The effects of disrupting cell interactions in early development were investigated by examining the accumulation of a primary mesenchyme specific transcript (SM50) and an aboral ectoderm-specific transcript (Spec 1) in cultures of sea urchin embryos that were dissociated at early stages and then cultured in CFSW. The expression of both SM50 and Spec 1 is temporally correct and remains restricted to the appropriate cell types, even if the embryo is dissociated as early as the 2-cell stage and maintained as a suspension of single cells. This result is consistent with the idea that the specificity of expression of these two genes, each characteristic of different lineages, is strongly regulated by information in the egg. Average SM50 expression is half that of intact embryos, but Spec 1 expression is very low, only 10–20% of intact controls, suggesting some differences in the response of the two genes to lack of close cell interactions.

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