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

Abstract

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.

Gata3 is required for early morphogenesis and Fgf10 expression during otic development

“…Close attachment of otic cup epithelium to neural tube basal lamina is thought to be necessary for normal invagination in chicken embryos (Brown et al, 1998;Moro-Balbás et al, 2000;Visconti and Hilfer, 2002). Mouse Gata3 starts to be expressed in otic placode around the time when it starts to invaginate and we show here that it controls the earliest otic morphogenetic steps.…”

Dlx gene expression during chick inner ear development

“…The adhesion molecules heparan sulfate proteoglycan, chondroitin sulfate proteoglycan, and ␣-laminin are also essential for adhesion of the otic placode to the hindbrain. In addition, their expression is not seen in the otic placode until after the appearance of Dlx3 (Gerchman et al, 1995;Moro-Balbas et al, 2000;Visconti and Hilfer, 2002).…”

“…Invagination of the otic placode in chick has been shown to require specific elements of the extracellular matrix and adhesion to the adjacent hindbrain (Gerchman et al, 1995;Brown et al, 1998;Moro-Balbas et al, 2000;Visconti and Hilfer, 2002). It is intriguing that Dlx3 is intensely expressed in otic ectoderm at the region of its attachment to the hindbrain as the placode begins to invaginate.…”

Wnt signals mediate a fate decision between otic placode and epidermis

“…In the CKO embryos, clearance of ␤-catenin protein from adherens junctions by E9.0 leads to secondary morphological defects in the remnants of the otic placode. As otic vesicle invagination is driven in part by contacts with the neural tube (Brown et al, 1998;Gerchman et al, 1995;Moro-Balbas et al, 2000;Visconti and Hilfer, 2002), it is likely that physical constraints prevent the greatly expanded placode of cAct embryos from invaginating to form an enlarged otic vesicle.…”