Basal lamina heparan sulphate proteoglycan is involved in otic placode invagination in chick embryos

Abstract

Formation of the otocyst from the otic placode appears to differ from invagination of other cup-shaped organ primordia. It is known that the cellular cytoskeleton plays a limited role in otic placode invagination, whilst the extracellular matrix underlying the otic primordium intervenes in the folding process. In this study we have analysed the role of the basal lamina heparan sulphate proteoglycan in otic primordium invagination. At 10 H.H. stage, heparan sulphate proteoglycan immunomarking begins to appear on the otic placode basal lamina, increasing noticeably at 13 H.H. stage, coinciding with maximum folding of the otic epithelium, and is still present at later stages. Enzyme degradation of heparan sulphate proteoglycan in the otic primordium basal lamina, by means of microinjection with heparinase III prior to folding, significantly disrupts invagination of the otic placode, which remains practically flat, with a significant reduction in the depth of the otic pit and an increase in the diameter of the otic opening. The immunocytochemistry analysis revealed a notable depletion of basal lamina heparan sulphate proteoglycan in the otic primordia microinjected with heparinase, with no statistically significant differences observed in the volume or rate of cell proliferation in the otic epithelium relative to the control, which suggests that heparan sulphate proteoglycan disruption does not interfere with the epithelial growth. In addition, a study of apoptosis distribution by the TUNEL method confirmed that treatment with heparinase does not cause interference with cell survival in the otic epithelium. Our findings support the theory that otic primordium invagination may be regulated, at least in part, by the basal lamina components, which might contribute towards anchoring the otic epithelium to adjacent structures.

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.…”

Lens Capsule HSPG-Perlecan Regulates Lens Fibre Differentiation during Chick Embryo Development

“…Previous studies by [26] have reported the presence of Perlecan in chick developing lens from morula to 17 H.H. stage, so during lens plate induction and invagination to form the lens vesicle but this period does not include the beginning of the lens fibre differentiation; at these stages, Perlecan could be related with invagination morphogenetic mechanisms such as has been described in otic placode invagination [27]. Furthermore they describe a strong Perlecan expression in the lens without specific localization.…”