Isolation and characterization of a novel connexin gene, Cx-60, in porcine ovarian follicles

A new member of the connexin family was isolated from the porcine ovary. The amino acid sequence deduced from the nucleotide sequence of genomic as well as complementary DNA clones predicted the reading frame encoding the 60-kDa protein product, indicating the largest molecular mass among the connexin family genes analyzed to date; we named this gene Cx-60 based on its predicted molecular mass. The features of its primary structure were compared with those of other connexin genes, and the characteristics of its expression profile were examined in mammalian ovarian follicles. Cx-60 shares significant similarities with other connexins in the transmembrane and extracellular domains, but showed a highly unique primary structure in the cytoplasmic and carboxyl-terminal domains. The Cx-60 gene was unique in that its messenger RNA was detected in both the theca interna compartment and cumulus cells in the ovary; of other tissues, Cx-60 expression was relatively evident in the colon, thymus, and spleen. Cx-60, in contrast to Cx-43, was expressed constitutively upon gonadotropin stimulation when examined in hypophysectomized rats. Taken together, these results indicate that at least the connexin genes Cx-60, Cx-43, Cx-32, Cx-30.3, and Cx-26 are expressed in porcine ovarian follicles with differing expression profiles, including cell specificity.

Differential expression of four connexin genes, Cx-26, Cx-30.3, Cx-32, and Cx-43, in the porcine ovarian follicle

Connexin genes expressed in porcine ovaries were isolated by reverse transcription-PCR, and the expression of four connexin genes (Cx-43, -32, -30.3, and -26) was detected by in situ hybridization in internal and surrounding compartments of large antral follicles. Cx-43 and Cx-30.3 were expressed in the theca interna as well as in the granulosa cell compartment. However, two zones were observed in the theca interna by probing with Cx-43; about a quarter of the region close to the lamina basalis appeared devoid of Cx-43 messenger RNA (mRNA) and protein as well. Cx-30.3, in contrast, seemed to be expressed ubiquitously in these two compartments. Cx-26 and Cx-32 were expressed only in the thecal cells. Both Cx-43 and -30.3 also gave positive signals in the cumulus cells to the same extent as obtained in the granulosa cells with the respective probes, whereas the expression of Cx-32 and -26 was undetectable. Cx-43 mRNA drastically decreased in the functioning stage of the corpus luteum, whereas Cx-30.3 mRNA increased significantly in the early stage of luteinization in the estrus cycles. These results suggest that Cx-43 is not the only gap junction protein to be expressed in the ovarian follicle; other proteins, such as Cx-32, -30.3, and -26 seem to be expressed, and their expressions are regulated differently.