogues such as aminoethyldextran without harming the cells. Using this exocytotic trigger, we found that the transcription of TMP genes undergoes rapid, transient and coâordinate 10âfold activation in response to massive exocytosis, leading to a 2.5âfold increase in the pool of TMP mRNA. Experiments with exocytosisâdeficient mutants show that the secretagogueâinduced increase in intracellular free calcium implicated in stimulus/secretion coupling is not sufficient to activate TMP gene expression. We present evidence that the state of occupation of the cortical exocytotic sites can affect TMP gene expression and suggest that these sites play a role in gene activation in response to exocytosis.