Human DAZL1 encodes a candidate fertility factor in women that localizes to the prenatal and postnatal germ cells

Porcine Germ Cells Phenotype during Embryonic and Adult Development

Primordial germ cells (PGCs) are the precursors of gametes. Due to their importance for the formation and reproduction of an organism, understanding the mechanisms and pathways of PGCs and the differences between males and females is essential. However, there is little research in domestic animals, e.g., swine, regarding the epigenetic and pluripotency profiles of PGCs during development. This study analyzed the expression of epigenetic and various pluripotent and germline markers associated with the development and differentiation of PGCs in porcine (pPGCs), aiming to understand the different gene expression profiles between the genders. The analysis of gonads at different gestational periods (from 24 to 35 days post fertilization (dpf) and in adults) was evaluated by immunofluorescence and RT-qPCR and showed phenotypic differences between the gonads of male and female embryos. In addition, the pPGCs were positive for OCT4 and VASA; some cells were H3k27me3 positive in male embryos and adult testes. In adults, the cells of the testes were positive for germline markers, as confirmed by gene expression analysis. The results may contribute to understanding the pPGC pathways during reproductive development, while also contributing to the knowledge needed to generate mature gametes in vitro.

Studying human reproductive biology through single-cell analysis and in vitro differentiation of stem cells into germ cell-like cells

BACKGROUND

Understanding the molecular and cellular mechanisms of human reproductive development has been limited by the scarcity of human samples and ethical constraints. Recently, in vitro differentiation of human pluripotent stem cells into germ cells and single-cell analyses have opened new avenues to directly study human germ cells and identify unique mechanisms in human reproductive development.

OBJECTIVE AND RATIONALE

The goal of this review is to collate novel findings and insightful discoveries with these new methodologies, aiming at introducing researchers and clinicians to the use of these tools to study human reproductive biology and develop treatments for infertility.

SEARCH METHODS

PubMed was used to search articles and reviews with the following main keywords: in vitro differentiation, human stem cells, single-cell analysis, spermatogenesis, oogenesis, germ cells and other key terms related to these subjects. The search period included all publications from 2000 until now.

OUTCOMES

Single-cell analyses of human gonads have identified many important gene markers at different developmental stages and in subpopulations of cells. To validate the functional roles of these gene markers, researchers have used the in vitro differentiation of human pluripotent cells into germ cells and confirmed that some genetic requirements are unique in human germ cells and are not conserved in mouse models. Moreover, transcriptional regulatory networks and the interaction of germ and somatic cells in gonads were elucidated in these studies.

WIDER IMPLICATIONS

Single-cell analyses allow researchers to identify gene markers and potential regulatory networks using limited clinical samples. On the other hand, in vitro differentiation methods provide clinical researchers with tools to examine these newly identify gene markers and study the causative effects of mutations previously associated with infertility. Combining these two methodologies, researchers can identify gene markers and networks which are essential and unique in human reproductive development, thereby producing more accurate diagnostic tools for assessing reproductive disorders and developing treatments for infertility.

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.

Is there a role for DAZL in human female fertility?

The RNA binding protein deleted in azoospermia-like (Dazl) is a key determinant of germ cell maturation and entry into meiosis in rodents and other animal species. Although the complex phenotype of Dazl deficiency in both sexes, with defects at multiple stages of germ cell development and during meiosis, demonstrates its obligate significance in fertility in animal models, its involvement in human fertility is less clear. As an RNA binding protein, identification of the in vivo mRNA targets of DAZL is necessary to understand its influence. Thus far, only a small number of Dazl targets have been identified, which typically have pivotal roles in germ cell development and meiotic progression. However, it is likely that there are a number of additional germ cell and meiosis-relevant transcripts whose translation is affected in the absence of Dazl. Efforts to identify these RNA targets have mainly been focused on spermatogenesis, and restricted to mouse. In women, prophase I occurs in fetal life and it is during this period that the ovarian follicle pool is established, thus factors that have a role in determining the quality and quantity of the ovarian reserve may have significant impact on reproductive outcomes later in adult life. Here, we suggest that DAZL may be one such factor, and there is a need for greater understanding of the role of DAZL in human oogenesis and its contribution to lifelong female fertility.

DAZ Family Proteins, Key Players for Germ Cell Development

DAZ family proteins are found almost exclusively in germ cells in distant animal species. Deletion or mutations of their encoding genes usually severely impair either oogenesis or spermatogenesis or both. The family includes Boule (or Boll), Dazl (or Dazla) and DAZ genes. Boule and Dazl are situated on autosomes while DAZ, exclusive of higher primates, is located on the Y chromosome. Deletion of DAZ gene is the most common causes of infertility in humans. These genes, encoding for RNA binding proteins, contain a highly conserved RNA recognition motif and at least one DAZ repeat encoding for a 24 amino acids sequence able to bind other mRNA binding proteins. Basically, Daz family proteins function as adaptors for target mRNA transport and activators of their translation. In some invertebrate species, BOULE protein play a pivotal role in germline specification and a conserved regulatory role in meiosis. Depending on the species, DAZL is expressed in primordial germ cells (PGCs) and/or pre-meiotic and meiotic germ cells of both sexes. Daz is found in fetal gonocytes, spermatogonia and spermatocytes of adult testes. Here we discuss DAZ family genes in a phylogenic perspective, focusing on the common and distinct features of these genes, and their pivotal roles during gametogenesis evolved during evolution.

The roles of DAZL in RNA biology and development

RNA-binding proteins play an important role in the regulation of gene expression by modulating translation and localization of specific messenger RNAs (mRNAs) during early development and gametogenesis. The DAZ (Deleted in Azoospermia) family of proteins, which includes DAZ, DAZL, and BOULE, are germ cell-specific RNA-binding proteins that are implicated in translational regulation of several transcripts. Of particular importance is DAZL, which is present in vertebrates and arose from the duplication of the ancestral BOULE during evolution. Identification of DAZL target mRNAs and characterization of the RNA-binding sequence through in vitro binding assays and crystallographic studies revealed that DAZL binds to GUU triplets in the 3' untranslated region of target mRNAs. Although there is compelling evidence for the role of DAZL in translation stimulation of target mRNAs, recent studies indicate that DAZL can also function in translational repression and transport of specific mRNAs. Furthermore, apart from the well-characterized function of DAZL in gametogenesis, recent data suggest its role in early embryonic development and differentiation of pluripotent stem cells toward functional gametes. In light of the mounting evidence for the role of DAZL in various cellular and developmental processes, we summarize the currently characterized biological functions of DAZL in RNA biology and development.

Deleted in azoospermia-like enhances in vitro derived porcine germ cell formation and meiosis

Evidence supporting that deleted in azoospermia-like (DAZL) plays a key role during gametogenesis and meiosis continues to emerge. Our study aimed to determine whether overexpression of DAZL using a lentiviral approach in a somatic stem cell to germ cell in vitro differentiation culture could enhance the formation of primordial germ cell-like cells (PLCs) and oocyte-like cells (OLCs). Introduction of DAZL at the beginning of induced differentiation significantly increased the formation of Fragilis-positive PLCs, which was independent of mitotic proliferation. In addition, mRNA levels of the germ cell markers Oct4, Stella, and Vasa were also higher in the DAZL-transduced group and suppressed when DAZL was knocked down using small interference RNA. At later stages of differentiation, the expression of several genes associated with meiosis, including Scp3, Dmc1, Rec8, and Stra8, was determined to be significantly higher when DAZL was overexpressed, which was abrogated by its knockdown. Exogenous introduction of DAZL also increased the protein levels of SCP3 and VASA, which again was reversed by its knockdown. Although not a common phenomenon in the in vitro differentiation system, the percentage of SCP3-positive cells displaying meiotic chromosome patterns in the DAZL-transduced group was higher than in the control, as was the overall percentage of OLCs that were generated. The introduction of factors such as DAZL into a stem cell-to-germ cell differentiation culture may provide an opportunity to better understand the key genes and their interactions during gametogenesis, also providing a means to enhance the generation of germ cells in vitro.

Markers of stem cells in human ovarian granulosa cells: is there a clinical significance in ART?

Background

The purpose of the study was to determine the incidence of gene expression of Oct-4 and DAZL, which are typical markers for stem cells, in human granulosa cells during ovarian stimulation in women with normal FSH levels undergoing IVF or ICSI and to discover any clinical significance of such expression in ART.

Methods

Twenty one women underwent ovulation induction for IVF or ICSI and ET with standard GnRH analogue-recombinant FSH protocol. Infertility causes were male and tubal factor. Cumulus–mature oocyte complexes were denuded separately and granulosa cells were analyzed for each patient separately using quantitative reverse-transcription–polymerase chain reaction analysis for Oct-4 and DAZL gene expression with G6PD gene as internal standard.

Results

G6PD and Oct-4 mRNA was detected in the granulosa cells in 47.6% (10/21). The median of Oct-4 mRNA/G6PD mRNA was 1.75 with intra-quarteral range from 0.10 to 98.21. The OCT-4 mRNA expression was statistically significantly correlated with the number of oocytes retrieved; when the Oct-4 mRNA expression was higher, then more than six oocytes were retrieved (p=0.037, Wilcoxon rank-sum). No detection of DAZL mRNA was found in granulosa cells. There was no additional statistically significant correlation between the levels of Oct-4 expression and FSH basal levels or estradiol peak levels or dosage of FSH for ovulation induction. No association was found between the presence or absence of Oct-4 mRNA expression in granulosa cells and ovarian response to gonadotropin stimulation. Also, no influence on pregnancy was observed between the presence or absence of Oct-4 mRNA expression in granulosa cells or to its expression levels accordingly.

Conclusions

Expression of OCT-4 mRNA, which is a typical stem cell marker and absence of expression of DAZL mRNA, which is a typical germ cell marker, suggest that a subpopulation of luteinized granulosa cells in healthy ovarian follicles (47.6%) consists of stem cells, which are not originated from primordial germ cells. Absence of Oct-4 gene expression in more than half of the cases means probably the end of the productive journey of these cells, towards the oocyte.

Widespread presence of human BOULE homologs among animals and conservation of their ancient reproductive function

Sex-specific traits that lead to the production of dimorphic gametes, sperm in males and eggs in females, are fundamental for sexual reproduction and accordingly widespread among animals. Yet the sex-biased genes that underlie these sex-specific traits are under strong selective pressure, and as a result of adaptive evolution they often become divergent. Indeed out of hundreds of male or female fertility genes identified in diverse organisms, only a very small number of them are implicated specifically in reproduction in more than one lineage. Few genes have exhibited a sex-biased, reproductive-specific requirement beyond a given phylum, raising the question of whether any sex-specific gametogenesis factors could be conserved and whether gametogenesis might have evolved multiple times. Here we describe a metazoan origin of a conserved human reproductive protein, BOULE, and its prevalence from primitive basal metazoans to chordates. We found that BOULE homologs are present in the genomes of representative species of each of the major lineages of metazoans and exhibit reproductive-specific expression in all species examined, with a preponderance of male-biased expression. Examination of Boule evolution within insect and mammalian lineages revealed little evidence for accelerated evolution, unlike most reproductive genes. Instead, purifying selection was the major force behind Boule evolution. Furthermore, loss of function of mammalian Boule resulted in male-specific infertility and a global arrest of sperm development remarkably similar to the phenotype in an insect boule mutation. This work demonstrates the conservation of a reproductive protein throughout eumetazoa, its predominant testis-biased expression in diverse bilaterian species, and conservation of a male gametogenic requirement in mice. This shows an ancient gametogenesis requirement for Boule among Bilateria and supports a model of a common origin of spermatogenesis.

Characterization of a Dazl-GFP germ cell-specific reporter

In this study, we characterized the promoter activity of a 1.7 kb sequence in the 5' flanking region of the mouse Deleted in Azoospermia-Like (Dazl) gene. We found the 1.7 kb sequence sufficient to drive robust germ cell-specific expression of green fluorescent protein (GFP) in adult mouse testis and lower levels of expression in adult ovary and in fetal and newborn gonads of both sexes. This expression pattern was confirmed in two independently-derived transgenic mouse lines. In adult testis, Dazl-GFP exhibited a developmentally-regulated, stage-specific expression pattern during spermatogenesis. GFP was highly expressed in spermatocyte stages, with strongest expression in pachytene spermatocytes. Weaker expression was observed in round and elongating spermatids, as well as spermatogonial cells. In the fetal gonad, GFP transcript was detected by e12.5 in both sexes; however, GFP fluorescence was only detected during later embryonic stages. In addition, we produced mouse embryonic stem cell (ESC) lines harboring the Dazl-GFP reporter and used this reporter to isolate putative germ cell populations derived from mouse ESCs following embryoid body differentiation and fluorescence activated cell sorting.

The DAZL and PABP families: RNA-binding proteins with interrelated roles in translational control in oocytes

Gametogenesis is a highly complex process that requires the exquisite temporal, spatial and amplitudinal regulation of gene expression at multiple levels. Translational regulation is important in a wide variety of cell types but may be even more prevalent in germ cells, where periods of transcriptional quiescence necessitate the use of post-transcriptional mechanisms to effect changes in gene expression. Consistent with this, studies in multiple animal models have revealed an essential role for mRNA translation in the establishment and maintenance of reproductive competence. While studies in humans are less advanced, emerging evidence suggests that translational regulation plays a similarly important role in human germ cells and fertility. This review highlights specific mechanisms of translational regulation that play critical roles in oogenesis by activating subsets of mRNAs. These mRNAs are activated in a strictly determined temporal manner via elements located within their 3′UTR, which serve as binding sites fortrans-acting factors. While we concentrate on oogenesis, these regulatory events also play important roles during spermatogenesis. In particular, we focus on the deleted in azoospermia-like (DAZL) family of proteins, recently implicated in the translational control of specific mRNAs in germ cells; their relationship with the general translation initiation factor poly(A)-binding protein (PABP) and the process of cytoplasmic mRNA polyadenylation.

An epigenetic mechanism regulates germ cell-specific expression of the porcine Deleted in Azoospermia-Like (DAZL) gene

The Deleted in Azoospermia-Like (DAZL) gene is specifically expressed in fetal and adult gonads. While DAZL is known to play a role during gametogenesis, the mechanisms governing its germ cell-specific expression remain unclear. We identified the 5' untranslated region (UTR) of the porcine DAZL gene and cloned and characterized 2 kilobase pairs of its TATA-less 5' flanking region, identifying CpG-rich regions within the proximal promoter. Nine of 18 CpG sites in proximity to one region were largely unmethylated in germ cells but hypermethylated in somatic cells, suggesting that DNA methylation may regulate DAZL promoter activity. Furthermore, DAZL expression was induced in fibroblasts treated with a demethylating agent. Deletion analyses revealed that the minimal 149 base pair promoter region was sufficient to activate transcription. In vitro methylation of a reporter construct corresponding to these 149 base pairs resulted in complete suppression of DAZL promoter activity in primordial germ cells, further supporting a role for methylation in regulating DAZL expression. Interestingly, the differentially methylated region was shown to harbor several putative Sp1-binding sites. Mutation of only the most highly conserved site significantly reduced promoter activity in a reporter assay. Furthermore, gel shift assays revealed that Sp1 was able to specifically bind to this site, and that complex formation was inhibited when CpG dinucleotides within this region were methylated. Chromatin immunoprecipitation (ChIP) assays revealed that in vivo Sp1 binding to the core DAZL promoter region was enriched in germ cells but not in fibroblasts. Our data suggests that DNA methylation may suppress DAZL expression in somatic cells by interfering with Sp1 binding. This study provides insights into the potential mechanisms underlying the regulation of germ cell-specific gene expression.

DAZL protein expression in mouse preimplantation embryo

OBJECTIVE

To evaluate the expression pattern of Dazl (deleted in azoospermia-like) protein in the mouse preimplantation embryo.

DESIGN

Experimental study.

SETTING

Medical research laboratory in a university hospital.

ANIMAL(S)

Twenty female 28- to 35-day-old FVB mice.

INTERVENTION(S)

Embryo collection at 1.5, 2.5, and 3.5 days postcoitus (plug date, 0.5 d postcoitus) to examine the Dazl protein expression from the two-cell embryo to the blastocyst.

MAIN OUTCOME MEASURE(S)

Dazl protein expression was analyzed by immunofluorescent staining.

RESULT(S)

There is abundant expression of Dazl protein in the cytoplasm of the blastomere. Strong fluorescent signals of Dazl protein expression were found in preimplantation embryo cytoplasm, including two-cell, eight-cell, morula, and blastocyst.

CONCLUSION(S)

By using an antibody raised against mouse Daz-like protein (Dazl), we showed that Dazl protein is present in all cleaving stages of the preimplantation embryo. This is the first report on the protein expression of a Dazl gene during embryogenesis in mice. However, further study is needed to evaluate the molecular functional role of Dazl.

Genomic structure and transcript variants of the bovine DAZL gene

The Deleted in AZoospermia Like (DAZL) gene is a member of the DAZ family and encodes an RNA-binding protein that is expressed in prenatal and postnatal germ cells of males and females. In the human, there are five highly-related members in the DAZ family, four (DAZ1-4) on the Y chromosome and one (DAZL) on an autosome (HSA3). Mutations in these genes have been linked to severe spermatogenic failure and infertility in men. In the present study, we have cloned and characterized the bovine DAZL (bDAZL) gene. The full-length bDAZL cDNA is predicted to encode a protein of 295 amino acids with an RNA recognition motif. The deduced protein sequence of bDAZL is 96 and 97% similar to human and mouse DAZL, respectively. Fluorescence in situ hybridization (FISH) maps bDAZL to the distal region on BTA1q. The bDAZL gene consists of 11 exons and 10 introns. A bDAZL pseudogene was identified on BTA16. Expression analysis of bDAZL in 13 different tissues by RT-PCR shows that two transcripts, variant 1 (2,996 bp) and variant 2 (1,373 bp), of the bDAZL gene are detected only in testis mRNA. The variants probably result from alternative RNA splicing as variant 1 contains an additional 1,623-bp insertion in the 3' UTR. Our results lay the groundwork for possible single nucleotide polymorphism (SNP) and functional studies of the DAZL gene in cattle.

Cloning and expression of medaka dazl during embryogenesis and gametogenesis

The Deleted in azoospermia family consists of RNA-binding proteins Boule, Daz, and Daz-like (Dazl) that are expressed in the germline. Here, we report the cloning and expression of the medakafish (Oryzias latipes) dazl gene (odazl). Interestingly, although the predicted medaka Dazl protein (oDazl) contains a RRM motif and a DAZ repeat characteristic of its mammalian homologs, it lacks 80 aa at the C-terminus. By RT-PCR, RNA in situ hybridization, Western blotting and fluorescent immunohistochemistry using a rabbit anti-Dazl antibody (alphaDazl), we analyzed the expression patterns of odazl and its protein. The odazl transcript persists throughout embryogenesis and delineates with primordial germ cells. In adults, the expression of odazl RNA and its protein is restricted to germ cells of both the testis and ovary. We observed differential expression of RNA and protein at critical stages of gametogenesis. In the testis, the odazl RNA is low at premeiotic stages, abundant at meiotic stages, but absent in postmeiotic stages; whereas the oDazl protein is rich in premeiotic stages, reduced at meiotic stages, becomes barely detectable or absent in postmeiotic round spermatids or sperm, respectively. This is in sharp contrast to the human situation where the Dazl transcript and protein are present in mature spermatozoa. In the ovary, the odazl RNA and protein persist throughout oogenesis and also show differential expression at premeiotic, meiotic and postmeiotic stages. Thus, the odazl or its protein is a marker for germ cells during embryogenesis and at critical stages of gametogenesis in both sexes of medaka.

Novel missense mutations of the Deleted-in-AZoospermia-Like (DAZL) gene in infertile women and men

BACKGROUND

The Deleted-in-AZoospermia-Like (DAZL) gene has homologs required for germ cell development in many organisms. Recently, we showed that there are several common polymorphisms within the DAZL gene that are associated with age at ovarian failure/menopause and sperm count.

METHODS

Here we sought to identify rare mutations in DAZL and examine their phenotypes in men and women. We sequenced the DAZL gene in 519 individuals; sequences spanned the entire coding region of the gene.

RESULTS

We report the identification of four putative missense mutations in DAZL. Three individuals that were heterozygous for a DAZL mutation reported having children, while two individuals that were homozygous reported no children. These mutations were found only in infertile men and women.

CONCLUSION

Given the strong data associating DAZL polymorphisms and deletions with fertility in humans and model organisms, we suggest that these mutations may be associated with age at menopause and/or sperm count and warrant further biochemical and genetic investigation.

Expression patterns of the DAZ-associated protein DAZAP1 in rat and human ovaries

OBJECTIVE

To evaluate the expression of DAZAP1 (deleted in azoospermia-associated protein 1) in rat and human ovaries.

DESIGN

Experimental study.

SETTING

University hospital.

PATIENT(S)

Twelve corpus luteum (CL) specimens were collected during operation, either by laparoscopic surgery for CL rupture or by laparotomy for benign gynecologic conditions.

INTERVENTION(S)

Surgical excision of 12 human CL.

MAIN OUTCOME MEASURE(S)

Proteins analyzed by immunohistochemical staining, Western blotting, and co-immunoprecipitation experiments.

RESULT(S)

DAZAP1 is expressed in rat and human luteal cells. Expression of DAZAP1 decreases with advancing stages of CL. Co-immunoprecipitation experiments show in vivo interaction of DAZ-like (DAZL) protein with DAZAP1 in the ovarian tissues.

CONCLUSION(S)

The expression patterns of DAZAP1 and DAZL are identical within rat and human ovaries. In mammalian species, DAZAP1 may be involved in diverse reproductive functions, ranging from cell cycle regulation and maturation of oocytes to differentiation of luteal cells.

DAZL expression in human oocytes, preimplantation embryos and embryonic stem cells

In humans, the Deleted in Azoospermia Like (DAZL) gene is believed to function in the development of primordial germ cells and in germ cell differentiation and maturation because the expression of DAZL is only found in the germ and non-germ lineage of the reproductive system and in embryonic stem (ES) cells. The present study examined the presence of DAZL transcripts in the last stages of oocyte maturation, in ES cells, and throughout the preimplantation development; the link between gametes and ES cells. The finding of DAZL transcripts in the last stages of oogenesis and during the first two cell cycles of the preimplantation development was expected, because DAZL is a germ cell marker and the transcripts present at that time are generally encoded by the maternal genome. During the third cell cycle, DAZL showed a variable expression pattern, which may point to the maternal to embryonic transition. After the third cell cycle, transcripts were again consistently detected, suggesting embryonic DAZL transcription. In blastocysts, DAZL transcripts were only detected in those of good quality and this as well in the inner cell mass (ICM) as in the trophectoderm (TE). The presence of DAZL transcripts in the ICM and in ES cells was not surprising since both can lead to the formation of germ cells, but TE cells cannot. The quality-related expression of DAZL in blastocysts, and especially its trophectodermal expression, might imply other functions for DAZL beyond germ cell development.

Identification of a novel gene, DZIP (DAZ-interacting protein), that encodes a protein that interacts with DAZ (deleted in azoospermia) and is expressed in embryonic stem cells and germ cells

Evidence from diverse organisms, including humans, suggests that the DAZ (Deleted in Azoospermia) gene and a closely related homolog, DAZL (DAZ-like), are required early in germ cell development to maintain initial germ cell populations. Here we report the identification and characterization of the DZIP (DAZ-Interacting Protein) gene, which encodes at least three different protein isoforms that contain a C2H2 zinc-finger domain. The DZIP gene is expressed predominantly in human embryonic stem cells and fetal and adult germ cells; moreover, two DZIP protein isoforms colocalize with DAZ and/or DAZL proteins in these tissues. Finally, we provide evidence indicating that DZIP may associate with DAZ and its other cofactors in an RNA-binding protein complex that functions in both ES cells and germ cells.

Putative biological functions of the DAZ family

The Deleted in Azoospermia (DAZ) gene belongs to a gene family that consists of three members: BOULE, DAZ-Like (DAZL) and DAZ. Members of the DAZ family are expressed exclusively in the germ cells, and their protein products contain a highly conserved RNA-binding motif and a unique DAZ repeat. Null mutations of the DAZ family members affect the fertility of either male or female, or both sexes. DAZ and DAZL are expressed throughout most of the life of germ cells and are required for the development of primordial germ cells and the differentiation and maturation of the germ cells. BOULE is expressed around the time of meiosis and has a more limited function. The DAZ proteins bind to RNAs in vitro and in vivo and are probably involved in the post-transcriptional regulation of mRNA expression. Their downstream RNA targets remain largely unknown, although members of the CDC25 gene family are potential candidates.

Feasibility of global gene expression analysis in testicular biopsies from infertile men

Numerous studies have documented the use of microarray analysis to identify patterns of global gene expression that distinguish normal development from that of the diseased state. Yet, there are no reports that compare global gene expression in the fertile and infertile human testis. Here, we report an initial study of global gene expression in testicular biopsies from several men with different infertility phenotypes. We found that microarray analysis of small biopsy samples was suitable for profiling expression of genes known to function in germ cell development and also identified expression of novel genes. Since it is now common for infertile men with spermatogenic failure to use intracytoplasmic sperm injection (ICSI) to achieve biological paternity, we hypothesize that molecular screening of testicular biopsies with microarrays may be suitable: (1) to categorize the molecular phenoytpes of infertile testes in a manner similar to standard morphologic analysis and (2) to initiate larger studies of gene expression in the infertile testes that may identify genetic signatures from biopsies that allow prediction of outcomes.

Screening of HBcAg interacting proteins in hepatocytes with yeast-two hybrid technique

AIM

To screen proteins in hepatocytes interacting with hepatitis B virus core protein (HBcAg) with yeast-two hybrid technique for investigating the biological functions of HBcAg.

METHODS

The HBcAg gene was amplified by polymerase chain reaction (PCR) and HBcAg bait plasmid was constructed with yeast-two hybrid system 3, then transformed into yeast AH109. The transformed yeast mated with yeast Y187 containing liver cDNA library plasmid in 2×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) and synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X-α-gal for selecting two times and screening. After extracting and sequencing of plasmid from blue colonies, the results were analyzed by bioinformatics.

RESULTS

Sixteen colonies were sequenced, of which, two colonies were metallothionein 2A, one NAD(P)H dehydrogenase, one complement component 8 a polypeptide, one retinoic acid receptor responder (tazarotene induced), one cytochromeb, one cytochrome c oxidase subunit II , one albumin, two DAZ associated protein 2, two mitochondrial ribosomal protein L41 and four new genes with unknown function.

CONCLUSION

Genes of HBcAg interacting proteins in hepatocytes were successfully cloned and the results provided some new clues for studying the biological functions of HBcAg and its associated proteins.

Conservation of a Pumilio-Nanos complex from Drosophila germ plasm to human germ cells

Germ cells are the cells which ultimately give rise to mature sperm and eggs. In model organisms such as flies and worms, several genes that are required for formation and maintenance of germ cells have been identified and their interactions are rapidly being delineated. By contrast, little is known of the genes required for development of human germ cells and it is not clear whether findings from model organisms will translate into knowledge of human germ cell development, especially given observations that reproductive pathways may evolve more rapidly than somatic pathways. The Pumilio and Nanos genes have been especially well-characterized in model organisms and encode proteins that interact and are required for development of germ stem cells in one or both sexes. Here we report the first characterization of a mammalian Nanos homolog, human NANOS1 ( NOS1). We show that human NOS1 protein interacts with the human PUMILIO-2 (PUM2) protein via highly conserved domains to form a stable complex. We also show that in men, the NOS1 and PUM2 proteins are particularly abundant in germline stem cells. These observations mirror those in distant species and document for the first time a conserved protein-protein interaction in germ cells from flies to humans. These results suggest the possibility that the interaction of PUM2 and NOS1 may play a conserved role in germ cell development and maintenance in humans as in model organisms.

Human Pumilio-2 is expressed in embryonic stem cells and germ cells and interacts with DAZ (Deleted in AZoospermia) and DAZ-like proteins

Early in development, a part of the embryo is set aside to become the germ cell lineage that will ultimately differentiate to form sperm and eggs and transmit genetic information to the next generation. Men with deletions encompassing the Y-chromosome DAZ genes have few or no germ cells but are otherwise healthy, indicating they harbor specific defects in formation or maintenance of germ cells. A DAZ homolog, DAZL (DAZ-Like), is found in diverse organisms, including humans and is required for germ cell development in males and/or females. We identified proteins that interact with DAZ proteins to better understand their function in human germ cells. Here, we show that PUM2, a human homolog of Pumilio, a protein required to maintain germ line stem cells in Drosophila and Caenorhabditis elegans, forms a stable complex with DAZ through the same functional domain required for RNA binding, protein-protein interactions and rescue of Pumilio mutations in flies. We also show that PUM2 is expressed predominantly in human embryonic stem cells and germ cells and colocalizes with DAZ and DAZL in germ cells. These data implicate PUM2 as a component of conserved cellular machinery that may be required for germ cell development.

Ovarian differentiation and human embryo quality. 1. Molecular and morphogenetic homologies between oocytes and embryos in Drosophila, C. elegans, Xenopus and mammals

Knowledge on the formation of oocytes and follicles in Drosophila, C. elegans and Xenopus, and the genetic regulation of polarities and embryo growth, has been related to comparable data in mammalian oocytes and embryos. Initially, details of the nature of the regulatory processes in the non-mammals are described, with considerable attention being paid to the role of individual genes and their specific functions. The molecular genetic aspects of these developmental processes are discussed in detail. Attention then turns to mammals, to identify, describe and evaluate their homologies with the lower animals and flies. Several of these homologies are described, including genes regulating primary ovarian failure and various aspects of early embryonic growth. The polarized distribution of genes in mammalian oocytes and embyros is discussed, together with the implications in the form of differentiation in the early embryo. Morphogenetic systems operative during follicle maturation, fertilization and cleavage are described and related to similar processes in lower forms. These events include ooplasmic and pronuclear rotations, the form of ooplasmic inheritance in early blastomeres and the establishment of embryonic axes. Models of early mammalian development are considered.

Male infertility, genetic analysis of the DAZ genes on the human Y chromosome and genetic analysis of DNA repair

Many genes that are required for fertility have been identified in model organisms (). Mutations in these genes cause infertility due to defects in development of the germ cell lineage, but the organism is otherwise healthy. Although human reproduction is undoubtedly as complex as that of other organisms, very few fertility loci have been mapped (). This is in spite of the prevalence of human infertility, the lack of effective treatments to remedy germ cell defects, and the cost to couples and society of assisted reproductive techniques. Fifteen percent of couples are infertile and half of all cases can be traced to the male partner. Aside from defects in sperm production, most infertile men are otherwise healthy. This review is divided into two distinct parts to discuss work that: (i) led to the identification of several genes on the Y chromosome that likely function in sperm production; and (ii) implicates DNA repair in male infertility via increased frequency of mutations in DNA from men with meiotic arrest.

Characterization of the genomic organization, localization and expression of four PRY genes (PRY1, PRY2, PRY3 and PRY4)

PRY (PTP-BL related on the Y chromosome) has been proposed as a candidate spermatogenesis gene. We report the characterization of the genomic structure, the number of copies on the Y chromosome and the expression of the gene. By comparison of the cDNA sequence with the genomic sequence, five exons were identified. Analysis of GenBank-derived clones on the Y chromosome revealed the presence of two full-length copies in azoospermia factor region b (AZFb) (PRY1 and PRY2) and two shorter versions of the PRY gene containing exons 3, 4 and 5 in AZFc (PRY3 and PRY4). A clone containing sequences homologous to exons 3, 4 and 5 is located in area 5L (between AZFa and AZFb), a clone containing a sequence homologous to exon 5 is located in area 5M (in AZFb) and a clone containing a fragment homologous to exon 3 is located in 6F. A repeat structure of exons 1 and 2 is present on the short arm of the Y chromosome as well as on the long arm. PRY1 and PRY2, two gene copies that are located in AZFb, a region often deleted in patients with severe male infertility, were shown to be expressed in the testis. PRY may therefore play an important role in spermatogenesis.

A gene family required for human germ cell development evolved from an ancient meiotic gene conserved in metazoans

The Deleted in AZoospermia (DAZ) genes encode potential RNA-binding proteins that are expressed exclusively in prenatal and postnatal germ cells and are strong candidates for human fertility factors. Here we report the identification of an additional member of the DAZ gene family, which we have called BOULE. With the identification of this gene, it is clear that the human DAZ gene family contains at least three members: DAZ, a Y-chromosome gene cluster that arose 30-40 million years ago and whose deletion is linked to infertility in men; DAZL, the "father" of DAZ, a gene that maps to human chromosome 3 and has homologs required for both female and male germ cell development in other organisms; and BOULE, a gene that we propose is the "grandfather" of DAZ and maps to human chromosome 2. Human and mouse BOULE resemble the invertebrate meiotic regulator Boule, the proposed ortholog of DAZ, in sequence and expression pattern and hence likely perform a similar meiotic function. In contrast, the previously identified human DAZ and DAZL are expressed much earlier than BOULE in prenatal germ stem cells and spermatogonia; DAZL also is expressed in female germ cells. These data suggest that homologs of the DAZ gene family can be grouped into two subfamilies (BOULE and DAZL) and that members of the DAZ family evolved from an ancestral meiotic regulator, Boule, to assume distinct, yet overlapping, functions in germ cell development.

Increased frequency of mutations in DNA from infertile men with meiotic arrest

In diverse organisms from yeast to mice, mutations in numerous genes required for DNA repair may lead to defects in meiosis. Although it is likely that meiosis is conserved throughout evolution, little is known about the genetics of meiosis in humans even though meiotic arrest associated with azoospermia is common. In this work, we compared the sequence fidelity of a polymorphic marker amplified from DNA of two groups of patients: those with testis biopsy suggesting meiotic arrest and those with normal spermatogenesis who were obstructed. We demonstrated that mutations are more common in DNA from testicular tissue derived from men with meiotic arrest than in DNA from testicular tissue derived from men with normal spermatogenesis and physical obstruction (P < 0.05). No mutations were observed in blood tissue from either group of men. This suggests the possibility that defects in genes required in DNA repair could contribute to meiotic arrest in men just as has been observed in other organisms.

Association of the mouse infertility factor DAZL1 with actively translating polyribosomes

The DAZ (Deleted in AZoospermia) gene family was isolated from a region of the human Y chromosome long arm that is deleted in about 10% of infertile men with idiopathic azoospermia. DAZ and an autosomal DAZ-like gene, DAZL1, are expressed in germ cells only. They encode proteins with an RNA recognition motif and with either a single copy (in DAZL1) or multiple copies (in DAZ) of a DAZ repeat. A role for DAZL1 and DAZ in spermatogenesis is supported by their homology to a Drosophila male infertility protein Boule and by sterility of Dazl1 knock-out mice. The biological function of these proteins remains unknown. We found that DAZL1 and DAZ bound similarly to various RNA homopolymers in vitro. We also used an antibody against the human DAZL1 to determine the subcellular localization of DAZL1 in mouse testis. The sedimentation profiles of DAZL1 in sucrose gradients indicate that DAZL1 is associated with polyribosomes, and further capture of DAZL1 on oligo(dT) beads demonstrates that the association is mediated through the binding of DAZL1 to poly(A) RNA. Our results suggest that DAZL1 is involved in germ-cell specific regulation of mRNA translation.

Genetics and male infertility

This article reviews chromosomal and genetic disorders in the context of male fertility. Particular emphasis is on those disorders, which are encountered, in clinical practice including Klinefelter's syndrome, Kallman's syndrome, Androgen insensitivity, Y microdeletions, Y fertility gene deletions, and cystic fibrosis gene mutations. These disorders are discussed in relation to the aetiology of male fertility and also risks to children who are born of fathers with these disorders. A list of fathers' categories is proposed for outcome studies for children born after IVF-ICSI. Finally a question is proposed to catalyse debate about germ line therapy.

Identification of two novel proteins that interact with germ-cell-specific RNA-binding proteins DAZ and DAZL1

The human DAZ (deleted in azoospermia) gene family on the Y chromosome and an autosomal DAZ-like gene, DAZL1, encode RNA-binding proteins that are expressed exclusively in germ cells. Their role in spermatogenesis is supported by their homology with a Drosophila male infertility gene boule and sterility of Daz11 knock-out mice. While all mammals contain a DAZL1 homologue on their autosomes, DAZ homologues are present only on the Y chromosomes of great apes and Old World monkeys. The DAZ and DAZL1 proteins differ in the copy numbers of a DAZ repeat and the C-terminal sequences. We studied the interaction of DAZ and DAZL1 with other proteins as an approach to investigate functional similarity between these two proteins. Using DAZ as bait in a yeast two-hybrid system, we isolated two DAZAP (DAZ-associated protein) genes. DAZAP1 encodes a novel RNA-binding protein that is expressed most abundantly in the testis, and DAZAP2 encodes a ubiquitously expressed protein with no recognizable functional motif. DAZAP1 and DAZAP2 bind similarly to both DAZ and DAZL1 through the DAZ repeats. The DAZAP genes were mapped to chromosomal regions 19p13.3 and 2q33-q34, respectively, where no genetic diseases affecting spermatogenesis are known to map.