Cell adhesion-dependent regulation of cell growth during sea urchin development

In the sea urchin embryo there are at least two cell adhesion molecules related to mammalian cadherins, one of them, similar to E-cadherin, is expressed in embryos at very early developmental stages, the second appears at the blastula stage (G. Ghersi et al. Mech. Dev. 41, 47-55 (1993)). We show here that when sea urchin embryos are treated with monovalent fragments of antibodies directed against the extracellular domain of these molecules, the decompaction of the embryo is accompanied by a sharp reduction of the rate of cell division. Treatment of the embryos with Fab fragments inhibits thymidine incorporation, but does not affect thymidine uptake or amino acid incorporation. After the first day of development treated embryos have 10 times less blastomeres than normal; later, however, they resume development and give eventually rise to normal-looking plutei. Analysis of putative second messengers shows that treatment of the embryos with anti-cadherin Fabs leads to a decreased tyrosine phosphorylation of the two cadherins and of two cadherin-associated proteins and to a doubling of the intracellular concentration of cAMP. These results are discussed in view of the importance of cell adhesion signals for cell growth control.