An efficient method for in vitro fertilization in rabbits

Effect of 16h of rabbit sperm incubation on capacitation and heterologous in vitro fertilization

In vitro fertilization (IVF) in rabbits is an important biotechnology, but its success remains low due to inefficient sperm capacitation. This study examines relationships between motility parameters (MP), protein tyrosine phosphorylation (PTP) and acrosomal exocytosis (AE) between sperm recovered after direct swim-up (DSU), and after 16 h of in vitro incubation under capacitating conditions, and heterologous IVF capacity. Variables were assessed in fresh ejaculates (ES), and after 2 h of DSU, and 16 h (T16) of incubation. PTP were grouped into four patterns in the different sperm structures according to their time-dependent appearance and AE. Throughout incubation, MP remained stable whereas AE increased after DSU and 16 h of incubation. Mid-piece PTP patterns increased after DSU and persisted until 16 h in reacted (R) and non-reacted spermatozoa (NR). In R and NR, annulus-ring PTP levels were also significantly higher in T16 versus DSU or ES. Flagellum PTP levels rose significantly during incubation such that highest levels were recorded in T16. In R sperm, levels of PTP patterns associated with the equatorial zone in T16 were significantly higher compared to NR and to DSU and ES. Cleavage rates were significantly higher at T16 than DSU and these were similar to rates recorded for homologous IVF used as positive control. Our capacitation protocol and PTP patterns at 16 h rendered the sperm competent to fertilize an oocyte in vitro. This time point matches the physiological timing of fertilization in vivo. We also describe a new annulus ring PTP pattern for this species.

Superovulation treatment of immature female rabbits increases the number of ovulated oocytes that can in vitro develop into blastocytes

To clarify the efficiency of superovulation in immature female rabbits, immature female rabbits were superovulated with equine chorionic gonadotropin, and the number of recovered oocytes, their maturity, and their ability to develop into blastocysts under in vitro fertilization and culture were examined in this study. More than 80 oocytes were recovered from 12-14-week-old immature female rabbits. In particular, an average of more than 100 oocytes were recovered from 13-week-old immature female rabbits. The number of oocytes in immature female rabbits was significantly-approximately 4 times-higher than in mature female rabbits. To compare oocyte maturity, oocytes from immature and mature female rabbits were compared by brilliant cresyl blue staining and mitochondrial distribution analysis. The proportion of mature oocytes detected by brilliant cresyl blue staining was higher in oocytes from mature female rabbits than in oocytes from immature female rabbits, but there were no significant differences in active mitochondrial distribution, fertilization rate, or blastocyst development rate. These results indicate that superovulation with immature female rabbits may be a useful technique for the collection of many oocytes.

In vivo and in vitro maturation of rabbit oocytes differently affects the gene expression profile, mitochondrial distribution, apoptosis and early embryo development

In vivo-matured cumulus–oocyte complexes are valuable models in which to assess potential biomarkers of rabbit oocyte quality that contribute to enhanced IVM systems. In the present study we compared some gene markers of oocytes and cumulus cells (CCs) from immature, in vivo-matured and IVM oocytes. Moreover, apoptosis in CCs, nuclear maturation, mitochondrial reallocation and the developmental potential of oocytes after IVF were assessed. In relation to cumulus expansion, gene expression of gap junction protein, alpha 1, 43 kDa (Gja1) and prostaglandin-endoperoxide synthase 2 (Ptgs2) was significantly lower in CCs after in vivo maturation than IVM. In addition, there were differences in gene expression after in vivo maturation versus IVM in both oocytes and CCs for genes related to cell cycle regulation and apoptosis (V-Akt murine thymoma viral oncogene homologue 1 (Akt1), tumour protein 53 (Tp53), caspase 3, apoptosis-related cysteine protease (Casp3)), oxidative response (superoxide dismutase 2, mitochondrial (Sod2)) and metabolism (glucose-6-phosphate dehydrogenase (G6pd), glyceraldehyde-3-phosphate dehydrogenase (Gapdh)). In vivo-matured CCs had a lower apoptosis rate than IVM and immature CCs. Meiotic progression, mitochondrial migration to the periphery and developmental competence were higher for in vivo-matured than IVM oocytes. In conclusion, differences in oocyte developmental capacity after IVM or in vivo maturation are accompanied by significant changes in transcript abundance in oocytes and their surrounding CCs, meiotic rate, mitochondrial distribution and apoptotic index. Some of the genes investigated, such as Gja1, could be potential biomarkers for oocyte developmental competence in the rabbit model, helping improve in vitro culture systems in these species.

Fertilization studies and assisted fertilization in mammals: their development and future

Studies of mammalian fertilization progressed very slowly in the beginning because of difficulties in obtaining a large quantity of fully mature eggs at one time. With progression of techniques to collect and handle eggs and spermatozoa, research in mammalian fertilization advanced rapidly. Today, far more papers are published on mammalian gametes and fertilization than those of all other animals combined. The development of assisted fertilization and related technologies revolutionized basic research as well as human reproductive medicine and animal husbandry. Reproduction is fundamental to human and animal lives. The author lists a few subjects of his personal interest for further development of basic and applied research of gametes and fertilization. Each reader will probably have more exciting subjects of future investigation.

Normal developmental competence to the blastocyst stage is preserved in rabbit ovarian tissue following cryopreservation and autografting to the mesometrium

The aim of the present study was to evaluate mesometrial autotransplantation of frozen–thawed ovarian tissue in the adult rabbit and investigate the developmental competence of oocytes retrieved from grafts by in vitro maturation, fertilisation and blastocyst formation. Twenty-five rabbits were divided into control, fresh tissue transplantation and frozen–thawed tissue transplantation groups. Rabbits were stimulated with follicle-stimulating hormone (FSH) and oocytes were retrieved 3 months after transplantation. Oocytes matured in vivo or in vitro were then fertilised by conventional in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI), followed by observation and evaluation of fertilisation and blastocyst formation rates. No significant differences were found in the percentage of oocytes, maturation, fertilisation, cleavage and blastocyst formation among the three groups. Significantly higher fertilisation rates of in vitro-matured (IVM) oocytes were observed with ICSI compared with IVF in each group (81.1% v. 58.5%, 79.2% v. 59.6% and 80.4% v. 56.0% in the control, fresh tissue transplantation and frozen–thawed tissue transplantation groups, respectively). The blastocyst formation rate of IVM oocytes was significantly lower than that of in vivo-matured oocytes in each group (25.5% v. 65.7%, 22.4% v. 61.8% and 28.9% v. 63.0% in the control, fresh tissue transplantation and frozen–thawed tissue transplantation groups, respectively). In concusion, the mesometrium is a promising site for ovarian autografts in the rabbit. Oocytes retrieved from mesometrial grafts can develop to the blastocyst stage.

Analysis of gene expression in rabbit nuclear transfer embryos: Use of single-embryo mRNA differential display

Lack of or abnormal expression of developmentally important genes is believed to hamper early development of the nuclear transfer (NT) embryo. To identify stage-specific genes in rabbit NT embryo development, mRNA differential display was used to compare the mRNA content of rabbit NT embryos at different developmental stages, from Metaphase II oocytes to 8-16-cell stage embryos. Thirty-four zygotic transcripts, which abruptly appeared at the 8-16-cell stage in rabbit NT embryos, were isolated; 11 of these were potential novel genes with no matches in the current databases. Of the remaining 23, 12 were matched with established sequence tags with functions uncharacterized and the other 11 were homologous to those in the European Molecular Biology Laboratory (EMBL) and GenBank databases. The differential expression of eight of the 34 amplicons were confirmed by reverse Northern blotting, and four positive clones were validated. Previous studies and present data indicated that these three genes were probably related to preimplantation rabbit embryo development.