Regulation of gene expression during cell differentiation in the cellular slime molds

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In the development of cellular slime molds, cells aggregate to form a tissue, in which two types of cells (prestalk and prespore) differentiate in the anterior and the posterior parts. To elucidate the mechanisms of cell differentiation and pattem formation, we made the following studies.(1) We have shown that cells cultured in liquid in a roller tube form an agglutinate in which prestalk, and prespore cells exhibit a definite pattern of differentiation without undergoing morphogenesis. Williams made a similar culture of cells whose expression of prestalk-specific ecmA and ecmB genes can be histochemically detected by BATA-galactosidase activity. In the agglutinates forined, cells expressing ecmA first arose randomly and then were collected to the center, while those expressing ecmB appeared on the surface layers. The result is consistent with the previous one obtained with the pattem of prespore differentiation and indicates that the differentiation pattem is tonned by sorting out of differentiated cells.(2) We have previously shown that the upstream region between -442 and -349 bp of presporespecific Dp87 gene is important for its expression. When this region is fused with the basal promoter of slime mold actin gene, the chimera gene was expressed from the vegetative stage and no difference in expression was detected between prestalk and prespore cells. This suggests that the upstream region only enhances the amount of transcription, but that cell-type-and development-specific expression is regulated by the region below -349 bp.(3) Expression of Dp87 gene during normal development was examined by using cells transformed with the promoter of Dp87 fused with BATA-galactosidase gene. Cells expressing Dp87 first appeared randomly in the aggregation streams and were later accumulated in the basal part of the aggregation centers, continuing the above notion that the differentiation pattem is formed by sorting out of differentiated cells.