Effects of Kit Ligand and anti-Kit antibody on growth of cultured mouse preantral follicles

PTEN inhibitor and kit ligand increase in vitro activation and survival of primordial follicles in alpaca

In mammals, activation of primordial follicles to primary follicle is a progressive and highly regulated process. There is evidence in mice that phosphatase and tensin homologue deleted on Chromosome 10 (PTEN) silencing is an important negative regulator of phosphatidylinositol 3-kinase (PI3K), which initiates activation of dormant follicles. The objective of the study was to evaluate the effect of the addition of PTEN inhibitor (bpV(HOpic)) (10 μM) and/or Kit Ligand (KL) (100 ng/mL) on the in vitro activation and survival of alpaca primordial follicles. Ovarian cortical fragments from 11 adult alpacas were cultured for 24 h in tissue culture medium (α-MEM+ ) supplemented with KL and bpV or the association of both. Subsequently, each sample was processed by classical histology and follicular counting and classification were performed. The results obtained show a reduction (p < 0.05) of primordial follicles in more than 50% in follicular tissue cultured in vitro in α-MEM+ or supplemented with bpV and/or KL versus the control (not cultured). Further, >25% increase in primary follicles in follicular tissue cultured in vitro in α-MEM+ or supplemented with KL and/or bpV versus control. However, the follicular survival rate showed a decrease of 20% in the cultured tissues, except for the α-MEM+ supplemented with KL and bpV. In conclusion, supplementation of bpV (HOpic) (10 μM) and KL (100 ng/mL) increased the activation in vitro of primordial follicles and survival after in vitro culture of alpaca ovarian tissue.

The FSH-mTOR-CNP signaling axis initiates follicular antrum formation by regulating tight junction, ion pumps, and aquaporins

The initial formation of the follicular antrum (iFFA) serves as a dividing line between gonadotropin-independent and gonadotropin-dependent folliculogenesis, enabling the follicle to sensitively respond to gonadotropins for its further development. However, the mechanism underlying iFFA remains elusive. Herein, we reported that iFFA is characterized by enhanced fluid absorption, energy consumption, secretion, and proliferation and shares a regulatory mechanism with blastula cavity formation. By use of bioinformatics analysis, follicular culture, RNA interference, and other techniques, we further demonstrated that the tight junction, ion pumps, and aquaporins are essential for follicular fluid accumulation during iFFA, as a deficiency of any one of these negatively impacts fluid accumulation and antrum formation. The intraovarian mammalian target of rapamycin-C-type natriuretic peptide pathway, activated by follicle-stimulating hormone, initiated iFFA by activating tight junction, ion pumps, and aquaporins. Building on this, we promoted iFFA by transiently activating mammalian target of rapamycin in cultured follicles and significantly increased oocyte yield. These findings represent a significant advancement in iFFA research, further enhancing our understanding of folliculogenesis in mammals.

The potential role of the KFG and KITLG proteins in preventing granulosa cell apoptosis in Bubalus bubalis

BACKGROUND

The dynamics of mammalian follicular development and atresia is an intricate process involving the cell-cell communication mediated by secreted ovarian factors. These interactions are critical for oocyte development and regulation of follicular atresia which in part are mediated by keratinocyte growth factor (KGF) and kit ligand (KITLG), but their roles in the regulation of apoptosis in buffalo granulosa cells have not yet been defined. During mammalian follicular development, granulosa cell apoptosis triggers the atresia so ~ 1% follicles reach the ovulation stage. In the present study, we used buffalo granulosa cells to examine the effects of KGF and KITLG in apoptosis regulation and investigated potential mechanism on Fas-FasL and Bcl-2 signaling pathways.

RESULT

Isolated buffalo granulosa cells were cultured with KGF and KITLG proteins using different doses (0, 10, 20, and 50 ng/ml) independently or in combination. Expression analysis for both anti-apoptotic (Bcl-2, Bcl-xL, and cFLIP) and pro-apoptotic (Bax, Fas, and FasL) genes at transcriptional levels were carried out by real-time PCR. Upon treatments, expression levels of anti-apoptotic genes were significantly upregulated in a dose-dependent manner, showing an upregulation at 50 ng/ml (independently), and at 10 ng/ml in combination. Additionally, upregulation of growth-promoting factors, bFGF, and α-Inhibin was also observed.

CONCLUSIONS

Our findings suggest the potential roles of KGF and KITLG in determining granulosa cell growth and regulating apoptosis.

Regulation of mouse primordial follicle formation by signaling through the PI3K pathway

Cell signaling mediated by the KIT receptor is critical for many aspects of oogenesis including the proliferation and migration of primordial germ cells, as well as the survival, growth, and maturation of ovarian follicles. We previously showed that KIT regulates cyst breakdown and primordial follicle formation, and in this study, have investigated the mechanisms downstream of the receptor by modulating the activity of two downstream signaling cascades: the phosphoinositide 3-kinase (PI3K) and the mitogen-activated protein kinase (MAPK) pathways. E17.5 ovaries were cultured for five days with a daily dose of media supplemented with either the PI3K inhibitor LY294002, the MEK inhibitor U0126, or a DMSO vehicle control. Our histological observations aligned with the established role of PI3K in oocyte growth and primordial follicle activation but also revealed that LY294002 treatment delayed the processes of cyst breakdown and primordial follicle formation. U0126 treatment also led to a reduction in oocyte growth and follicle development but did not appear to affect cyst breakdown. The delay in cyst breakdown was mitigated when ovaries were dually dosed with LY294002 and KITL, suggesting that while KIT may signal through PI3K to promote cyst breakdown, other signaling networks downstream of the receptor could compensate. These observations unearth a role for PI3K signaling in the establishment of the ovarian reserve and suggest that PI3K might be the primary mediator of KIT-induced cyst breakdown and primordial follicle formation in the mouse ovary.

Effects of Stem Cell Factor/c-Kit Signaling on In Vitro Maturation of Porcine Oocytes and Subsequent Developmental Competence After Fertilization

Stem cell factor (SCF), also known as c-Kit ligand, plays an important role in the proliferation of primordial germ cells and the survival of oocytes during follicular development. The aim of this study was to investigate the effect of SCF/c-Kit signaling on in vitro maturation (IVM) of porcine oocytes by analyzing nuclear and cytoplasmic maturation, oocyte size, cumulus cell expansion, and developmental competence to the blastocyst stage. Moreover, mRNA expression patterns of porcine cumulus cells and oocytes were evaluated using qRT-PCR. Following 42 h of IVM, 10 and 50 ng/mL SCF-treated groups exhibited significantly (P < 0.05) increased polar body extrusion rates and intracellular glutathione levels compared with the control group. The cumulus expansion index significantly (P < 0.05) increased in all SCF-treated groups compared with the control samples. mRNA levels of the proapoptotic gene Bax and apoptosis-related cysteine peptidase Caspase3 were lower in SCF-treated cumulus cells than in the control group. Notably, the diameter of oocytes after IVM, the mRNA expression of well-known oocyte-secreted factors (GDF9 and BMP15), and an oocyte-specific protein essential for ovulation and oocyte health (YBX2) were significantly (P < 0.05) higher in SCF-treated than in non-treated oocytes. Inhibition of c-Kit during porcine IVM using ACK2, an antagonistic blocker of c-Kit, significantly (P < 0.05) decreased the polar body extrusion rate compared with the control, as well as blastocyst formation rate compared with the 10 ng/mL SCF-treated group. In conclusion, the effect of SCF/c-Kit-mediated signaling during porcine IVM could be ascribed to the reduced expression of apoptosis-related genes and higher expression of oocyte-specific/secreted factors.

Activation-induced cytidine deaminase is a possible regulator of cross-talk between oocytes and granulosa cells through GDF-9 and SCF feedback system

Activation-induced cytidine deaminase (AID, Aicda) is a master gene regulating class switching of immunoglobulin genes. In this study, we investigated the significance of AID expression in the ovary. Immunohistological study and RT-PCR showed that AID was expressed in murine granulosa cells and oocytes. However, using the Aicda-Cre/Rosa-tdRFP reporter mouse, its transcriptional history in oocytes was not detected, suggesting that AID mRNA in oocytes has an exogenous origin. Microarray and qPCR validation revealed that mRNA expressions of growth differentiation factor-9 (GDF-9) in oocytes and stem cell factor (SCF) in granulosa cells were significantly decreased in AID-knockout mice compared with wild-type mice. A 6-h incubation of primary granuloma cells markedly reduced AID expression, whereas it was maintained by recombinant GDF-9. In contrast, SCF expression was induced by more than threefold, whereas GDF-9 completely inhibited its increase. In the presence of GDF-9, knockdown of AID by siRNA further decreased SCF expression. However, in AID-suppressed granulosa cells and ovarian tissues of AID-knockout mice, there were no differences in the methylation of SCF and GDF-9. These findings suggest that AID is a novel candidate that regulates cross-talk between oocytes and granulosa cells through a GDF-9 and SCF feedback system, probably in a methylation-independent manner.

Regulation of Folliculogenesis by Growth Factors in Piglet Ovary Exposed Prenatally to β-Hydroxy-β-Methylbutyrate (HMB)

Β-hydroxy-β-methylbutyrate (HMB) is one of the leucine metabolites with protein anabolic effects which makes it very popular among athletes. Previously, it was shown that HMB administered during the prenatal period reduced the pool of primordial follicles and increased the proportion of developing follicles in newborn piglets. This work is a further step to understand these morphological alterations. Therefore, the aim of this study was to examine the effect of prenatal HMB treatment on the expression of the Kit ligand, BMP-4, bFGF, and the IGF-1/IGF-1R system which are the main growth factors controlling follicular development. Excised ovaries from 12 newborn piglets, originated from the control (n=6) and HMB-treated (n=6) sows were used for immunohistochemical and western-blot analysis. The tested proteins were localized within egg nests and ovarian follicles. Furthermore, the western-blot assay indicated higher BMP-4, Kit ligand, and IGF-1R expression, while the level of bFGF and IGF-1 proteins decreased after HMB dietary treatment. These findings show that HMB included into sow diet can modulate the expression of growth factors and thereby alter ovarian morphology in offspring. Therefore, this study opens a discussion about the benefits and risks of the diet supplemented with HMB and its potential application in medicine and animal husbandry, and further research is necessary in this area.

Scaffold-based tissue engineering approaches in treating infertility

Tissue engineering and the use of scaffolds have shown high therapeutic potentialities about male and female infertility. Nowadays, many couples are suffering from infertility problems. There are different causes for infertility including chemotherapy (for male and female), uterine injuries, and intrauterine adhesions. Extra-cellular matrix in tissue engineering provides a supportive medium for blood or lymphatic vessels making it a suitable substrate for cell implantation and growth. Dominant successes in this branch have been in use of patient-derived primary cells, these cells loaded in scaffolds and used to generate tissue for re-implantation. However, this method has limitations, because of the invasive nature of cell collection, also the cells patient-derived may be not healthy and become the source of disease. Therefore, use of stem cells, including embryonic stem (ES) cells, bone marrow mesenchymal stem cells (BM-MSCs) and umbilical cord-derived mesenchymal stem cells (UC-MSCs) have been considered. Cell/scaffold systems have a substantial role in fertility organs or agents repair or regeneration. This review summarizes the novel scaffold-based tissue engineering approaches to treat infertility.

Effects of stem cell factor on in vitro growth of buffalo oocytes

Stem cell factor (SCF) plays important roles in primordial follicle activation, oocyte growth and survival, granulosa cell proliferation, theca cell recruitment, and ovarian steroidogenesis. The aim of this study was to investigate the effect of SCF on in vitro growth of buffalo oocytes. Oocyte-granulosa cell complexes (OGCs) were dissected from early antral follicles of slaughtered buffalo ovaries and cultured for 6 days in media supplemented with 0, 50 or 100 ng/mL SCF. In vitro grown oocytes were further cultured for in vitro maturation for 24 h. The results showed that SCF significantly (P < 0.05) increased oocyte diameter in vitro. The percentages of surviving oocytes were 60, 81 and 92 in 0, 50 and 100 ng/mL SCF supplemented group, respectively. SCF promoted formation of antrum-like structures in culture. The results also showed that SCF enhanced the maturation of in vitro grown buffalo oocytes. Here, 14% in vitro grown oocytes reached metaphase II (MII) stage in 50 ng/mL SCF supplemented group, whereas the percentage was increased to 26% in 100 ng/mL SCF treated group. These results show that SCF supports the growth, viability and nuclear maturation of buffalo oocytes in vitro.

Follicle development as an orchestrated signaling network in a 3D organoid

The ovarian follicle is the structural and functional unit of the ovary, composed of the female gamete (the oocyte) and supportive somatic cells. Follicles are not only the source of a female's germ cell supply, but also secrete important hormones necessary for proper endocrine function. Folliculogenesis, the growth and maturation of the follicular unit, is a complex process governed by both intrafollicular crosstalk and pituitary-secreted hormones. While the later stages of this process are gonadotropin-dependent, early folliculogenesis appears to be controlled by the ovarian microenvironment and intrafollicular paracrine and autocrine signaling. In vitro follicle culture remains challenging because of the limited knowledge of growth factors and other cytokines influencing early follicle growth. Here we discuss the current state of knowledge on paracrine and autocrine signaling influencing primary follicles as they develop into the antral stage. Given the importance of intrafollicular signaling and the ovarian microenvironment, we reviewed the current engineering approaches for in vitro follicle culture, including 3D systems using natural hydrogels such as alginate and synthetic hydrogels such as poly(ethylene glycol). Our discussion is focused on what drives the proliferation of granulosa cells, development of the thecal layer, and antrum formation-three processes integral to follicle growth up to the antral stage. Further research in this area may reveal the mechanisms behind these complex signaling relationships within the follicle, leading to more successful and physiologically-relevant in vitro culture methods that will translate well to clinical applications.

Expression of kit ligand and insulin-like growth factor binding protein 3 during in vivo or in vitro development of ovarian follicles in sheep

Expression of Kit ligand (KL) and insulin-like growth factor binding protein (IGFBP3) genes was studied at different in vivo and corresponding in vitro stages of development of the ovarian follicles in sheep. The expression of both KL and IGFBP3 was significantly higher in the primordial follicles relative to any other stage of development. Compared to the other stages, the KL expression in the cumulus cells from in vivo grown large antral follicles and that of IGFBP3 in COCs' isolated from large antral follicles matured in vitro for 24 hr were significantly higher. In the oocytes from in vivo grown ovarian follicles, the expression of KL was the same at all the stages of development. Insulin-like growth factor binding protein 3 expression was also the same in the oocytes at all the stages of the development except for a significantly lower expression in those from antral follicles. The expression of KL in the cumulus cells decreased significantly in the in vitro grown early antral follicles but did not change further as the development progressed. The expression of IGFBP3 in the cumulus cells from in vitro grown ovarian follicles appeared to increase as the development progressed although the increase was not significant between any two consecutive stages of development. In the oocytes in in vitro grown ovarian follicles, the expression levels of KL and IGFBP3 genes did not change with development. It is concluded that (i) KL and IGFBP3 genes follow specific patterns of expression during ovarian folliculogenesis and (ii) in vitro culture of preantral follicles compromises the development potential through alterations in the stage-specific patterns of expression of these and other developmentally important genes.

Stem cell factor promotes in vitro ovarian follicle development in the domestic cat by upregulating c-kit mRNA expression and stimulating the phosphatidylinositol 3-kinase/AKT pathway

In the present study we examined the effects of stem cell factor (SCF; 50 vs 100 ng mL–1) alone or in combination with epidermal growth factor (EGF; 100 ng mL–1) on: (1) the in vitro viability and growth of cat follicles within ovarian cortices; (2) phosphatidylinositol 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) phosphorylation; and (3) c-kit and FSH receptor (FSHr) mRNA expression. At 100 ng mL–1, SCF increased (P ≤ 0.05) the percentage and size of secondary follicles after 14 days of in vitro culture and sustained AKT phosphorylation after 3 days incubation. EGF suppressed this beneficial effect and reduced (P ≤ 0.05) the percentage of structurally normal follicles and FSHr expression when combined with 100 ng mL–1 SCF. Expression of c-kit mRNA was higher (P ≤ 0.05) in the presence of 100 ng mL–1 SCF compared with fresh follicles and cohorts cultured under other conditions. A c-kit inhibitor suppressed follicle growth and reduced AKT phosphorylation. Collectively, the results demonstrate that SCF promotes cat follicle development by upregulating c-kit mRNA expression and AKT phosphorylation. EGF suppresses the stimulating effect of SCF, leading to downregulation of FSHr expression.

LH prevents cisplatin-induced apoptosis in oocytes and preserves female fertility in mouse

Premature ovarian failure and female infertility are frequent side effects of anticancer therapies, owing to the extreme sensitivity of the ovarian reserve oocytes to the damaging effects of irradiation and chemotherapy on DNA. We report here a robust protective effect of luteinizing hormone (LH) on the primordial follicle pool of prepubertal ovaries against the cisplatin (Cs)-induced apoptosis. In vitro LH treatment of prepubertal ovarian fragments generated anti-apoptotic signals by a subset of ovarian somatic cells expressing LH receptor (LHR) through cAMP/PKA and Akt pathways. Such signals, reducing the oocyte level of pro-apoptotic TAp63 protein and favoring the repair of the Cs-damaged DNA in the oocytes, prevented their apoptosis. Noteworthy, in vivo administration to prepubertal female mice of a single dose of LH together with Cs inhibited the depletion of the primordial follicle reserve caused by the drug and preserved their fertility in reproductive age, preventing significant alteration in the number of pregnancy and of delivered pups. In conclusion, these findings establish a novel ovoprotective role for LH and further support the very attracting prospective to use physiological 'fertoprotective' approaches for preventing premature infertility and risks linked to precocious menopause in young patients who survived cancer after chemotherapy.

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Spatio-Temporal Gene Expression Profiling during In Vivo Early Ovarian Folliculogenesis: Integrated Transcriptomic Study and Molecular Signature of Early Follicular Growth

Background

The successful achievement of early ovarian folliculogenesis is important for fertility and reproductive life span. This complex biological process requires the appropriate expression of numerous genes at each developmental stage, in each follicular compartment. Relatively little is known at present about the molecular mechanisms that drive this process, and most gene expression studies have been performed in rodents and without considering the different follicular compartments.

Results

We used RNA-seq technology to explore the sheep transcriptome during early ovarian follicular development in the two main compartments: oocytes and granulosa cells. We documented the differential expression of 3,015 genes during this phase and described the gene expression dynamic specific to these compartments. We showed that important steps occurred during primary/secondary transition in sheep. We also described the in vivo molecular course of a number of pathways. In oocytes, these pathways documented the chronology of the acquisition of meiotic competence, migration and cellular organization, while in granulosa cells they concerned adhesion, the formation of cytoplasmic projections and steroid synthesis. This study proposes the involvement in this process of several members of the integrin and BMP families. The expression of genes such as Kruppel-like factor 9 (KLF9) and BMP binding endothelial regulator (BMPER) was highlighted for the first time during early follicular development, and their proteins were also predicted to be involved in gene regulation. Finally, we selected a data set of 24 biomarkers that enabled the discrimination of early follicular stages and thus offer a molecular signature of early follicular growth. This set of biomarkers includes known genes such as SPO11 meiotic protein covalently bound to DSB (SPO11), bone morphogenetic protein 15 (BMP15) and WEE1 homolog 2 (S. pombe)(WEE2) which play critical roles in follicular development but other biomarkers are also likely to play significant roles in this process.

Conclusions

To our knowledge, this is the first in vivo spatio-temporal exploration of transcriptomes derived from early follicles in sheep.

Kit ligand promotes the transition from primordial to primary follicles afterin vitroculture of ovine ovarian tissue

This study evaluated the effects of kit ligand (KL) on the morphology and development of ovine preantral follicles (fresh control) and after 7 days ofin vitroculture in α-Minimal Essential Medium (α-MEM; control medium) or the presence of KL (1, 10, 50, 100 or 200 ng/ml). There was an increase in the percentage of primary follicles at the concentration of 100 ng/ml KL, compared with the fresh control, control medium (α-MEM) and the other KL concentrations. Follicle diameter was significantly higher than the control medium only at concentrations of 50 and 100 ng/ml KL. In conclusion, 100 ng/ml KL promoted the transition from primordial to primary follicles (follicular activation) afterin vitroculture of ovine ovarian tissue.

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.

Differential regulation of kit ligand A (kitlga) expression in the zebrafish ovarian follicle cells--evidence for the existence of a cyclic adenosine 3', 5' monophosphate-mediated binary regulatory system during folliculogenesis

Kit ligand (Kitl) is an important paracrine factor involved in the activation of primordial follicles from the quiescent pool and in the maintenance of meiotic arrest before germinal vesicle breakdown (GVBD). It has been reported that follicle-stimulating hormone (FSH) stimulates but luteinizing hormone (LH) suppresses the expression of Kitl in the granulosa cells in mammals. Considering that both gonadotropins signal in the follicle cells mainly by activating cyclic adenosine 3', 5'-monophosphate (cAMP) pathway, we are intrigued by how cAMP differentially regulates Kitl expression. In the present study, we demonstrated that both human chorionic gonadotropin (hCG) and pituitary adenylate cyclase activating polypeptide (PACAP) inhibited insulin-like growth factor I (IGF-I)-induced Akt phosphorylation and kitlga expression in the zebrafish follicle cells. Further experiments showed that cAMP was involved in regulating the expression of kitlga. However, two cAMP-activated effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), had converse effects. PKA promoted whereas Epac inhibited the expression of kitlga, as demonstrated by the respective activators. Interestingly, cAMP also appeared to exert differential effects on kitlga expression at different stages of follicle development during folliculogenesis, significantly stimulating kitlga expression at the early growth stage but suppressing it at the full-grown stage before final oocyte maturation, implying a potential mechanism for differential effects of the same pathway at different stages. The inhibitory effect of forskolin (activator of adenylate cyclase) and H89 (inhibitor of PKA) on IGF-I-induced expression of kitlga suggested cross-talk between the cAMP and IGF-I-activated PI3K-Akt pathways. This study, together with our previous findings on IGF-I regulation of kitlga expression, provides important clues to the underlying mechanism that regulates Kit ligand expression during folliculogenesis in the ovary.

The effect of lysophosphatidic acid during in vitro maturation of bovine oocytes: embryonic development and mRNA abundances of genes involved in apoptosis and oocyte competence

In the present study we examined whether LPA can be synthesized and act during in vitro maturation of bovine cumulus oocyte complexes (COCs). We found transcription of genes coding for enzymes of LPA synthesis pathway (ATX and PLA2) and of LPA receptors (LPAR 1–4) in bovine oocytes and cumulus cells, following in vitro maturation. COCs were matured in vitro in presence or absence of LPA (10⁻⁵ M) for 24 h. Supplementation of maturation medium with LPA increased mRNA abundance of FST and GDF9 in oocytes and decreased mRNA abundance of CTSs in cumulus cells. Additionally, oocytes stimulated with LPA had higher transcription levels of BCL2 and lower transcription levels of BAX resulting in the significantly lower BAX/BCL2 ratio. Blastocyst rates on day 7 were similar in the control and the LPA-stimulated COCs. Our study demonstrates for the first time that bovine COCs are a potential source and target of LPA action. We postulate that LPA exerts an autocrine and/or paracrine signaling, through several LPARs, between the oocyte and cumulus cells. LPA supplementation of maturation medium improves COC quality, and although this was not translated into an enhanced in vitro development until the blastocyst stage, improved oocyte competence may be relevant for subsequent in vivo survival.

Differential regulation of Kit ligand A expression in the ovary by IGF-I via different pathways

Kit ligand (KITL) plays indispensable roles both in primordial follicle activation and in the maintenance of meiotic arrest of the oocyte. The regulation of KITL expression in the ovary, however, remains largely unknown. In the zebrafish, there are 2 paralogues of KITL, kitlga and kitlgb, and 2 Kit receptors, kita and kitb. Consistent with the situation in mammals, kitlga is only expressed in the ovarian follicle cells, and its cognate receptor kita is expressed in the oocyte. In the present study, we demonstrated that the expression of kitlga was promoted by IGF-I through its receptor IGF-IR. The stimulation involved transcription but not translation, suggesting that the kitlga gene is likely a direct downstream target of IGF-I signaling. Further experiments showed that the stimulatory effect of IGF-I was mediated by phosphatidyl inositol 3-kinase (PI3K)-Akt pathway. IGF-I also activated MEK-ERK pathway; however, this pathway suppressed kitlga expression. The regulation of kitlga expression by IGF-I appeared to depend on the stage of follicle development with a greater induction at early stage than late stage. This may be related to changes in IGF-I signaling pathways and/or local paracrine environment. In support of this were the differential expression of IGF-I receptors (igf1ra and igf1rb) and responsiveness of IGF-I signaling pathways, especially the PI3K-Akt pathway. Furthermore, the IGF-I-induced kitlga expression was inhibited by epidermal growth factor, an oocyte-derived paracrine factor in the zebrafish follicle. This study provides evidence for a controlling mechanism underlying the regulation of KITL expression in the ovary.

Incorporation of phosphatase inhibitor in culture prompts growth initiation of isolated non-growing oocytes

In vitro folliculogenesis of primordial and early preantral follicles is necessary for increment of reproductive efficiency in domestic animals, humans and endangered species. Recent study in phosphatase and tensin homolog (Pten) -knockout mice has revealed that this phosphatase acts as an inhibitory factor in follicle activation of primordial pool with the resultant inhibition of oocyte growth. To test in vitro effect of a phosphatase inhibitor on growth initiation of isolated non-growing oocytes in neonatal ovaries, we applied a specific inhibitor (bpV (HOpic)) for PTEN in culturing system. Non-growing oocytes isolated from the ovaries of newborn BDF1 (C57BL/6 × DBA/2) pups were divided to four culture groups. Five days after culture, the oocytes in 14 μmol/l bpV only, 14 μmol/l bpV plus 100 ng/ml Kit Ligand (KL), and 100 ng/ml KL groups showed significantly (P<0.05) growth (19.3±0.55, 25.8±0.53 and 21.6±0.29 μm, respectively) compared with that of the control (no additive) (16.9±0.53 μm). In addition, western blotting in those groups showed enhanced expression of phosphorylated Akt. In conclusion, we clearly demonstrate that isolated non-growing oocytes develop in phosphatase inhibitor, especially to PTEN, incorporated culturing system, and show first as we know that oocytes with zona Pellucidae can be obtained in vitro from isolated non-growing oocytes.

Development of a serum-free defined system employing growth factors for preantral follicle culture

This study was conducted to evaluate if mouse preantral follicles can yield developmentally competent oocytes following culture in serum-free, defined medium. Donor follicles were obtained from 14-day-old B6CBAF1 mice, and cultured in α-MEM-Glutamax medium. The replacement of fetal bovine serum with knockout serum replacement (KSR) did not significantly reduce follicle growth or oocyte maturation in vitro, although it significantly reduced the development of oocytes after activation. Regardless of the replacement medium, follicle growth was not influenced by the addition of leukemia inhibitory factor (LIF). The addition of 100 ng/ml stem cell factor (SCF) to the KSR-supplemented serum-free medium significantly stimulated follicle development, which further improved blastocyst formation after oocyte activation. On Day 3 of culture, a significant increase in Bmp7 expression was detected in the SCF-containing medium compared with the serum-containing medium, whereas Gdf9 and Amh were increased in the serum-containing medium. A significant increase in estradiol production was detected under serum-free conditions, but minimal progesterone secretion was detected throughout the culture period. In conclusion, serum-free media can be used to optimize ovarian follicle cultures, and the addition of SCF is beneficial for deriving developmentally competent oocytes through follicle culture.

Spatial distribution and receptor specificity of zebrafish Kit system--evidence for a Kit-mediated bi-directional communication system in the preovulatory ovarian follicle

Consisting of Kit ligand and receptor Kit, the Kit system is involved in regulating many ovarian functions such as follicle activation, granulosa cell proliferation, and oocyte growth and maturation. In mammals, Kit ligand is derived from the granulosa cells and Kit receptor is expressed in the oocyte and theca cells. In the zebrafish, the Kit system contains two ligands (Kitlga and Kitlgb) and two receptors (Kita and Kitb). Interestingly, Kitlga and Kitb are localized in the somatic follicle cells, but Kitlgb and Kita are expressed in the oocyte. Using recombinant zebrafish Kitlga and Kitlgb, we demonstrated that Kitlga preferentially activated Kita whereas Kitlgb specifically activated Kitb by Western analysis for receptor phosphorylation. In support of this, Kitlgb triggered a stronger and longer MAPK phosphorylation in follicle cells than Kitlga, whereas Kitlga but not Kitlgb activated MAPK in the denuded oocytes, in agreement with the distribution of Kita and Kitb in the follicle and their specificity for Kitlga and Kitlgb. Further analysis of the interaction between Kit ligands and receptors by homology modeling showed that Kitlga-Kita and Kitlgb-Kitb both have more stable electrostatic interaction than Kitlgb-Kita or Kitlga-Kitb. A functional study of Kit involvement in final oocyte maturation showed that Kitlga and Kitlgb both suppressed the spontaneous maturation significantly; in contrast, Kitlgb but not Kitlga significantly promoted 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) -induced oocyte maturation. Our results provided strong evidence for a Kit-mediated bi-directional communication system in the zebrafish ovarian follicle, which could be part of the complex interplay between the oocyte and the follicle cells in the development of follicles.

Transplantation of an alginate-matrigel matrix containing isolated ovarian cells: first step in developing a biodegradable scaffold to transplant isolated preantral follicles and ovarian cells

For women diagnosed with leukemia, transplantation of cryopreserved ovarian tissue after disease remission is not advisable. Therefore, to restore fertility in these patients, we aim to develop a biodegradable artificial ovary that offers an environment where isolated follicles and ovarian cells (OCs) can survive and grow. Four NMRI mice were ovariectomized and their ovaries used to isolate OCs. Groups of 50,000 OCs were embedded in an alginate-matrigel matrix for further fixation (fresh controls), one week of in vitro culture (IVC) or heterotopic autografting. OC proliferation (Ki67), apoptosis (TUNEL), scaffold degradation, vessel formation (CD34) and inflammation (CD45) were analyzed. Ki67-positive OCs were found in 2.3%, 9.0% and 15.5% cells of cases in fresh, IVC and grafted beads respectively, while cells were TUNEL-positive in 0%, 1.5% and 6.9% of cases. After IVC or grafting, the beads degraded, losing their original round aspect, and infiltrating blood capillaries could be observed in the grafted beads. CD34-positive cells and 22% CD45-positive cells were found around and inside the matrix. In conclusion, our results demonstrate that an alginate-based matrix is a promising proposition to graft isolated OCs. After transplantation, this matrix was able to degrade, allowed vascularization and elicited a low inflammatory response.

How to make a gonad: cellular mechanisms governing formation of the testes and ovaries

Sex determination of the gonad is an extraordinary process by which a single organ anlage is directed to form one of two different structures, a testis or an ovary. Morphogenesis of these two organs utilizes many common cellular events; differences in the timing and execution of these events must combine to generate sexually dimorphic structures. In this chapter, we review recent research on the cellular processes of gonad morphogenesis, focusing on data from mouse models. We highlight the shared cellular mechanisms in testis and ovary morphogenesis and examine the differences that enable formation of the two organs responsible for the perpetuation of all sexually reproducing species.

Xenobiotic effects on ovarian preantral follicles

Women are born with a finite population of ovarian follicles, which are slowly depleted during their reproductive years until reproductive failure (menopause) occurs. The rate of loss of primordial follicles is determined by genetic and environmental influences, but certain toxic exposures can accelerate this process. Ionizing radiation reduces preantral follicle numbers in rodents and humans in a dose-dependent manner. Cigarette smoking is linked to menopause occurring 1-4 yr earlier than with nonsmokers, and components of smoke, polycyclic aromatic hydrocarbons, can cause follicle depletion in rodents or in ovaries in vitro. Chemotherapeutic agents, such as alkylating drugs and cisplatin, also cause loss of preantral ovarian follicles. Effects depend on dose, type, and reactivity of the drug, and the age of the individual. Evidence suggests DNA damage may underlie follicle loss induced by one common alkylating drug, cyclophosphamide. Occupational exposures have also been linked to ovarian damage. In an industrial setting, 2-bromopropane caused infertility in men and women, and it can induce ovarian follicle depletion in rats. Solvents, such as butadiene, 4-vinylcyclohexene, and their diepoxides, can also cause specific preantral follicle depletion. The mechanism(s) underlying effects of the latter compound may involve alterations in apoptosis, survival factors such as KIT/Kit Ligand, and/or the cellular signaling that maintains primordial follicle dormancy. Estrogenic endocrine disruptors may alter follicle formation/development and impair fertility or normal development of offspring. Thus, specific exposures are known or suspected of detrimentally impacting preantral ovarian follicles, leading to early ovarian failure.

Presence of c-kit mRNA in goat ovaries and improvement of in vitro preantral follicle survival and development with kit ligand

This study evaluated the levels of c-kit mRNA in goat follicles and the effects of kit ligand (KL) on the in vitro development of cultured preantral follicles. Preantral follicles isolated from goat ovarian cortex were cultured for 18 days in α-MEM(+) supplemented with KL (0, 50 or 100 ng/mL) in the absence or presence of follicle stimulating hormone (FSH). Real-time PCR showed that c-kit mRNA was higher in primordial and primary follicles than in secondary stage. Regarding the culture, KL addition in the absence of FSH improved the follicular survival, antrum formation, oocyte growth and meiotic resumption. KL-positive effects were not observed in the presence of FSH. In conclusion, c-kit mRNAs are detected in all follicular categories. KL promotes the survival and antral cavity formation of caprine preantral follicles after in vitro culture, as well as the growth and meiotic resumption of their oocytes in the absence of FSH.

Reinterpretation of evidence advanced for neo-oogenesis in mammals, in terms of a finite oocyte reserve

The central tenet of ovarian biology, that the oocyte reserve in adult female mammals is finite, has been challenged over recent years by proponents of neo-oogenesis, who claim that germline stem cells exist in the ovarian surface epithelium or the bone marrow. Currently opinion is divided over these claims, and further scrutiny of the evidence advanced in support of the neo-oogenesis hypothesis is warranted - especially in view of the enormous implications for female fertility and health. This article contributes arguments against the hypothesis, providing alternative explanations for key observations, based on published data. Specifically, DNA synthesis in germ cells in the postnatal mouse ovary is attributed to mitochondrial genome replication, and to DNA repair in oocytes lagging in meiotic progression. Lines purported to consist of germline stem cells are identified as ovarian epithelium or as oogonia, from which cultures have been derived previously. Effects of ovotoxic treatments are found to negate claims for the existence of germline stem cells. And arguments are presented for the misidentification of ovarian somatic cells as de novo oocytes. These clarifications, if correct, undermine the concept that germline stem cells supplement the oocyte quota in the postnatal ovary; and instead comply with the theory of a fixed, unregenerated reserve. It is proposed that acceptance of the neo-oogenesis hypothesis is erroneous, and may effectively impede research in areas of ovarian biology. To illustrate, a novel explanation that is consistent with orthodox theory is provided for the observed restoration of fertility in chemotherapy-treated female mice following bone marrow transplantation, otherwise interpreted by proponents of neo-oogenesis as involving stimulation of endogenous germline stem cells. Instead, it is proposed that the chemotherapeutic regimens induce autoimmunity to ovarian antigens, and that the haematopoietic chimaerism produced by bone marrow transplantation circumvents activation of an autoreactive response, thereby rescuing ovarian function. The suggested mechanism draws from animal models of autoimmune ovarian disease, which implicate dysregulation of T cell regulatory function; and from a surmised role for follicular apoptosis in the provision of ovarian autoantigens, to sustain self-tolerance during homeostasis. This interpretation has direct implications for fertility preservation in women undergoing chemotherapy.

Steady-state level of kit ligand mRNA in goat ovaries and the role of kit ligand in preantral follicle survival and growth in vitro

The aims of this study were to investigate steady-state level of Kit Ligand (KL) mRNA and its effects on in vitro survival and growth of caprine preantral follicles. RT-PCR was used to analyze caprine steady-state level of KL mRNA in primordial, primary, and secondary follicles, and in small (1-3 mm) and large (3-6 mm) antral follicles. Furthermore, ovarian fragments were cultured for 1 or 7 days in Minimal Essential Medium (MEM(+)) supplemented with KL (0, 1, 10, 50, 100, or 200 ng/ml). Noncultured (control) and cultured fragments were processed for histology and transmission electron microscopy (TEM). RT-PCR demonstrated an increase in steady-state level of KL mRNA during the transition from primary to secondary follicles. Small antral follicles had higher steady-state levels of KL mRNA in granulosa and theca cells than large follicles. After 7 days, only 50 ng/ml of KL had maintained the percentage of normal follicles similar to control. After 1 day, all KL concentrations reduced the percentage of primordial follicles and increased the percentage of growing follicles. KL at 10, 50, 100, or 200 ng/ml increased primary follicles, compared to MEM(+) after 7 days. An increase in oocyte and follicular diameter was observed at 50 ng/ml of KL. TEM confirmed ultrastructural integrity of follicles after 7 days at 50 ng/ml of KL. In conclusion, the KL mRNAs were detected in all follicular categories. Furthermore, 50 ng/ml of KL maintained the integrity of caprine preantral follicle cultured for 7 days and stimulated primordial follicle activation and follicle growth.

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.

Rapid effects of LH on gene expression in the mural granulosa cells of mouse periovulatory follicles

LH acts on periovulatory granulosa cells by activating the PKA pathway as well as other cell signaling cascades to increase the transcription of specific genes necessary for ovulation and luteinization. Collectively, these cell signaling responses occur rapidly (within minutes); however, presently no high throughput studies have reported changes before 4 h after the LH surge. To identify early response genes that are likely critical for initiation of ovulation and luteinization, mouse granulosa cells were collected before and 1 h after hCG. Fifty-seven gene transcripts were significantly (P<0.05) upregulated and three downregulated following hCG. Twenty-four of these transcripts were known to be expressed after the LH/hCG surge at later time points, while 36 were unknown to be expressed by periovulatory granulosa cells. Temporal expression of several transcripts, including the transcription factors Nr4a1, Nr4a2, Egr1, Egr2, Btg1, and Btg2, and the epidermal growth factor (EGF)-like ligands Areg and Ereg, were analyzed by quantitative RT-PCR, and their putative roles in granulosa cell function are discussed. Epigen (Epgn), another member of the family of EGF-like ligands was identified for the first time in granulosa cells as rapidly induced by LH/hCG. We demonstrate that Epgn initiates cumulus expansion, similar to the other EGF-receptor ligands Areg and Ereg. These studies illustrate that a number of changes in gene expression occur in vivo in response to LH, and that many of the differentially expressed genes are transcription factors that we would predict in turn modulate granulosa cell gene expression to ultimately impact the processes of ovulation and luteinization.

[State of the art on in vitro folliculogenesis in mouse]

Follicle culture systems have been developed so as to achieve in vitro fertilization of oocytes coming from immature follicles. The in vitro folliculogenesis methods would be especially useful in reproductive medicine to restore fertility in women having undergone ovarian cryopreservation. Several culture systems allowing in vitro growth of small follicles have been developed in mouse. These have proven to be successful by the birth of healthy offsprings. Some elements determine the outcome of culture: follicle isolations at a defined stage of development, follicular morphology preservation, and supplementation of growth factors or hormones. Development of follicle culture in the mouse model led to a better understanding of ovarian physiology, in particular the relation between endocrine and paracrine factors on follicle development. The in vitro techniques in mouse became a valuable tool for improving reproductive technics improvement, and for toxicology studies.

Specificity of the requirement for Foxo3 in primordial follicle activation

Primordial follicles are long-lived structures assembled early in life. The mechanisms that control the balance between the conservation and the activation of primordial follicles are critically important for fertility and dictate the onset of menopause. The forkhead transcription factor Foxo3 serves an essential role in these processes by suppressing the growth of primordial follicles, thereby preserving them until later in life. While other factors regulating primordial follicle growth have been described, most serve multiple functions at several stages of female germ cell or follicle development, and corresponding mouse mutants exhibit pleiotropic phenotypes with disruption of multiple stages of follicle assembly, development, or survival. To investigate the possibility that Foxo3 also functions in other aspects of ovarian development beyond its known role in primordial follicle activation (PFA), we performed detailed analyses of mouse ovaries including electron microscopy to study primordial follicle structure, assembly, and early growth. These analyses revealed that the timing of primordial follicle assembly, early oocyte survival, and the expression of early germ line markers were unaffected in early Foxo3 ovaries. Taken together, these studies demonstrate that the phenotype associated with Foxo3 deficiency is remarkably specific for PFA and further support the placement of Foxo3 in a unique phenotypic class among mammalian female sterile mutants. Lastly, we discuss the implications of the specificity of this mutant phenotype with regard to the hypothesis that oocyte regeneration may occur in adults and serves as a means to replenish oocytes lost via natural physiological processes.

Oocyte growth and follicular development in KIT-deficient Fas-knockout mice

In mammals, oocyte growth and follicular development are known to be regulated by KIT, a tyrosine kinase receptor. Fas is a member of the death receptor family inducing apoptosis. Here, we investigated germ cell survival, oocyte growth and follicular development in KIT-deficient (Wv/Wv:Fas+/+), Fas-deficient (+/+:Fas-/-), and both KIT- and Fas-deficient (Wv/Wv:Fas-/-) mice during fetal and postnatal periods. Further, the ovaries of these mice were transplanted in immunodeficient mice to compare oocyte growth and follicular development under a condition isolated from the extraovarian effects of KIT- and Fas-deficiency. Higher numbers of germ cells were found in the fetal and postnatal ovaries of Fas-deficient mice than in the same-aged wild-type mice. In KIT-deficient mice, ovaries at 13 days postcoitum (dpc) contained 1106+/-72 (n=3) germ cells, but the ovaries contained no oocytes after birth. Twenty-one days after transplantation of the ovaries at 13 dpc, no oocytes/germ cells were found. A higher number of germ cells (3843+/-108; n=3) were observed in the Wv/Wv:Fas-/- genotypes than in Wv/Wv:Fas+/+ mice at 13 dpc. Furthermore, Wv/Wv:Fas-/- mice contained 528+/-91 (n=3) oocytes at 2 days, and follicles developed to the antral stage at 14 days of age. After transplantation of fetal and neonatal ovaries from Wv/Wv:Fas-/- mice, increased numbers of growing oocytes and developing follicles were obtained compared with those in 14-day old ovaries in vivo. These results show that oocytes grow and follicles develop without KIT signaling, although KIT might be essential for the survival of germ cells/oocytes in mice.

Tissue-engineered follicles produce live, fertile offspring

Oocytes grown in vitro are of low quality and yield few live births, thus limiting the ability to store or bank the ova of women wishing to preserve their fertility. We applied tissue engineering principles to the culture of immature mouse follicles by designing an alginate hydrogel matrix to maintain the oocyte's 3- dimensional (3D) architecture and cell-cell interactions in vitro. A 3D culture mimics the in vivo follicle environment, and hydrogel-encapsulated follicles develop mature oocytes within the capacity for fertilization similar to that of oocytes matured in vivo. Embryos derived from cultured oocytes fertilized in vitro and transferred to pseudopregnant female mice were viable, and both male and female offspring were fertile. Our results demonstrate that alginate hydrogel-based 3D in vitro culture of follicles permits normal growth and development of follicles and oocytes. This system creates new opportunities for discovery in follicle biology and establishes a core technology for human egg banks for preservation of fertility.

The Kit ligand/c-Kit receptor system in goat ovaries: gene expression and protein localization

Relatively little information is available on the local factors that regulate folliculogenesis in goats. To examine the possibility that the Kit ligand (KL) system is expressed throughout the folliculogenesis, we studied the presence and distribution of KL and its receptor, c-Kit, in goat ovaries. Ovaries of goats were collected and either fixed in paraformaldehyde for immunohistochemical localization of KL and c-Kit proteins, or used for the isolation of follicles, luteal cells, surface epithelium and medullary samples to study mRNA expression for KL and c-Kit, using the reverse transcriptase polymerase chain reaction (RT-PCR). KL protein and mRNA were found in follicles at all stages of development, i.e. primordial, primary, secondary, small and large antral follicles, as well as in corpora lutea, surface epithelium and medullary tissue. Antral follicles expressed both KL-1 and KL-2 mRNAs, while earlier staged follicles expressed KL-1 transcript only. KL protein was demonstrated in granulosa cells from the primordial follicle onward. Its mRNA could be detected in granulosa cells isolated from antral follicles and occasionally in their theca cells. c-Kit mRNA was expressed in all antral follicular compartments and at all stages of follicular development. c-Kit protein was predominantly found in oocytes from the primordial follicle stage onwards, in theca cells of antral follicles, as well as in corpora lutea, surface epithelium and medullary tissue, particularly in the wall of blood vessels, which may indicate these cells as the main sites of action of KL. It is concluded that the KL/c-Kit system, in goat ovaries, is widespread and that it may be involved in the regulation of various local processes, including folliculogenesis and luteal activity.