Fbxw15/Fbxo12J is an F-box protein-encoding gene selectively expressed in oocytes of the mouse ovary

Heterozygous Eif4nif1 Stop Gain Mice Replicate the Primary Ovarian Insufficiency Phenotype in Women

We created the c.1286C>G stop-gain mutation found in a family with primary ovarian insufficiency (POI) at age 30 years. The Eif4enif1 C57/Bl6 transgenic mouse model contained a floxed exon 10-19 cassette with a conditional knock-in cassette containing the c.1286C>G stop-gain mutation in exon 10. The hybrid offspring of CMV- Cre mice with Eif4enif1 WT/flx mice were designated Eif4enif1 WT/ Δ for simplicity. A subset of female heterozygotes ( Eif4enif1 WT/ Δ ) had no litters. In those with litters, the final litter was earlier (5.4±2.6 vs. 10.5±0.7 months; p=0.02). Heterozygous breeding pair ( Eif4enif1 WT/ Δ x Eif4enif1 WT/ Δ ) litter size was 60% of WT litter size (3.9±2.0 vs. 6.5±3.0 pups/litter; p <0.001). The genotypes were 35% Eif4enif1 WT/flx and 65% Eif4enif1 WT/ Δ , with no homozygotes. Homozygote embryos did not develop beyond the 4-8 cell stage. The number of follicles in ovaries from Eif4enif1 WT/ Δ mice was lower starting at the primordial (499±290 vs. 1445±381) and primary follicle stage (1069±346 vs. 1450±193) on day 10 (p<0.05). The preantral follicle number was lower starting on day 21 (213±86 vs. 522±227; p<0.01). Examination of ribosome protected mRNAs (RPR) demonstrated altered mRNA expression. The Eif4enif1 stop-gain mice replicate the POI phenotype in women. The unique mouse model provides a platform to study regulation of protein translation across oocyte and embryo development in mammals.

Expression Analysis of Lipocalin 2 (LCN2) in Reproductive and Non-Reproductive Tissues of Esr1-Deficient Mice

Estrogen receptor alpha (ERα) is widely expressed in reproductive organs, but also in non-reproductive tissues of females and males. There is evidence that lipocalin 2 (LCN2), which has diverse immunological and metabolic functions, is regulated by ERα in adipose tissue. However, in many other tissues, the impact of ERα on LCN2 expression has not been studied yet. Therefore, we used an Esr1-deficient mouse strain and analyzed LCN2 expression in reproductive (ovary, testes) and non-reproductive tissues (kidney, spleen, liver, lung) of both sexes. Tissues collected from adult wild-type (WT) and Esr1-deficient animals were analyzed by immunohistochemistry, Western blot analysis, and RT-qPCR for Lcn2 expression. In non-reproductive tissues, only minor genotype- or sex-specific differences in LCN2 expression were detected. In contrast, significant differences in LCN2 expression were observed in reproductive tissues. Particularly, there was a strong increase in LCN2 in Esr1-deficient ovaries when compared to WTs. In summary, we found an inverse correlation between the presence of ERα and the expression of LCN2 in testes and ovaries. Our results provide an important basis to better understand LCN2 regulation in the context of hormones and in health and disease.

Comparative maternal protein profiling of mouse biparental and uniparental embryos

Background

Maternal proteins have important roles during early embryonic development. However, our understanding of maternal proteins is still very limited. The integrated analysis of mouse uniparental (parthenogenetic) and biparental (fertilized) embryos at the protein level creates a protein expression landscape that can be used to explore preimplantation mouse development.

Results

Using label-free quantitative mass spectrometry (MS) analysis, we report on the maternal proteome of mouse parthenogenetic embryos at pronucleus, 2-cell, 4-cell, 8-cell, morula, and blastocyst stages and highlight dynamic changes in protein expression. In addition, comparison of proteomic profiles of parthenogenotes and fertilized embryos highlights the different fates of maternal proteins. Enrichment analysis uncovered a set of maternal proteins that are strongly correlated with the subcortical maternal complex, and we report that in parthenogenotes, some of these maternal proteins escape the fate of protein degradation. Moreover, we identified a new maternal factor-Fbxw24, and highlight its importance in early embryonic development. We report that Fbxw24 interacts with Ddb1-Cul4b and may regulate maternal protein degradation in mouse.

Conclusions

Our study provides an invaluable resource for mechanistic analysis of maternal proteins and highlights the role of the novel maternal factor Fbw24 in regulating maternal protein degradation during preimplantation embryo development.

SCF Ligases and Their Functions in Oogenesis and Embryogenesis-Summary of the Most Important Findings throughout the Animal Kingdom

SCF-dependent proteolysis was first discovered via genetic screening of budding yeast almost 25 years ago. In recent years, more and more functions of SCF (Skp1-Cullin 1-F-box) ligases have been described, and we can expect the number of studies on this topic to increase. SCF ligases, which are E3 ubiquitin multi-protein enzymes, catalyse protein ubiquitination and thus allow protein degradation mediated by the 26S proteasome. They play a crucial role in the degradation of cell cycle regulators, regulation of the DNA repair and centrosome cycle and play an important role in several diseases. SCF ligases seem to be needed during all phases of development, from oocyte formation through fertilization, activation of the embryonic genome to embryo implantation. In this review, we summarize known data on SCF ligase-mediated degradation during oogenesis and embryogenesis. In particular, SCF^βTrCP and SCF^SEL-10/FBXW7 are among the most important and best researched ligases during early development. SCF^βTrCP is crucial for the oogenesis of Xenopus and mouse and also in Xenopus and Drosophila embryogenesis. SCF^SEL-10/FBXW7 participates in the degradation of several RNA-binding proteins and thereby affects the regulation of gene expression during the meiosis of C. elegans. Nevertheless, a large number of SCF ligases that are primarily involved in embryogenesis remain to be elucidated.

Classification and Computational Analysis of Arabidopsis thaliana Sperm Cell-Specific F-Box Protein Gene 3p.AtFBP113

In plants, F-box proteins (FBPs) constitute one of the largest superfamilies of regulatory proteins. Most F-box proteins are shown to be an integral part of SCF complexes, which carry out the degradation of proteins and regulate diverse important biological processes. Anthers and pollen development have a huge importance in crop breeding. Despite the vast diversity of FBPs in Arabidopsis male reproductive organs, their role in anther and pollen development is not much explored. Moreover, a standard nomenclature for naming FBPs is also lacking. Here, we propose a standard nomenclature for naming the FBPs of Arabidopsis thaliana uniformly and carry out a systematic analysis of sperm cell-specific FBP gene, i.e., 3p.AtFBP113 due to its reported high and preferential expression, for detailed functional annotation. The results revealed that 3p.AtFBP113 is located on the small arm of chromosome and encodes 397 amino acid long soluble, stable, and hydrophilic protein with the possibility of localization in various cellular compartments. The presence of the C-terminal F-box associated domain (FBA) with immunoglobulin-like fold anticipated its role in protein binding. Gene ontology based functional annotation and tissue-specific gene co-expression analysis further strengthened its role in protein binding and ubiquitination. Moreover, various potential post/co-translational modifications were anticipated and the predicted tertiary structure also showed the presence of characteristic domains and fold. Thus, the outcomes of the study will be useful in developing a better understating of the function of 3p.AtFBP113 during the process of pollen development, which will be helpful for targeting the gene for manipulation of male fertility that has immense importance in hybrid breeding.

The gonadal expression pattern of lipocalin‑2 and 24p3 receptor is modified in the gonads of the offspring of obese rats

Obesity represents a global health and economic burden, affecting millions of individuals worldwide. This pathology is associated with a chronic low-grade inflammatory state that is partially responsible for the development of other cardiometabolic complications. Clinical studies have reported an association between high circulating levels of lipocalin-2 (Lcn2) and increased body weight. Additionally, there is scientific evidence demonstrating the impact of maternal obesity on fetal programming. The latter and the fact that the authors previously found that Lcn2 and its receptor (24p3R) are expressed in the gonads of wild-type rats, led to the analysis of their mRNA profile and cellular localization in gonads collected from the offspring of obese rats at 21 days postconception (dpc), and 0, 2, 4, 6, 12, 20 and 30 days postnatal (dpn) in the present study. Semi-quantitative PCR revealed a statistically significant downregulation of Lcn2 and 24p3R mRNA at 21 dpc in the ovaries (P<0.01) and testicles (P<0.001) of the offspring of obese mothers. At 30 dpn, the relative expression of Lcn2 mRNA decreased significantly in the ovaries of the experimental group (P<0.05), while Lcn2 mRNA expression was not detectable in testicles. Regarding 24p3R, its mRNA was only significantly decreased at 21 dpc in ovaries of pups of obese mothers. At 30 dpn, the change in females was not significant. Conversely, in testicles, 24p3R mRNA levels increased slightly in the experimental group at 30 dpn. The Lcn2 protein signal was less intense in gonadal tissue sections from 30 dpn offspring of obese rats (P<0.001), whereas the 24p3R signal was downregulated in ovaries (P<0.001) and slightly upregulated in testicles. It was concluded that maternal obesity changes the expression of Lcn2 and 24p3R in the gonads of the offspring of obese rats, possibly through fetal programming. The consequences of this dysregulation for the offspring's gonadal function remains to be determined.

The role of SCF ubiquitin-ligase complex at the beginning of life

As the largest family of E3 ligases, the Skp1-cullin 1-F-box (SCF) E3 ligase complex is comprised of Cullins, Skp1 and F-box proteins. And the SCF E3 ubiquitin ligases play an important role in regulating critical cellular processes, which promote degradation of many cellular proteins, including signal transducers, cell cycle regulators, and transcription factors. We review the biological roles of the SCF ubiquitin-ligase complex in gametogenesis, oocyte-to-embryo transition, embryo development and the regulation for estrogen and progestin. We find that researches about the SCF ubiquitin-ligase complex at the beginning of life are not comprehensive, thus more in-depth researches will promote its eventual clinical application.

Lhx8 ablation leads to massive autophagy of mouse oocytes associated with DNA damage

Following proliferation of oogonia in mammals, great numbers of germ cells are discarded, primarily by apoptosis, while the remainder form primordial follicles (the ovarian reserve) that determine fertility and reproductive lifespan. More massive, rapid, and essentially total loss of oocytes, however, occurs when the transcription factor Lhx8 is ablated-though the cause and mechanism of germ cell loss from the Lhx8-/- ovaries has been unknown. We found that Lhx8-/- ovaries maintain the same number of germ cells throughout embryonic development; rapid decrease in the pool of oocytes starts shortly before birth. The loss results from activation of autophagy, which becomes overwhelming within the first postnatal week, with extracellular matrix proteins filling the space previously occupied by follicles to produce a fibrotic ovary. Associated with this process, as early as a few days before birth, Lhx8-/- oocytes failed to repair DNA damage-which normally occurs when meiosis is initiated during embryonic development; and DNA damage repair genes were downregulated throughout the oocyte short lifespan. Based on gene expression analyses and morphological changes, we propose a model in which lineage-restricted failure of DNA repair triggers germ cell autophagy, causing premature depletion of the ovarian reserve in Lhx8-/- mice.

Expression profiling of lipocalin-2 and 24p3 receptor in murine gonads at different developmental stages

Numerous clinical studies have reported the association between high circulating levels of lipocalin-2 (LCN2) and metabolic diseases. However, only few studies have addressed sexually dimorphic, either in its circulating concentration or in its expression in other organs. To the best of our knowledge, LCN2 and the 24p3 receptor (24p3R), have not been identified in gonads; therefore, the present study analyzed their mRNA expression profile and cellular localization in gonads collected from fetal rats at 21 days post coitum, as well as from neonatal rats at 0, 2, 4, 6, 12, 20 and 30 postnatal days. Semiquantitative polymerase chain reaction and immunohistochemical assays revealed that the LCN2 mRNA during perinatal and pre-pubertal stages presented a sex-specific expression pattern, being higher in ovaries than in testes collected at these stages. Furthermore, the mRNA levels of the long and short isoforms of the 24p3R (507 and 350 bp, respectively), were lower in female gonads from postnatal day 0 onwards in comparison with the levels observed in males, but before birth, the short isoform of the 24p3R was higher in ovaries than in testes. In addition, in females, the abundance of mRNA of this isoform was drastically diminished at 24 h after birth. Furthermore, this specific expression profile of LCN2 and 24p3R at perinatal and prepubertal stages coincides with events of cellular proliferation and apoptosis within both gonads. Immunohistochemical assays revealed that in ovaries, LCN2 and 24p3R are present in germinal and somatic cells of follicles, while in testes, this adipokine and its receptor are only located in germinal cells. These findings suggest that in murine gonads, LCN2/24p3R signaling may be involved either in cell proliferation or cell death driven by gonadotropin-independent or -dependent mechanisms.

Roles of F-box proteins in cancer

F-box proteins, which are the substrate-recognition subunits of SKP1-cullin 1-F-box protein (SCF) E3 ligase complexes, have pivotal roles in multiple cellular processes through ubiquitylation and subsequent degradation of target proteins. Dysregulation of F-box protein-mediated proteolysis leads to human malignancies. Notably, inhibitors that target F-box proteins have shown promising therapeutic potential, urging us to review the current understanding of how F-box proteins contribute to tumorigenesis. As the physiological functions for many of the 69 putative F-box proteins remain elusive, additional genetic and mechanistic studies will help to define the role of each F-box protein in tumorigenesis, thereby paving the road for the rational design of F-box protein-targeted anticancer therapies.

Cloning and characterization of a novel oocyte-specific gene encoding an F-Box protein in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Oocyte-specific genes play critical roles in oogenesis, folliculogenesis and early embryonic development. The objectives of this study were to characterize the expression of a novel oocyte-specific gene encoding an F-box protein during ovarian development in rainbow trout, and identify its potential interacting partners in rainbow trout oocytes.

METHODS

Through analysis of expressed sequence tags (ESTs) from a rainbow trout oocyte cDNA library, a novel transcript represented by ESTs only from the oocyte library was identified. The complete cDNA sequence for the novel gene (named fbxoo) was obtained by assembling sequences from an EST clone and a 5'RACE product. The expression and localization of fbxoo mRNA and protein in ovaries of different developmental stages were analyzed by quantitative real time PCR, immunoblotting, in situ hybridization and immunohistochemistry. Identification of Fbxoo binding proteins was performed by yeast two-hybrid screening.

RESULTS

fbxoo mRNA is specifically expressed in mature oocytes as revealed by tissue distribution analysis. The fbxoo cDNA sequence is 1,996 bp in length containing an open reading frame, which encodes a predicted protein of 514 amino acids. The novel protein sequence does not match any known protein sequences in the NCBI database. However, a search of the Pfam protein database revealed that the protein contains an F-box motif at the N-terminus, indicating that Fbxoo is a new member of the F-box protein family. The expression of fbxoo mRNA and protein is high in ovaries at early pre-vitellogenesis stage, and both fbxoo mRNA and protein are predominantly expressed in early pre-vitellogenic oocytes. Several proteins including tissue inhibitor of metalloproteinase 2 (Timp2) were identified as potential Fbxoo protein binding partners.

CONCLUSIONS

Results suggest that the novel oocyte-specific F-box protein may play an important role in early oocyte development by regulating other critical proteins involved in oogenesis in rainbow trout.

SCF(Fbxw15) mediates histone acetyltransferase binding to origin recognition complex (HBO1) ubiquitin-proteasomal degradation to regulate cell proliferation

Histone acetyltransferase binding to origin recognition complex (HBO1) plays a crucial role in DNA replication licensing and cell proliferation, yet its molecular regulation in cells is relatively unknown. Here an uncharacterized protein, Fbxw15, directly interacts with HBO1, a labile protein (t&frac12; = ∼3 h), to mediate its ubiquitination (Lys(338)) and degradation in the cytoplasm. Fbxw15-mediated HBO1 depletion required mitogen-activated protein kinase 1 (Mek1), which was sufficient to trigger HBO1 phosphorylation and degradation in cells. Mek1 ability to produce HBO1 degradation was blocked by Fbxw15 silencing. Lipopolysaccharide induced HBO1 degradation, an effect abrogated by Fbxw15 or Mek1 cellular depletion. Modulation of Fbxw15 levels was able to differentially regulate histone H3K14 acetylation and cellular proliferation by altering HBO1 levels. These studies authenticate Fbxw15 as a ubiquitin E3 ligase subunit that mediates endotoxin-induced HBO1 depletion in cells, thereby controlling cell replicative capacity.

Maternal control of mouse preimplantation development

Mammalian preimplantation development is a process of dedifferentiation from the terminally differentiated eggs to the totipotent blastomeres at the cleavage stage, and then to the pluripotent cells at the blastocyst stage. Maternal factors that accumulate during oogenesis dominate early preimplantation development until the embryonic factors gain control after the activation of the embryonic genome. Recently, a handful of maternal factors that are encoded by the maternal-effect genes have been characterized in genetically modified mouse models. These factors are shown to participate in many aspects of preimplantation development, such as the degradation of maternal macromolecues, epigenetic modification, protein translation, cellular signaling transduction, and cell compaction. Even so, little is known about the interactions between different maternal factors. In this chapter, we have summarized the functions of known maternal factors and hopefully this will lead to a better understanding of the regulation of preimplantation embryogenesis by the maternal regulatory network.

Neurotrophins acting via TRKB receptors activate the JAGGED1-NOTCH2 cell-cell communication pathway to facilitate early ovarian development

Tropomyosin-related kinase (TRK) receptor B (TRKB) mediates the supportive actions of neurotrophin 4/5 and brain-derived neurotrophic factor on early ovarian follicle development. Absence of TRKB receptors reduces granulosa cell (GC) proliferation and delays follicle growth. In the present study, we offer mechanistic insights into this phenomenon. DNA array and quantitative PCR analysis of ovaries from TrkB-null mice revealed that by the end of the first week of postnatal life, Jagged1, Hes1, and Hey2 mRNA abundance is reduced in the absence of TRKB receptors. Although Jagged1 encodes a NOTCH receptor ligand, Hes1 and Hey2 are downstream targets of the JAGGED1-NOTCH2 signaling system. Jagged1 is predominantly expressed in oocytes, and the abundance of JAGGED1 is decreased in TrkB(-/-) oocytes. Lack of TRKB receptors also resulted in reduced expression of c-Myc, a NOTCH target gene that promotes entry into the cell cycle, but did not alter the expression of genes encoding core regulators of cell-cycle progression. Selective restoration of JAGGED1 synthesis in oocytes of TrkB(-/-) ovaries via lentiviral-mediated transfer of the Jagged1 gene under the control of the growth differentiation factor 9 (Gdf9) promoter rescued c-Myc expression, GC proliferation, and follicle growth. These results suggest that neurotrophins acting via TRKB receptors facilitate early follicle growth by supporting a JAGGED1-NOTCH2 oocyte-to-GC communication pathway, which promotes GC proliferation via a c-MYC-dependent mechanism.

Proteome of mouse oocytes at different developmental stages

The mammalian oocyte possesses powerful reprogramming factors, which can reprogram terminally differentiated germ cells (sperm) or somatic cells within a few cell cycles. Although it has been suggested that use of oocyte-derived transcripts may enhance the generation of induced pluripotent stem cells, the reprogramming factors in oocytes are undetermined, and even the identified proteins composition of oocytes is very limited. In the present study, 7,000 mouse oocytes at different developmental stages, including the germinal vesicle stage, the metaphase II (MII) stage, and the fertilized oocytes (zygotes), were collected. We successfully identified 2,781 proteins present in germinal vesicle oocytes, 2,973 proteins in MII oocytes, and 2,082 proteins in zygotes through semiquantitative MS analysis. Furthermore, the results of the bioinformatics analysis indicated that different protein compositions are correlated with oocyte characteristics at different developmental stages. For example, specific transcription factors and chromatin remodeling factors are more abundant in MII oocytes, which may be crucial for the epigenetic reprogramming of sperm or somatic nuclei. These results provided important knowledge to better understand the molecular mechanisms in early development and may improve the generation of induced pluripotent stem cells.

Comparative analyses of genotype dependent expressed sequence tags and stress-responsive transcriptome of chickpea wilt illustrate predicted and unexpected genes and novel regulators of plant immunity

BACKGROUND

The ultimate phenome of any organism is modulated by regulated transcription of many genes. Characterization of genetic makeup is thus crucial for understanding the molecular basis of phenotypic diversity, evolution and response to intra- and extra-cellular stimuli. Chickpea is the world's third most important food legume grown in over 40 countries representing all the continents. Despite its importance in plant evolution, role in human nutrition and stress adaptation, very little ESTs and differential transcriptome data is available, let alone genotype-specific gene signatures. Present study focuses on Fusarium wilt responsive gene expression in chickpea.

RESULTS

We report 6272 gene sequences of immune-response pathway that would provide genotype-dependent spatial information on the presence and relative abundance of each gene. The sequence assembly led to the identification of a CaUnigene set of 2013 transcripts comprising of 973 contigs and 1040 singletons, two-third of which represent new chickpea genes hitherto undiscovered. We identified 209 gene families and 262 genotype-specific SNPs. Further, several novel transcription regulators were identified indicating their possible role in immune response. The transcriptomic analysis revealed 649 non-cannonical genes besides many unexpected candidates with known biochemical functions, which have never been associated with pathostress-responsive transcriptome.

CONCLUSION

Our study establishes a comprehensive catalogue of the immune-responsive root transcriptome with insight into their identity and function. The development, detailed analysis of CaEST datasets and global gene expression by microarray provide new insight into the commonality and diversity of organ-specific immune-responsive transcript signatures and their regulated expression shaping the species specificity at genotype level. This is the first report on differential transcriptome of an unsequenced genome during vascular wilt.

Oct-4 regulates the expression of Stella and Foxj2 at the Nanog locus: implications for the developmental competence of mouse oocytes

BACKGROUND

Our knowledge of what determines the mammalian oocyte developmental competence is meagre. By comparing the transcriptional profiles of developmentally competent surrounded nucleolus (SN) and incompetent not surrounded nucleolus (NSN) mouse MII oocytes, we recently demonstrated that Oct-4 and Stella are key factors in the establishment of the oocytes' developmental competence.

METHODS

Using RT-PCR, microarray and immunocytochemistry assays, we analysed expression of genes and proteins in oocytes isolated throughout folliculogenesis and classified based on their SN- or NSN-type of chromatin organization.

RESULTS

We show that: (1) Oct-4 and Stella are expressed concurrently at the beginning of oocytes' growth and only in SN oocytes; (2) Germ Cell Nuclear Factor is a putative regulator of Oct-4 expression in MII oocytes; (3) the function of Oct-4 is directed at the Nanog locus, regulating the expression of Stella and Foxj2.

CONCLUSIONS

(1) A number of factors that act upstream and downstream of Oct-4 emerge as candidate players in the acquisition of the oocyte's developmental competence; (2) we define molecular markers that identify a specific group of ovarian oocytes (SN) that have a potential to acquire developmental competence; (3) the presence of SN and NSN oocytes in human ovaries extends the interest of these results to the field of human reproduction.

Gene expression analysis of human fetal ovarian primordial follicle formation

CONTEXT

Primordial follicle formation dictates the maximal potential female reproductive capacity and establishes the ovarian reserve. Currently, little is known about this process in the human.

OBJECTIVE

The aim of the study was to identify genes associated with the onset of human fetal primordial follicle formation in morphologically normal human fetuses.

DESIGN

We conducted an observational study of the female fetal gonad, comparing gene expression before and during primordial follicle formation.

SETTING

The study was conducted at the Universities of Aberdeen, Glasgow, and Nottingham.

PATIENTS/PARTICIPANTS

Ovaries were collected from 51 morphologically normal human female fetuses of women undergoing elective termination of normal second trimester pregnancies.

MAIN OUTCOME MEASURES

We performed fetal ovarian transcript expression by Affymetrix array and quantitative RT-PCR and gene product expression and localization by Western blot and immunohistochemistry.

RESULTS

Five transcripts were down-regulated and 61 were up-regulated in ovaries from older fetuses (18-20 wk) in which primordial follicle formation had started compared with younger (15-16 wk) fetuses in which no primordial follicles were observed. The altered genes contribute to major functions, including gene expression, tissue morphology, and apoptosis, that are essential for ovarian development. NALP5, the most highly regulated transcript, is an oocyte-specific maternal effect gene that is regulated downstream of FIGLA.

CONCLUSIONS

NALP5 probably plays a key role in the onset of human primordial follicle formation and thus the establishment of ovarian reserve in women.

Role of neurotrophic factors in early ovarian development

Much is known about the endocrine hormonal mechanisms controlling ovarian development. More recently, attention has focused on identifying regulatory pathways that, operating within the ovarian microenvironment, contribute to the acquisition of ovarian reproductive competence. Within this framework, the concept has developed that neurotrophins (NTs) and their Trk tyrosine kinase receptors, long thought to be exclusively required for the development of the nervous system, are also involved in the control of ovarian maturation. The ovary of several species, including rodents, sheep, cows, nonhuman primates, and humans, produce NTs and express both the high-affinity receptors and the common p75 (NTR) receptor required for signaling. Studies in humans and rodents have shown that this expression is initiated during fetal life, before the formation of primordial follicles. Gene targeting approaches have identified TrkB, the high-affinity receptor for neurotrophin-4/5 and brain-derived neurotrophic factor, as a signaling module required for follicular assembly, early follicular growth, and oocyte survival. A similar approach has shown that nerve growth factor contributes independently to the growth of primordial follicles into gonadotropin-responsive structures. Altogether, these observations indicate that NTs are important contributors to the gonadotropin-independent process underlying the formation and initiation of ovarian follicular growth.