The Exact Timing of Microinjection of Parthenogenetic Silkworm Embryos Is Crucial for Their Successful Transgenesis

The use of parthenogenetic silkworm (Bombyx mori) strains, which eliminate the problem of recombination, is a useful tool for maintaining transgenic clonal lines. The generation of genetically identical individuals is becoming an important tool in genetic engineering, allowing replication of an existing advantageous trait combination without the mixing that occurs during sexual reproduction. Thus, an animal with a particular genetic modification, such as the ability to produce transgenic proteins, can reproduce more rapidly than by natural mating. One obstacle to the widespread use of parthenogenesis in silkworm genetic engineering is the relatively low efficiency of downstream transgenesis techniques. In this work, we seek to optimize the use of transgenesis in conjunction with the production of parthenogenetic individuals. We found that a very important parameter for the introduction of foreign genes into a parthenogenetic strain is the precise timing of embryo microinjection. Our modification of the original method increased the efficiency of transgene injection as well as the survival rate of injected embryos. We also provide a detailed description of the methodological procedure including a graphical overview of the entire protocol.

Initial steps in reconstruction of the human ovary: survival of pre-antral stage follicles in a decellularized human ovarian scaffold

STUDY QUESTION

Can a reconstructed ovary using decellularized human ovarian tissue (DCT) support survival of pre-antral stage follicles?

SUMMARY ANSWER

We have demonstrated an effective protocol for decellularization of human ovarian tissues and successful recellularization with isolated human ovarian cells and pre-antral follicles.

WHAT IS KNOWN ALREADY

Survivors of leukemia or ovarian cancer run a risk of reintroducing malignancy when cryopreserved ovarian tissue is transplanted to restore fertility. A reconstructed ovary free of malignant cells could provide a safe alternative. Decellularization of ovarian tissue removes all cells from the extracellular matrix (ECM) including possible malignancies and leaves behind a physiological scaffold. The ECM offers the complex milieu that facilitates the necessary interaction between ovarian follicles and their surroundings to ensure their growth and development. Previous studies have shown that decellularized bovine ovarian scaffolds supported murine follicle growth and restoration of ovarian function in ovariectomized mice.

STUDY DESIGN, SIZE, DURATION

Optimizing a decellularization protocol for human ovarian tissues and testing biofunctionality of the decellularized scaffolds in vitro and in vivo by reseeding with both murine and human pre-antral follicles and ovarian cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Donated human ovarian tissue and isolated pre-antral follicles were obtained from women undergoing ovarian tissue cryopreservation for fertility preservation. Ovarian cortical and medullary tissues were decellularized using 0.1% sodium dodecyl sulfate (SDS) for 3, 6, 18 and 24 hours followed by 24 hours of 1 mg/mL DNase treatment and washing. Decellularization of ovarian tissues and preservation of ECM were characterized by morphological evaluation using Periodic Acid-Schiff (PAS) staining, DNA quantification, histochemical quantification of collagen content and immunofluorescence analysis for collagen IA, laminin, fibronectin and DNA. Human ovarian stromal cells and isolated human pre-antral follicles were reseeded on the DCT and cultured in vitro. Isolated murine (N = 241) and human (N = 20) pre-antral follicles were reseeded on decellularized scaffolds and grafted subcutaneously to immunodeficient mice for 3 weeks.

MAIN RESULTS AND THE ROLE OF CHANCE

Incubation in 0.1% SDS for 18-24 hours adequately decellularized both human ovarian medullary and cortical tissue by eliminating all cells and leaving the ECM intact. DNA content in DCT was decreased by >90% compared to native tissue samples. Histological examination using PAS staining confirmed that the cortical and medullary tissues were completely decellularized, and no visible nuclear material was found within the decellularized sections. DCT also stained positive for collagen I and collagen quantities in DCT constituted 88-98% of the individual baselines for native samples. Human ovarian stroma cells were able to recellularize the DCT and isolated human pre-antral follicles remained viable in co-culture. Xenotransplantation of DCT reseeded with human or murine pre-antral follicles showed, that the DCT was able to support survival of human follicles and growth of murine follicles, of which 39% grew to antral stages. The follicular recovery rates after three weeks grafting were low but similar for both human (25%) and murine follicles (21%).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Further studies are needed to increase recovery and survival of the reseeded follicles. Longer grafting periods should be evaluated to determine the developmental potential of human follicles. Survival of the follicles might be impaired by the lack of stroma cells.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first time that isolated human follicles have survived in a decellularized human scaffold. Therefore, this proof-of-concept could be a potential new strategy to eliminate the risk of malignant cell re-occurrence in former cancer patients having cryopreserved ovarian tissue transplanted for fertility restoration.

STUDY FUNDING/COMPETING INTEREST(S)

This study is part of the ReproUnion collaborative study, co-financed by the European Union, Interreg V ÖKS. Furthermore, Project ITN REP-BIOTECH 675526 funded by the European Union, European Joint Doctorate in Biology and Technology of the Reproductive Health, the Research Pools of Rigshospitalet, the Danish Cancer Foundation and Dagmar Marshalls Foundation are thanked for having funded this study. The funders had no role in the study design, data collection and interpretation, or in the decision to submit the work for publication.

Influence of graft size, histocompatibility,and cryopreservation on reproductive outcome following ovary transplantation in mice

Purpose

Transplantation of ovarian tissue is a valuable method to rescue mouse strains with fertility problems and to revitalize archived strains. The purpose of this study was to investigate the effect of (i) different sizes of transplanted ovary pieces on reproductive outcome, (ii) use of immunodeficient recipients to overcome the limitation of histocompatibility, and (iii) to compare different protocols for cryopreservation of ovarian tissue.

Methods

Halves, quarters, and eights of mouse ovaries were transplanted. Half ovaries from B6 donors were transferred into immunodeficient mice. Halves of ovaries were frozen according to four different protocols, thawed and transferred.

Results

Pregnancy rate after transplantation of ovarian tissue was high (90–100%) independent of the transplant size. Although, the average litter size was significantly lower for recipients of quarters and eights (4.4 and 4.6 vs. 6.5), the total number of offspring produced per donor ovary was higher compared with recipients of halves. Pregnancy rate of immunodeficient recipients was 40% (mean 4.7 offspring per litter). All four cryopreservation protocols used were able to preserve functionality of the ovarian tissue.

Conclusions

Transplantation of ovarian tissue smaller than halves resulted in reduced litter sizes. The distribution of ovarian tissue of one donor female to 4 or 8 recipients will therefore yield in a higher total number of offspring in a certain time period. The use of immunodeficient recipients is an option for non-histocompatible donors. Cryopreservation of ovarian tissue is generally feasible but the function of frozen-thawed ovary halves after transplantation differs depending on the freezing protocol used.

Folliculogenesis following syngeneic transplantation of young murine ovaries into the testes

Background and Aim:  To examine the effects of intratesticular transplantation on the growth and maturation of young murine ovaries. Methods:  Two-week-old ovaries from transgenic mice with enhanced green fluorescent protein expression were transplanted under the testicular capsule of 4-week-old non-transgenic mice. Results:  Two months after transplantation all successfully grafted ovaries had survived, based on the presence of bright green fluorescence. The grafts showed various stages of folliculogenesis, including expanded follicles. The neighboring seminiferous tubules had a normal structure and mature sperm in their lumens, indicating active spermatogenesis, and all the recipient males were fertile. There was no evidence of extensive cell migration from the grafted ovaries into the testis. Similar findings were obtained for the grafted ovaries 6 months after surgery, although cell death (as evidenced by yellowish or pale fluorescence) was more frequent. Conclusion:  Young murine ovaries can grow and mature autonomously for at least 6 months unaffected by the male hormonal environment. (Reprod Med Biol 2006; 5: 71-77).

Age of ovary determines remaining life expectancy in old ovariectomized mice

We investigated the capacity of young ovaries, transplanted into old ovariectomized CBA mice, to improve remaining life expectancy of the hosts. Donor females were sexually mature 2-month-olds; recipients were prepubertally ovariectomized at 3 weeks and received transplants at 5, 8 or 11 months of age. Relative to ovariectomized control females, life expectancy at 11 months was increased by 60% in 11-month recipient females and by 40% relative to intact control females. Only 20% of the 11-month transplant females died in the 300-day period following ovarian transplantation, whereas nearly 65% of the ovariectomized control females died during this same period. The 11-month-old recipient females resumed oestrus and continued to cycle up to several months beyond the age of control female reproductive senescence. Across the three recipient age groups, transplantation of young ovaries increased life expectancy in proportion to the relative youth of the ovary. Our results relate to recent findings on the gonadal input upon aging in Caenorhabditis elegans and may suggest how the mammalian gonad, including that of humans, could regulate aging and determine longevity.