Dazl can bind to dynein motor complex and may play a role in transport of specific mRNAs

AXDND1 is required to balance spermatogonial commitment and for sperm tail formation in mice and humans

Dynein complexes are large, multi-unit assemblies involved in many biological processes via their critical roles in protein transport and axoneme motility. Using next-generation sequencing of infertile men presenting with low or no sperm in their ejaculates, we identified damaging variants in the dynein-related gene AXDND1. We thus hypothesised that AXDND1 is a critical regulator of male fertility. To test this hypothesis, we produced a knockout mouse model. Axdnd1-/- males were sterile at all ages but presented with an evolving testis phenotype wherein they could undergo one round of histologically replete spermatogenesis followed by a rapid depletion of the seminiferous epithelium. Marker experiments identified a role for AXDND1 in maintaining the balance between differentiation-committed and self-renewing spermatogonial populations, resulting in disproportionate production of differentiating cells in the absence of AXDND1 and increased sperm production during initial spermatogenic waves. Moreover, long-term spermatogonial maintenance in the Axdnd1 knockout was compromised, ultimately leading to catastrophic germ cell loss, destruction of blood-testis barrier integrity and immune cell infiltration. In addition, sperm produced during the first wave of spermatogenesis were immotile due to abnormal axoneme structure, including the presence of ectopic vesicles and abnormalities in outer dense fibres and microtubule doublet structures. Sperm output was additionally compromised by a severe spermiation defect and abnormal sperm individualisation. Collectively these data identify AXDND1 as an atypical dynein complex-related protein with a role in protein/vesicle transport of relevance to spermatogonial function and sperm tail formation in mice and humans. This study underscores the importance of studying the consequences of gene loss-of-function on both the establishment and maintenance of male fertility.

High cholesterol diet-induced testicular dysfunction in rats

PURPOSE

Hypercholesterolemia due to a high-cholesterol diet is linked to numerous diseases and may lead to male infertility. However, the underlying mechanism remains unknown. The maintenance of male fertility requires intact testicular structures (including seminiferous tubules and mesenchyme) and functioning cells (Leydig cells, Sertoli cells and germ cells, etc.), production of appropriate concentrations of sex hormones, and cooperation among testicular cells. Thus, we considered whether male fertility declined as the structure and function of testicular cells were altered in rats on a high-cholesterol diet.

METHODS

Male Sprague Dawley rats were fed either a standard or a high-cholesterol diet for 16 weeks. Serum sex hormones, lipid components, semen quality, and fertility rate were assayed in the rats. The 3β-hydroxysteroid dehydrogenase (3β-HSD), Wilms tumor 1 (WT-1), and deleted in azoospermia-like (DAZL) were regarded as specific markers of Leydig, Sertoli, and germ cells in rats. In addition, the ultrastructure of the testis and expression levels of particular marker molecules of testicular cells were further investigated.

RESULTS

Compared to rats fed on a regular diet, the serum testosterone levels and sperm progressive motility decreased in rats fed high cholesterol. Moreover, we observed a deformed nucleus, dilated smooth endoplasmic reticulum, and swollen mitochondria of Leydig cells and a schizolytic nucleus of Sertoli cells in rats on a high-cholesterol diet. The 3β-HSD, WT-1, and DAZL protein expression levels were significantly reduced in rats on a high-cholesterol diet.

CONCLUSIONS

Our results showed that a high-cholesterol diet adversely affected testosterone production and sperm progressive motility, possibly due to Leydig, Sertoli, and germ cell abnormalities.

AXDND1 is required to balance spermatogonial commitment and for sperm tail formation in mice and humans

Dynein complexes are large, multi-unit assemblies involved in many biological processes including male fertility via their critical roles in protein transport and axoneme motility. Previously we identified a pathogenic variant in the dynein gene AXDND1 in an infertile man. Subsequently we identified an additional four potentially compound heterozygous variants of unknown significance in AXDND1 in two additional infertile men. We thus tested the role of AXDND1 in mammalian male fertility by generating a knockout mouse model. Axdnd1 -/- males were sterile at all ages but could undergo one round of histologically complete spermatogenesis. Subsequently, a progressive imbalance of spermatogonial commitment to spermatogenesis over self-renewal occurred, ultimately leading to catastrophic germ cell loss, loss of blood-testis barrier patency and immune cell infiltration. Sperm produced during the first wave of spermatogenesis were immotile due to abnormal axoneme structure, including the presence of ectopic vesicles and abnormalities in outer dense fibres and microtubule doublet structures. Sperm output was additionally compromised by a severe spermiation defect and abnormal sperm individualisation. Collectively, our data highlight the essential roles of AXDND1 as a regulator of spermatogonial commitment to spermatogenesis and during the processes of spermiogenesis where it is essential for sperm tail development, release and motility.

Interactions between two regulatory proteins of microtubule dynamics, HDAC6, TPPP/p25, and the hub protein, DYNLL/LC8

Degradation of unwanted proteins is important in protein quality control cooperating with the dynein/dynactin-mediated trafficking along the acetylated microtubule (MT) network. Proteins associated directly/indirectly with tubulin/MTs play crucial roles in both physiological and pathological processes. Our studies focus on the interrelationship of the tubulin deacetylase HDAC6, the MT-associated TPPP/p25 with its deacetylase inhibitory potency and the hub dynein light chain DYNLL/LC8, constituent of dynein and numerous other protein complexes. In this paper, evidence is provided for the direct interaction of DYNLL/LC8 with TPPP/p25 and HDAC6 and their assembly into binary/ternary complexes with functional potency. The in vitro binding data was obtained with recombinant proteins and used for mathematical modelling. These data and visualization of their localizations by bimolecular fluorescence complementation technology and immunofluorescence microscopy in HeLa cells revealed the promoting effect of TPPP/p25 on the interaction of DYNLL/LC8 with both tubulin and HDAC6. Localization of the LC8-2-TPPP/p25 complex was observed on the MT network in contrast to the LC8-2-HDAC6 complex, which was partly translocated to the nucleus. LC8-2 did not influence directly the acetylation of the MT network. However, the binding of TPPP/p25 to a new binding site of DYNLL/LC8, outside the canonical binding groove, counteracted the TPPP/p25-derived hyperacetylation of the MT network. Our data suggest that multiple associations of the regulatory proteins of the MT network could ensure fine tuning in the regulation of the intracellular trafficking process either by the complexation of DYNLL/LC8 with new partners or indirectly by the modulation of the acetylation level of the MT network.

The chaperone dynein LL1 mediates cytoplasmic transport of empty and mature hepatitis B virus capsids

BACKGROUND & AIMS

Hepatitis B virus (HBV) has a DNA genome but replicates within the nucleus by reverse transcription of an RNA pregenome, which is converted to DNA in cytoplasmic capsids. Capsids in this compartment are correlated with inflammation and epitopes of the capsid protein core (Cp) are a major target for T cell-mediated immune responses. We investigated the mechanism of cytoplasmic capsid transport, which is important for infection but also for cytosolic capsid removal.

METHODS

We used virion-derived capsids containing mature rcDNA (matC) and empty capsids (empC). RNA-containing capsids (rnaC) were used as a control. The investigations comprised pull-down assays for identification of cellular interaction partners, immune fluorescence microscopy for their colocalization and electron microscopy after microinjection to determine their biological significance.

RESULTS

matC and empC underwent active transport through the cytoplasm towards the nucleus, while rnaC was poorly transported. We identified the dynein light chain LL1 as a functional interaction partner linking capsids to the dynein motor complex and showed that there is no compensatory transport pathway. Using capsid and dynein LL1 mutants we characterized the required domains on the capsid and LL1.

CONCLUSIONS

This is the first investigation on the detailed molecular mechanism of how matC pass the cytoplasm upon infection and how empC can be actively removed from the cytoplasm into the nucleus. Considering that hepatocytes with cytoplasmic capsids are better recognized by the T cells, we hypothesize that targeting capsid DynLL1-interaction will not only block HBV infection but also stimulate elimination of infected cells.

LAY SUMMARY

In this study, we identified the molecular details of HBV translocation through the cytoplasm. Our evidence offers a new drug target which could not only inhibit infection but also stimulate immune clearance of HBV infected cells.

Transcriptional regulation of P63 on the apoptosis of male germ cells and three stages of spermatogenesis in mice

Infertility affects 10-15% of couples worldwide, and male factors account for 50%. Spermatogenesis is precisely regulated by genetic factors, and the mutations of genes result in abnormal spermatogenesis and eventual male infertility. The aim of this study was to explore the role and transcriptional regulation of P63 in the apoptosis and mouse spermatogenesis. P63 protein was decreased in male germ cells of P63^(+/-) mice compared with wild-type mice. There was no obvious difference in testis weight, sperm motility, and fecundity between P63^(+/-) and wild-type mice. However, abnormal germ cells were frequently observed in P63^(+/-) mice at 2 months old. Notably, apoptotic male germ cells and the percentage of abnormal sperm were significantly enhanced in P63^(+/-) mice compared to wild-type mice. Spermatogonia, pachytene spermatocytes and round spermatids were isolated from P63^(+/-) and wild-type mice using STA-PUT velocity sedimentation, and they were identified phenotypically with high purities. RNA sequencing demonstrated distinct transcription profiles in spermatogonia, pachytene spermatocytes, and round spermatids between P63^(+/-) mice and wild-type mice. In total, there were 645 differentially expressed genes (DEGs) in spermatogonia, 106 DEGs in pachytene spermatocytes, and 1152 in round spermatids between P63^(+/-) mice and wild-type mice. Real time PCR verified a number of DEGs identified by RNA sequencing. Gene ontology annotation and pathway analyzes further indicated that certain key genes, e.g., Ccnd2, Tgfa, Hes5, Insl3, Kit, Lef1, and Jun were involved in apoptosis, while Dazl, Kit, Pld6, Cdkn2d, Stra8, and Ubr2 were associated with regulating spermatogenesis. Collectively, these results implicate that P63 mediates the apoptosis of male germ cells and regulates three stages of spermatogenesis transcriptionally. This study could provide novel targets for the diagnosis and treatment of male infertility.

The Drosophila LC8 homolog cut up specifies the axonal transport of proteasomes

Because of their functional polarity and elongated morphologies, microtubule-based transport of proteins and organelles is critical for normal neuronal function. The proteasome is required throughout the neuron for the highly regulated degradation of a broad set of protein targets whose functions underlie key physiological responses, including synaptic plasticity and axonal degeneration. Molecularly, the relationship between proteasome transport and the transport of the targets of proteasomes is unclear. The dynein motor complex is required for the microtubule-based motility of numerous proteins and organelles in neurons. Here, we demonstrate that microtubule-based transport of proteasomes within the neuron in Drosophila utilizes a different dynein light chain to that used by synaptic proteins. Live imaging of proteasomes and synaptic vesicle proteins in axons and synapses finds that these cargoes traffic independently, and that proteasomes exhibit significantly reduced retrograde transport velocities compared to those of synaptic vesicle proteins. Genetic and biochemical analyses reveals that the Drosophila homolog of the LC8 dynein light chains (mammalian DYNLL1 and DYNLL2), called Cut up, binds proteasomes and functions specifically during their transport. These data support the model that Cut up functions to specify the dynein-mediated transport of neuronal proteasomes.

BOULE, a Deleted in Azoospermia Homolog, Is Recruited to Stress Granules in the Mouse Male Germ Cells

High temperature adversely affects normal development of male germ cells in mammals. Acute heat stress induces the formation of stress granules (SGs) in a set of male germ cells, and the SGs have been proposed to protect those cells from heat-induced apoptosis. DAZL, one of DAZ (Deleted in Azoospermia) family proteins, was shown to be an essential component of SGs, which is required for SG formation in the mouse testis. In the present study, we asked whether BOULE, the founding member of DAZ family proteins, is a component of the SGs. We show that BOULE is recruited to the SGs upon heat stress, and that these SGs are developmental stage-specific. These results suggest that DAZ family proteins may have conserved roles in the SGs of male germ cells.

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.

Maternal dazap2 Regulates Germ Granules by Counteracting Dynein in Zebrafish Primordial Germ Cells

Primordial germ cells (PGCs) are the stem cells of the germline. Generally, germline induction occurs via zygotic factors or the inheritance of maternal determinants called germ plasm (GP). GP is packaged into ribonucleoprotein complexes within oocytes and later promotes the germline fate in embryos. Once PGCs are specified by either mechanism, GP components localize to perinuclear granular-like structures. Although components of zebrafish PGC germ granules have been studied, the maternal factors regulating their assembly and contribution to germ cell development are unknown. Here, we show that the scaffold protein Dazap2 binds to Bucky ball, an essential regulator of oocyte polarity and GP assembly, and colocalizes with the GP in oocytes and in PGCs. Mutational analysis revealed a requirement for maternal Dazap2 (MDazap2) in germ-granule maintenance. Through molecular epistasis analyses, we show that MDazap2 is epistatic to Tdrd7 and maintains germ granules in the embryonic germline by counteracting Dynein activity.

Scaffold remodeling in space and time controls synaptic transmission

Scaffolding proteins that are associated with glutamate receptors in dendritic spines govern the location and function of receptors to control synaptic transmission. Unraveling the spatio-temporal dynamics of protein-protein interactions within components of the scaffolding complex will bring to light the function of these interactions. Combining bioluminescence resonance energy transfer (BRET) imaging to electrophysiological recordings, we have recently shown that GKAP, a core protein of the scaffolding complex, interacts with DLC2, a protein associated with molecular motors. Synaptic activity-induced GKAP-DLC2 interaction in spines stabilizes the scaffolding complex and enhances the NMDA currents. Interestingly, this work placed emphasis on the bioarchitectural dependence of protein-protein interaction dynamics. Depending on physiological conditions, the modulation in space and time of protein-protein interaction is acutely regulated, engendering a subtle control of synaptic transmission in the state of the individual synapse.

Ribonomic analysis of human DZIP1 reveals its involvement in ribonucleoprotein complexes and stress granules

BACKGROUND

DZIP1 (DAZ-interacting protein 1) has been described as a component of the Hh signaling pathway with a putative regulatory role in ciliogenesis. DZIP1 interacts with DAZ RNA binding proteins in embryonic stem cells and human germ cells suggesting a role in mRNA regulation.

RESULTS

We investigated DZIP1 function in HeLa cells and its involvement in ribonucleoprotein complexes. DZIP1 was predominantly located in granules in the cytoplasm. Under oxidative stress conditions, DZIP1 re-localized to stress granules. DZIP appears to be important for the formation of stress granules during the stress response. We used immunoprecipitation assays with antibodies against DZIP1 and microarray hybridization to identify mRNAs associated with DZIP1. The genetic networks formed by the DZIP1-associated mRNAs were involved in cell cycle and gene expression regulation. DZIP1 is involved in the Hedgehog signaling pathway. We used cyclopamine, a specific inhibitor of this pathway, to analyze the expression of DZIP1 and its associated mRNAs. The abundance of DZIP1-associated mRNAs increased with treatment; however, the silencing or overexpression of DZIP1 in HeLa cells had no effect on the accumulation of the associated mRNAs. Polysomal profile analysis by sucrose gradient centrifugation demonstrated the presence of DZIP1 in the polysomal fraction.

CONCLUSIONS

Our results suggest that DZIP1 is part of an RNP complex that occupies various subcellular locations. The diversity of the mRNAs associated with DZIP1 suggests that this protein is a component of different RNPs associated with translating polysomes and with RNA granules.

Association between DAZL polymorphisms and susceptibility to male infertility: systematic review with meta-analysis and trial sequential analysis

Several studies have investigated the association between polymorphisms in the Deleted in AZoospermia-Like (DAZL) gene and male infertility risk, but with inconsistent results. We aimed to derive a more precise estimation of the relationship, therefore a meta-analysis was performed. A total of 13 case-control studies, including 2556 cases and 1997 controls, were selected. Two polymorphisms in DAZL were investigated, namely T12A (Thr12 → Ala) and T54A (Thr54 → Ala). Our meta-analysis showed that A > G is a risk factor for male infertility (P = 0.047, OR = 1.262, 95%CI = 1.003–1.587). However, when using trial sequential analysis (TSA) to confirm, we found that A > G risk effect turned out to be false positive. In addition, significant association was found between the T54A polymorphism and male infertility under co-dominant model (AG vs. AA: OR = 4.364, 95%CI = 2.207–8.630, P < 0.001) and dominant model (OR = 4.584, 95%CI = 2.320–9.058, P < 0.001). Stratified analysis showed that significantly strong association between T54A polymorphism and male infertility was present only in Asians, but not in Caucasians. Further studies of T12A and T54A with their biological functions are needed to understand the role of these polymorphisms in the development of male infertility.

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.

NMR Characterization of Self-Association Domains Promoted by Interactions with LC8 Hub Protein

Most proteins in interaction networks have a small number of partners, while a few, called hubs, participate in a large number of interactions and play a central role in cell homeostasis. One highly conserved hub is a protein called LC8 that was originally identified as an essential component of the multi-subunit complex dynein but later shown to be also critical in multiple protein complexes in diverse systems. What is intriguing about this hub protein is that it does not passively bind its various partners but emerging evidence suggests that LC8 acts as a dimerization engine that promotes self-association and/or higher order organization of its primarily disordered monomeric partners. This structural organization process does not require ATP but is triggered by long-range allosteric regulation initiated by LC8 binding a pair of disordered chains forming a bivalent or polybivalent scaffold. This review focuses on the role of LC8 in promoting self-association of two of its binding partners, a dynein intermediate chain and a non dynein protein called Swallow.

Stoichiometry of scaffold complexes in living neurons - DLC2 as a dimerization engine for GKAP

Quantitative spatio-temporal characterization of protein interactions in living cells remains a major challenge facing modern biology. We have investigated in living neurons the spatial dependence of the stoichiometry of interactions between two core proteins of the NMDA receptor-associated scaffolding complex, GKAP and DLC2, using a novel variation of Fluorescence Fluctuation Microscopy called two-photon scanning Number and Brightness (sN&B). We found that dimerization of DLC2 was required for its interaction with GKAP, which in turn potentiated GKAP self-association. In dendritic shaft, the DLC2-GKAP hetero-oligomeric complexes were composed mainly of 2 DLC2 and 2 GKAP monomers, while in spines, the hetero-complexes were much larger, with an average of ∼16 DLC2 and ∼13 GKAP. Disruption of the GKAP-DLC2 interaction strongly destabilized the oligomers, decreasing the spine-preferential localization of GKAP and inhibiting NMDA receptor activity. Hence, DLC2 serves a hub function in the control of glutamatergic transmission via ordering of GKAP-containing complexes in dendritic spines. Beyond illuminating the role of DLC2–GKAP interactions in glutamergic signalling, these data underscore the power of the sN&B approach for quantitative spatio-temporal imaging of other important protein complexes.

A developmental stage-specific switch from DAZL to BOLL occurs during fetal oogenesis in humans, but not mice

The Deleted in Azoospermia gene family encodes three germ cell-specific RNA-binding proteins (DAZ, DAZL and BOLL) that are essential for gametogenesis in diverse species. Targeted disruption of Boll in mice causes male-specific spermiogenic defects, but females are apparently fertile. Overexpression of human BOLL promotes the derivation of germ cell-like cells from genetically female (XX), but not male (XY) human ES cells however, suggesting a functional role for BOLL in regulating female gametogenesis in humans. Whether BOLL is expressed during oogenesis in mammals also remains unclear. We have therefore investigated the expression of BOLL during fetal oogenesis in humans and mice. We demonstrate that BOLL protein is expressed in the germ cells of the human fetal ovary, at a later developmental stage than, and almost mutually-exclusive to, the expression of DAZL. Strikingly, BOLL is downregulated, and DAZL re-expressed, as primordial follicles form, revealing BOLL expression to be restricted to a narrow window during fetal oogenesis. By quantifying the extent of co-expression of DAZL and BOLL with markers of meiosis, we show that this window likely corresponds to the later stages of meiotic prophase I. Finally, we demonstrate that Boll is also transiently expressed during oogenesis in the fetal mouse ovary, but is simultaneously co-expressed within the same germ cells as Dazl. These data reveal significant similarities and differences between the expression of BOLL homologues during oogenesis in humans and mice, and raise questions as to the validity of the Boll(-/-) mouse as a model for understanding BOLL function during human oogenesis.

Heat stress response of male germ cells

The vast majority of mammalian testes are located outside the body cavity for proper thermoregulation. Heat has an adverse effect on mammalian spermatogenesis and eventually leads to sub- or infertility. Recent studies have provided insights into the molecular response of male germ cells to high temperatures. Here, we review the effects of heat on male germ cells and discuss the mechanisms underlying germ cell loss and impairment. We also discuss the role of translational control in male germ cells as a potential protective mechanism against heat-induced germ cell apoptosis.

Mouse Dazl and its novel splice variant functions in translational repression of target mRNAs in embryonic stem cells

Dazl (deleted in azoospermia-like) is an RNA binding protein that is important for germ cell differentiation in vertebrates. In the present study, we report the identification of a novel Dazl isoform (Dazl_Δ8) that results from alternative splicing of exon8 of mouse Dazl. We observed the expression of Dazl_Δ8 in various pluripotent cell types, but not in somatic cells. Furthermore, the Dazl_Δ8 splice variant was expressed along with the full-length isoform of Dazl (Dazl_FL) throughout male germ-cell development and in the ovary. Sub-cellular localization studies of Dazl_Δ8 revealed a diffused cytoplasmic and large granular pattern, which is similar to the localization patterns of Dazl_FL protein. In contrast to the well documented translation stimulation function in germ cells, overexpression and downregulation studies of Dazl isoforms (Dazl_FL and Dazl_Δ8) revealed a role for Dazl in the negative translational regulation of Mvh, a known target of Dazl, as well as Oct3/4 and Sox2 in embryonic stem cells (ESCs). In line with these observations, a luciferase reporter assay with the 3'UTRs of Oct3/4 and Mvh confirmed the translational repressive role of Dazl isoforms in ESCs but not in germ cells derived cell line GC-1. Further, we identified several putative target mRNAs of Dazl_FL and Dazl_Δ8 in ESCs through RNA-binding immunoprecipitation followed by whole genome transcriptome analysis. Collectively, our results show a translation repression function of Dazl in pluripotent stem cells.

Sex, rebellion and decadence: the scandalous evolutionary history of the human Y chromosome

It can be argued that the Y chromosome brings some of the spirit of rock&roll to our genome. Equal parts degenerate and sex-driven, the Y has boldly rebelled against sexual recombination, one of the sacred pillars of evolution. In evolutionary terms this chromosome also seems to have adopted another of rock&roll's mottos: living fast. Yet, it appears to have refused to die young. In this manuscript the Y chromosome will be analyzed from the intersection between structural, evolutionary and functional biology. Such integrative approach will present the Y as a highly specialized product of a series of remarkable evolutionary processes. These led to the establishment of a sex-specific genomic niche that is maintained by a complex balance between selective pressure and the genetic diversity introduced by intrachromosomal recombination. Central to this equilibrium is the "polish or perish" dilemma faced by the male-specific Y genes: either they are polished by the acquisition of male-related functions or they perish via the accumulation of inactivating mutations. Thus, understanding to what extent the idiosyncrasies of Y recombination may impact this chromosome's role in sex determination and male germline functions should be regarded as essential for added clinical insight into several male infertility phenotypes. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

DAZL is essential for stress granule formation implicated in germ cell survival upon heat stress

Mammalian male germ cells should be maintained below body temperature for proper development. Here, we investigated how male germ cells respond to heat stress. A short exposure of mouse testes to core body temperature induced phosphorylation of eIF2α and the formation of stress granules (SGs) in male germ cells. We observed that DAZL, a germ cell-specific translational regulator, was translocated to SGs upon heat stress. Furthermore, SG assembly activity was significantly diminished in the early male germ cells of Dazl-knockout mice. The DAZL-containing SGs played a protective role against heat stress-induced apoptosis by the sequestration of specific signaling molecules, such as RACK1, and the subsequent blockage of the apoptotic MAPK pathway. Based on these results, we propose that DAZL is an essential component of the SGs, which prevent male germ cells from undergoing apoptosis upon heat stress.

GKAP-DLC2 interaction organizes postsynaptic scaffold complex to enhance synaptic NMDA receptor activity

At glutamatergic brain synapses, scaffolding proteins regulate receptor location and function. The targeting and organization of scaffolding proteins in the postsynaptic density (PSD) is poorly understood. A core protein of the glutamatergic receptor postsynaptic scaffold complex, GKAP, interacts with DLC2, a protein associated with molecular motors. In the present study, we combined BRET imaging, immuno-staining and electrophysiological recording to assess the role of GKAP-DLC2 interaction in the functional organization of the glutamatergic synapse. We found that GKAP-DLC2 interaction in dendritic spine stabilizes scaffolding protein expression at the PSD and enhances synaptic NMDA receptor activity. Moreover, the GKAP-DLC2 functional interaction is favored by sustained synaptic activity. These data provide a novel regulatory pathway of synaptic transmission that depends on activity-induced remodeling of the postsynaptic scaffold protein complex.

Molecular motor proteins and amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting motor neurons in the brain, brainstem and spinal cord, which is characterized by motor dysfunction, muscle dystrophy and progressive paralysis. Both inherited and sporadic forms of ALS share common pathological features, however, the initial trigger of neurodegeneration remains unknown. Motor neurons are uniquely targeted by ubiquitously expressed proteins in ALS but the reason for this selectively vulnerability is unclear. However motor neurons have unique characteristics such as very long axons, large cell bodies and high energetic metabolism, therefore placing high demands on cellular transport processes. Defects in cellular trafficking are now widely reported in ALS, including dysfunction to the molecular motors dynein and kinesin. Abnormalities to dynein in particular are linked to ALS, and defects in dynein-mediated axonal transport processes have been reported as one of the earliest pathologies in transgenic SOD1 mice. Furthermore, dynein is very highly expressed in neurons and neurons are particularly sensitive to dynein dysfunction. Hence, unravelling cellular transport processes mediated by molecular motor proteins may help shed light on motor neuron loss in ALS.

RNA-binding proteins, RNA granules, and gametes: is unity strength?

Changes in mRNA translation and degradation represent post-transcriptional processes operating during gametogenesis and early embryogenesis to ensure regulated protein synthesis. Numerous mRNA-binding proteins (RBPs) have been described in multiple animal models that contribute to the control of mRNA translation and decay during oogenesis and spermatogenesis. An emerging view from studies performed in germ cells and somatic cells is that RBPs associate with their target mRNAs in RNA–protein (or ribonucleoprotein) complexes (mRNPs) that assemble in various cytoplasmic RNA granules that communicate with the translation machinery and control mRNA storage, triage, and degradation. In comparison withXenopus, Caenorhabditis elegans, orDrosophila, the composition and role of cytoplasmic RNA-containing granules in mammalian germ cells are still poorly understood. However, regained interest for these structures has emerged with the recent discovery of their role in small RNA synthesis and transposon silencing through DNA methylation. In this review, we will briefly summarize our current knowledge on cytoplasmic RNA granules in murine germ cells and describe the role of some of the RBPs they contain in regulating mRNA metabolism and small RNA processing during gametogenesis.

DYNLL/LC8: a light chain subunit of the dynein motor complex and beyond

The LC8 family members of dynein light chains (DYNLL1 and DYNLL2 in vertebrates) are highly conserved ubiquitous eukaryotic homodimer proteins that interact, besides dynein and myosin 5a motor proteins, with a large (and still incomplete) number of proteins involved in diverse biological functions. Despite an earlier suggestion that LC8 light chains function as cargo adapters of the above molecular motors, they are now recognized as regulatory hub proteins that interact with short linear motifs located in intrinsically disordered protein segments. The most prominent LC8 function is to promote dimerization of their binding partners that are often scaffold proteins of various complexes, including the intermediate chains of the dynein motor complex. Structural and functional aspects of this intriguing hub protein will be highlighted in this minireview.

Comparative analysis on mRNA expression level and methylation status of DAZL gene between cattle-yaks and their parents

The autosomal gene Deleted in Azoospermia Like (DAZL) is essential for spermatogenesis. The absence of DAZL gene will lead to meiotic arrest, spermatogenetic failure and male infertility, and so it was usually considered as a candidate gene for male infertility in cattle-yaks. To study the regulatory mechanism of DAZL expression in cattle-yaks, DAZL mRNA expression and DAZL gene methylation patterns in testes of cattle, yaks and cattle-yaks were examined using real-time PCR and bisulfite sequencing. The results showed that DAZL mRNA expression in testes of cattle-yaks was lower than that in cattle and yak (about 1/2-1/3 of cattle and yak). The methylation level of DAZL in cattle-yaks (85.6%) was significantly higher than that in cattle (69.8%) and yaks (71.4%) (P<0.01). The methylation and mRNA expression level of DAZL was significantly negatively correlated in the testes of cattle-yaks and their parents (P<0.01). We propose that the methylation of DAZL gene plays an important role in DAZL transcriptional regulation and maybe have a severe effect on spermatogenesis and male sterility in cattle-yaks.

Identification and characterization of RBM44 as a novel intercellular bridge protein

Intercellular bridges are evolutionarily conserved structures that connect differentiating germ cells. We previously reported the identification of TEX14 as the first essential intercellular bridge protein, the demonstration that intercellular bridges are required for male fertility, and the finding that intercellular bridges utilize components of the cytokinesis machinery to form. Herein, we report the identification of RNA binding motif protein 44 (RBM44) as a novel germ cell intercellular bridge protein. RBM44 was identified by proteomic analysis after intercellular bridge enrichment using TEX14 as a marker protein. RBM44 is highly conserved between mouse and human and contains an RNA recognition motif of unknown function. RBM44 mRNA is enriched in testis, and immunofluorescence confirms that RBM44 is an intercellular bridge component. However, RBM44 only partially localizes to TEX14-positive intercellular bridges. RBM44 is expressed most highly in pachytene and secondary spermatocytes, but disappears abruptly in spermatids. We discovered that RBM44 interacts with itself and TEX14 using yeast two-hybrid, mammalian two-hybrid, and immunoprecipitation. To define the in vivo function of RBM44, we generated a targeted deletion of Rbm44 in mice. Rbm44 null male mice produce somewhat increased sperm, and show enhanced fertility of unknown etiology. Thus, although RBM44 localizes to intercellular bridges during meiosis, RBM44 is not required for fertility in contrast to TEX14.

The roles of the DAZ family in spermatogenesis: More than just translation?

The DAZ family of genes are important fertility factors in animals, including humans. The family consists of Y-linked DAZ, and autosomal homologs Boule and Dazl. All three genes encode RNA-binding proteins that are nearly exclusively expressed in germ cells. The DAZ family is highly conserved, with ancestral Boule present in sea anemones through humans, Dazl conserved among vertebrates, and DAZ present only in higher primates. Here we review studies on DAZ family genes from multiple organisms, and summarize the common features of each DAZ gene and their roles during spermatogenesis in animals. DAZ family proteins are thought to activate the translation of RNA targets, but recent work has uncovered additional functions. Boule, Dazl, and DAZ likely function through similar mechanisms, and we present known functions of the DAZ family in spermatogenesis, and discuss possible mechanisms in addition to translation activation.

Genetic dissection of the AZF regions of the human Y chromosome: thriller or filler for male (in)fertility?

The azoospermia factor (AZF) regions consist of three genetic domains in the long arm of the human Y chromosome referred to as AZFa, AZFb and AZFc. These are of importance for male fertility since they are home to genes required for spermatogenesis. In this paper a comprehensive analysis of AZF structure and gene content will be undertaken. Particular care will be given to the molecular mechanisms underlying the spermatogenic impairment phenotypes associated to AZF deletions. Analysis of the 14 different AZF genes or gene families argues for the existence of functional asymmetries between the determinants; while some are prominent players in spermatogenesis, others seem to modulate more subtly the program. In this regard, evidence supporting the notion that DDX3Y, KDM5D, RBMY1A1, DAZ, and CDY represent key AZF spermatogenic determinants will be discussed.

Testis transcriptome analysis in male infertility: new insight on the pathogenesis of oligo-azoospermia in cases with and without AZFc microdeletion

BACKGROUND

About 10% of cases of male infertility are due to the presence of microdeletions within the long arm of the Y chromosome (Yq). Despite the large literature covering this critical issue, very little is known about the pathogenic mechanism leading to spermatogenesis disruption in patients carrying these microdeletions. In order to identify the presence of specific molecular pathways leading to spermatogenic damage, testicular gene expression profiling was carried out by employing a microarray assay in 16 patients carrying an AZFc microdeletion or affected by idiopathic infertility. Hierarchical clustering was performed pooling the data set from 26 experiments (16 patients, 10 replicates).

RESULTS

An intriguing and unexpected finding is that all the samples showing the AZFc deletion cluster together irrespectively of their testicular phenotypes. This cluster, including also four patients affected by idiopathic infertility, showed a downregulation of several genes related to spermatogenesis that are mainly involved in testicular mRNA storage. Interestingly, the four idiopathic patients present in the cluster showed no testicular expression of DAZ despite the absence of AZFc deletion in the peripheral blood.

CONCLUSIONS

Our expression profiles analysis indicates that several forms of infertility can be triggered by a common pathogenic mechanism that is likely related to alterations in testicular mRNA storage. Our data suggest that a lack of testicular DAZ gene expression may be the trigger of such mechanism. Furthermore, the presence of AZFc deletions in mosaic or the loss of function of AZFc genes in absence of Yq deletion can perhaps explain these findings. Finally, based on our data, it is intriguing to hypothesize that DAZ gene dysfunctions can account for a larger number of previously thought "idiopathic" infertility cases and investigation of such testicular gene dysfunction can be important to reveal the molecular determinant of infertility than are undetected when only testing Yq deletions in peripheral blood.

The AZFc region of the Y chromosome: at the crossroads between genetic diversity and male infertility

BACKGROUND

The three azoospermia factor (AZF) regions of the Y chromosome represent genomic niches for spermatogenesis genes. Yet, the most distal region, AZFc, is a major generator of large-scale variation in the human genome. Determining to what extent this variability affects spermatogenesis is a highly contentious topic in human reproduction.

METHODS

In this review, an extensive characterization of the molecular mechanisms responsible for AZFc genotypical variation is undertaken. Such data are complemented with the assessment of the clinical consequences for male fertility imputable to the different AZFc variants. For this, a critical re-evaluation of 23 association studies was performed in order to extract unifying conclusions by curtailing methodological heterogeneities.

RESULTS

Intrachromosomal homologous recombination mechanisms, either crossover or non-crossover based, are the main drivers for AZFc genetic diversity. In particular, rearrangements affecting gene dosage are the most likely to introduce phenotypical disruptions in the spermatogenic profile. In the specific cases of partial AZFc deletions, both the actual existence and the severity of the spermatogenic defect are dependent on the evolutionary background of the Y chromosome.

CONCLUSIONS

AZFc is one of the most genetically dynamic regions in the human genome. This property may serve as counter against the genetic degeneracy associated with the lack of a meiotic partner. However, such strategy comes at a price: some rearrangements represent a risk factor or a de-facto causative agent of spermatogenic disruption. Interestingly, this precarious balance is modulated, among other yet unknown factors, by the evolutionary history of the Y chromosome.

Evolutionary conservation of Dazl genomic organization and its continuous and dynamic distribution throughout germline development in gynogenetic gibel carp

To investigate germline development and germ cell specification, we identified a Dazl homolog (CagDazl) from gynogenetic gibel carp (Carassius auratus gibelio). Its cDNA sequence and BAC clone sequence analyses revealed the genomic organization conservation and conserved synteny of the Dazl family members and their neighborhood genes among vertebrates, especially in fish. Moreover, a polyclonal antibody specific to CagDazl was produced and used to examine its expression and distribution throughout germline development at protein level. Firstly, ovary-specific expression pattern of CagDazl was confirmed in adult tissues by RT-PCR and Western blot. In addition, in situ hybridization and immunofluorescence localization demonstrated its specific expression in germ cells, and both its transcript and protein were localized to germ plasm. Then, co-localization of CagDazl and mitochondrial cloud was found, confirming that CagDazl transcript and its protein are germ plasm component and move via METRO pathway during oogenesis. Furthermore, the CagDazl is abundant and continuous throughout germline development and germ cell specification including primordial germ cell (PGC) formation, oogonium differentiation, oocyte development, and embryogenesis, and the dynamic distribution occurs at different development stages. The data suggest that maternal CagDazl might play an important role in gibel carp PGC formation. Therefore, CagDazl is a useful and specific marker for tracing germ plasm and germ cell development in the gynogenetic gibel carp. In addition, in comparison with previous studies in sexual reproduction species, the continuous and dynamic distribution of CagDazl protein in the germ plasm throughout the life cycle seems to have significant implication in sex evolution of vertebrates.

A role for dynein in the inhibition of germ cell proliferative fate

During normal development as well as in diseased states such as cancer, extracellular "niches" often provide cues to proximal cells and activate intracellular pathways. Activation of such signaling pathways in turn instructs cellular proliferation and differentiation. In the Caenorhabditis elegans gonad, GLP-1/Notch signaling instructs germ line stem cells to self-renew through mitotic cell division. As germ cells progressively move out of the niche, they differentiate by entering meiosis and eventually form gametes. In this model system, we uncovered an unexpected role for the dynein motor complex in promoting normal differentiation of proliferating germ cells. We demonstrate that dynein light chain 1 (DLC-1) and its partner, dynein heavy chain 1, inhibit the proliferative cell fate, in part through regulation of METT-10, a conserved putative methyltransferase. We show that DLC-1 physically interacts with METT-10 and promotes both its overall levels and nuclear accumulation. Our results add a new dimension to the processes controlled by the dynein motor complex, demonstrating that dynein can act as an antiproliferative factor.

Dynein light chain regulates axonal trafficking and synaptic levels of Bassoon

Bassoon and the related protein Piccolo are core components of the presynaptic cytomatrix at the active zone of neurotransmitter release. They are transported on Golgi-derived membranous organelles, called Piccolo-Bassoon transport vesicles (PTVs), from the neuronal soma to distal axonal locations, where they participate in assembling new synapses. Despite their net anterograde transport, PTVs move in both directions within the axon. How PTVs are linked to retrograde motors and the functional significance of their bidirectional transport are unclear. In this study, we report the direct interaction of Bassoon with dynein light chains (DLCs) DLC1 and DLC2, which potentially link PTVs to dynein and myosin V motor complexes. We demonstrate that Bassoon functions as a cargo adapter for retrograde transport and that disruption of the Bassoon-DLC interactions leads to impaired trafficking of Bassoon in neurons and affects the distribution of Bassoon and Piccolo among synapses. These findings reveal a novel function for Bassoon in trafficking and synaptic delivery of active zone material.

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.

Polymorphic expression of DAZ proteins in the human testis

BACKGROUND

DAZ is a male infertility gene located at the AZFc region of the Y chromosome. There are four copies of the DAZ gene that share a strong homology but are not identical to one another. In the present study, we carried out cDNA cloning and immunoblot analyses to determine whether all of the DAZ genes are actively expressed in the human testis.

METHODS

AZFc deletion was detected by sequence-tagged site polymerase chain reaction (PCR) of genomic DNA isolated from blood samples. DAZ cDNAs were cloned with RT-PCR followed by sequence analysis. The expression of DAZ proteins in human testis was determined by immunoblot and compared with DAZ cDNA expression.

RESULTS

Immunoblot analysis revealed four DAZ protein bands in testis samples that showed no deletions in the AZFc region. No specific bands were observed in samples from AZFc deletion patients. Testis samples from individuals with the partial AZFc deletion, gr/gr, showed two DAZ-specific bands. Interestingly, the sizes of DAZ-specific bands varied among individuals. Analysis of DAZ transcripts in testis samples revealed that the DAZ proteins were translated from the largest of the multiple transcripts originating from each single DAZ gene.

CONCLUSIONS

All four DAZ genes are expressed in the human testis, and their products are highly polymorphic among men.

Dynein motor contributes to stress granule dynamics in primary neurons

Mobilization and translation of mRNAs, two important events believed to involve stress granules (SGs), in neurons are important for their survival and activities. However, the formation and disassembly of SGs in neurons remains unclear. By using an arsenite-induced neuronal stress model of rat primary spinal cord neuron cultures, we demonstrate the formation of SGs that contain common SG components and RNAs in both stressed neuronal cell bodies and their neurites. By employing small interfering RNA (siRNA) knockdown, we discovered that dynein motor subunit localizes in SG, and is important for SG assembly in neurons. Under stress, dynein motor subunit also facilitates translational repression and enhances the formation and integrity of SG in neurons. By blocking the energy source of dynein motor, both the formation and disassembly of SG are attenuated. These findings demonstrate, for the first time, that dynein motor complex plays a critical role in the dynamics of neuronal SGs, as well as translation of certain mRNAs.

The interplay of ligand binding and quaternary structure in the diverse interactions of dynein light chain LC8

Dynein light chain LC8 is a small, dimeric, and very highly conserved globular protein that is an integral part of the dynein and myosin molecular motors but appears to have a broader role in multiple protein complexes unrelated to molecular motors. LC8 binds to two families of targets: those having a KXTQT sequence fingerprint and those having a GIQVD fingerprint. All known LC8 binding partners containing these fingerprints share a common binding site on LC8 that raises the question of what determines binding specificity. Here, we present the crystal structure of apo-LC8 at 1.7-A resolution, which, when compared with the crystal structures of several LC8 complexes, gives insight into the mechanism underlying the binding diversity of LC8. Peptide binding is associated with a shift in quaternary structure that expands the hydrophobic binding surface available to the ligand, in addition to changes in tertiary structure and ordering of LC8 around the binding groove. The observed quaternary shift suggests a mechanism by which binding at one of the two identical sites can influence binding at the other. NMR spectra of titrations with peptides from each fingerprint family show evidence of allosteric interaction between the two binding sites, to a differing degree in the two ligand families. Allosteric interaction between the binding sites may be a mechanism to promote simultaneous binding of ligands from the same family, providing a physiological role for the two fingerprints.

DAZL binds to the transcripts of several Tssk genes in germ cells

The Dazl gene encodes a germ-cell-specific RNA-binding protein which is essential for spermatogenesis. It has been proposed that this protein (DAZL) binds to RNA in the cytoplasm of germ cells and controls spermatogenesis. Using the specific nucleic acids associated with proteins (SNAAP) technique, we identified 17 target mRNAs bound by mDAZL. Among these transcripts, we focused on TSSK2, which encodes a testis-specific serine/threonine kinase. To date, five TSSK family members have been cloned, and all are exclusively expressed in the testis. We demonstrated that in addition to the TSSK1 3'UTR , the 3'UTRs of TSSKs 2 and 4 were bound by human and mouse DAZL, and that human DAZL (hDAZL) bound to the 3'UTR of human TSSK5 (hTSSK5). Our results suggest that the Dazl gene may play different roles in human and mouse spermatogenesis by regulating different members of the downstream gene family.

Cytoplasmic dynein could be key to understanding neurodegeneration

A new mouse mutant uncovers an essential role of cytoplasmic dyenin in sensory nervous system.

A new mouse mutation, Sprawling, highlights an essential role for the dynein heavy chain in sensory neuron function, but it lacks the ability of other known heavy-chain mutations to ameliorate neurodegeneration due to defective superoxide dismutase.

Structure and Dynamics of LC8 Complexes with KXTQT-Motif Peptides: Swallow and Dynein Intermediate Chain Compete for a Common Site

The dynein light chain LC8 is an integral subunit of the cytoplasmic dynein motor complex that binds directly to and promotes assembly of the dynein intermediate chain (IC). LC8 interacts also with a variety of putative dynein cargo molecules such as Bim, a proapoptotic Bcl2 family protein, which have the KXTQT recognition sequence and neuronal nitric oxide synthase (nNOS), which has the GIQVD fingerprint but shares the same binding grooves at the LC8 dimer interface. The work reported here investigates the interaction of LC8 with IC and a putative cargo, Swallow, which share the KXTQT recognition sequence, and addresses the apparent paradox of how LC8, as part of dynein, mediates binding to cargo. The structures of Drosophila LC8 bound to peptides from IC and Swallow solved by X-ray diffraction show that the IC and Swallow peptides bind in the same grooves at the dimer interface. Differences in flexibility between bound and free LC8 were evaluated from hydrogen isotope exchange experiments using heteronuclear NMR spectroscopy. Peptide binding causes an increase in protection from exchange primarily in residues that interact directly with the peptide, such as the beta-strand intertwined at the interface and the N-terminal end of helix alpha2. There is considerably more protection upon Swallow binding, consistent with tighter binding relative to IC. Comparison with the LC8/nNOS complex shows how both the GIQVD and KXTQT fingerprints are recognized in the same groove. The similar structures of LC8/IC and LC8/Swa and the tighter binding of Swallow call into question the role for LC8 as a cargo adaptor protein, and suggest that binding of LC8 to Swallow serves another function, possibly that of a dimerization engine, which is independent of its role in dynein.

Translation of the synaptonemal complex component Sycp3 is enhanced in vivo by the germ cell specific regulator Dazl

DAZ-related genes are essential for gametogenesis in diverse metazoa: in human males, a loss of DAZ genes is associated with infertility. These genes, expressed only in germ cells, regulate the translation of a yet undefined set of specific transcripts, and loss of function results in numerous defects throughout the mitotic and meiotic process of germ cell development. In a mouse model, absence of the autosomal Dazl gene results in a final block at zygotene of meiotic prophase. Sycp3 is also essential for meiosis, specifically for the formation of the synaptonemal complex lateral element with a mouse knockout model displaying a block in meiotic prophase similar to the Dazl knock out. Sycp3 was identified as a potential target for translational regulation by Dazl in male mouse germ cells. This was confirmed by both RNA binding and translation assays. In the Dazl knockout mouse model, Sycp3 protein levels were decreased, indicating that Dazl is required for efficient translation of the Sycp3 mRNA in vivo. Taken together these data support Sycp3 as a biologically relevant target of Dazl-mediated translation in mammals. This suggests that azoospermia associated with a decrease in DAZ gene function in humans may in part be a consequence of failure at synapsis caused by reduced levels of SYCP3 protein.