Disruptions of the extracellular matrix and expression of spicule matrix genes

The vegetal-most blastomeres of the 16-cell sea urchin embryo are determined to give rise to the primary mesenchyme cells (PMCs), which in turn secrete the calcified larval skeleton, the spicule. Results presented here contribute to a body of evidence demonstrating that an intact extracellular matrix (ECM) is required for the differentiation and morphogenesis of the PMCs. Specifically, it is demonstrated that perturbations of collagen deposition by the lathrytic agent ;Northern hybridization of RNA blots from whole embryos treated with BAPN shows almost total suppression of the expression of the SN30 gene, while the SM50 gene is relatively unaffected. Disruption of proteoglycan synthesis by the addition of ;The suppression by BAPN of the expression of the spicule matrix genes, as well as the inhibition of spiculogenesis, is shown to be stage-specific in both embryos and micromere cultures. If the drug is added after the PMCs have ingressed into the blastocoel, both SM30 and SM50 are expressed at close to control levels in treated embryos and micromere cultures. If BAPN is not added to the culture medium until after the start of invagination, spicule production in both embryos and micromere cultures is close to that in control cultures.;The effect of BAPN on RNA synthesis is examined by ;The effect of BAPN treatment on spicule matrix gene expression in dissociated whole embryo cultures is shown to be similar to the effect of the drug in whole embryos. The expression of SM50 is not suppressed when BAPN is added to cultures of dissociated whole embryos. This indicates that there is some factor present in the whole embryo, which alleviates the suppression of SM50 expression by BAPN treatment in embryos, and which is missing in isolated micromere cultures. (Abstract shortened by UMI.).