IMMUNOCYTOCHEMISTRY OF CARBONIC-ANHYDRASE AND NONRADIOACTIVE DETECTION OF ITS RNA BY IN-SITU HYBRIDIZATION IN THE CHICK-EMBRYO MEMBRANOUS LABYRINTH

An immunocytochemical study was carried out with the aim to localize c arbonic anhydrase isozymes (CA I and CA II) in the chick membranous la byrinth. CA I and CA II were localized in the same cells and, during t he early developmental stages, were diffusely present in the labyrinth ine epithelium. At later stages, the sensorial epithelium of the macul ae acusticae, crista ampullaris and papilla basilaris, as well as laby rinthine dark cells and the epithelium of the endolymphatic sac strong ly stained by the immunocytochemical procedure. In 1-day and 1-week ol d chicks, CA was present in the same sites as at advanced embryonal st ages. In order to detect mRNA for carbonic anhydrase II, in situ hybri dization was also used. Strong hybridization signals were observed in the sensorial epithelium of the saccule, utricle and crista ampullaris , in the tegmentum vasculosum, the endolymphatic sac, the erythrocytes and the choroid plexus in embryos older than 10 days. This positivity persisted until the day after hatching. The authors discuss the signi ficance of labyrinthine CA and, based on in situ hybridization results , suggest that melanocytes do not provide labyrinthine dark cells with enzyme protein.