Is there a role for DAZL in human female fertility?

Dietary Exposure to Pesticide and Veterinary Drug Residues and Their Effects on Human Fertility and Embryo Development: A Global Overview

Drug residues that contaminate food and water represent a serious concern for human health. The major concerns regard the possible irrational use of these contaminants, since this might increase the amplitude of exposure. Multiple sources contribute to the overall exposure to contaminants, including agriculture, domestic use, personal, public and veterinary healthcare, increasing the possible origin of contamination. In this review, we focus on crop pesticides and veterinary drug residues because of their extensive use in modern agriculture and farming, which ensures food production and security for the ever-growing population around the world. We discuss crop pesticides and veterinary drug residues with respect to their worldwide distribution and impacts, with special attention on their harmful effects on human reproduction and embryo development, as well as their link to epigenetic alterations, leading to intergenerational and transgenerational diseases. Among the contaminants, the most commonly implicated in causing such disorders are organophosphates, glyphosate and antibiotics, with tetracyclines being the most frequently reported. This review highlights the importance of finding new management strategies for pesticides and veterinary drugs. Moreover, due to the still limited knowledge on inter- and transgenerational effects of these contaminants, we underlie the need to strengthen research in this field, so as to better clarify the specific effects of each contaminant and their long-term impact.

Role of parthenolide in paclitaxel-induced oxidative stress injury and impaired reproductive function in rat testicular tissue

The chemotherapeutic agent paclitaxel (PTX) causes testicular toxicity due to oxidative stress. Parthenolide (PTL), the active ingredient of the Tanacetum parthenium plant, is used to treat inflammation, dizziness, and spasms. In the present study, we evaluated the therapeutic effect of PTL on PTX-induced testicular toxicity in rats and its role in reproductive function. To this end, 6 groups were formed: control, PTX, sham, T1, T2, and T3. After testicular toxicity was induced in rats with 8 mg/kg PTX, the rats were treated with 1 mg/kg, 2 mg/kg, and 4 mg/kg PTL for 14 days. GSH and MDA levels were measured in rat testicular tissue after the last dose of PTL was administered. To determine the damage caused by PTX to testicular tissue by detecting 8-OHdG and iNOS, sections were prepared and examined histopathologically and immunohistochemically. Furthermore, the gene expressions and enzymatic activities of SOD, CAT, GPx, GST, and GR were investigated in all groups. After PTL treatment, MDA, 8-OHdG, and iNOS levels decreased while GSH levels increased in testicular tissue. Increased levels of antioxidant genes and enzymes also reduced oxidative stress. Additionally, the expression levels of the Dazl, Ddx4, and Amh genes, which are involved in gametogenesis and sperm production, decreased in case of toxicity and increased with PTL treatment. The data from this study show that PTL may have a therapeutic effect in the treatment of testicular damage by eliminating the oxidative stress-induced damage caused by PTX in testicular tissue, providing an effective approach to alleviating testicular toxicity, and playing an important role in reproduction/sperm production, especially at a dose of 4 mg/kg.

BCAS2 regulates oocyte meiotic prophase I by participating in mRNA alternative splicing

Oocyte meiotic prophase I (MI) is an important event in female reproduction. Breast cancer amplified sequence 2 (BCAS2) is a component of the spliceosome. Previous reports have shown that BCAS2 is critical in male germ cell meiosis, oocyte development, and early embryo genome integrity. However, the role of BCAS2 in oocyte meiosis has not been reported. We used Stra8-GFPCre mice to knock out Bcas2 in oocytes during the pachytene phase. The results of fertility tests showed that Bcas2 conditional knockout (cKO) in oocytes results in infertility in female mice. Morphological analysis showed that the number of primordial follicles in the ovaries of 2-month-old (M) mice was significantly reduced and that follicle development was blocked. Further analysis showed that the number of primordial follicles decreased and that follicle development was slowed in 7-day postpartum (dpp) ovaries. Moreover, primordial follicles undergo apoptosis, and DNA damage cannot be repaired in primary follicle oocytes. Meiosis was abnormal; some oocytes could not reach the diplotene stage, and more oocytes could not develop to the dictyotene stage. Alternative splicing (AS) analysis revealed abnormal AS of deleted in azoospermia like (Dazl) and diaphanous related formin 2 (Diaph2) oogenesis-related genes in cKO mouse ovaries, and the process of AS was involved by CDC5L and PRP19.

Cloning, expression analysis and localization of DAZL gene implicated in germ cell development of male Hezuo pig

Deleted in azoospermia-like (DAZL) is essential for mammalian testicular function and spermatogenesis. To explore the molecular characterization, expression patterns, and cellular localization of the DAZL in Hezuo pig testes, testicular tissue was isolated from Hezuo pig at five development stages including 30 days old (30 d), 90 days old (90 d), 120 days old (120 d), 180 days old (180 d), and 240 days old (240 d). DAZL cDNA was first cloned using the RT-PCR method, and its molecular characterization was analyzed using relevant bioinformatics software. Subsequently, the expression patterns and cellular localization of DAZL were evaluated using quantitative real-time PCR (qRT-PCR), Western blot, and immunohistochemistry. The cloning and sequence analysis showed that the Hezuo pig DAZL cDNA fragment contained 888 bp open reading frame (ORF) capable of encoding 295 amino acid residues and exhibited high identities with some other mammals. The qRT-PCR and Western blot results indicated that DAZL was specifically expressed in Hezuo pig testes, and DAZL levels of both mRNA and protein were expressed at all five reproductive stages of Hezuo pig testes, with extremely significant higher expression levels in 90 d, 120 d, 180 d, and 240 d than those in 30 d (p < 0.01). Additionally, immunohistochemistry results revealed that DAZL protein was mainly localized in gonocytes at 30 d testes, primary spermatocytes, and spermatozoon at other developmental stages, and Leydig cells throughout five development stages. Together, these results suggested that DAZL may play an important role by regulating the proliferation or differentiation of gonocytes, development of primary spermatocytes and spermatozoon, and functional maintenance of Leydig cells in testicular development and spermatogenesis of Hezuo pig. Nevertheless, the specific regulatory mechanisms underlying these phenomena still requires further investigated and verified.

Making a good egg: human oocyte health, aging, and in vitro development

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

Meiotic Chromosome Structure, the Synaptonemal Complex, and Infertility

In meiosis, homologous chromosome synapsis is mediated by a supramolecular protein structure, the synaptonemal complex (SC), that assembles between homologous chromosome axes. The mammalian SC comprises at least eight largely coiled-coil proteins that interact and self-assemble to generate a long, zipper-like structure that holds homologous chromosomes in close proximity and promotes the formation of genetic crossovers and accurate meiotic chromosome segregation. In recent years, numerous mutations in human SC genes have been associated with different types of male and female infertility. Here, we integrate structural information on the human SC with mouse and human genetics to describe the molecular mechanisms by which SC mutations can result in human infertility. We outline certain themes in which different SC proteins are susceptible to different types of disease mutation and how genetic variants with seemingly minor effects on SC proteins may act as dominant-negative mutations in which the heterozygous state is pathogenic.

The Beginning of Meiosis in Mammalian Female Germ Cells: A Never-Ending Story of Intrinsic and Extrinsic Factors

Meiosis is the unique division of germ cells resulting in the recombination of the maternal and paternal genomes and the production of haploid gametes. In mammals, it begins during the fetal life in females and during puberty in males. In both cases, entering meiosis requires a timely switch from the mitotic to the meiotic cell cycle and the transition from a potential pluripotent status to meiotic differentiation. Revealing the molecular mechanisms underlying these interrelated processes represents the essence in understanding the beginning of meiosis. Meiosis facilitates diversity across individuals and acts as a fundamental driver of evolution. Major differences between sexes and among species complicate the understanding of how meiosis begins. Basic meiotic research is further hindered by a current lack of meiotic cell lines. This has been recently partly overcome with the use of primordial-germ-cell-like cells (PGCLCs) generated from pluripotent stem cells. Much of what we know about this process depends on data from model organisms, namely, the mouse; in mice, the process, however, appears to differ in many aspects from that in humans. Identifying the mechanisms and molecules controlling germ cells to enter meiosis has represented and still represents a major challenge for reproductive medicine. In fact, the proper execution of meiosis is essential for fertility, for maintaining the integrity of the genome, and for ensuring the normal development of the offspring. The main clinical consequences of meiotic defects are infertility and, probably, increased susceptibility to some types of germ-cell tumors. In the present work, we report and discuss data mainly concerning the beginning of meiosis in mammalian female germ cells, referring to such process in males only when pertinent. After a brief account of this process in mice and humans and an historical chronicle of the major hypotheses and progress in this topic, the most recent results are reviewed and discussed.

The emerging risk of microplastics and nanoplastics on the microstructure and function of reproductive organs in mammals: A systematic review of preclinical evidence

AIMS

Plastic particles (PP) pollution is a global environmental concern. Although the reproductive toxicity of PP is primarily understood for invertebrates, the evidence for mammals is still fragmented. We used a systematic review framework to investigate the reproductive impact of microplastics and nanoplastics (MNP) on mammals.

MATERIALS AND METHODS

Research records were screened from Embase, Medline, Scopus and Web of Science. Twelve original papers were identified and reviewed. Immunological, oxidative and morphofunctional outcomes, and the risk of bias in all studies reviewed were analyzed.

KEY FINDINGS

These studies indicated that PP can accumulate in the gonads, triggering seminiferous degeneration, Sertoli cells death, blood-testis barrier disruption, sperm degeneration, malformation, reduced number and mobility, ovarian cysts, reduced follicular growth and granulosa cells death. Gonadal damage was associated with upregulation of prooxidant mediators (oxygen reactive species, lipid and DNA oxidation), cell death, proinflammatory molecular pathways and cytokines, as well as inhibition of enzymatic and non-enzymatic antioxidant defense mechanisms. Spermatogenesis, folliculogenesis, testosterone, progesterone and estrogen levels were also impaired in PP-treated animals, which were potentially associated with down-regulation of molecules involved in germ cells microstructural organization (occludin, N-cadherin, β-catenin and connexin 43) and steroidogenesis, such as hydroxysteroid dehydrogenases, steroidogenic acute regulatory proteins, follicle stimulating and luteinizing hormones. Selection, performance and detection bias were the main limitations identified.

SIGNIFICANCE

Current evidence indicates that PP can induce dose-dependent microstructural and functional gonadal damage, which is orchestrated by pro-oxidant and pro-inflammatory mechanisms that disrupt genes, molecular effectors, and hormones that control spermatogenesis and folliculogenesis.

The Dynamic Regulation of mRNA Translation and Ribosome Biogenesis During Germ Cell Development and Reproductive Aging

The regulation of mRNA translation, both globally and at the level of individual transcripts, plays a central role in the development and function of germ cells across species. Genetic studies using flies, worms, zebrafish and mice have highlighted the importance of specific RNA binding proteins in driving various aspects of germ cell formation and function. Many of these mRNA binding proteins, including Pumilio, Nanos, Vasa and Dazl have been conserved through evolution, specifically mark germ cells, and carry out similar functions across species. These proteins typically influence mRNA translation by binding to specific elements within the 3′ untranslated region (UTR) of target messages. Emerging evidence indicates that the global regulation of mRNA translation also plays an important role in germ cell development. For example, ribosome biogenesis is often regulated in a stage specific manner during gametogenesis. Moreover, oocytes need to produce and store a sufficient number of ribosomes to support the development of the early embryo until the initiation of zygotic transcription. Accumulating evidence indicates that disruption of mRNA translation regulatory mechanisms likely contributes to infertility and reproductive aging in humans. These findings highlight the importance of gaining further insights into the mechanisms that control mRNA translation within germ cells. Future work in this area will likely have important impacts beyond germ cell biology.

Translational activation of maternally derived mRNAs in oocytes and early embryos and the role of embryonic poly(A) binding protein (EPAB)

Transcription ceases upon stimulation of oocyte maturation and gene expression during oocyte maturation, fertilization, and early cleavage relies on translational activation of maternally derived mRNAs. Two key mechanisms that mediate translation of mRNAs in oocytes have been described in detail: cytoplasmic polyadenylation-dependent and -independent. Both of these mechanisms utilize specific protein complexes that interact with cis-acting sequences located on 3'-untranslated region (3'-UTR), and both involve embryonic poly(A) binding protein (EPAB), the predominant poly(A) binding protein during early development. While mechanistic details of these pathways have primarily been elucidated using the Xenopus model, their roles are conserved in mammals and targeted disruption of key regulators in mouse results in female infertility. Here, we provide a detailed account of the molecular mechanisms involved in translational activation during oocyte and early embryo development, and the role of EPAB in this process.

Gene expression patterns and protein cellular localization suggest a novel role for DAZL in developing Tibetan sheep testes

Deleted in azoospermia-like (DAZL) is essential for mammalian spermatogenesis as it regulates proliferation, development, maturation and functional maintenance of male germ cells. Its expression and regulation vary with different species or in the same animal at different developmental stages, and despite its importance, very little is known about its roles in sheep, especially Tibetan sheep. To investigate the expression patterns and regulatory roles of DZAL in Tibetan sheep testis, testicular tissue was isolated from sheep at three crucial development stages: 3 months old, 1 year old and 3 years old. Using quantitative real-time PCR and Western blot, we found that DAZL mRNA first decreased and then increased with advancing age, while DAZL protein exhibited an opposite expression pattern, with first increased and subsequently decreased levels. Immunohistochemistry and immunofluorescence revealed that DAZL protein was located predominantly in the cytoplasm of Leydig cells and in both the cytoplasm and nucleus of spermatids. ELISA indicated that testosterone content within developing testes was first enhanced and then declined. Our results, taken together, demonstrate, for the first time, that DAZL gene is involved in Tibetan sheep spermatogenesis by regulating the development of spermatids in post-pubertal rams, along with a novel role in functional maintenance of Leydig cells in postnatal rams.

Dazl determines primordial follicle formation through the translational regulation of Tex14

Deleted in azoospermia-like (DAZL) is a germ cell RNA-binding protein that is essential for entry and progression through meiosis. The phenotype of the Dazl knockout mouse has extensive germ cell loss because of incomplete meiosis. We have created a Dazl hypomorph model using short interfering RNA knockdown in mouse fetal ovary cultures, allowing investigation of Dazl function in germ cell maturation. Dazl hypomorph ovaries had a phenotype of impaired germ cell nest breakdown with a 66% reduction in total follicle number and an increase in the proportion of primordial follicles (PMFs), with smaller oocytes within these follicles. There was no significant early germ cell loss or meiotic delay. Immunostaining of intercellular bridge component testis-expressed protein (Tex)14 showed ∼59% reduction in foci number and size, without any change in Tex14 mRNA levels. TEX14 expression was also confirmed in the human fetal ovary across gestation. Using 3'UTR-luciferase reporter assays, translational regulation of TEX14 was demonstrated to be DAZL-dependant. Dazl is therefore essential for normal intercellular bridges within germ cell nests and their timely breakdown, with a major impact on subsequent assembly of PMFs.-Rosario, R., Crichton, J. H., Stewart, H. L., Childs, A. J., Adams, I. R., Anderson, R. A. Dazl determines primordial follicle formation through the translational regulation of Tex14.

The timeline development of female canine germ cells

During the sex differentiation, the primordial germ cells (PGCs) pass through a differentiation, becoming spermatogonial cells in males and oocytes in females. In this phase, there is difference in gene expression and differentiation potency between males and females. Specific cell markers have been essential in the PGC meiosis beginning and become oocyte cells. However, there are few studies about germline in domestic animals. The domestic dog (Canis lupus familiaris) is an interesting animal model to be used in the investigation about the mammal development because it has several biochemical and physiological similarities to humans. In addition, some additional investigations about dogs may contribute to a better understanding of the biology and genetic components, improving clinical veterinary and zoological sciences. Here, we elucidated by immunofluorescence and quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR), the dynamics of the expression of pluripotent (POU5F1 and NANOG) and germline (DDX4, DAZL and DPPA3) markers that are very important in the development of female canine germ cells during 35-50 days post-fertilization (dpf). The female canine germ cells were positive for pluripotent markers during middle developmental period. The number of DDX4, DAZL and DPPA3 cells increased along the germ cell maturation from 45 to 50 dpf. We provided an expression analysis of the pluripotent and germline markers in paraffin sections using the middle and later periods in female canine germ cells. The results can contribute the understanding about the timeline of each marker along the maturation of female canine germ cells. These results have a great significance to demonstrate the germ cell profile changes because it may allow the development of protocols about in vitro germ cell derivation.

A genome-wide single nucleotide polymorphism and copy number variation analysis for number of piglets born alive

Background

In this study we integrated the CNV (copy number variation) and WssGWAS (weighted single-step approach for genome-wide association) analyses to increase the knowledge about number of piglets born alive, an economically important reproductive trait with significant impact on production efficiency of pigs.

Results

A total of 3892 samples were genotyped with the Porcine SNP80 BeadChip. After quality control, a total of 57,962 high-quality SNPs from 3520 Duroc pigs were retained. The PennCNV algorithm identified 46,118 CNVs, which were aggregated by overlapping in 425 CNV regions (CNVRs) ranging from 2.5 Kb to 9718.4 Kb and covering 197 Mb (~ 7.01%) of the pig autosomal genome. The WssGWAS identified 16 genomic regions explaining more than 1% of the additive genetic variance for number of piglets born alive. The overlap between CNVR and WssGWAS analyses identified common regions on SSC2 (4.2–5.2 Mb), SSC3 (3.9–4.9 Mb), SSC12 (56.6–57.6 Mb), and SSC17 (17.3–18.3 Mb). Those regions are known for harboring important causative variants for pig reproductive traits based on their crucial functions in fertilization, development of gametes and embryos. Functional analysis by the Panther software identified 13 gene ontology biological processes significantly represented in this study such as reproduction, developmental process, cellular component organization or biogenesis, and immune system process, which plays relevant roles in swine reproductive traits.

Conclusion

Our research helps to improve the understanding of the genetic architecture of number of piglets born alive, given that the combination of GWAS and CNV analyses allows for a more efficient identification of the genomic regions and biological processes associated with this trait in Duroc pigs. Pig breeding programs could potentially benefit from a more accurate discovery of important genomic regions.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5687-0) contains supplementary material, which is available to authorized users.

Histomorphological Comparisons and Expression Patterns of BOLL Gene in Sheep Testes at Different Development Stages

BOLL is implicated in mammalian testicular function maintenance and spermatogenesis. To understand the expression patterns and biological functions of sheep BOLL, we examined the expression and immunolocalization of BOLL in the developing testes of Small-Tail Han sheep aged 0 days (D0), 2 months (2M), 5 months (5M), 1 year (1Y), and 2 years (2Y), by qPCR, Western blot, and immunohistochemistry methods. Firstly, morphological studies revealed that, in addition to spermatogonia, ordered and clear spermatocytes, as well as round and elongated spermatids and sperm, were found in the 1Y and 2Y testicular seminiferous tubules of the sheep testes, compared with the D0, 2M, and 5M testes, as analyzed by hematoxylin and eosin (H&amp;E) staining. The diameter and area of the seminiferous tubules, epithelial thickness, and the area and perimeter of the tubule lumens gradually increased with age. BOLL was specifically expressed in testes and upregulation of BOLL transcript expression was higher in the testes of the 1Y and 2Y groups than in those of the D0, 2M, and 5M groups. Similarly, BOLL protein was expressed mainly in the 1Y and 2Y testes, ranging from primary spermatocytes to round spermatids, as well as in the spermatozoa. This study is the first demonstration that sheep BOLL might serve as a key regulator of the spermiogenesis involved in sperm maturity, in addition to its role as a crucial meiotic regulator.

Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

Infertility affects ~7% of couples of reproductive age with little change in incidence in the last two decades. ART, as well as other interventions, have made major strides in correcting this condition. However, and in spite of advancements in the field, the age of the female partner remains a main factor for a successful outcome. A better understanding of the final stages of gamete maturation yielding an egg that can sustain embryo development and a pregnancy to term remains a major area for improvement in the field. This review will summarize the major cellular and molecular events unfolding at the oocyte-to-embryo transition. We will provide an update on the most important processes/pathways currently understood as the basis of developmental competence, including the molecular processes involved in mRNA storage, its recruitment to the translational machinery, and its degradation. We will discuss the hypothesis that the translational programme of maternal mRNAs plays a key role in establishing developmental competence. These regulations are essential to assemble the machinery that is used to establish a totipotent zygote. This hypothesis further supports the view that embryogenesis begins during oogenesis. A better understanding of the events required for developmental competence will guide the development of novel strategies to monitor and improve the success rate of IVF. Using this information, it will be possible to develop new biomarkers that may be used to better predict oocyte quality and in selection of the best egg for IVF.

RNA immunoprecipitation identifies novel targets of DAZL in human foetal ovary

Study question

Can novel meiotic RNA targets of DAZL (deleted in azoospermia-like) be identified in the human foetal ovary?

Summary answer

SYCP1 (synaptonemal complex protein-1), TEX11 (testis expressed 11) and SMC1B (structural maintenance of chromosomes 1B) are novel DAZL targets in the human foetal ovary, thus DAZL may have previously unrecognised roles in the translational regulation of RNAs involved in chromosome cohesion and DNA recombination in the oocyte from the time of initiation of meiosis.

What is known already

The phenotype of Dazl deficiency in mouse is infertility in both sexes and DAZL has also been linked to infertility in humans. Few studies have explored targets of this RNA-binding protein. The majority of these investigations have been carried out in mouse, and have focussed on the male thus the basis for its central function in regulating female fertility is largely unknown.

Study design size, duration

We carried out RNA sequencing after immunoprecipitation of endogenous DAZL from human foetal ovarian tissue (17 weeks of gestation, obtained after elective termination of pregnancy) to identify novel DAZL targets involved in meiosis (n = 3 biological replicates).

Participants/materials, setting, methods

Using quantitative RT-PCR, we examined the expression of selected RNAs identified by our immunoprecipitation across gestation, and visualised the expression of potential target SMC1B in relation to DAZL, with a combination of in situ hybridisation and immunohistochemistry. 3′ untranslated region (3′UTR)-luciferase reporter assays and polysome profile analysis were used to investigate the regulation of three RNA targets by DAZL, representing key functionalities: SYCP1, TEX11 and SMC1B.

Main results and the role of chance

We identified 764 potential RNA targets of DAZL in the human foetal ovary (false discovery rate 0.05 and log-fold change ≥ 2), with functions in synaptonemal complex formation (SYCP1, SYCP3), cohesin formation (SMC1B, RAD21), spindle assembly checkpoint (MAD2L1, TRIP13) and recombination and DNA repair (HORMAD1, TRIP13, TEX11, RAD18, RAD51). We demonstrated that the translation of novel targets SYCP1 (P = 0.004), TEX11 (P = 0.004) and SMC1B (P = 0.002) is stimulated by the presence of DAZL but not by a mutant DAZL with impaired RNA-binding activity.

Large scale data

The raw data are available at GEO using the study ID: GSE81524.

Limitations, reasons for caution

This analysis is based on identification of DAZL targets at the time when meiosis starts in the ovary: it may have other targets at other stages of oocyte development, and in the testis. Representative targets were validated, but detailed analysis was not performed on the majority of putative targets.

Wider implications of the findings

These data indicate roles for DAZL in the regulation of several key functions in human oocytes. Through the translational regulation of novel RNA targets SMC1B and TEX11, DAZL may have a key role in regulating chromosome cohesion and DNA recombination; two processes fundamental in determining oocyte quality and whose establishment in foetal life may support lifelong fertility.

Study funding and competing interest(s)

This study was supported by the UK Medical Research Council (grant no G1100357 to R.A.A. and an intramural MRC programme grant to I.R.A.). The authors declare no competing interests.

Role of tripartite motif protein 27 as a gametogenesis-related protein in human germ cells

BACKGROUND

The distribution and functional integrity of members of the tripartite motif (TRIM) protein family are essential for cell proliferation, development and apoptosis, and TRIM proteins have been linked to various cancers. To explore the diagnostic potential and mechanisms of TRIM27 in human spermatogenesis and oogenesis, we analyzed its localization pattern and putative roles in human testes and ovaries.

METHODS

TRIM27 mRNA and protein levels in human testes and ovaries were investigated using RT-PCR and western blotting, respectively. TRIM27 was abundantly transcribed in human testes and ovaries, particularly during the early stages of spermatogenesis, and localized in the nuclei of primary spermatocytes. Immunofluorescence also revealed a diffuse distribution in the cytoplasm of round spermatids, and the protein was abundant in ovary tissue during various stages of oogenesis development.

RESULTS

TRIM27 mRNA and protein was abundantly transcribed in male and female human germ cells by RT-PCR and western blotting in the human testes followed by the ovary. Immunohistochemical results revealed TRIM27 protein was abundant in the sex body of primary spermatocytes undergoing meiotic prophase during the first cycle of spermatogenesis. Moreover, Trim27 was diffusely localized in the cytoplasm of spermatids and round spermatids. Furthermore, TRIM27 was localized to both the nucleus and cytoplasm of human ovary cells.

CONCLUSIONS

TRIM27 as a gametogenesis-related protein could play multiple roles in the regulation of sex body formation and germ cell proliferation during spermatogenesis and oogenesis. The identification and characterization of TRIM27 enhances our understanding of the molecular mechanisms underpinning its functions, and provides insight into its potential role in the pathogenesis of germ cell differentiation and infertility.

In vitro differentiation of human embryonic stem cells into ovarian follicle-like cells

Understanding the unique mechanisms of human oogenesis necessitates the development of an in vitro system of stem cell differentiation into oocytes. Specialized cell types and organoids have been derived from human pluripotent stem cells in vitro, but generating a human ovarian follicle remains a challenge. Here we report that human embryonic stem cells can be induced to differentiate into ovarian follicle-like cells (FLCs) in vitro. First, we find that two RNA-binding proteins specifically expressed in germ cells, DAZL and BOULE, regulate the exit from pluripotency and entry into meiosis. By expressing DAZL and BOULE with recombinant human GDF9 and BMP15, these meiotic germ cells are further induced to form ovarian FLCs, including oocytes and granulosa cells. This robust in vitro differentiation system will allow the study of the unique molecular mechanisms underlying human pluripotent stem cell differentiation into late primordial germ cells, meiotic germ cells and ovarian follicles.

RNA-binding proteins in human oogenesis: Balancing differentiation and self-renewal in the female fetal germline

Primordial germ cells undergo three significant processes on their path to becoming primary oocytes: the initiation of meiosis, the formation and breakdown of germ cell nests, and the assembly of single oocytes into primordial follicles. However at the onset of meiosis, the germ cell becomes transcriptionally silenced. Consequently translational control of pre-stored mRNAs plays a central role in coordinating gene expression throughout the remainder of oogenesis; RNA binding proteins are key to this regulation. In this review we examine the role of exemplars of such proteins, namely LIN28, DAZL, BOLL and FMRP, and highlight how their roles during germ cell development are critical to oogenesis and the establishment of the primordial follicle pool.

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RNA-binding proteins (RBPs) are key regulators of gene expression during oogenesis.

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RBPs LIN28, DAZL, BOLL and FMRP display stage-specific expression in fetal oocytes.

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LIN28 and DAZL may regulate self-renewal and progression into meiosis respectively.

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BOLL and FMRP may be involved in the later stages of prophase I and oocyte growth.

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RBPs may have critical roles in establishing the ovarian reserve during fetal life.