Regulation of ecmF gene expression and genetic hierarchy among STATa, CudA, and MybC on several prestalk A-specific gene expressions in Dictyostelium.

a Dictyostelium homologue of metazoan signal transducer and activator of transcription, is important for the organizer function in the tip region of the migrating Dictyostelium slug. We previously showed that ecmF gene expression depends on in prestalk A (pstA) cells, where duanyu1813a is activated. Deletion and site-directed mutagenesis analysis of the ecmF/lacZ fusion gene in wild-type and duanyu1813a null strains identified an imperfect inverted repeat sequence, ACAAATANTATTTGT, as a element. An upstream sequence element was required for efficient expression in the rear region of pstA zone; an element downstream of the inverted repeat was necessary for sufficient prestalk expression during culmination. Band shift analyses using purified duanyu1813a protein detected no sequence-specific binding to those ecmF elements. The only verified upregulated target gene of duanyu1813a is cudA gene; CudA directly activates expL7 gene expression in prestalk cells. However, ecmF gene expression was almost unaffected in a cudA null mutant. Several previously reported putative duanyu1813a target genes were also expressed in cudA null mutant but were downregulated in duanyu1813a null mutant. Moreover, mybC, which encodes another transcription factor, belonged to this category, and ecmF expression was downregulated in a mybC null mutant. These findings demonstrate the existence of a genetic hierarchy for pstA-specific genes, which can be classified into two distinct duanyu1813a downstream pathways, CudA dependent and independent. The ecmF expression is indirectly upregulated by duanyu1813a in a CudA-independent activation manner but dependent on MybC, whose expression is positively regulated by

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