Extracellular matrix receptors and their effects on cell behaviour during gastrulation in the sea urchin
Date
1993
Authors
Crawford, Bryan Douglas
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Abstract
During gastrulation in sea urchins cells at the tip of the archenteron extend filopodia that attach to the wall of the blastocoel and are thought to assist in the elongation of the archenteron. At the completion of gastrulation these cells ingress and migrate into the blastocoel. Time-lapse video records were made of preparations in which ectodermal cells were removed, leaving the archenteron, mesenchyme cells and blastocoelar extracellular matrix (BECM). In preparations of late gastrulae, cells at the tip of the archenteron extend filopodia which attach to the basal lamina and pull it inward, collapsing the preparation. This collapse does not occur in preparations made prior to the elongation phase and can be inhibited with cytochalasin B and azide, but not with colchicine. Increased migratory behaviour was observed in preparations treated with the laminin derived peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). Cells extend and retract filopodia, collapse the ECM, and migrate out of the preparation. This behaviour was not observed in preparations treated with whole laminin, fibronectin, or Arg-Gly-Asp-Ser (RGDS) peptides. Cells in BECM preparations incubated in YIGSR extend significantly more processes than those incubated in RGDS, laminin, fibronectin or BSA. This effect is titratable between 8 µM and 1 mM. Laminin has a significant inhibitory effect on the number of cell processes observed. Double labelling experiments with biotinylated laminin or biotinylated Cys-Asp-Pro-Gly-Tyr-Ile-Gly-Ser-Arg (CDPGYIGSR) and a monoclonal antibody against mesenchyme cells (Sp12) reveal that laminin and CDPGYIGSR label specific cells within the blastocoel, some of which are mesenchyme. A laminin affinity column binds several ¹²⁵I-labelled cell surface components, one of which elutes with YIGSR and has an Mᵣ of 70 k on SDS-PAGE. Eluent from a CDPGYIGSR affinity column contains only a 70 k protein. I propose that cells at the tip of the archenteron attach to, and exert a force on the basal lamina during archenteron elongation, and that YIGSR containing domains of laminin at the roof of the blastocoel interact with a 70 k cell surface receptor which stimulates migratory behaviour in these cells at the completion of gastrulation.