Searching for excystment-regulated genes in Sterkiella histriomuscorum (Ciliophora, Oxytrichidae): a mRNA differential display analysis of gene expression in excysting cells.

In the absence of food, the oxytrichid Sterkiella histriomuscorum transforms like many ciliates into resting cysts. When transferred back into feeding medium, the cyst re-transforms into a vegetative cell. The entry into and exit from the dormant cyst stage are complex developmental processes still poorly investigated at the molecular level. Assuming that these changes in state could involve changes in gene expression, we have used the technique of mRNA differential display to detect differentially expressed genes in cysts and two different stages of excysting cell. Variation in the temporal expression pattern of transcripts could be detected and, in using an inverse-PCR strategy on circularized macronuclear DNA, we have sequenced the macronuclear genes of three of the isolated cDNAs. which correspond to 1) a nucleotide-binding domain-encoding gene, 2) a DHHC-domain-carrying gene, and 3) a phosphatase type 2C-encoding gene. For the first two genes, Northern blot analyses supported an excystment-associated regulated gene expression. We discuss their possible role during excystment and we show that the combination of differential display and inverse PCR constitutes a powerful approach to isolate excystment-regulated genes in hypotrichs.