Resting cyst wall glycoproteins isolated from two colpodid ciliates are glycine-rich proteins

Analysis of fruiting body development in the aggregative ciliate Sorogena stoianovitchae (Ciliophora, Colpodea)

The fruiting body-forming ciliate Sorogena stoianovitchae is a protist that is multicellular in one stage of its life cycle. When nutrient levels are depleted, a number of Sorogena cells aggregate beneath the water surface to form an aerial fruiting body. Based on morphologies and the inhibition of protein synthesis, fruiting body development is divided into five distinct stages: (1) aggregation before sunrise, (2) compact aggregation after sunrise, (3) secretion of mucous matrix, (4) stalk-elongation, and (5) completion of the fruiting-body. In the aggregation stage, the cells were trapped in a matrix material that stained orange with 4',6-diamino-2-phenylindole (DAPI), but differed from the mucous matrix in the later stage. A short interruption of the dark period, at 6-8 h after the onset of dark, inhibited fruiting body development. Irrespective of the length of the dark period (10-16 h), the cells remained in the aggregation stage until the beginning of the light period. Therefore, an uninterrupted dark period of more than 8 h is critical for the initial aggregation of cells, but subsequent development is triggered by light.

Cysteine proteases and cell differentiation: excystment of the ciliated protist Sterkiella histriomuscorum

The process of excystment of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) leads in a few hours, through a massive influx of water and the resorption of the cyst wall, from an undifferentiated resting cyst to a highly differentiated and dividing vegetative cell. While studying the nature of the genes involved in this process, we isolated three different cysteine proteases genes, namely, a cathepsin B gene, a cathepsin L-like gene, and a calpain-like gene. Excystation was selectively inhibited at a precise differentiating stage by cysteine proteases inhibitors, suggesting that these proteins are specifically required during the excystment process. Reverse transcription-PCR experiments showed that both genes display differential expression between the cyst and the vegetative cells. A phylogenetic analysis showed for the first time that the cathepsin B tree is paraphyletic and that the diverging S. histriomuscorum cathepsin B is closely related to its Giardia homologues, which take part in the cyst wall breakdown process. The deduced cathepsin L-like protein sequence displays the structural signatures and phylogenetic relationships of cathepsin H, a protein that is known only in plants and animals and that is involved in the degradation of extracellular matrix components in cancer diseases. The deduced calpain-like protein sequence does not display the calcium-binding domain of conventional calpains; it belongs to a diverging phylogenetic cluster that includes Aspergillus palB, a protein which is involved in a signal transduction pathway that is sensitive to ambient pH.