Fertilization and early embryonic development in the blue fox (Alopex lagopus)

Assisted reproductive technologies for endangered species conservation: developing sophisticated protocols with limited access to animals with unique reproductive mechanisms

Assisted reproductive technologies (ARTs) have been proposed as a means of overcoming the significant challenges of managing small, isolated populations of endangered species in zoos. However, efficient protocols for ARTs do not exist for most endangered species. This review will focus on research efforts to characterize unique reproductive mechanisms and develop species-specific ARTs. Central to these studies are assays to measure steroid metabolites in urine or feces and/or training programs to allow unrestrained blood collections and ultrasound evaluations. The resulting information about estrous cycle dynamics, combined with studies of semen collection and processing, provides the foundation for the development of artificial insemination (AI). In vitro fertilization and embryo transfer are also discussed in relation to the advantages these techniques could provide relative to AI, as well as the significant challenges involved with technologies that require oocytes and embryos. Finally, an argument is made for additional research of nontraditional model species (e.g., domestic cats and dogs) and the development of novel models representing unique taxa. Whether these species are studied by zoo-based researchers with the expressed intent of developing ARTs for conservation or academic scientists interested in basic biology, the resulting information will provide a unique, evolutionary perspective on reproduction that could have wide-reaching benefits. The more information we have available, the better our chances will be of developing effective ARTs and making a difference in conservation efforts for endangered species.

Ovulation, fertilization and preimplantation embryonic development in raccoon dogs (Nyctereutes procyonoides)

A study involving 32 sexual mature females was conducted to characterize ovulation, fertilization and early embryonic development in vivo in raccoon dogs. Oocytes and embryos were collected from the oviducts and uteri, evaluated by stereomicroscopy. Ovulation occurred 25-32h after a female first accepted mounting, regardless of copulation, when the females were paired with a male in the same cage. Ovulated oocytes were at the primary stage. The number of ovulated eggs in females with or without mating was 9.96±2.65 and 9.00±1.92, respectively. Embryos at 2-4 cell, 8-16 cell, morula, blastocyst, and hatched blastocyst stage were observed at 29-73, 48-100, 98-126, 169-198 and 217-268h after first mating, respectively. Embryos were located in the oviduct prior to 4-cell stage and moved into the uterus after 16-cell stage. Embryos at different stages were often obtained from the same female. During the zygote underwent a series of cleavage divisions, the diameter of the embryo cell mass continuously increased through the 2-cell and 4-cell stage, then started to decrease and was the minimum size at the morula stage. At the blastocyst stage, embryos increased in volume, and finally developed into a hatching blastocyst with a thinner zona pellucida. This is the first full report of preimplantation embryonic development in the raccoon dog, which will facilitate the application of advanced assisted reproductive technology in canine species.

Embryo biotechnology in the dog: a review

Canine embryos are a scarce biological material because of difficulties in collecting in vivo-produced embryos and the inability, to date, to produce canine embryos in vitro. The procedure for the transfer of in vivo-produced embryos has not been developed adequately, with only six attempts reported in the literature that have resulted in the birth of 45 puppies. In vitro, the fertilisation rate is particularly low (∼10%) and the incidence of polyspermy particularly high. So far, no puppy has been obtained from an in vitro-produced embryo. In contrast, cloning of somatic cells has been used successfully over the past 4 years, with the birth of 41 puppies reported in the literature, a yield that is comparable to that for other mammalian species. Over the same period, canine embryonic stem sells and transgenic cloned dogs have been obtained. Thus, the latest reproductive technologies are further advanced than in vitro embryo production. The lack of fundamental studies on the specific features of reproductive physiology and developmental biology in the canine is regrettable in view of the increasing role of dogs in our society and of the current demand for new biological models in biomedical technology.

In vivo canine oocyte maturation, fertilization and early embryogenesis: A review

This review reports existing and original data concerning the biology of the canine oocyte and early embryo. It describes specific aspects of intra- and extra-follicular maturation of the oocyte during the peri-ovulatory period, methods to detect ovulation, sperm survival and fertilization and timing of preimplantation embryo development.

In vivo meiotic resumption, fertilization and early embryonic development in the bitch

Early development in canine species follows a very specific pattern. Oocytes are ovulated at the germinal vesicle stage and meiotic resumption occurs in the oviduct. However, because of difficulties in the accurate determination of ovulation time and in the observation of oocyte nuclear stage by light microscopy, these early events have not been fully described. Moreover, the oocyte stage at which sperm penetration occurs is still uncertain since fertilization of immature oocytes has been reported in vivo and in vitro. The aim of this study was to establish the exact timing of in vivo meiotic resumption, fertilization and early embryo development in the bitch with reference to ovulation. Ovulation was first determined by ultrasonography, artificial inseminations were performed daily and oocytes/embryos were collected between 17 and 138 h after ovulation. After fixation and DNA/tubulin staining, the nuclear stage was observed by confocal microscopy. Of the 195 oocytes/embryos collected from 50 bitches, the germinal vesicle stage was the only one present until 44 h post-ovulation, and the first metaphase II stage was observed for the first time at 54 h. Sperm penetration of immature oocytes appeared to be exceptional (three out of 112 immature oocytes). In most cases, fertilization occurred from 90 h post-ovulation in metaphase II oocytes. Embryonic development was observed up to the eight-cell stage. No significant influence of bitch breed and age on ovulation rate, maturation and developmental kinetics was observed. However, some heterogeneity in the maturation/development process was observed within the cohort of oocytes/embryos collected from one bitch. In conclusion, the most peculiar aspect of the canine species remains oocyte meiotic maturation whereas fertilization follows the same pattern as in other mammals.

Factors involved in vivo and in vitro maturation of canine oocytes

The domestic dog could be a valuable model for studying and developing assisted reproduction in taxonomically related endangered Canids. However, the efficiency of in vitro oocyte maturation is very low in this species compared to that of other mammalian species and this limits the development of reproductive biotechnologies, such as in vitro embryo production, cryopreservation, or nucleus transfer. In canine species the female gamete has unique characteristics: the oocyte is exposed to high concentration of progesterone in the follicular environment, it is ovulated in the dictyate state, and resumes and completes meiosis in the oviduct. Therefore, optimum conditions for in vitro maturation of dog oocytes may differ from other mammalian models in which follicles, where estrogens are the dominant hormones, ovulate oocytes at the Metaphase II stage of the first meiotic division. An in vitro culture system needs to be based on in vivo conditions in order to create a microenvironment similar to that in which oocyte development occurs physiologically, but little is known on mechanisms regulating oocyte maturation in the dog. This review analyzes the known factors involved in canine oocyte maturation in vivo and in vitro in order to suggest on which aspects future investigations may be focused.

Meiosis and embryo technology: renaissance of the nucleolus

The nucleolus is the site of rRNA and ribosome production. This organelle presents an active fibrillogranular ultrastructure in the oocyte during the growth of the gamete but, at the end of the growth phase, the nucleolus is transformed into an inactive remnant that is dissolved when meiosis is resumed at germinal vesicle breakdown. Upon meiosis, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities harbour the development of fibrillogranular nucleoli and re-establishment of nucleolar function in conjunction with the major activation of the embryonic genome. This so-called nucleologenesis occurs at a species-specific time of development and can be classified into two different models: one where nucleolus development occurs inside the NPBs (e.g. cattle) and one where the nucleolus is formed on the surface of the NPBs (e.g. pigs). A panel of nucleolar proteins with functions during rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) are localised to specific compartments of the oocyte nucleolus and those engaged in late processing are, to some degree, re-used for nucleologenesis in the embryo, whereas the others require de novo embryonic transcription in order to be allocated to the developing nucleolus. In the oocyte, inactivation of the nucleolus coincides with the acquisition of full meiotic competence, a parameter that may be of importance in relation to in vitro oocyte maturation. In embryo, nucleologenesis may be affected by technological manipulations: in vitro embryo production apparently has no impact on this process in cattle, whereas in the pig this technology results in impaired nucleologenesis. In cattle, reconstruction of embryos by nuclear transfer results in profound disturbances in nucleologenesis. In conclusion, the nucleolus is an organelle of great importance for the developmental competence of oocytes and embryos and may serve as a morphological marker for the completion of oocyte growth and normality of activation of the embryonic genome.

In vitro maturation of bitch oocytes from advanced preantral follicles in synthetic oviduct fluid medium: serum is not essential

The ability of oocytes from preantral follicles to mature in vitro was assessed using a synthetic oviduct fluid (SOF) medium. Advanced preantral follicles (approximately 210 microm diameter) were isolated from the ovaries of domestic bitches and assigned to one of four treatment groups: (1) SOF (n = 230); (2) SOF + 3 mg/ml bovine serum albumin (+BSA, n = 220); (3) SOF + 20% fetal bovine serum (+FBS, n = 227); or (4) SOF + 3 mg/ml BSA + 20% FBS (+BSA+FBS, n = 232), then cultured for up to 72 h. A group of control follicles was not cultured (n = 103). The percentages of oocytes reaching metaphase I to metaphase II stages (MI to MII) did not differ between treatments at each culture period. Within treatments, the percentages of oocytes at MI to MII stages did not differ with duration of culture. However, when compared to the control group (0.97%) the percentages of oocytes at MI to MII increased (P < 0.05) in the SOF group after 48 h (10.0%) and 72 h (12.2%) of culture. In the +BSA (10.1%) and +FBS (9.7%) groups, the percentages of oocytes at MI to MII increased (P < 0.05) above control values only after 72 h of culture. The percentage of oocytes at MI to MII did not significantly increase in the +BSA+FBS group (3.9,6.6 and 7.6% at 24,48 and 72 h of culture, respectively) compared to the control group. These results indicate that under the described conditions supplementation of culture medium with BSA or FBS is not essential, and the simple medium SOF can support nuclear maturation of a small proportion of bitch oocytes in vitro.

Current state in biotechnology in canine and feline reproduction

Biotechnology has proceeded much further in cats than in canines, although the pregnancy rate after in vitro maturation (IVM), IVC and embryo transfer (ET) is still relatively low. The use of AI with frozen-thawed semen as a breeding tool to overcome breeding incompatibility or to preserve male genetic material has been limited in felines in contrast to the situation in domestic dogs and foxes. In many research scenarios and endangered felid species programs, the in vitro production of feline embryos with subsequent transfer has complemented the use of AI. Improvement of IVM, in vitro fertilization (IVF) and embryo culture coupled with ovarian tissue grafting, cryobanking of follicles, oocytes, semen, or embryos, with subsequent ET into surrogate females, may render this technology feasible for use in endangered wild felids. In canines, reliable systems for in vitro production of embryos, embryo cryopreservation and transfer are yet to be developed. The refinement of invasive fertilization techniques, such as intracytoplasmic sperm injection (ICSI), may eventually provide a tool for removal of recipient oocyte nuclei and transfer of selected embryonic or somatic cell donor nuclei into domestic cat ooplasm, thereby providing a tool for genetic modification, or for preservation of valuable genetic material.

Reproduction in foxes: current research and future challenges

Basic information on fox reproduction, such as endocrinology, oocyte maturation, artificial insemination, fertilisation and embryo development, ovarian and testicular function, parturition, milk production and neonatology has been gained from studies of farmed animals. Fox farming is an industry with considerable economic importance in countries such as Norway and Finland, and the use of farmed animals as models to study wild canine species has proven valuable. This paper reviews some major research accomplishments and new knowledge and identifies future challenges in research regarding both the wild and domestic variants of the fox species.

Nuclear staining and culture requirements for in vitro maturation of domestic bitch oocytes

Oocyte nuclear staining and culture requirements for in vitro maturation (IVM) in the bitch have yet to be fully investigated. In the first part of this study we investigated 7 methods for labeling nuclear material (573 oocytes). The most favorable method involved fixation plus aceto-orcein staining and light microscopy. The influence of serum supplementation of the culture medium for IVM was then investigated (1292 oocytes). Culture was performed in media supplemented with no serum or with 5, 10 and 20% fetal calf serum (FCS) and 0.3 or 4% bovine serum albumin (BSA). Identifiable nuclear material was either a germinal vesicle (GV) or GV breakdown (GVBD). After 48 h in medium plus 0, 5, 10 or 20% FCS and 0.3 or 4% BSA, the percentage of oocytes matured to GVBD was 13, 9, 15, 23, 36 and 40%, and the percentage matured to metaphase I/anaphase I/metaphase II was 4, 12, 24, 14, 36 and 13%, respectively. After 96 h, maturation to GVBD was 31, 14, 21, 11, 50 and 38%, and to metaphase I/anaphase I/metaphase II it was 6, 5, 3, 19, 15 and 9%, respectively. Within the limits of this study, BSA or high concentrations of FCS appear to be optimal for bitch oocyte maturation in vitro.