EXPRESSION AND LOCALIZATION OF COL2A1 MESSENGER-RNA AND TYPE-II COLLAGEN IN HUMAN FETAL COCHLEA

The expression and localization of COL2A1 mRNA and protein was examine d in human fetal cochlea to study the role of this gene in hearing and to begin to understand the pathogenesis of mutations in COL2A1 in hea ring disorders. Northern blot analysis revealed COL2A1 expression in f etal membranous cochlea to be markedly greater than that in fetal skin , kidney, cartilage, eye and brain. In situ hybridization revealed COL 2A1 expression in marrow cells, osteoblasts, fibroblasts and some oste ocytes, in addition to chondrocytes in otic capsule. In the membranous cochlea, connective tissue elements (spiral ligament, spiral limbus a nd modiolar connective tissue), neuronal cells, secretory cells (stria vascularis) and organ of Corti cells (sensory hair cells) were found to express COL2A1. Immunohistochemistry was performed to assess distri bution of type TI collagen and correlation with COL2A1 mRNA in these m orphologically and functionally diverse cell populations. In otic caps ule, only cartilage was found to stain positively, and in membranous c ochlea, only connective tissue structures including spiral ligament, s piral limbus, tectorial and basilar membranes, modiolar and spiral lam ina cartilage contained type II collagen. Nonconnective tissue cells, marrow cells and osteoblasts did not contain immunohistochemically ide ntifiable protein. Absence of type II collagen in a subset of cochlear cells may reflect potentially either inability to detect low levels o f protein in these cells or posttranscriptional regulation.