Transcription of the Spec 1-like gene of Lytechinus is selectively inhibited in response to disruption of the extracellular matrix

The influence of the extracellular matrix (ECM) on differential gene expression during sea urchin develop­ment was explored using cell-type-specific cDNA probes. The ECM of three species of sea urchins, Strongylocen- trotus purpuratus, Lytechinus variegatus and Lytechinus pictus, was disrupted with the lathrytic agent /5-amino- propionitrile (BAPN), which inhibits collagen deposition in the ECM and arrests gastrulation (Wessel & McClay, Devi Biol. 121: 149, 1987). The levels of several mRNAs (Spec 1, Spec 2, Cylla actin, Cyllla actin and collagen in S. purpuratus, and metallothionine, ubiquitin and LpS3 in L. pictus and L. variegatus) were compared in BAPN- treated and control embryos. These mRNAs accumu­lated normally during BAPN treatment, even though the embryos did not gastrulate. To determine if the ex­pression of any gene product is sensitive to ECM disruption, a differential cDNA screen compared poly (A⁺) RNA from BAPN-arrested and control embryos in Lytechinus. A cDNA clone was isolated from this screen that represented a 2Ί kb mRNA that did not accumulate during BAPN treatment. Removal of BAPN resulted in the accumulation of this transcript coincident with the onset of gastrulation. This cDNA clone encodes a L. variegatus homologue of LpSl, recently demonstrated to be an ancestral homologue of the aboral ectoderm- specific Spec 1-Spec 2 gene family in S. purpuratus. Nuclear run-on assays in L. pictus suggested that transcriptional activity of LpSl was selectively inhibited by BAPN treatment. Thus, although the accumulation of many gene products occurred independently of the embryonic collagenous matrix, the accumulation of LpSl and LvSl appeared to be mediated by the ECM.