Developmental expression of proteoglycans in the tectorial and basilar membrane of the gerbil cochlea.

The appearance and distribution of specific proteoglycans (PGs) was assessed during development and maturation of the tectorial (TM) and basilar membranes (BM) in the gerbil cochlea. At birth, monoclonal antibodies against keratan sulfate (KSPG) and chondroitin 4- or 6-sulfate (4S CSPG, 6S CSPG) reacted with the upper fibrous layer of the TM with staining for anti-KSPG predominating. Reactivity for 4S CSPG remained constant whereas that for 6S CSPG increased through day 20 when it exceeded that of 4S CSPG. The region of Köllikers organ near the developing tunnel of Corti stained positively with all three PG antibodies from birth through day 8. In contrast, cells in the developing inner spiral sulcus lacked immunoreactive KSPG but expressed CSPG. PGs were first detectable in the BM of the basal turn at day 8 and increased to near adult levels by 16 days after birth. Anti-KSPG again showed the strongest staining with labeling density for 4S and 6S CSPG being about equal at maturity. Staining with all three antibodies was localized along the margins of the BM. Reactivity of the TM and BM in the upper turns lagged behind that of the basal turns by 24-48 h. Our results show that the TM is relatively mature at birth, needing only minor changes in its PG content to reach adult levels. In contrast, the BM showed a marked increase in its content of PGs during a period corresponding to the onset and rapid development of auditory function.