Folliculogenesis, Ovulation and Endocrine Control of Oocytes and Embryos in the Dog (original) (raw)
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Multioocyte follicles in domestic dogs: A survey of frequency of occurrence
Theriogenology, 2008
Multioocyte follicles (MOFs) or polyovular follicles have been reported infrequent in the ovaries of the bitch, decreasing with the age. In this study, the routine observation of the ovaries allowed to verify that the existence of MOFs was far more frequent than previously reported. Ovaries from 150 genitalia, excised during ovariohysterectomy of bitches of different breeds and ages were used. The mean prevalence of MOFs was 40.7%, and the prevalence was higher in young animals (68.4 and 62.2%, in prepubertal and in bitches under 1 year, respectively). In 7–8 years old bitches, the occurrence decreased to 30.4%, and it decreased again to 14.3% in 10 or more years old bitches. It was also more frequent in mongrels than in pure-breeds (52.3–25.5%, respectively). Most follicles contained 2–3 oocytes, but follicles containing up to 10 oocytes were also observed. When the number of oocytes was higher than 3, oocytes of various morphological appearances could be noticed within the follicle. These observations show that the presence of MOFs can affect the number of oocytes recovered in assisted reproductive protocols and may also influence the ovulation rate and prolificity of these animals.
Biology of Reproduction of the Dog and Modern Reproductive Technology
2007
The dog has been used in medical research as a model for humans, but the lack of appreciation of the differences especially in reproductive pattern and hormonal effects and sensitivity has led to some classic misconceptions for instance regarding the tumorigenic effects of progestagens on mammary glands. In contrast, the dog has proved to be a very useful model in
The canine oocyte: uncommon features of in vivo and in vitro maturation
The biology of the canine oocyte is unusual compared with that of other mammalian females. The present paper reviews both in vivo and in vitro specificities of canine oocytes. Final follicular growth in the bitch is characterised by an early appearance of LH binding sites in the granulosa, a high proportion of polyovular follicles and a preovulatory luteinisation, starting at the time of the LH surge. Through follicular fluid, preovulatory oocytes are thus exposed to high levels of progesterone, as high as 1000-fold plasma concentrations. The composition of the follicular fluid is affected by the size of the female. The more specific aspect of oocyte biology in the bitch is ovulation: oocytes are expelled immature, at the Prophase I stage. Ovulatory follicles are 6-8 mm in diameter, releasing oocytes from 110 mm, with dark cytoplasm. Resumption of meiosis occurs from 48 h postovulation, MII stages appearing 48-54 h after ovulation. The mechanisms controlling such a late meiotic resumption are still unknown. Granulosa cells seem to play a central role as in other mammalian species, but not with cAMP as the principal mediator. The importance of a transient reactivation of oocyte transcription a few hours before meiotic resumption is to be explored. These specific features may contribute to the low efficiency of IVM. Only 10-20% oocytes reach the metaphase stage and suffer from a poor cytoplasmic maturation. Moreover, in vitro culture of canine oocytes is associated with a high proportion of degeneration. To date, IVM of the oocytes is the main limiting factor for the development of assisted reproductive techniques in the canine. A better knowledge of the basic physiology of folliculogenesis and the molecular mechanisms controlling oocyte meiosis resumption in this species may allow us to overcome this obstacle.
Zygote, 2005
Canine oocytes are ovulated at prophase of the first meiotic division and undergo maturation in the distal part of the oviduct for at least 48–72 h. Because of these differences from other domestic mammals, the efficiency of in vitro maturation (IVM) of canine oocyte is very low. The present study was conducted to evaluate the effects of canine serum on IVM of canine oocytes recovered from ovaries in various reproductive states (follicular, luteal or anestrous stages). Oocytes were recovered by mincing ovaries from bitches presented for ovariohysterectomy at various stages of the estrous cycle. Heat-inactivated canine serum was prepared with blood taken from dogs at the anestrous, estrous or diestrous stage of the estrous cycle as determined by progesterone concentration and vaginal cytology. Oocytes were cultured for 72 h in tissue culture medium (TCM)-199 supplemented with 10% canine anestrous, estrous or diestrous serum or fetal bovine serum (FBS) (experiment 1), or supplemented ...
Intraovarian regulation of folliculogenesis in the dog: A review
Reproduction in Domestic Animals, 2020
Dog reproductive cycle is unique among other mammals in that females experience long and variable periods of ovarian inactivity. Neuroendocrine controls of the reproductive cycle have been thoroughly studied in the dog. However, there is little information regarding endocrine, paracrine and autocrine controls of dog ovarian folliculogenesis. Advancements in the understanding of mechanisms regulating dog ovarian follicle development will be helpful in the development of an approach to control cyclicity in this species. Furthermore, such information will likely be useful for the establishment of an in vitro follicle culture system to preserve fertility of genetically valuable disease models or endangered canids. This review highlights current knowledge on dog folliculogenesis with emphasis on endocrine, paracrine and autocrine controls of follicular development.
Reproduction in Domestic Animals, 2009
Remarkably little is known about folliculogenesis in the dog. Objectives were to characterize (1) changes in follicle/oocyte diameter and granulosa cell number and (2) expression of Fibroblast Growth Factor-2 (FGF-2) and-7 (FGF-7) during ovarian follicle development in this species. Fourteen ovarian pairs were excised and processed for histological evaluation. Two to four serial sections/bitch were stained with hematoxylin, and follicle/oocyte diameters and granulosa cell number were determined at each developmental stage. Means follicle and oocyte size were compared among stages by ANOVA. Relationships between follicle diameter and oocyte size and granulosa cell number were determined using correlation and regression analysis, respectively. Another eight serial ovarian sections/bitch were processed for immuno-staining to determine FGF-2 and-7 expression. Primordial and primary follicles were similar in size (P < 0.05), but smaller than the progressively increasing (P < 0.05) diameters of later stage counterparts. Oocyte diameter gradually increased (P < 0.05) among oocytes derived from primordial, primary, secondary and early antral follicles with no difference (P > 0.05) thereafter. Oocyte size and granulosa cell number increased (P < 0.01) with follicular diameter. Except during anestrus, FGF-2 was detectable in oocytes and granulosa cells of primordial to secondary follicles. In adult bitches, FGF-7 was localized in granulosa cells of primary and secondary follicles and also occurred in the theca layer of antral follicles during proestrus and estrus. In summary, folliculogenesis in the domestic dog occurs in two phases with a preantral phase characterized by increasing follicle size in association with oocyte growth and granulosa cell proliferation. The subsequent antral phase is linked with marked granulosa cell proliferation and accumulation of antral cavity fluid. Finally, the temporal expression pattern of FGF-2 implies its role in follicular activation, whereas FGF-7 activities appear related to later folliculogenesis.
Endocrine and paracrine controls of canine follicular development and function
Reproduction in Domestic Animals, 2017
Canid reproduction is unique among other mammals in that females experience long and variable periods of ovarian inactivity. While the domestic dog exhibits a nonseasonal, largely sporadic monoestrus occurring once or twice a year, most wild canids, such as the gray wolf (Canis lupus) and red wolf (Canis rufus), are seasonal breeders with onset apparently dependent on species, latitudinal location and/or variety of environment factors. Neuroendocrine controls of ovarian functions have been mostly studied in the dog, but less so in their wild counterparts, due to difficulties in regular blood sampling. Yet, development of non-invasive hormone monitoring has advanced the understanding of reproductive cycle in wild canids. Recent advances in in vitro follicle culture technology also have begun to provide insights into paracrine controls of canid ovarian folliculogenesis. This review highlights current knowledge on canid reproduction with emphasis on endocrine and paracrine controls of follicular development. We also discuss future research priorities, including advancing the understanding of anoestrous termination and role of paracrine factors in canine folliculogenesis.
Progesterone Plays a Critical Role in Canine Oocyte Maturation and Fertilization
Biology of reproduction, 2015
Canine oocyte maturation and fertilization take place within the oviducts under increasing plasma levels of progesterone (P4). In order to investigate the role of P4 in these processes, 51 beagle bitches were treated with the P4 receptor antagonist aglepristone at the end of proestrus and 32 females were kept untreated. Fifteen treated and 13 control bitches were inseminated at Days +1 and +2 after ovulation (Day 0). Stages of oocyte maturation and embryo development were determined after ovariectomy at different time points after ovulation. Aglepristone did not prevent ovulation but delayed the resumption of oocyte meiosis and inhibited its progression: first metaphase I (MI) stage was observed at 173 h postovulation and 39% of oocytes reached MII as late as 335 h postovulation in treated females whereas first MI occurred at 76 h and 100% of oocytes were in MII at 109 h postovulation in controls. Aglepristone extended the stay of morphologically normal oocytes within the oviducts: ...