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

Impact of the SCF signaling pathway on leukemia stem cell-mediated ATL initiation and progression in an HBZ transgenic mouse model

Adult T-cell leukemia (ATL) is a malignant disease caused by human T-lymphotropic virus type 1. In aggressive ATL, the response to chemotherapy is extremely poor. We hypothesized that this poor response is due to the existence of chemotherapy-resistant cells, such as leukemic stem cells. Previously, we successfully identified an ATL stem cell (ATLSC) candidate as the c-kit⁺/CD38⁻/CD71⁻ cells in an ATL mouse model using Tax transgenic mice. Here, with a new ATL mouse model using HBZ-transgenic mice, we further discovered that the functional ATLSC candidate, which commonly expresses c-kit, is drug-resistant and has the ability to initiate tumors and reconstitute lymphomatous cells. We characterized the ATLSCs as c-kit⁺/CD4⁻/CD8⁻ cells and found that they have a similar gene expression profile as T cell progenitors. Additionally, we found that AP-1 gene family members, including Junb, Jund, and Fosb, were up-regulated in the ATLSC fraction. The results of an in vitro assay showed that ATLSCs cultured with cytokines known to promote stem cell expansion, such as stem cell factor (SCF), showed highly proliferative activity and maintained their stem cell fraction. Inhibition of c-kit–SCF signaling with the neutralizing antibody ACK2 affected ATLSC self-renewal and proliferation. Experiments in Sl/Sld mice, which have a mutation in the membrane-bound c-kit ligand, found that ATL development was completely blocked in these mice. These results clearly suggest that the c-kit–SCF signal plays a key role in ATLSC self-renewal and in ATL initiation and disease progression.

Morphometric characteristics of preantral and antral follicles and expression of factors involved in folliculogenesis in ovaries of adult baboons (Papio anubis)

PURPOSE

Baboons are commonly utilized as an animal model for studies of human reproduction. However, folliculogenesis in this species has not been fully documented. The aim of this study was to assess follicle morphometry and expression of essential proteins involved in folliculogenesis in baboons.

METHODS

Ovaries were recovered from four adult baboons and processed for histological evaluation and immunohistochemical analyses. Follicle proportion, follicle and oocyte diameter, theca layer thickness, number of granulosa cells, and follicle density were calculated. Immunohistochemical staining was also carried out for connexin 43 (Cx43), aromatase, and zona pellucida 3 (ZP3).

RESULTS

A total of 2221 follicles were counted and measured. Proportions of primordial, primary, secondary, small antral, and large antral follicles were 49, 26, 23, 1, and 1 %, respectively. The increase in follicle diameter was due not only to the increase in oocyte diameter but also to granulosa cell proliferation. Almost all antral follicles were positive for Cx43 (89.8 %), aromatase (84.8 %), and ZP3 (100 %). Most secondary follicles were positive for Cx43 (65 %) and ZP3 (64.5 %), and some primary follicles were positive only for Cx43. No primordial follicles stained positive in any of these immunohistochemical analyses. Only antral follicles showed aromatase activity.

CONCLUSIONS

On the basis of these results, we can conclude that folliculogenesis in baboons appears to be similar to that in humans, and this animal therefore constitutes a valuable model.

Expression and localisation of c-kit and KITL in the adult human ovary

BACKGROUND

The c-kit/kit ligand (KITL) signalling axis is an essential component of ovarian folliculogenesis in mammals, but little is known about expression and localisation of its key components in the ovaries of reproductive age women. This study aimed to characterise mRNA expression of c-kit and KITL isoforms and the localisation of c-kit and KITL proteins in adult human premenopausal ovaries.

METHODS

This study utilised granulosa cells obtained from the preovulatory follicles of women undergoing assisted reproduction, pieces of ovarian tissue obtained from premenopausal women undergoing gynaecological surgeries and archival paraffin-embedded premenopausal ovarian tissues. Methodology included PCR for gene expression and Western blot or immunohistochemistry for protein expression.

RESULTS

Both c-kit mRNA isoforms, known as GNNK+ and GNNK-, were detected in human ovarian cortex, while KITL protein isoforms (KITL1 and KITL2) were present in ovarian cortex and human granulosa cells. Immunohistochemistry showed expression of KITL and c-kit protein in multiple cell types within follicles throughout development, from primordial follicles to large antral follicles, in addition to atretic follicles. Oocytes of all follicle stages expressed c-kit protein exclusively. Interestingly, unlike animal models, expression of both proteins displayed a less cell-type specific distribution with immunostaining present in granulosa, theca and stromal cells, suggesting that autocrine signalling occurs within the human ovary.

CONCLUSION

The results of this study indicate that c-kit/KITL signalling also occurs in the human ovary, as established in various animal models, and may involve previously unknown autocrine signalling.

Immunolocalization of growth, inhibitory, and proliferative factors involved in initial ovarian folliculogenesis from adult common squirrel monkey (Saimiri collinsi)

We performed an immunohistochemical (IHC) study to determine the follicular expression of growth differentiation factor 9 (GDF-9), anti-Müllerian hormone (AMH), Kit Ligand (KL), and c-Kit in squirrel monkey ovary. Ovarian tissue fragments from 4 squirrel monkeys were collected by laparotomy and processed for classical histology and IHC. Additionally, follicle development was assessed by Ki67 immunostaining to evaluate proliferative status of granulosa cells. A total of 4025 follicles were examined (1475 for classical histology and 2550 for immunohistochemistry). More than 80% of the evaluated follicles were morphologically normal. The GDF-9 protein was detectable in oocyte cytoplasm from primordial (100%), primary (99.1%), and secondary (100%) follicles. The AMH was not expressed in primordial follicles but just in few primary follicles (13.8%). On the other hand, it was highly expressed in granulosa cells from secondary follicles (67.9%). c-Kit, KL receptor, was found in the oolemma of primordial (100%), primary (100%), and secondary (100%) follicles. The KL expression was observed in oocytes and granulosa cells from primordial (94.9%), primary (91.6%) and secondary follicles (100%). Ki67 immunostaining was observed in granulosa cells from primary (5.7%) and secondary (54.8%) follicles but not in primordial follicles. In conclusion, we described the localization of GDF-9, KL, c-Kit, and Ki67 proteins and confirmed the presence of AMH protein in preantral follicles from squirrel monkey. Our results offer contribution for understanding of folliculogenesis in neotropical nonhuman primates. Moreover, these markers can be used to assess follicular viability and functionality after cryopreservation, transplantation, or in vitro culture of ovarian tissue.

The impact of culture conditions on early follicle recruitment and growth from human ovarian cortex biopsies in vitro

OBJECTIVE

To investigate the effects of a dynamic fluidic culture system on early in vitro folliculogenesis in standardized ovarian cortex biopsies.

DESIGN

Cortical small strips were cultured for 6 days in a conventional static or in a dynamic fluidic culture system.

SETTING

University-affiliated laboratory with an associated cryobank facility.

PATIENT(S)

Ovarian cortex from postpuberal female cancer patients (26.1 ± 1.3 y) who opted for cryopreservation of their tissue for fertility protection before gonadotoxic cancer therapy. With informed consent of the Institutional Ethics Committee, part of the tissue was available for patient-related research studies.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The viability and proliferative capacity of the cortex biopsies were evaluated by chemiluminescent microparticle immunoassay for detection of in vitro produced E2 and P in the supernate, by viable follicle counting via calcein staining, by histologic analyses, and by total RNA preparation and reverse transcription for real-time polymerase chain reaction of selected early folliculogenesis genes.

RESULT(S)

The data support the notion that early follicle development can be better achieved in vitro in a dynamic fluidic culture system. The findings are based on the presence of more viable follicles, higher expression levels of early folliculogenesis genes KIT-L, INHB, and GDF9, and the absence of premature luteinization of follicles.

CONCLUSION(S)

This study provides evidence that dynamic fluidic culture is a promising approach for investigating early follicular recruitment and growth in cortical biopsies. It may serve as a first step in a multistep culture system to design a complex in vitro system for complete folliculogenesis.

Effect of cryopreservation and transplantation on the expression of kit ligand and anti-Mullerian hormone in human ovarian tissue

BACKGROUND

Although cryopreservation and transplantation of ovarian tissue represent a promising alternative to safeguard fertility in cancer patients, low recovery rates of oocytes aspirated from antral follicles and a significant number of empty follicles have been observed in women with transplanted frozen-thawed ovarian tissue. In order to understand how freezing and/or grafting may affect follicular development, the follicular expression of kit ligand (KL) and anti-Müllerian hormone (AMH), two key factors activating and inhibiting follicle growth, were assessed after long-term grafting in severe combined immunodeficient (SCID) mice.

METHODS

Ovarian biopsies from eight patients were used for fresh and frozen-thawed tissue xenografting in 13 SCID mice for a period of 28 weeks, including 2 weeks of gonadotrophin stimulation. KL, AMH and proliferating cell nuclear antigen (PCNA) immunostaining were quantified before and after grafting in the two treatment groups (fresh and frozen-thawed grafted ovarian tissue).

RESULTS

Lower expression of KL was found in primordial and primary follicles after grafting of both fresh and frozen-thawed tissue. Consistent expression of AMH was found in most growing follicles at a similar rate in both graft types. In fresh and frozen-thawed grafts, 13-14% of primordial follicles were PCNA-positive, indicating a similar maintenance of quiescent follicles despite follicle activation.

CONCLUSIONS

Grafting and/or gonadotrophin stimulation appear to affect the follicular expression of KL, which may alter oocyte quality. AMH expression in growing follicles after ovarian tissue transplantation may be one of the factors contributing to the preservation of resting follicles in 28-week-old grafts.

Circulating concentration of stem cell factor in serum of stimulated IVF patients

Stem cell factor (SCF) plays a major role in haematopoiesis and spermatogenesis, and possibly female fertility. This study investigated the role of changes in SCF concentrations in 74 assisted conception patients. In group 1 (n=74) SCF concentration was assessed in serum and follicular fluid (FF) on the day of follicular puncture (FP) and compared in serum and FF in response to ovarian stimulation between low (n=25), moderate (n=26) and high (n=14) responders. In group 2 (n=30) serum for SCF assessment was collected throughout the menstrual cycle until gestation. SCF concentration related to the number of follicles in serum and in FF decreased from low to moderate and high responders (P<0.001); pregnancy rates were 20.0%, 34.6% and 50.1%, respectively (P=0.05). SCF in serum increased from stimulation days 6-8 to 9-11 and peaked on the day of human chorionic gonadotrophin injection (P=0.03). The SCF concentrations dropped slightly on the day of FP, increased significantly to the day of pregnancy confirmation and reached highest concentration (P=0.02) during gestation. SCF is involved in follicle development and may be a predictor of IVF outcome.

Oogenesis and cell death in human prenatal ovaries: what are the criteria for oocyte selection?

Prenatal oogenesis produces hundreds of thousands of oocytes, most of which are discarded through apoptosis before birth. Despite this large-scale selection, the survivors do not constitute a perfect population, and the factors at the cellular level that result in apoptosis or survival of any individual oocyte are largely unknown. What then are the selection criteria that determine the size and quality of the ovarian reserve in women? This review focuses on new data at the cellular level, on human prenatal oogenesis, offering clues about the importance of the timing of entry to meiotic prophase I by linking the stages and progress through MPI with the presence or absence of apoptotic markers. The characteristics and responsiveness of cultured human fetal ovarian tissue at different gestational ages to growth factor supplementation and the impact of meiotic abnormalities upon apoptotic markers are discussed. Future work will require the use of a tissue culture model of prenatal oogenesis in order to investigate the fate of individual live oocytes at different stages of development.

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.

Primordial follicular assembly in humans – revisited

Recent interest in the initial phases of ovarian follicular formation and development has lead to a number of publications in this area, most of which address the autocrine and paracrine factors involved in primordial follicle activation to primary follicle. Primordial follicle assembly (first step in follicle formation) determines the lifetime supply of primordial follicles and remains a poorly understood phenomenon. Despite a number of recent articles that are concentrating on immuno-histochemistry, basic steps in the process are not clear. Hence, we feel it is time to take a step back and see what is available in the literature and identify the gaps in which future research about primordial follicle assembly in humans needs to be directed.

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.

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.