A tissue-specific repressor in the sea urchin embryo of Lytechinus pictus binds the distal G-string element in the LpS1-beta promoter.

LpS1 RNA transcripts and proteins are expressed exclusively in the aboral ectoderm of the embryo in the sea urchin Lytechinus pictus. We have characterized the LpS1-beta promoter to identify the cis-acting elements that may be involved in the aboral ectoderm-specific expression of the LpS1-beta gene. The distal G-string site, composed of six contiguous guanine deoxynucleotides located at -721 to -726, was analyzed. A mutation at the distal G-string caused over a two-fold increase in reporter chloramphenicol acetyltransferase gene activity and inappropriate expression of reporter green fluorescent protein in nonaboral ectoderm cells in L. pictus embryos. These results suggest that the proteins that bind the distal G-string act as a spatial repressor in the nonaboral ectoderm cells of the developing embryo.