Perturbation of extracellular matrix prevents association of the otic primordium with the posterior rhombencephalon and inhibits subsequent invagination.

In the avian embryo, the otic primordia become visible by Hamburger and Hamilton stage 10 as a pair of thickened regions of head ectoderm. In contrast to other epithelial primordia, invagination occurs by means of formation of a series of folds in distinct areas of the primordium, giving the otic vesicle a box-like appearance. Because previous work has shown that otic invagination is ATP and calcium independent, it is unlikely that cytoskeletal changes are the primary mechanism responsible for invagination as in other epithelial primordia. Interaction of the primordium with surrounding tissues may provide the force for otic invagination. These extracellular forces may be transduced through extracellular matrix macromolecules and their cell surface receptors. This investigation tests the hypothesis that fusion of the otic and hindbrain basal laminae between stages 11 and 13 is necessary for normal invagination. Perturbation of binding of the otic primordium to the neural tube was accomplished by means of microinjection of antibodies to various extracellular matrix components and integrin subunits into the head mesenchyme in the otic region at stage 10. Only antibodies to laminin and integrins caused detachment of the otic primordium from the hindbrain. These experiments suggest that fusion of the otic and hindbrain basal laminae is required for subsequent invagination and, furthermore, that this event is mediated by components of the extracellular matrix.