Cloning of GJA1 (connexin43) and its expression in canine ovarian follicles throughout the estrous cycle

GJA1 (also known as connexin43 or Cx43) is the most abundant gap junction protein in mammalian tissues including the ovary. Here, it facilitates intercellular communication among granulosa cells and growing oocytes, thereby connecting the developing gamete to the hormonal axis as well as to the essential network of supporting granulosa cells. To date, the pattern of follicular GJA1 expression has not yet been defined for canines, a species with unique reproductive physiology including delays in follicle development, ovulation, oocyte maturation and fertilization. Here, we report the complete mRNA sequence for canine GJA1 and identify not only increases (P < 0.05) in GJA1 mRNA expression in follicles at the secondary stage and larger, but also differences in expression levels between estrous cycle stages in both secondary and antral stage follicles. Expression of GJA1 mRNA in secondary follicles during proestrus was higher than in anestrus or estrus (P < 0.01), and at diestrus (P < 0.10). Antral follicles obtained during estrus expressed lower levels of GJA1 mRNA than any other cycle stage (P < 0.01). GJA1 mRNA expression in primary and large antral follicles was similar across the estrous cycle. Despite the extensive length of the canine estrous cycle as compared with that of other mammals, the GJA1 mRNA and protein expression profiles are not significantly different from those reported for other species and suggests that mechanisms regulating GJA1 transcription are not likely to contribute to the extended delays in follicle and oocyte development in the dog.