Differentially expressed genes during fruiting body development in the aggregative ciliate Sorogena stoianovitchae (Ciliophora: Colpodea)

Sorogena stoianovitchae is the only ciliate that undergoes fruiting body development. Previously, we demonstrated that the developmental process is divided into five distinct stages: aggregation, compact aggregation, secretion of a mucous matrix, stalk elongation, and completion of the fruiting body. When S. stoianovitchae is mildly starved, several hundreds of cells aggregate beneath the water surface, and the aggregate develops into an aerial fruiting body. Essential requirements for fruiting body development are high-cell density, a light-dark cycle, and a dark period of more than 8 consecutive hours. In addition, the initial aggregation begins during the night, and light stimulation at sunrise triggers subsequent development. To elucidate the genes involved in fruiting body development, we carried out a reverse transcription-polymerase chain reaction (RT-PCR) in cells before and after such development. Thirty-six sequences with stage-specific expression patterns were cloned and partially sequenced. BLASTX search revealed that sequences with high identity for extracellular proteins (mucin, proteophosphoglycan) or membrane proteins (surface protein, TM9SF) are likely candidates for aggregation material, mucous matrix, and stalk material. Other sequences showed similarities to proteins, such as the casein kinase related to exocytosis in Paramecium, suggesting that they are involved in exocytosis signaling pathways for fruiting body development.