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Multiple cis-acting elements act cooperatively in directing trochoblast-specific expression of the alpha-tubulin-4 gene in Patella embryos.

During early embryogenesis of the mollusc Patella vulgata the alpha-tubulin-4 gene is specifically expressed in the differentiation process of a particular cell type, the trochoblasts. The 5' region of the gene has been analysed for elements that are required for the regulation of the cell-type-specific activation of the gene. In a functional assay, seven elements that play a role in the spatiotemporal activation of the gene were detected in the promoter sequence. They are not required all together at the same time. A core of two elements, together with two or three auxiliary elements, are sufficient in controlling trochoblast-specific expression of the gene in the Patella embryo. One of the core elements is always required, without it, the gene is not expressed at all. The other core element acts as a positive element in trochoblasts and as a negative element in non-trochoblasts and thus is involved in directing the cell-type specificity of expression. The seven elements act cooperatively, and at least some of them can substitute for each other. Sequence comparison revealed that six of the seven fragments contain the sequence element GTTAA, including one of the core elements. Both core elements seem to play a crucial role in the expression of the alpha-tubulin-4 gene during the differentiation process of trochoblasts in the Patella embryo. A model for the regulation of the cell-type specificity of the gene during trochoblast differentiation is proposed.