Characterization of Vegetal Plate Cells Separated from Cytochalasin B-Treated Blastulae of the Sea Urchin, Clypeaster japonicus. (cytochalasin B/cell isolation/presumptive primary mesenchyme cell/vegetal plate cell/sea urchin)

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Abstract
Vegetal plate forming cells (VPCs) of the vegetal plate blastulae of the sea urchin, Clypeaster japonicus had a layer of microfilaments on the basal side. The VPCs specifically protrude from the embryos after a treatment with 1 .mu.g/ml of cytochalasin B (CB). Based on scanning electron microscopy, unlike other epithelial cells the protruded VPCs possessed neither cilium nor microvilli on their surface. The protruded VPCs were easily separated from the embryos by stirring the embryo suspension with pipette. An in vitro immunohistochemistry using a primary mesenchyme cell (PMC) surface-specific monoclonal antibody (MAb) raised against PMCs of Strongylocentrotus purpuratus showed that the MAb also specifically bound to the PMCs in mesenchyme blastulae of C. japonicus. The MAb bound in 81% of the separated VPCs in C. japonicus vegetal plate blastulae examined. However, the MAb binding occurred only after the separated VPCs were incubated in artificial sea water (ASW) for at least 1 hr. In the VPC-deprived embryos, gastrulation occurred after they were transferred to normal ASW. However, the PMCs and the spicules were not formed in these embryos. In conclusion, a majority of the VPCs separated from the CB-treated blastulae were presumptive PMCs. These VPCs provide an excellent source of presumptive PMCs.