ABSTRACT
DNA synthesis, protein synthesis, and the accumulation of two tissue-specific transcripts were examined in cultures of sea urchin embryos that were completely dissociated during early cleavage stages and raised in Ca2+ -free sea water for 24 hr. In Strongylocentrotus purpuratus, both DNA and protein synthesis were severely reduced by dissociation treatment. Previous studies using this species indicated that aboral ectoderm-specific transcript accumulation is severely reduced while mesenchyme-specific transcripts generally accumulate more normally (11, 17). We therefore examined the accumulation of tissue-specific transcripts in another specific of sea urchin (Lytechinus pictus) whose DNA and protein synthetic rates were found to be less affected by dissociation. We find that accumulation of an aboral ectoderm-specific transcript (Spec 1) is also extremely low in L. pictus while a primary measenchyme-specific transcript (LSM) accumulates to normal levels. When DNA synthesis was restored to 77% of normal by keeping dissociatesd cells apposed with the fertilization membranes, Spec 1 accumulation was not improved. Adding Ca2+ to the sea water 8 hours after fertilization and allowing cells to reassociate into small, tight clusters restored Spec 1 accumulation to 70% of controls. Hence, there is no direct correlation between the reduced metabolic acitivities and lowered Spec 1 accumulation in dispersed cell cultures.
