Histochemical study of otoconial formation in chick embryos

Histochemical investigation was done to clarity the distributon of glyacocojugates in the otolithic organs of developing chick embryos. Two kinds of lectins, wheat germ agglutinin and concanacalin A, were appilied to detect the localization of N-acethyl-glucosaminyl and mannosyl residues. FITC- and TRITC-labelled lectins were applied in preparation for fluorescence microscopy and colloidal-gold labelled lectins for transmission electron microscopy. In the 6-day-old chick embryo, the globular and the granular lectin-positive substances, which are regarded as the precursors of the otoconia, were observed both on the surface of and within the sensory epithelium of the macula. The otoconia were intensely labelled with lectins at every developmental stage of the chick embryo, while the labelling on the macular sensory epithelium decreased as the otoconia matured. Transmission electron microscopic observation revealed the localization of the glycoconjugates on secretory gramules of suppoerting cells of the sensory erithelium. At every stage of the developing chick embryuos, the lectin labellings in the otoconia were more intense in the peripheral electron dense zones, which had a higher calcium content, than in the central electron lucent zone. It was concluded that the precursors of the otoconia were secreted from the supprting cells of the macular sensory epithelium, and that the glycoconjugates play an important role in otoconial formation, strongly relating to calcium deposition.