In vitro development of growing oocytes from fetal mouse oocytes: stage-specific regulation by stem cell factor and granulosa cells

Instructing an embryonic stem cell-derived oocyte fate: lessons from endogenous oogenesis

Female reproductive potential is limited in the majority of species due to oocyte depletion. Because functional human oocytes are restricted in number and accessibility, a robust system to differentiate oocytes from stem cells would enable a thorough investigation of the genetic, epigenetic, and environmental factors affecting human oocyte development. Also, the differentiation of functional oocytes from stem cells may permit the success of human somatic cell nuclear transfer for reprogramming studies and for the production of patient-specific embryonic stem cells (ESCs). Thus, ESC-derived oocytes could ultimately help to restore fertility in women. Here, we review endogenous and ESC-derived oocyte development, and we discuss the potential and challenges for differentiating functional oocytes from ESCs.

Kit ligand promotes first polar body extrusion of mouse preovulatory oocytes

BACKGROUND

Shortly after stimulation by the preovulatory surge of luteinizing hormone (LH), oocytes arrested at the late prophase I resume meiosis characterized by germinal vesicle breakdown (GVBD), chromosome condensation, and extrusion of the first polar body in preparation for fertilization and early embryonic development. However, oocytes express few or no LH receptors and are insensitive to direct LH stimulation. Thus, factors released by granulosa or theca cells expect to convey the LH stimuli to oocytes. To identify candidate ligand-receptor pairs potentially involved in the process of oocyte maturation, we performed DNA microarray analyses of ovarian transcripts in mice and identified Kit ligand (Kitl) as an ovarian factor stimulated by the LH/hCG surge. The purpose of this study is to investigate the roles of KITL in the nuclear and cytoplasmic maturation of preovulatory mouse oocytes.

METHODS

The levels of Kitl and c-kit transcripts in mouse ovaries and isolated ovarian cells were determined by real-time RT-PCR, while expression of KITL protein was examined by immunohistochemistry. Follicle culture, cumulus-oocyte complexes (COC) and denuded oocytes culture were used to evaluate the effect of KITL on mouse oocyte nuclear maturation. To assess the effect of KITL treatment on the cytoplasmic maturation of preovulatory oocytes, we performed in vitro maturation of oocytes followed by in vitro fertilization.

RESULTS

Major increase of Kitl transcripts in granulosa cells and mouse ovaries, and predominant expression of c-kit in preovulatory oocytes were identified by real-time RT-PCR. Predominant expression of KITL protein was found in granulosa cells of preovulatory and small antral follicles at 4 h after hCG treatment. In vitro cultures demonstrated that treatment with KITL enhanced first polar body extrusion in a dose-dependent manner. Moreover, treatment of COC with KITL enhanced first polar body extrusion with increase in cyclin B1 synthesis which is important for the progression of meiotic maturation after GVBD. In contrast, treatment of cultured preovulatory follicles with KITL did not affect GVBD and KITL has no effect on cytoplasmic maturation of preovulatory oocytes.

CONCLUSION

Our findings suggest potential paracrine roles of KITL in the nuclear maturation of preovulatory oocytes by promoting first polar body extrusion.

Developmental and Ultrastructual Characteristics of Mouse Oocytes Grown in Vitro from Primordial Germ Cells

The aim of this study was to clarify the developmental and ultrastructual characteristics of oocytes grown in vitro from primordial germ cells. The female genital ridges at 12.5 days post coitus were cultured for 18 days on an insert membrane in Waymouth's MB752/1 medium, supplemented with 15% fetal bovine serum and 1 mM sodium pyruvate; subsequently, the follicles isolated from the tissue were cultured for eight days in Waymouth's medium supplemented with 5 microg/ml insulin, 5 microg/ml transferrin, 5 ng/ml selenium, 10 mIU/ml follicle stimulating hormone, and 100 ng/ml stem cell factor. The primordial germ cells developed in vitro into oocytes of more than 60 microm in diameter. The transmission electron microscopic analysis indicated that the oocytes, which developed in vitro, showed no obvious abnormality in their ultrastructure and had organelles appropriate for the oocyte size. However, a delay in the progressive changes of morphology in some of the organelles during oocyte growth was often found when comparing them to oocytes grown in vivo.

Expression of SRG3, a chromatin-remodelling factor, in the mouse oocyte and early preimplantation embryos

SRG3 (Smarcc1) is a core subunit of the SWI/SNF complex. In the absence of SRG3, embryonic development ceases during peri-implantation stages, indicating that SRG3, as well as the chromatin-remodelling process, plays an essential role in early mouse development. To gain a better understanding of chromatin remodelling during the early stages of development, we examined SRG3 expression during oogenesis and preimplantation stages using immunofluorescence and western blot assays. SRG3 was detected in nuclei of oocytes during growth and maturation. Following fertilization, SRG3 was detected in pronuclei shortly after their formation. Nuclear concentrations of SRG3 increased in a time-dependent fashion and were found to be greater in the male pronucleus than in the female pronucleus. The increase in nuclear SRG3 was partially inhibited by a protein synthesis inhibitor, but not by a transcriptional inhibitor. Expression of SRG3 is accompanied by expression of Brg1 and Ini1, two other core subunits of the SWI/SNF complex. The expression of these three remodelling factors parallels that of SP1 and TBP, both spatially and temporally, in the mouse embryo, suggesting a role for remodelling factors in chromatin structure and function during early development.

Expression of growth differentiation factor 9, bone morphogenetic protein 15, and anti-Müllerian hormone in cultured mouse primary follicles

Growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), and anti-Müllerian hormone (AMH) play an important role in the primary to secondary follicle transition and follicle activation in vivo. In organ culture of neonatal mouse ovaries, it was observed that significantly fewer primary follicles develop to the secondary stage. The objectives of this study were: (1) to compare ovarian follicular populations between organ-cultured neonatal mouse ovaries and freshly isolated age-matched control ovaries; (2) to quantify RNA levels of Gdf9, Bmp15, and Amh in cultured primary follicles; and (3) to immunolocalize GDF9 and AMH in cultured ovaries. Ovaries from 3-day-old (PND 3) mice were cultured for 7 or 10 days in the absence or presence of FSH. Follicular populations were counted in freshly isolated 13-day-old (PND 13) ovaries and organ-cultured ovaries. Transcripts were quantified in isolated primary follicles using real-time RT-PCR, and protein expressions were localized using immunohistochemistry. The number of secondary follicles in organ-cultured ovaries was significantly lower than in vivo controls. Gdf9 and Bmp15 mRNA expression levels were similar as in controls. Amh mRNA levels were significantly (P<0.05) lower after day 10 of culture in the absence of FSH. GDF9 and AMH proteins were respectively detected in the oocytes and the granulosa cells (GC) beginning at the primary and primordial stages onward. GDF9 and BMP15 production in cultured primary follicles are not different from in vivo controls; hence abnormal early follicular growth was not related to a deficient transcription of these factors.

Activin signals via SMAD2/3 between germ and somatic cells in the human fetal ovary and regulates kit ligand expression

Ovarian germ cell survival is dependent upon the formation of primordial follicles, which occurs during fetal life in the human. Activin contributes to germ cell proliferation and survival at this time. SMADs2 and 3 are central elements in the activin signalling pathway and thus indicate sites of activin action. We have investigated the expression and localisation of SMADs2 and 3 in the fetal ovary between 14 and 20 weeks gestation, i.e. preceding and during primordial follicle formation. SMAD3 mRNA expression increased 1.9 fold (P=0.02). SMAD2 and 3 proteins were localised by immunofluorescence to the nuclei of three distinct populations of somatic cells: (a) stromal cells between clusters of germ cells; (b) some somatic cells intermingled with activin beta A-expressing germ cells; (c) pre-granulosa cells surrounding primordial follicles. Germ cells did not express SMAD2 or 3. Activin A increased and follistatin decreased phosphorylation of SMAD2/3 in vitro, and activin increased SMAD2 and decreased KITLG mRNA expression. It therefore appears that somatic cells are the targets for activin signalling in the developing ovary. The effects of activin on germ cells are indirect and include mediation by the kit ligand/c-Kit pathway, rather than being an autocrine germ cell effect.

Induction of oocyte-like cells from mouse embryonic stem cells by co-culture with ovarian granulosa cells

In vitro derivation of oocytes from embryonic stem (ES) cells has the potential to be an important tool for studying oogenesis as well as advancing the field of therapeutic cloning by providing an alternative source of oocytes. Here, we demonstrate a novel, two-step method for inducing mouse ES cells to differentiate into oocyte-like cells using mouse ovarian granulosa cells. First, primordial germ cells (PGCs) were differentiated within the embryonic body (EB) cells around day 4 as defined by the expression of PGC-specific markers and were distinguished from undifferentiated ES cells. Second, day 4 EB cells were co-cultured with ovarian granulosa cells. After 10 days, these cells formed germ cell colonies as indicated by the expression of the two germ cell markers Mvh and SCP3. These cells also expressed the oocyte-specific genes Figalpha, GDF-9, and ZP1-3 but not any testis-specific genes by RT-PCR analysis. EB cultured alone or cultured in granulosa cell-conditioned medium did not express any of these oocyte-specific markers. In addition, EB co-cultured with Chinese hamster ovary (CHO) cells or cultured in CHO cell-conditioned medium did not express all of these oocyte-specific markers. Immunocytochemistry analysis using Mvh and GDF-9 antibodies confirmed that some Mvh and GDF-9 double-positive oocyte-like cells were generated within the germ cell colonies. Our results demonstrate that granulosa cells were effective in inducing the differentiation of ES cell-derived PGCs into oocyte-like cells through direct cell-to-cell contacts. Our method offers a novel in vitro system for studying oogenesis; in particular, for studying the interactions between PGCs and granulosa cells.

In vitro development of mouse fetal germ cells into mature oocytes

Little is known about the mechanisms underlying primordial follicular formation and the acquisition of competence to resume meiosis by growing oocytes. It is therefore important to establish an in vitro experimental model that allows one to study such mechanisms. Mouse follicular development has been studied in vitro over the past several years; however, no evidence has been presented showing that mature oocytes can be obtained from mouse fetal germ cells prior to the formation of primordial follicles. In this study, a method has been established to obtain mature oocytes from the mouse fetal germ cells at 16.5 days postcoitum (dpc). From the initiation of primordial follicular formation to the growth of early secondary follicles, ovarian tissues from 16.5 dpc fetal mice were cultured in vitro for 14 days. Subsequently, 678 intact secondary follicles were isolated from 182 mouse fetal ovaries and cultured for 12 days. A total of 141 oocytes inside antral follicles were matured in vitro, and 102 oocytes underwent germinal vesicle breakdown. We found that 97 oocytes were fertilized and 15 embryos were able to form morula-blastocysts. We also analyzed various genomic imprinting markers and showed that the erasure of genomic imprinting markers in the parental generation was also imposed on the oocytes that developed from fetal germ cells. Our results demonstrate that mouse fetal germ cells are able to form primordial follicles with ovarian cells, and that oocytes within the growing follicles are able to mature normally in vitro.

Kit ligand 2 promotes murine oocyte growth in vitro

Oocyte-granulosa cell communication, mediated by paracrine factors, is essential for oocyte development. Kit ligand (KITL) is expressed in granulosa cells as soluble (KITL1) or membrane-associated (KITL2) proteins. However, the relative biopotency of each isoform during oocyte development is unknown. Our initial results showed that Kitl2 was down-regulated in cultured granulosa cells. To determine the effect of the two isoforms of KITL on oocyte growth, Kitl-deficient fibroblasts were transfected with constructs expressing either KITL1 or KITL2, and growing oocytes were isolated from 12-day-old mice and cultured on the transfected fibroblasts for 2 days. At the end of culture, oocyte diameters were measured, the incidence of spontaneous germinal vesicle breakdown (GVBD) was noted, and oocytes were analyzed for KIT receptor expression. Oocyte growth occurred only in the presence of the KITL2-producing fibroblasts, and suppression of KITL2 expression impaired oocyte growth. Up-regulation of KIT expression occurred in the presence of KITL2 but not KITL1. The presence of KITL2 inhibited spontaneous GVBD. Meiosis inhibitors did not attenuate the GVBD that occurred in the absence of KITL2, suggesting that this process reflects oocyte degeneration rather than meiotic progression. These results indicate that KITL2 is the principal KITL isoform required for oocyte growth and survival in vitro.

Mouse oocytes derived from fetal germ cells are competent to support the development of embryos by in vitro fertilization

Mouse oocyte development in vitro has been studied in the past several years, but no evidence showed that the fertilizable oocytes could be obtained from the fetal mouse germ cells before the formation of the primordial follicles. In this study, an efficient and simple method has been established to obtain the mature oocytes from the fetal mouse germ cells at 16.5 days post-coitum (dpc). For the initial of follicular formation, fetal mouse 16.5 dpc ovaries were transplanted to the recipient under the kidney capsule, and the ovaries were recovered after 14 days. Subsequently, the growing preantral follicles in the ovarian grafts were isolated and cultured in vitro for 12 days. Practically, the mature oocytes ovulated from the antral follicles were able to be fertilized in vitro and support the embryonic development. The results demonstrate that the fetal mouse 16.5 dpc germ cells are able to form primordial follicles with the ovarian pregranulosa cells during the period of transplantation in the ectopic site, and the oocytes within the growing follicles are able to mature in vitro, then are able to support the embryonic development.

KIT/KIT Ligand in Mammalian Oogenesis and Folliculogenesis: Roles in Rabbit and Murine Ovarian Follicle Activation and Oocyte Growth1

In rodent ovaries Kit ligand (KITL) and its receptor KIT have diverse roles, including the promotion of primordial follicle activation, oocyte growth, and follicle survival. Studies were undertaken to determine whether KITL and KIT carry out similar activities in rabbits. KitlandKitmRNA and protein were localized to oocytes and granulosa cells, respectively, in the rabbit ovary. Ovarian cortical explants from juvenile rabbits and neonatal mouse ovaries were subsequently cultured with recombinant mouse KITL and/or KITL neutralizing antibody. Indices of follicle growth initiation were compared with controls and between treatment groups for each species. Recombinant mouse KITL had no stimulatory effect on primordial follicle recruitment in cultured rabbit ovarian explants. However, the mean diameter of oocytes from primordial, early primary, primary, and growing primary follicles increased significantly in recombinant mouse KITL-treated explants compared with untreated tissues. In contrast, recombinant mouse KITL promoted both primordial follicle activation and an increase in the diameter of oocytes from primordial and early primary follicles in the mouse, and these effects were inhibited by coculture with KITL-neutralizing antibody. Recombinant mouse KITL had no effect on follicle survival for either species. These data demonstrate that KITL promotes the growth of rabbit and mouse oocytes and stimulates primordial follicle activation in the mouse but not in the rabbit. We propose that the physiologic roles of KITL and KIT may differ between species, and this has important implications for the design of in vitro culture systems for folliculogenesis in mammals, including the human.

Live offspring produced by mouse oocytes derived from premeiotic fetal germ cells

Mature mouse oocytes currently can be generated in vitro from the primary oocytes of primordial follicles but not from premeiotic fetal germ cells. In this study we established a simple, efficient method that can be used to obtain mature oocytes from the premeiotic germ cells of a fetal mouse 12.5 days postcoitum (dpc). Mouse 12.5-dpc fetal ovaries were transplanted under the kidney capsule of recipient mice to initiate oocyte growth from the premeiotic germ cell stage, and they were recovered after 14 days. Subsequently, the primary and early secondary follicles generated in the ovarian grafts were isolated and cultured for 16 days in vitro. The mature oocytes ovulated from these follicles were able to fertilize in vitro to produce live offspring. We further show that the in vitro fertilization offspring were normal and able to successfully mate with both females and males, and the patterns of the methylated sites of the in vitro mature oocytes were similar to those of normal mice. This is the first report describing premeiotic fetal germ cells able to enter a second meiosis and support embryonic development to term by a combination of in vivo transplantation and in vitro culture. In addition, we have shown that the whole process of oogenesis, from premeiotic germ cells to germinal vesicle (GV)-stage oocytes, can be carried out under the kidney capsule.

Preservation of female germ cells from ovaries of cat species

This review provides an overview on recent knowledge on female germ cell population within cat ovaries; on isolation, culture and cryopreservation of feline preantral follicles and on ovarian tissue preservation.

Oocyte-granulosa cell interactions during mouse follicular development: regulation of kit ligand expression and its role in oocyte growth

Ovarian folliculogenesis is regulated by both endocrine and intraovarian mechanisms that coordinate the processes of oocyte growth and somatic cell proliferation and differentiation. Within the follicle, paracrine interactions between the oocyte and surrounding granulosa cells are critical for normal cell development and function. This review focuses on the role of paracrine interactions during early oocyte and follicular development that ensure proper coordination of oocyte and somatic cell function. Particular emphasis is given to granulosa cell-derived Kit Ligand (KitL), whose functional importance for oocyte growth has been demonstrated by a wide range of in vivo and in vitro studies. Reported interactions between KitL and oocyte-derived growth differentiation factor-9 (GDF9) and bone morphogenetic protein-15 (BMP15) suggest the molecular basis of oocyte-granulosa cell interactions, but also hint at the complexity of these communications. These paracrine interactions and the structure of the oocyte-granulosa cell interface are follicle stage-specific and regulated by FSH. Elucidation of the molecular mechanisms that promote the development of healthy oocytes with good developmental competence has potential applications for improving fertility and for in vitro growth systems for oocytes from domestic animals and humans.

Kit ligand and c-Kit are expressed during early human ovarian follicular development and their interaction is required for the survival of follicles in long-term culture

The receptor tyrosine c-Kit and its cognate ligand, c-Kit ligand (KL, stem cell factor, SCF), are involved in ovarian follicular development in several animal species. We studied the expression of KL and c-Kit usingin situhybridization and immunohistochemistry in donated human ovarian cortical tissue. The KL transcripts were expressed in granulosa cells of primary follicles, whereas the expression of c-Kit was confined to the oocyte and granulosa cells in primary and secondary follicles. We employed an ovarian organ culture using firstly serum-containing and then serum-free medium to study the effects of KL and an anti-c-Kit antibody, ACK2, on the development and survival of ovarian folliclesin vitro. Culture of ovarian cortical slices for 7 days resulted in a 37% increase in the number of primary follicles and a 6% increase in secondary follicles. The proportion of viable follicles decreased in all cultures. The addition of KL (1, 10 and 100 ng/ml) into the culture media did not affect the developmental stages of the follicles or the proportion of atretic follicles. Inclusion of ACK2 (800 ng/ml) in the culture medium significantly increased the proportion of atretic follicles on days 7 (49 vs 28% in control cultures) and 14 (62 vs 38%) of culture. In conclusion, c-Kit and KL are expressed in human ovaries during follicular development. Blocking the c-Kit receptor induces follicular atresia. The KL/c-Kit signaling system is likely to control the survival of human ovarian follicles during early follicular development.

Kit ligand and c-Kit have diverse roles during mammalian oogenesis and folliculogenesis

Paracrine signalling between the oocyte and its surrounding somatic cells is fundamental to the processes of oogenesis and folliculogenesis in mammals. The study of animal models has revealed that the interaction of granulosa cell-derived kit ligand (KL) with oocyte and theca cell-derived c-Kit is important for multiple aspects of oocyte and follicle development, including the establishment of primordial germ cells within the ovary, primordial follicle activation, oocyte survival and growth, granulosa cell proliferation, theca cell recruitment and the maintenance of meiotic arrest. Though little is known about the specific roles of KL and c-Kit during human oogenesis, the expression profiles for KL and c-Kit within the human ovary suggest that they are also functionally relevant to female fertility. This review details our current understanding of the roles of KL and c-Kit within the mammalian ovary, with a particular focus on the functional diversity of this receptor-ligand interaction at different stages of oocyte and follicle development.

Testicular Cell Conditioned Medium Supports Differentiation of Embryonic Stem Cells into Ovarian Structures Containing Oocytes

Previous reports and the current study have found that germ cell precursor cells appear in embryoid bodies (EBs) formed from mouse embryonic stem cells as identified by positive expression of specific germ cell markers such as Oct-3/4, Mvh, c-kit, Stella, and DAZL. We hypothesized that if exposed to appropriate growth factors, the germ cell precursor cells within the EBs would differentiate into gametes. The source for growth factors used in the present study is conditioned medium collected from testicular cell cultures prepared from the testes of newborn males. Testes at this stage of development contain most growth factors required for the transformation of germ stem cells into differentiated gametes. When EBs were cultured in the conditioned medium, they developed into ovarian structures, which contained putative oocytes. The oocytes were surrounded by one to two layers of flattened cells and did not have a visible zona pellucida. However, oocyte-specific markers such as Fig-alpha and ZP3 were found expressed by the ovarian structures. The production of oocytes using this method is repeatable and reliable and may be applicable to other mammalian species, including the human.

Growth factors sustain primordial germ cell survival, proliferation and entering into meiosis in the absence of somatic cells

It is known that mammalian primordial germ cells (PGCs), the precursors of oocytes and prospermatogonia, depend for survival and proliferation on specific growth factors and other undetermined compounds. Adhesion to neighboring somatic cells is also believed to be crucial for preventing PGC apoptosis occurring when they lose appropriate cell to cell contacts. This explains the current impossibility to maintain isolated mouse PGCs in culture for periods longer than a few hours in the absence of suitable cell feeder layers producing soluble factors and expressing surface molecules necessary for preventing PGTC apoptosis and stimulating their proliferation. In the present paper, we identified a cocktail of soluble growth factors, namely KL, LIF, BMP-4, SDF-1, bFGF and compounds (N-acetyl-L-cysteine, forskolin, retinoic acid) able to sustain the survival and self-renewal of mouse PGCs in the absence of somatic cell support. We show that under culture conditions allowing PGC adhesion to an acellular substrate, such growth factors and compounds were able to prevent the occurrence of significant levels of apoptosis in PGCs for two days, stimulate their proliferation and, when LIF was omitted from the cocktail, allow most of them to enter into and progress through meiotic prophase I. These results consent for the first time to establish culture conditions for purified mammalian PGCs in the absence of somatic cell support and should make easier the molecular dissection of the processes governing the development of such cells crucial for early gametogenesis.

Involvement of gap junctional communication in secretion

Glands were the first type of tissues in which the permissive role of gap junctions in the cell-to-cell transfer of membrane-impermeant molecules was shown. During the 40 years that have followed this seminal finding, gap junctions have been documented in all types of multicellular secretory systems, whether of the exocrine, endocrine or pheromonal nature. Also, compelling evidence now indicates that gap junction-mediated coupling, and/or the connexin proteins per se, play significant regulatory roles in various aspects of gland functions, ranging from the biosynthesis, storage and release of a variety of secretory products, to the control of the growth and differentiation of secretory cells, and to the regulation of gland morphogenesis. This review summarizes this evidence in the light of recent reports.

In vitro growth of oocytes from primordial follicles isolated from frozen-thawed lamb ovaries

A study was conducted to develop an in vitro culture system for growing sheep oocytes from isolated primordial follicles. Enzymatically isolated neonatal sheep primordial follicles were cultured in Waymouth MB752/1 medium containing BSA (3 mg/ml) + ITS (1%, v/v) over 28 days. In Experiment 1, primordial follicles (average diameter 40.2+/-0.60 microm) were cultured at densities of 20, 50 and 100 follicles per well. Less than 20% of the oocytes survived to day 28 but there was a significant (P < 0.05) increase in median oocyte diameter from day 2 to day 28 for oocytes cultured at the higher densities of 50 and 100 follicles. In Experiment 2, two methods to improve oocyte:granulosa cell associations were tested. Altering the fibronectin coating regime did not improve oocyte survival and growth. In contrast lectin-aggregated primordial follicles cultured on non-coated wells showed significantly (P < 0.05) improved oocyte survival to 50% and increased median oocyte diameter compared to non-aggregated follicles. In Experiment 3, the effect of KIT ligand (KL) at 0 ng/ml, 10 ng/ml and 100 ng/ml, on lectin-aggregated primordial follicles cultured on non-coated wells was tested. KL at 100 ng/ml significantly (P < 0.05) increased median oocyte diameter compared to non-treated controls but had no effect on oocyte survival. In addition, follicles cultured with 100 ng/ml KL expressed mRNA for AMH, a gene expressed only in granulosa cells of growing follicles. In conclusion, culture of lectin-aggregated primordial follicles supported the long-term survival and growth of oocytes from isolated sheep primordial follicles. Culture of lectin-aggregates with 100 ng/ml KL further increased oocyte growth and induced granulosa cell differentiation.

Granulosa cell-oocyte interactions

Throughout oogenesis the oocyte and follicle cells establish an intricate system of mutual interactions that ultimately lead to the acquisition of their respective competences. Paracrine factors released by both cell types are believed to stimulate formation of the primordial follicle and support the initial phases of follicle growth. At the same time, these processes are also dependent on gap junction communication between the germinal and somatic compartment. At later stages of follicle development, activities released by the oocyte induce the adjacent granulosa cells to express a specialized phenotype. In their turn, these cells crucially regulate the ability of the oocyte to progress through the meiotic process and acquire full developmental potential.

Expression of stem cell factor and its receptor in human fetal and adult ovaries

OBJECTIVE

To investigate the immunocytochemical expression and presence of mRNA transcripts of stem cell factor (SCF) and its receptor (SCF-R) in ovaries from human adults and fetuses.

DESIGN

Immunocytochemical and reverse transcription polymerase chain reaction (RT-PCR) study.

SETTING

Major tertiary care and referral academic centers.

PATIENT(S)

Seven women and girls undergoing laparoscopic ovarian biopsy and 13 women undergoing second and third trimester pregnancy terminations.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Microscopic morphometric analysis, immunocytochemistry for SCF and SCF-R, and RT-PCR analyses.

RESULT(S)

There was strong to moderate immunocytochemical staining for SCF and its receptor in oocytes from primordial stages onward, but not in granulosa cells, in both fetal and adult ovarian samples. Transcripts of SCF and SCF-R RNA were detected by RT-PCR analyses for SCF and SCF-R.

CONCLUSION(S)

The expression of SCF and its receptor in ovarian tissue from fetuses and women suggests a possible role of SCF in growth initiation of human primordial follicles.

The murine winged-helix transcription factor Foxl2 is required for granulosa cell differentiation and ovary maintenance

Human Blepharophimosis/ptosis/epicanthus inversus syndrome (BPES) type I is an autosomal dominant disorder associated with premature ovarian failure (POF) caused by mutations in FOXL2, a winged-helix/forkhead domain transcription factor. Although it has been shown that FOXL2 is expressed in adult ovaries, its function during folliculogenesis is not known. Here, we show that the murine Foxl2 gene is essential for granulosa cell differentiation and ovary maintenance. In Foxl2(lacZ) homozygous mutant ovaries granulosa cells do not complete the squamous to cuboidal transition leading to the absence of secondary follicles and oocyte atresia. We further demonstrate that activin-betaA and anti-Mullerian inhibiting hormone expression is absent or strongly diminished in Foxl2(lacZ) homozygous mutant ovaries. Unexpectedly, two weeks after birth most if not all oocytes expressed Gdf9 in Foxl2(lacZ) homozygous mutant ovaries, indicating that nearly all primordial follicles have already initiated folliculogenesis at this stage. This activation, in the absence of functional granulosa cells, leads to oocyte atresia and progressive follicular depletion. In addition to providing a molecular mechanism for premature ovarian failure in BPES, these results suggest that granulosa cell function is not only crucial for oocyte growth but also to maintain follicular quiescence in vivo.