Sea urchin micromeres arise at the vegetal pole of the embryo by unequal cleavage in the vegetal tier of four cells. Primary mesenchyme, the cleavage products of the micromeres, migrate into the blastocoel of the embryo where they interact with the extracellular matrix (ECM) and differentiate to produce the embryonic skeleton or spicule. Evidence from in vitro and in vivo studies suggests that the micromeres require a permissive environment or signal to initiate differentiation. An intact embryonic ECM is a major component of the permissive environment. The PI has recently shown that micromeres will differentiate in vitro if cultured on a reconstituted basal lamina (matrigel). Isolated micromeres cultured in sea water alone will not differentiate. What is the molecule in the matrigel which initiates differentiation and how is it related to the endogenous signalling molecule in the embryo. The PI proposes to: (1) identify and purify the spicule inducing activity (SIA) from the matrigel, (2) characterize the general mechanism of action of SIA, and (3) identify and initiate characterization of the homologous SIA activity from the sea urchin embryo.
