Orthotopic transplantation of rat ovaries as a tool for strain rescue

Cryopreservation and Transplantation of Laboratory Rodent Ovarian Tissue for Genome Banking and Biomedical Research

Genetic modifications in combination with highly sophisticated assisted reproductive technologies such as in vitro oocyte maturation and development, in vitro fertilization, intracytoplasmic sperm injection, and in vitro embryo culture have opened many research avenues and treatment options for both animals and humans. The number of genetically modified (GM) rodent strains increased considerably during the last several decades, and their numbers are expected to increase due to efficient gene editing technologies including the CRISPR/Cas9. Rodent ovarian tissues (OT) cryopreservation and transplantation procedures have several applications in biomedical field: they provide a fertility restoration option for GM rodent strains in some circumstances. They also serve as models to investigate OT cryopreservation as potential alternatives for human infertility patients as well as other domestic and wildlife species for the development of improved cryopreservation and subsequent transplantation strategies. The modeling studies enable determining effective cryoprotective agents (CPA), CPA and water permeability kinetics, and cooling and warming rates during the development of OT cryopreservation procedures. Furthermore, rodent models are extremely useful for determining post-thaw OT graft sites as well as potential medical interventions in an effort to expedite angiogenesis and inhibit inflammatory/immune response, OT longevity, and follicular integrity. Here we describe methodologies for rodent OT cryopreservation and potential transplantation sites for frozen-thawed rat and mouse OT.

Ovarian tissue vitrification is more efficient than slow freezing to preserve ovarian stem cells in CF-1 mice

OBJECTIVE

The aim of this study was to investigate the efficacy of protocols for mice ovary cryopreservation to compare the differences in Mouse Vasa Homologue expression (a germline cell marker) and ovarian viability after vitrification or slow freezing.

METHODS

Female CF1 mice aged 40-45 days were randomly divided into three groups: Control, vitrification or slow freezing. Their ovaries were surgically removed, rinsed in saline solution and cryopreserved. For vitrification, we used a commercial protocol and for slow freeze, we used 1.5 M ethylene glycol (EG) as cryoprotectant. After that, the ovaries were processed for histological an immunohistochemical analysis, and counting of primordial, primary, pre-antral and antral follicles.

RESULTS

No significant difference was found in the proportion of high-quality primordial, primary and pre-antral follicles after thawing/warming in the slow freezing and vitrification groups. The immunohistochemistry for MVH antibody demonstrated that the slow freeze group had a higher number of unmarked cells (p=0.012), indicating a harmful effect on the MVH expression in the ovarian tissue, where the cell structure is complex.

CONCLUSION

Although both protocols indicated similar results in the histological analysis of follicular counts, the vitrification protocol was significantly better to preserve ovarian stem cells, an immature germ cell population. These cells are able to self-renew having regeneration potential, and may be effective for the treatment of ovarian failure and consequently infertility.

Preliminary results of the application of gonadal tissue transfer in various chicken breeds in the poultry gene conservation

The aim of the study was to devise a technique to allow transfer of ovarian and testicular tissues obtained from one day old chicks to recipient animals. The following combinations of chicken breeds were used: Tetra SL/Tetra SL, Tetra SL/Harco, Tetra SL/Black Transylvanian Naked Neck, Godollo New Hampshire/Speckled Transylvanian Naked Neck (recipient/donor), respectively. Only animals less than 24h old from hatching were used as either recipient or donor. Eggs yielding recipients were treated with busulfan to hinder the development of the recipient's own gonads. Gonads were transferred surgically to the new host which was then immunosuppressed for two months. The animals were checked at 8 or 16 weeks for the existence of implanted gonads, and if found, the gonads were removed for histology examination. Tetra SL/Tetra SL pairing resulted in successfully adhered and functioning gonads in most cases. In other combinations, no gonads originating from the donors were found in the recipients. We conclude that not all breeds seem to be suitable recipients; some breeds or individuals may show incompatibility to each other and further examination is needed to find the cause of incompatibility and to establish a suitable breed combination, which can be used for gonad transfer.

Viability and function of the cryopreserved whole rat ovary: comparison between slow-freezing and vitrification

OBJECTIVE

To investigate four different protocols for cryopreservation of the whole rat ovary with intact vasculature to evaluate whether differences exist in post-thawing viability of the ovary after either vitrification or slow freezing.

DESIGN

Experimental study.

SETTING

Obstetrics and gynecology department.

ANIMAL(S)

Immature Sprague-Dawley female rats.

INTERVENTION(S)

Ovaries were isolated with the vascular tree intact up to the bifurcation of the abdominal aorta and were subsequently cannulated. The ovaries were flushed with increasing concentrations of the cryoprotectant dimethyl sulfoxide (DMSO) to either 1.5 or 7 M. The ovaries underwent cryopreservation by vitrification or passive slow freezing.

MAIN OUTCOME MEASURE(S)

After thawing, the ovaries were subjected to neutral red viability staining to assess the density of viable small follicles and for long-term (48 hours) incubation evaluation of steroid secretion, histology, and apoptosis assay.

RESULT(S)

The follicular viability was decreased in both vitrification groups and in the slow-freezing group with the high concentration of DMSO, as compared with fresh controls. Estradiol levels in the incubation medium followed the same pattern. Light microscopy revealed well-preserved morphology in all groups after 48 hours' incubation. Apoptosis was increased in both vitrified and cryopreserved ovaries.

CONCLUSION(S)

We have developed a new method that can be used in basic studies to improve cryopreservation protocols. Our initial findings suggest that a moderate concentration of the cryoprotectant DMSO is superior to a high DMSO concentration for both vitrification and slow freezing.

Cryopreservation and orthotopic transplantation of rat ovaries

The number of rat strains increased considerably in the last decade and will increase continuously during the next years. This requires enough space for maintaining vital strains and techniques for cryobanking, which can be applied not only in specialised rat resource centres but also in regular animal houses. Here we describe an easy and fast method for the cryopreservation and transplantation of frozen-thawed ovaries of the rat. With dimethyl sulfoxide as cryoprotectant rat ovaries can be stored at -196 degrees C for unlimited time. For revitalisation thawed ovaries have to be orthotopically transplanted into appropriate ovarectomised recipients. Reestablishment of the reproductive cycle in the recipients can be confirmed by vaginal cytology shortly after transplantation. The recipients are able to produce 2-3 litters after mating with males of an appropriate strain. Cyropreservation of ovaries thus can be considered a reliable method to preserve scientifically and economically important stocks and strains of rats that are currently not required.

Orthotopic transplantation of neonatal GFP rat ovary as experimental model to study ovarian development and toxicology

The rat is one of the most commonly used experimental animal species in biomedical research. The availability of new research tools in rats could therefore provide considerable advances in the areas where this mammal is extensively used. We report the development of a new green fluorescent protein (GFP) rat strain suitable for organ transplantation and the birth of GFP rats following orthotopic transplantation of neonatal ovaries from this newly developed GFP rat strain to a wild-type Fischer 344 (F344) strain. A new GFP rat strain was developed by backcrossing eGFP Sprague-Dawley (SD-Tg(CAG-EGFP)Cz-004Osb) to wild-type F344 for eight generations. Whole ovaries from postnatal day (PND) 8 or PND 21 GFP rats were transplanted orthotopically to bilaterally ovariectomized wild-type adult females (n=6). All recipients were mated, and three of the five resulting litters contained GFP pups. In the PND 8 group, all recipients cycled regularly and the ovarian morphology appeared normal when collected at 9 months post-transplantation. In the PND 21 group, 60% of the recipients displayed regular estrous cycles at 9 months post-transplantation, but showed reduced ovarian size. This new strain and neonatal orthotopic transplantation could be useful for many biomedical fields including transplantation, development, and reproductive toxicology.

Offspring Produced from Orthotopic Transplantation of Chicken Ovaries

The loss of avian genetic variation and the threat of disease lend urgency to the cryopreservation of remaining poultry stocks. However, techniques for freezing ova and embryos are not available for birds, and the recovery of genetic material has been a major obstacle to cryopreservation. To overcome this problem, we transplanted chicken ovarian tissue just after hatch with or without subsequent treatment of the recipient with an immunosuppressant. Nine of 12 hens in the nonimmunosuppressed group and 6 of 9 birds in the immunosuppressed group produced eggs, whereas 3 hens in each group produced donor-derived offspring. These results suggest that transplantation of ovarian tissue of chickens is possible if performed just after hatch. This finding should allow efficient cryopreservation of female germ cells in chickens with regeneration in live birds. In addition, ovarian transplantation could be useful for studies in genetics or developmental biology or could provide convenient access to the female germline for genetic manipulation.