Developmental expression of a cell-surface protein involved in calcium uptake and skeleton formation in sea urchin embryos.

The developmental expression of a cell-surface protein involved in Ca2+ accumulation and skeleton formation in sea urchin embryos has been studied. In Strongylocentrotus purpuratus, this protein is present in the egg and in all cell types of the early embryo. After gastrulation, its synthesis and expression are restricted to the skeleton-forming primary mesenchyme cells. In Lytechinus pictus, the protein cannot be detected in eggs or in embryos until the mesenchyme blastula stage. Hybrid embryos demonstrate a pattern of expression indistinguishable from that of the species contributing the maternal genome, which suggests that early expression of the protein in S. purpuratus embryos is due to utilization of maternal transcripts from the egg. Later expression of this protein in primary mesenchyme cells is the result of cell-type-specific synthesis, likely encoded by embryonic transcripts. This cell-type-specific expression in primary mesenchyme cells correlates temporally with Ca2+ accumulation during skeleton formation in the embryo.