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

Abstract

Invagination of other cup-shaped organ primordia. It is known that the cellular cytoskele- ton plays a Abstract Formation of the otocyst from the otic placode appears to differ from limited role in otic placode invagination, whilst the extracellular matrix underlying the otic pri- mordium 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 im-

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 adja- cent structures.

Key words Otic development • Heparinase • Microinjection • Epithelial folding • Extracellular matrix

munomarking begins to appear on the otic placode basal

lamina, increasing noticeably at 13 H.H. stage, coincid- ing with maximum folding of the otic epithelium, and is still present at later stages. Enzyme degradation of hepa- ran 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 sig- nificant reduction in the depth of the otic pit and an in- crease in the diameter of the otic opening. The immuno- cytochemistry analysis revealed a notable depletion of basal lamina heparan sulphate proteoglycan in the otic primordia microinjected with heparinase, with no statis- tically significant differences observed in the volume or rate of cell proliferation in the otic epithelium relative to the control, which suggests that heparan sulphate prot- eoglycan disruption does not interfere with the epithelial growth. In addition, a study of apoptosis distribution by the TUNEL method confirmed that treatment with hepa- rinase does not cause interference with cell survival in