Immunohistochemical localization of steroidogenic enzymes in human follicle following xenotransplantation of the human ovarian cortex into NOD-SCID mice

Hormonal Stimulation of Human Ovarian Xenografts in Mice: Studying Folliculogenesis, Activation, and Oocyte Maturation

Ovarian tissue cryopreservation and banking provides a fertility preservation option for patients who cannot undergo oocyte retrieval; it is quickly becoming a critical component of assisted reproductive technology programs across the world. While the transplantation of cryopreserved ovarian tissue has resulted in over 130 live births, the field has ample room for technological improvements. Specifically, the functional timeline of grafted tissue and each patient's probability of achieving pregnancy is largely unpredictable due to patient-to-patient variability in ovarian reserve, lack of a reliable method for quantifying follicle numbers within tissue fragments, potential risk of reintroduction of cancer cells harbored in ovarian tissues, and an inability to control follicle activation rates. This review focuses on one of the most common physiological techniques used to study human ovarian tissue transplantation, xenotransplantation of human ovarian tissue to mice and endeavors to inform future studies by discussing the elements of the xenotransplantation model, challenges unique to the use of human ovarian tissue, and novel tissue engineering techniques currently under investigation.

Development of human Graafian follicles following transplantation of human ovarian tissue into NOD/SCID/gammac null mice

PROBLEM

Transplantation of human ovarian cortex into host mice may permit various kinds of challenges in reproductive medicine. A novel immunodeficient mouse strain (NOD/SCID/gammacnull: NOG) has been developed as a host of transplantation of human tissue.

METHOD OF STUDY

Human ovarian cortex was transplanted into various sites of NOG mice and human follicular development was examined by immunohistochemistry.

RESULTS

Transplantation of human ovarian tissue into NOG mice resulted in approximately similar tissue survival and follicle growth as did transplantation into non-obese diabetic-severe combined immunodeficient mice. The human Graafian follicle from NOG mouse expressed the same steroidogenic enzymes as observed in human Graafian follicles, which developed in the human body. The NOG mice's ovarian bursa was better placed for transplantation than the back skin or kidney capsule.

CONCLUSION

These results represent the successful generation and biological confirmation of the human Graafian follicles from the human ovarian cortex in the NOG mice.

DNA methylation reprogramming in the germ line

In mammals, methylation occurs almost exclusively on the CpG dinucleotide in DNA and shows no preference for sequence context surrounding this target. CpGs are found on many different sequence classes and methylation of this dinucleotide is associated with repression of transcription. Reprogramming methylation in the primordial germ cells establishes monoallelic expression of imprinted genes which exhibit monoallelic expression throughout the lifetime of an organism, maintains retrotransposons in an inactive state and inactivates one of the two X chromosomes. In addition to direct transcriptional silencing, DNA methylation is important for suppression of recombination, and resetting this information is therefore necessary for maintenance of genomic stability. In this chapter, we will review the recent progress in our understanding of the time course and extent of DNA methylation reprogramming of many different sequence classes. We focus on the mouse germline, since this has been the model system from which we have gained the most knowledge of the process. In addition we will examine some of the evidence suggesting a link between repeat methylation and methylation of epigenetically controlled single-copy genes. To do this, we will look at the temporal sequence of methylation events from the time the germ cells become recognizable as a discrete population until the mature male and female gametes fuse and form the early embryo.

In vitro growth and maturation of mouse oocyte-granulosa cell complex from cryopreserved ovaries and achievement of pup birth

Ovarian tissue banking is a feasible strategy for fertility preservation for young women after cancer treatments. Ovarian tissue, after thawing, is used for several options; orthotopic grafting (normal site), autologous heterotopic grafting and collection of ovarian follicles for culture. Recent reports of live birth encouraged clinicians and researchers to apply this technology to premature ovarian failure (POF) resulting from strong cancer therapy. Grafting, however, carries a risk of malignant cell recurrence. For safety, development of a culture method is necessary but optimum culturing conditions for less-developed follicles abundant in the ovary are not well known. In the present article, the current status of ovarian tissue cryopreservation, and in vitro oocyte growth and maturation from the preserved ovaries are reviewed.

Pup birth from mouse oocytes in preantral follicles derived from vitrified and warmed ovaries followed by in vitro growth, in vitro maturation, and in vitro fertilization

OBJECTIVE

To determine an optimum condition for vitrification of various animal species and to examine the developing capacity into pups of mouse oocytes in preantral follicles originating from cryopreserved ovaries.

DESIGN

Experimental animal study.

SETTING

Laboratory environment.

ANIMAL(S)

Normal (C57BL/6 x DBA2) F1 mice.

INTERVENTION(S)

Vitrification of animal ovaries using polyester sheets as a storage device; collection of oocyte-granulosa cell complexes by enzymatic treatment; and in vitro growth (IVG), in vitro maturation (IVM), and IVF, with embryo transplantation to pseudopregnant mice.

MAIN OUTCOME MEASURE(S)

Histological analysis of vitrified and warmed ovaries from several animal species; measurement of successful rates in IVG, IVM, and IVF of mouse oocytes in oocyte-granulosa cell complexes collected from the vitrified and warmed ovaries; and achievement of pup birth.

RESULT(S)

The vitrification method used was effective for storage of various animal ovaries. The oocytes enclosed in preantral follicles that were yielded from the vitrified-warmed ovaries preserved the capacity for developing into pups after IVG, IVM, and IVF.

CONCLUSION(S)

The findings indicated that ovarian cryopreservation by vitrification and subsequent IVG, IVM, and IVF are promising methods for restoring young cancer patients' fertility. The practical information presented here is applicable to human ovarian tissues.

Transient expression of SOX9 protein during follicular development in the adult mouse ovary

SOX9 is an essential activating transcription factor that plays a critical role in Sertoli cell differentiation and subsequent testis cord formation. Cytoplasmic SOX9 is present in both sexes during early gonadal embryogenesis. While in males the protein is later translocated into the nucleus of pre-Sertoli cells, its expression is rapidly turned off in females. In mammalian male gonads, SOX9 activates the expression of anti-Müllerian hormone (AMH), a male hormone that initiates Müllerian ducts regression and that is also expressed in postnatal ovarian follicles. Here, we confirm that the SOX9 protein is not present in the immature ovary but also show that SOX9 is transiently expressed in the mature ovary depending on the follicular cycle. Indeed, SOX9 protein was found in the nuclear compartment of the inner cells of the theca interna cell layer which surrounds the pre-antral/antral follicles. In contrast, no expression was detected in the AMH expressing granulosa cells. While these findings exclude the possibility that SOX9 regulates AMH expression in the ovary, they show that SOX9 could nevertheless play a role in the developing follicle.

Reproduction of menstrual changes in transplanted human endometrial tissue in immunodeficient mice

BACKGROUND

Cultures of human endometrial tissue are useful for analysing the mechanisms underlying the menstrual cycle. However, long-term culture of endometrial tissue is difficult in vitro. Xenotransplantation of normal human endometrial tissue into immunodeficient mice could allow prolonged survival of the transplanted tissues.

METHODS

Proliferative-phase endometrial tissue samples from three women were transplanted into the subcutaneous space of ovariectomized, immunodeficient, non-obese diabetic (NOD)/severe combined immunodeficiency (SCID)/gammaC(null) (NOG) mice. The mice were treated with 17beta-estradiol (E2) for the first 14 days after transplantation, followed by E2 plus progesterone for the next 14 days. The transplants were investigated morphologically and immunohistochemically at various times after implantation.

RESULTS

The transplanted tissues contained large numbers of small glands, pseudostratification of the nuclei and dense stroma after treatment with E2 alone. After treatment with E2 plus progesterone, subnuclear vacuolation, luminal secretion and decidualization of the stroma were observed. When the hormone treatment ceased, tissue destruction occurred and the transplants returned to the proliferative phase. Lymphocytes were identified immunohistochemically: the numbers of CD56-positive and CD16-negative cells increased significantly in the stroma during the late secretory phase (day 28).

CONCLUSIONS

Human endometrial tissue transplanted into NOG mice showed similar histological changes to eutopic endometrial tissue during treatment with sex steroid hormones for 1 month. Moreover, lymphocytes were produced in the transplanted human endometrial tissue. This system represents a new experimental model of the human endometrium in vivo.