Abstract
Simple SummaryThe oestrous cycle in canines is specifically more extended than that in other mammals. This implies that the oocytes do not reach maturity within the ovarian follicle but undergo final maturation in the oviducts. Besides oocyte maturation, the oviduct provides the necessary milieu for fertilization and preimplantation embryonic development. Consequently, the oviductal environment presumably changes in the postovulatory period and throughout the entire reproductive cycle to provide a suitable condition for supporting different functions. In this study, we evaluated the gene expression of different genes associated with oocyte-embryo development, such as progesterone receptor, cyclooxygenase-2, growth differentiation factor 9, and bone morphogenetic protein 15 in the canine oviductal cells at different phases of the oestrous cycle. Using quantitative PCR (qPCR) analysis in bitch oviductal cells, this study revealed the ovarian cycle’s influence on the oviductal essential transcripts in the bitch. It also assessed the influence of the ovulated cumulus-oocytes complexes on the expression of GDF-9 and BMP-15 genes. Thus, the oestrous-cycle-dependent gene expression pattern of PR, COX-2, GDF-9, BMP-15 in the canine oviduct was found to execute the oviductal cell interactions necessary for the development and function of the canine reproductive tract.The gene expression in the canine oviduct, where oocyte maturation, fertilization, and early embryonic development occur, is still elusive. This study determined the oviductal expression of (PR), cyclooxygenase-2 (COX-2), growth differentiation factor 9 (GDF-9), and bone morphogenetic protein 15 (BMP-15) during the canine oestrous cycle. Samples were collected from bitches at anoestrus (9), proestrus (7), oestrus (8), and dioestrus (11), after routine ovariohysterectomy and the ovarian surface structures and plasma progesterone concentration evaluated the physiological status of each donor. The oviductal cells were isolated and pooled. Total RNA was isolated, and gene expression was assessed by qPCR followed by analysis using the t-test and ANOVA. The PR mRNA increased (P < 0.05) from the anoestrus to dioestrus with the plasma progesterone concentration (r = 0.8). COX-2 mRNA expression was low in the anoestrus and proestrus, and negligible in the oestrus, while it was around 10-fold higher (P < 0.05) in the dioestrus. The GDF-9 mRNA was expressed during all phases of the oestrous cycle and was most abundant (P < 0.05) during oestrus phase. The BMP-15 mRNA decreased (P < 0.05) in the anoestrus and proestrus phases. Thus, the transcripts were differentially expressed in a stage-dependent manner, suggesting the importance of oestrous cycle regulation for successful reproduction in dogs.
Highlights
One of the most intriguing characteristics of canine reproductive physiology is the long oocyte maturation process, which prolongs the presence of the oocyte at the oviductal level
Progesterone values of the donors submitted to ovariohysterectomy were undetectable to 0.4 ng/mL in anoestrus phase, 0.9 to 1.03 ng/mL, in proestrus, 6.20 to 16.02 ng/mL in oestrus and 18.01 to 30.10 ng/mL in dioestrus
The expression of growth differentiation factor 9 (GDF-9) and progesterone receptor (PR) mRNA was detected in the oviducts during the whole oestrous cycle, but the bone morphogenetic protein 15 (BMP-15) gene expression was detected only in the anoestrus and proestrus phases, whereas COX-2 was not detected in oestrus
Summary
One of the most intriguing characteristics of canine reproductive physiology is the long oocyte maturation process, which prolongs the presence of the oocyte at the oviductal level. The oviducts play a decisive role for final oocyte maturation and is an important environment for gamete interaction, fertilization, and early embryonic development, the oviduct micro-environment is still poorly understood in canines. Several agents such as the ovarian hormones [1,2,3], prostaglandins [4,5], and growth factors [6] are known to influence oviductal functions in several species [7]. Ovarian steroids, including progesterone, affect the oviduct by regulating secretory functions in the lumen [3,8], which in turns affect the oocyte final maturation and embryo growth. Different reports in other species reinforce that COX-2-derived
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