EXPRESSION OF SPICULE MATRIX PROTEIN GENE SM30 IN EMBRYONIC AND ADULTMINERALIZED TISSUES OF SEA-URCHIN HEMICENTROTUS-PULCHERRIMUS

We have isolated a cDNA clone for spicule matrix protein, SM30, from s ea urchin Hemicentrotus pulcherrimus and have studied the expression o f this gene in comparison with that of another spicule matrix protein gene, SM50. In cultured micromeres as well as in intact embryos transc ripts of SM30 were first detectable around the onset of spicule format ion and rapidly increased with the growth of spicules, which accompani ed accumulation of glycosylated SM30 protein(s). When micromeres were cultured in the presence of Zn2+, spicule formation and SM30 expressio n were suppressed, while both events resumed concurrently after the re moval of Zn2+ from the culture medium. Expression of SM50, in contrast , started before the appearance of spicules and was not sensitive to Z n2+. Differences were also observed in adult tissues; SM30 mRNA was de tected in spines and tube feet but not in the test, while SM50 mRNA wa s apparent in all of these mineralized tissues at similar levels. Thes e results strongly suggest that the SM30 gene is regulated by a differ ent mechanism to that of the SM50 gene and that the products of these two genes are differently involved in sea urchin biomineralization. A possible role of SM30 protein in skeleton formation is discussed.