Developmental expression patterns of connexin26 and-30 in the rat cochlea

Connexin proteins Form transmembranous gap junction channels that connect a djacent cells. Connexin26 and connexin30 have been previously shown to be s trongly expressed in the inner ear of adult rats and to be mainly colocaliz ed. Because intercellular connections maturation of gap junction proteins a re crucial for maturation of different tissues, we investigated the develop mental expression of connexin26 and connexin30 in pre- and postnatal rats u sing immunocytochemistry. in the rat otocyst, staining for connexin26 as we ll as for connexin30 appeared at the 17th day of gestation. However, at thi s stage, expression of connexin30 was low and restricted to the neurosensor y epithelium. Beginning from the 3rd postnatal day connexin26 and -30 were expressed with highest immunoreaction in the spiral limbus, the neurosensor y epithelium, and between the stria vascularis and the spiral ligament. Beg inning from postnatal day 12 the staining pattern resembled thai of adult a nimals, with additional strong staining between all fibrocytes of the spira l ligament. Double labeling experiments demonstrated strongest colocalizati on of both connexins between the stria vascularis and the spiral ligament. These results demonstrate that development of the cochlear gap junction sys tem precedes the functional maturation of the rat inner ear, which takes pl ace between the 2nd and 3rd postnatal week. In the cochlea of a 22-week-old human embryo, connexin26 and connexin30 could be detected in the lateral w all, suggesting that both connexins also play a crucial role in function of the human inner ear. Dev. Genet. 25:306-311, 1999. (C) 1999 Wiley-Liss, In c.