Meeting Abstract

P2.45  Jan. 5  Inhibition of first cleavage modifies MAP kinase activity and embryonic patterning in squid. CRAWFORD, K.; St. Mary’s College of Maryland, MD and Marine Biological Laboratory, Woods Hole, MA kcrawford@smcm.edu

Ablation and isolation experiments performed on gastropod embryos demonstrate that the D macromere plays a critical role in axial patterning as the founder cell of the dorsal lineage. More recently, MAP kinase (MAPK) signaling cascades in the gastropod Ilyanassa obsolete have been linked to cell fate specification within the D macromere lineage and micromeres of the A, B, and C quadrants (Lambert and Nagy, 2001). To determine whether a similar signaling mechanism was present in squid, early cleavage stage embryos were studied by immunocytochemistry. That study revealed that following second cleavage MAPK expression was present in the two posterior blastomeres and with third cleavage became localized within the two posterior mid-line macromeres flanking the first cleavage furrow. To determine whether a relationship exists between first cleavage, MAPK and embryonic patterning, first cleavage was inhibited by cold shock treatment from 4-5 hours post fertilization (Crawford, 2000). Inhibition of first cleavage resulted in equalization of third cleavage and loss or reduction of MAPK expression in the posterior mid-line blastomeres. When cultured to organogenesis these embryos develop into one of two phenotypes and are either bilaterally symmetric but deficient in many of the tissues normally associated with the D lineage including: shell gland, heart, gills and mantle, or are severely radialized possessing little more than an enlarged cyclopic eye. These results link first cleavage, MAPK and the D lineage in cephalopods and support the notion that squid possess mirror image A, B, C, and D quadrants organized along their first cleavage furrow as described in the Cephalopoda by Adolf Naef (1928). Supported by an ROA to KC from the NSF.