A G C-RICH DNA-REGULATORY ELEMENT CONTROLS POSITIVE EXPRESSION OF THESEA-URCHIN LYTECHINUS-PICTUS ABORAL ECTODERM-SPECIFIC LPS1 GENE/

The LpS1 beta gene of Lytechinus pictus is activated at the late cleav age stage about 12 hr after fertilization. LpS1 beta transcripts accum ulate exclusively in aboral ectoderm lineages, LpS1 beta is thus a cla ssic example of a gene whose expression is tightly controlled both tem porally and spatially during early development. Previous studies on th e LpS1 beta promoter identified two G-string DNA elements, one proxima l and one distal to the LpS1 beta transcriptional start site, which bi nd to an ectoderm-enriched nuclear factor. In this report, we show tha t the ectoderm G-string factor binds to a G/C-rich region larger than the G-string itself and that the binding of the G-string factor requir es sequences immediately downstream from the G-string. These downstrea m sequences are essential for full promoter activity. Two regions of 5 '-flanking DNA are required for positive control of LpS1 beta, region I from base pairs -762 to -511, and region II, which includes the G/C- rich element, from base pairs -108 to -61. Region I also contains a me senchyme cell repressor element, The results indicate that LpS1 beta e xpression is regulated positively in ectoderm cells and negatively in mesenchyme cells. Similar positive and negative control mechanisms reg ulate the expression of the related Spec genes of Strongylocentrotus p urpuratus, but in this gene family the DNA elements are entirely diffe rent. We hypothesize that cis-regulatory elements are evolutionarily d ynamic and that many different combinations of DNA elements are capabl e of given rise to aboral ectoderm-specific expression.