The Reaggregation of Dissociated Embryonic Sea Urchin Cells

Studies carried out on reaggregating sea urchin embryonic cells reveal that reaggregating cells can give rise to normal pluteus larvae by three developmental pathways: (i) from clusters, (ii) from chains of beads, and (iii) from a tissue culture phase. Experiments carried out on a mixture of cells from two different species, Arbacia punctulata and Lytechinus pictus, demonstrate that reaggregation is species specific and that the sorting out of cells according to species occurs. Movement of cells within an aggregate is non-random and unidirectional. Electron microscope analysis of mixed aggregates of cells of the two species indicates that cells of the same species make initial contact and adhere to one another by means of numerous microvilli and with the formation of an intercellular hyaline-like material. Cells of the two different species adhere, but never by means of microvilli and no hyaline-like material can be detected on the cell surfaces. The results indicate a role in reaggregation of an intercellular material, possibly an intercellular cement.