The canine oocyte: uncommon features of in vivo and in vitro maturation

Abstract

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 µm, 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.

A Pedigree-Based Map of Recombination in the Domestic Dog Genome

“…In contrast, meiosis in female dogs begins later, in the neonatal period. While recombination is complete prior to ovulation in humans, dogs ovulate immature oocytes, after which meiosis must complete before the oocyte becomes fertile, around 48 hr after ovulation (Freixa et al 1987; Chastant-Maillard et al 2011). …”

Dog cloning with in vivo matured oocytes obtained using electric chemiluminescence immunoassay-predicted ovulation method

“…Unlike other mammalian oocytes, dog oocytes mature after ovulation in the oviduct [10]. After ovulation, the oocytes resume meiotic division and progress to the metaphase II stage within three days.…”

Reliability of Hoechst 33342 Staining under Wide-Field Microscopy for Evaluation of the Nuclear Status of Living Dog Oocytes

“…This specific oocyte biology may largely contribute to the low efficiency of the canine in vitro maturation~IVM! process, with usually only 10-20% of the metaphase oocytes obtained after 72 h in culture when oocytes originate from anestrus ovaries~Luvoni et al, Chastant-Maillard et al, 2011!. IVM therefore appears to be the main limiting factor for in vitro embryo production, and to date no puppy has been born after IVM. Moreover, at the end of the IVM period, the nuclear stage cannot be assessed in 20% to 60% of the cultured oocytes because the nuclear stage cannot be recognized or chromatin cannot be found~Otoi Luvoni et al, 2003;Rodrigues & Rodrigues, 2003;Vannucchi et al, 2006Vannucchi et al, , 2009Rodrigues et al, 2006Rodrigues et al, , 2009Lee et al, 2007c;Silva et al, 2009;Alhaider & Watson, 2009!. Such disorganized chromatin or absence of DNA may result from oocyte degeneration during the long IVM culture, due to suboptimal culture media that inappropriately match the oocyte requirements.…”

“…In a specific endocrine environment high blood progesterone level!, bitch oocytes are ovulated in an immature stage~prophase I! and require around 48-60 h in the oviduct to complete meiosis~Reynaud et al, 2005; for review Chastant-Maillard et al, 2011!. This specific oocyte biology may largely contribute to the low efficiency of the canine in vitro maturation~IVM!…”