INVOLVEMENT OF EXTRACELLULAR-MATRIX IN THE FORMATION OF THE INNER-EAR

Formation of the inner ear from the otic placode differs from invagina tion of other cup-shaped organ primordia. Activation of the actin cyto skeleton seems to play a limited role because precocious invagination does not occur upon treatment with activators of a contractile event a nd cannot be prevented by inhibitors. In this study, the possibility t hat invagination is mediated by changes in the surrounding mesenchyme was tested by treating embryos with agents which interfere with the in tegrity of extracellular matrix. Enzymes degrading hyaluronate and/or chondroitin sulfate were microinjected into the otic region prior to f olding. Synthesis of chondroitin sulfate proteoglycan was inhibited by microinjection of beta-xyloside, All treatments inhibited otic pit fo rmation by interfering with fold formation within the placode, Immunoc ytochemical procedures showed depletion of the appropriate extracellul ar matrix components for a short time period after enzyme treatments a nd for up to 24 hr after beta-xyloside injection. Invagination of the otic primordium is concluded to be controlled in part by anchorage of the epithelium to adjacent structures and possibly by expansion of the mesenchymal extracellular matrix. (C) 1995 Wiley-Liss, Inc.