Expression of type I and type V collagen mRNAs in the elasmoid scales of ateleost fish as revealed by in situ hybridization

The ability of scale-forming cells to produce both type I and type V collag ens was investigated by ill situ hybridization at the light and electron mi croscope levels. Biochemical analyses reported that type I collagen, the pr edominant component, was associated with the minor type V collagen in the c ollagenous matrix of the teleost scales where, thin and thick collagen fibr ils formed distinct layers. Thin collagen fibrils of the external layer wer e produced by the episquamal scleroblasts scattered on the outer scale surf ace, while thick collagen fibrils forming the compact basal plate were prod uced by the hyposquamal scleroblasts lining the inner surface of the scale. We demonstrated that episquamal and hyposquamal scleroblasts contained mRN As for alpha 1(I) and alpha 1(V) collagens. Quantification by image analysi s of the relative amount of alpha 1(I) and alpha 1(V) mRNAs in episquamal a nd hyposquamal scleroblasts suggests that the gene expression of type V col lagen was proportionally higher in episquamal scleroblasts. These results s upport our hypothesis that the diameter of the thin fibrils of the external layer is regulated by the significant amount of type V collagen that inter acts with type I collagen.