Regulation of the mec‐3 gene by the C.elegans homeoproteins UNC‐86 and MEC‐3.

The mec‐3 gene encodes a homeodomain protein with LIM repeats that is required for the specification of touch cell fate in Caenorhabditis elegans. Previous experiments suggested that mec‐3 expression requires the product of the unc‐86 gene, a POU‐type homeoprotein, and mec‐3 itself. We have analyzed the control of mec‐3 expression by identifying potential cis regulatory elements in the mec‐3 gene (by conservation in a related nematode and by DNase I footprinting using unc‐86 and mec‐3 proteins) and testing their importance by transforming C.elegans with mec‐3lacZ fusions in which these sites have been mutagenized in vitro. Both unc‐86 and mec‐3 proteins bind specifically to the promoter of the mec‐3 gene, suggesting that both proteins may be directly involved in the regulation of the mec‐3 gene. In addition, the footprint pattern with mec‐3 protein is altered in the presence of unc‐86 protein. In vivo transformation experiments reveal that some of the binding regions of the two proteins are needed for general positive control and maintenance of mec‐3 expression while others have no detectable, unique function. Interestingly, the unc‐86 gene appears to be required not only to initiate mec‐3 expression but also to maintain it.