Expression and localization of collagen type IV α1 chain in medaka ovary

A cDNA clone coding for the collagen type IV alpha1 chain was obtained from the ovary of the medaka, Oryzias latipes. The clone encoded a protein of 1639 amino acids including a putative 21-residue signal peptide, and the deduced amino acid sequence of the alpha1 chain was homologous to those of the proteins from other species. The mRNA of the collagen type IV alpha1 chain was expressed in various tissues of the adult fish. In situ hybridization analysis revealed that the alpha1 chain mRNA was localized in the follicle layer of all growing follicles. In the post-ovulatory follicle that had released its oocyte during ovulation, the alpha1 chain transcript was detected in a winding line surrounding the tissue. This localization pattern was different from that of gelatinase B, a marker gene for granulosa cells. A specific antibody was prepared for the medaka collagen type IV alpha1 chain. Immunohistochemical analysis with this antibody yielded results consistent with those obtained by in situ hybridization. These data indicate that, in the medaka ovary, collagen type IV is synthesized by theca cells and is localized in the basement membrane.