A TB-RBP and Ter ATPase complex accompanies specific mRNAs from nuclei through the nuclear pores and into intercellular bridges in mouse male germ cells

Expression of Protein Markers in Spermatogenic and Supporting Sertoli Cells Affected by High Abdominal Temperature in Cryptorchidism Model Mice

Cryptorchidism is a congenital abnormality resulting in increased rates of infertility and testicular cancer. We used cryptorchidism model mice that presented with the translocation of the left testis from the scrotum to the abdominal cavity. Mice underwent the surgical procedure of the left testis at day 0 and were sacrificed at days 3, 5, 7, 14, 21, and 28 post-operatively. The weight of the left cryptorchid testis decreased significantly at days 21 and 28. The morphological changes were observed after 5 days and showed detached spermatogenic cells and abnormal formation of acrosome at day 5, multinucleated giant cells at day 7, and atrophy of seminiferous tubules at days 21 and 28. The high abdominal temperature disrupted the normal expression of cell adhesion molecule-1, Nectin-2, and Nectin-3 which are essential for spermatogenesis. In addition, the pattern and alignment of acetylated tubulin in cryptorchid testes were also changed at days 5, 7, 14, 21, and 28. Ultrastructure of cryptorchid testes revealed giant cells that had been formed by spermatogonia, spermatocytes, and round and elongating spermatids. The study's findings reveal that cryptorchidism's duration is linked to abnormal changes in the testis, impacting protein marker expression in spermatogenic and Sertoli cells. These changes stem from the induction of high abdominal temperature.

TSNAXIP1 is required for sperm head formation and male fertility

Purpose

TRANSLIN (TSN) and its binding partner TSNAX have been reported to contribute to a wide spectrum of biological activities including spermatogenesis. TSN accompanies specific mRNA transport in male germ cells through intercellular bridges. A testis-expressed protein TSNAXIP1 was reported to interact with TSNAX. However the role of TSNAXIP1 in spermatogenesis remained unclear. This study aimed to elucidate the role of TSNAXIP1 in spermatogenesis and male fertility in mice.

Methods

TSNAXIP1 knockout (KO) mice were generated using the CRISPR-Cas9 system. The fertility, spermatogenesis, and sperm of TSNAXIP1 KO males were analyzed.

Results

TSNAXIP1, and especially its domains, are highly conserved between mouse and human. Tsnaxip1 was expressed in testis, but not in ovary. TSNAXIP1 KO mice were generated, and TSNAXIP1 KO males were found to be sub-fertile with smaller testis and lower sperm count. Although no overt abnormalities were observed during spermatogenesis, lack of TSNAXIP1 induced sperm head malformation, resulting in a unique flower-shaped sperm head. Moreover, abnormal anchorage of the sperm neck was frequently observed in TSNAXIP1 null sperm.

Conclusion

A testis-expressed gene TSNAXIP1 has important roles in sperm head morphogenesis and male fertility. Moreover, TSNAXIP1 could be a causative gene for human infertility.

Plant and animal small RNA communications between cells and organisms

Since the discovery of eukaryotic small RNAs as the main effectors of RNA interference in the late 1990s, diverse types of endogenous small RNAs have been characterized, most notably microRNAs, small interfering RNAs (siRNAs) and PIWI-interacting RNAs (piRNAs). These small RNAs associate with Argonaute proteins and, through sequence-specific gene regulation, affect almost every major biological process. Intriguing features of small RNAs, such as their mechanisms of amplification, rapid evolution and non-cell-autonomous function, bestow upon them the capacity to function as agents of intercellular communications in development, reproduction and immunity, and even in transgenerational inheritance. Although there are many types of extracellular small RNAs, and despite decades of research, the capacity of these molecules to transmit signals between cells and between organisms is still highly controversial. In this Review, we discuss evidence from different plants and animals that small RNAs can act in a non-cell-autonomous manner and even exchange information between species. We also discuss mechanistic insights into small RNA communications, such as the nature of the mobile agents, small RNA signal amplification during transit, signal perception and small RNA activity at the destination.

Microtubule and Actin Cytoskeletal Dynamics in Male Meiotic Cells of Drosophila melanogaster

Drosophila dividing spermatocytes offer a highly suitable cell system in which to investigate the coordinated reorganization of microtubule and actin cytoskeleton systems during cell division of animal cells. Like male germ cells of mammals, Drosophila spermatogonia and spermatocytes undergo cleavage furrow ingression during cytokinesis, but abscission does not take place. Thus, clusters of primary and secondary spermatocytes undergo meiotic divisions in synchrony, resulting in cysts of 32 secondary spermatocytes and then 64 spermatids connected by specialized structures called ring canals. The meiotic spindles in Drosophila males are substantially larger than the spindles of mammalian somatic cells and exhibit prominent central spindles and contractile rings during cytokinesis. These characteristics make male meiotic cells particularly amenable to immunofluorescence and live imaging analysis of the spindle microtubules and the actomyosin apparatus during meiotic divisions. Moreover, because the spindle assembly checkpoint is not robust in spermatocytes, Drosophila male meiosis allows investigating of whether gene products required for chromosome segregation play additional roles during cytokinesis. Here, we will review how the research studies on Drosophila male meiotic cells have contributed to our knowledge of the conserved molecular pathways that regulate spindle microtubules and cytokinesis with important implications for the comprehension of cancer and other diseases.

Loss of TDP-43 in male germ cells causes meiotic failure and impairs fertility in mice

Meiotic arrest is a common cause of human male infertility, but the causes of this arrest are poorly understood. Transactive response DNA-binding protein of 43 kDa (TDP-43) is highly expressed in spermatocytes in the preleptotene and pachytene stages of meiosis. TDP-43 is linked to several human neurodegenerative disorders wherein its nuclear clearance accompanied by cytoplasmic aggregates underlies neurodegeneration. Exploring the functional requirement for TDP-43 for spermatogenesis for the first time, we show here that conditional KO (cKO) of the Tardbp gene (encoding TDP-43) in male germ cells of mice leads to reduced testis size, depletion of germ cells, vacuole formation within the seminiferous epithelium, and reduced sperm production. Fertility trials also indicated severe subfertility. Spermatocytes of cKO mice showed failure to complete prophase I of meiosis with arrest at the midpachytene stage. Staining of synaptonemal complex protein 3 and γH2AX, markers of the meiotic synaptonemal complex and DNA damage, respectively, and super illumination microscopy revealed nonhomologous pairing and synapsis defects. Quantitative RT-PCR showed reduction in the expression of genes critical for prophase I of meiosis, including Spo11 (initiator of meiotic double-stranded breaks), Rec8 (meiotic recombination protein), and Rad21L (RAD21-like, cohesin complex component), as well as those involved in the retinoic acid pathway critical for entry into meiosis. RNA-Seq showed 1036 upregulated and 1638 downregulated genes (false discovery rate <0.05) in the Tardbp cKO testis, impacting meiosis pathways. Our work reveals a crucial role for TDP-43 in male meiosis and suggests that some forms of meiotic arrest seen in infertile men may result from the loss of function of TDP-43.

Novel localizations and interactions of intercellular bridge proteins revealed by proteomic profiling†

Intercellular bridges (ICBs) connecting germ cells are essential for spermatogenesis, and their deletion causes male infertility. However, the functions and component factors of ICBs are still unknown. We previously identified novel ICB-associated proteins by proteomics analysis using ICB enrichment. Here, we performed immunoprecipitation-proteomics analyses using antibodies specific to known ICB proteins MKLP1, RBM44, and ectoplasmic specialization-associated protein KIAA1210 and predicted protein complexes in the ICB cores. KIAA1210, its binding protein topoisomerase2B (TOP2B), and tight junction protein ZO1 were identified as novel ICB proteins. On the other hand, as well as KIAA1210 and TOP2B, MKLP1 and RBM44, but not TEX14, were localized at the XY body of spermatocytes, suggesting that there is a relationship between ICB proteins and meiotic chromosomes. Moreover, small RNAs interacted with an ICB protein complex that included KIAA1210, RBM44, and MKLP1. These results indicate dynamic movements of ICB proteins and suggest that ICB proteins could be involved not only in the communication between germ cells but also in their epigenetic regulation. Our results provide a novel perspective on the function of ICBs and could be helpful in revealing the biological function of the ICB.

Sperm proteins and cancer-testis antigens are released by the seminiferous tubules in mice and men

Sperm develop from puberty in the seminiferous tubules, inside the blood-testis barrier to prevent their recognition as "non-self" by the immune system, and it is widely assumed that human sperm-specific proteins cannot access the circulatory or immune systems. Sperm-specific proteins aberrantly expressed in cancer, known as cancer-testis antigens (CTAs), are often pursued as cancer biomarkers and therapeutic targets based on the assumption they are neoantigens absent from the circulation in healthy men. Here, we identify a wide range of germ cell-derived and sperm-specific proteins, including multiple CTAs, that are selectively deposited by the Sertoli cells of the adult mouse and human seminiferous tubules into testicular interstitial fluid (TIF) that is "outside" the blood-testis barrier. From TIF, the proteins can access the circulatory- and immune systems. Disruption of spermatogenesis decreases the abundance of these proteins in mouse TIF, and a sperm-specific CTA is significantly decreased in TIF from infertile men, suggesting that exposure of certain CTAs to the immune system could depend on fertility status. The results provide a rationale for the development of blood-based tests useful in the management of male infertility and indicate CTA candidates for cancer immunotherapy and biomarker development that could show sex-specific and male-fertility-related responses.

EXOC1 plays an integral role in spermatogonia pseudopod elongation and spermatocyte stable syncytium formation in mice

The male germ cells must adopt the correct morphology at each differentiation stage for proper spermatogenesis. The spermatogonia regulates its differentiation state by its own migration. The male germ cells differentiate and mature with the formation of syncytia, failure of forming the appropriate syncytia results in the arrest at the spermatocyte stage. However, the detailed molecular mechanisms of male germ cell morphological regulation are unknown. Here, we found that EXOC1, a member of the Exocyst complex, is important for the pseudopod formation of spermatogonia and spermatocyte syncytia in mice. EXOC1 contributes to the pseudopod formation of spermatogonia by inactivating the Rho family small GTPase Rac1 and also functions in the spermatocyte syncytia with the SNARE proteins STX2 and SNAP23. Since EXOC1 is known to bind to several cell morphogenesis factors, this study is expected to be the starting point for the discovery of many morphological regulators of male germ cells.

Mechanisms of meiotic drive in symmetric and asymmetric meiosis

Meiotic drive, the non-Mendelian transmission of chromosomes to the next generation, functions in asymmetric or symmetric meiosis across unicellular and multicellular organisms. In asymmetric meiosis, meiotic drivers act to alter a chromosome's spatial position in a single egg. In symmetric meiosis, meiotic drivers cause phenotypic differences between gametes with and without the driver. Here we discuss existing models of meiotic drive, highlighting the underlying mechanisms and regulation governing systems for which the most is known. We focus on outstanding questions surrounding these examples and speculate on how new meiotic drive systems evolve and how to detect them.

Genome-wide association studies for sperm traits in Assaf sheep breed

Sperm quality traits routinely collected by artificial insemination (AI) center for rams progeny test are related with the capacity to produce sperm doses for AI and, in more or less grade, with males' fertility. Low-quality ejaculates are unuseful to perform AI sperm doses, which suppose high economic loses for the AI center. Moreover, sperm quality traits have low heritability values which make traditional genetic selection little efficient to its improvement. In this work, a genome-wide association study (GWAS) was conducted by using sperm quality traits data and 50 K Affymetrix custom chip genotypes of 429 rams of Assaf breed from OVIGEN AI centre. Furthermore, 47 of these rams were also genotyped with the Illumina HD Ovine BeadChip, and therefore HD genotypes were imputed for all rams with phenotype data. Previous to the GWAS, a linear regression model was fitted including sperm traits as dependent variables; the flock of origin, date of sperm collection, and jump number as fixed effects; rams age at collection in months as covariate; and ram permanent effect as random. Pseudo-phenotypes obtained from this model were used as input for GWAS. Associations at the chromosome-wise level (FDR 10%) of 76 single-nucleotide polymorphisms (SNPs) in 4 chromosomes for ejaculate concentration (CON), 20 SNPs in 3 chromosomes for ejaculate volume (VOL), 32 SNPs in 1 chromosome for ejaculate number of spermatozoa (SPZ), and 23 SNPs for spermatozoa mass motility (MOT) in 17 chromosomes were found. Only SNPs associated with MOT overcame the genome-wide significance level. Some candidate genes for sperm traits variability were SLC9C1 (OAR1), TSN (OAR2), and FUT10 (OAR26) for MOT;. DOCK2, CPLANE1, SPEF2, and RAI14 (OAR16) for CON; SCAPER and PSMA4 (OAR18) for VOL; and PARM1 and LOC101110593 (OAR6) for SPZ. SNPs associated with sperm traits were not found to be correlated with milk production genetic variation; however, the high frequencies of some SNPs with negative effect over sperm traits found in animals at the top milk yield estimated breeding values (EBVs) ranking would allow to exert some selective presure to improve rams sperm performances. Effects and frequencies of some of the SNPs detected over sperm quality traits make these variants good candidates to be used in marker-assisted selection to improve sperm characteristics of Assaf rams and AI center efficiency to produce sperm doses.

Drosophila sperm development and intercellular cytoplasm sharing through ring canals do not require an intact fusome

Animal germ cells communicate directly with each other during gametogenesis through intercellular bridges, often called ring canals (RCs), that form as a consequence of incomplete cytokinesis during cell division. Developing germ cells in Drosophila have an additional specialized organelle connecting the cells called the fusome. Ring canals and the fusome are required for fertility in Drosophila females, but little is known about their roles during spermatogenesis. With live imaging, we directly observe the intercellular movement of GFP and a subset of endogenous proteins through RCs during spermatogenesis, from two-cell diploid spermatogonia to clusters of 64 post-meiotic haploid spermatids, demonstrating that RCs are stable and open to intercellular traffic throughout spermatogenesis. Disruption of the fusome, a large cytoplasmic structure that extends through RCs and is important during oogenesis, had no effect on spermatogenesis or male fertility under normal conditions. Our results reveal that male germline RCs allow the sharing of cytoplasmic information that might play a role in quality control surveillance during sperm development.

Advances and challenges in genetic technologies to produce single-sex litters

There is currently a requirement for single-sex litters for many applications, including agriculture, pest control, and reducing animal culling in line with the 3Rs principles: Reduction, Replacement, and Refinement. The advent of CRISPR/Cas9 genome editing presents a new opportunity with which to potentially generate all-female or all-male litters. We review some of the historical nongenetic strategies employed to generate single-sex litters and investigate how genetic and genome editing techniques are currently being used to produce all-male or all-female progeny. Lastly, we speculate on future technologies for generating single-sex litters and the possible associated challenges.

The aryl hydrocarbon receptor mediates sex ratio distortion in the embryos sired by TCDD-exposed male mice

Many reports describe an association between preconceptional paternal exposure to environmental chemicals, including the persistent organic pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with an increased number of female offspring. We chronically treated wild-type C57BL/6 male mice with TCDD to investigate a role for the aryl hydrocarbon receptor (AHR) transcription factor. These mice had a 14 % lower male:female sex ratio than control mice, which was not observed in TCDD-treated Ahr knock out mice. AHR target genes Cyp1a1 and Ahrr were upregulated in the liver and testis of WT mice and Ahr expression was higher in the epididymis (2-fold) and liver (18-fold) than in whole testis tissue. The AHR protein was localized to round spermatids, elongating spermatids, and Leydig cells in the testis of WT mice. These studies demonstrate AHR involvement in the sex ratio distortion of TCDD-exposed males and the need for evaluating the molecular and genetic mechanism of this process.

Sex and suicide: The curious case of Toll-like receptors

During in vitro fertilisation (IVF), pharmacological activation of the murine X chromosome-encoded receptor proteins Toll-like receptor (TLR) 7 and TLR8 reportedly results in male-biased litters by selectively disrupting the motility of X-bearing sperm cells. Thus-in the context of agonist treatment during IVF-these receptors act as 'suicidal' segregation distorters that impair their own transmission to the next generation. Such behaviour would, from an evolutionary perspective, be strongly selected against if present during natural fertilisation. Consequently, TLR7/8 biology in vivo must differ significantly from this in vitro situation to allow these genes to persist in the genome. Here, we use our current understanding of male germ cell biology and TLR function as a starting point to explore the mechanistic and evolutionary aspects of this apparent paradox.

Evaluating genetic causes of azoospermia: What can we learn from a complex cellular structure and single-cell transcriptomics of the human testis?

Azoospermia is a condition defined as the absence of spermatozoa in the ejaculate, but the testicular phenotype of men with azoospermia may be very variable, ranging from full spermatogenesis, through arrested maturation of germ cells at different stages, to completely degenerated tissue with ghost tubules. Hence, information regarding the cell-type-specific expression patterns is needed to prioritise potential pathogenic variants that contribute to the pathogenesis of azoospermia. Thanks to technological advances within next-generation sequencing, it is now possible to obtain detailed cell-type-specific expression patterns in the testis by single-cell RNA sequencing. However, to interpret single-cell RNA sequencing data properly, substantial knowledge of the highly sophisticated data processing and visualisation methods is needed. Here we review the complex cellular structure of the human testis in different types of azoospermia and outline how known genetic alterations affect the pathology of the testis. We combined the currently available single-cell RNA sequencing datasets originating from the human testis into one dataset covering 62,751 testicular cells, each with a median of 2637 transcripts quantified. We show what effects the most common data-processing steps have, and how different visualisation methods can be used. Furthermore, we calculated expression patterns in pseudotime, and show how splicing rates can be used to determine the velocity of differentiation during spermatogenesis. With the combined dataset we show expression patterns and network analysis of genes known to be involved in the pathogenesis of azoospermia. Finally, we provide the combined dataset as an interactive online resource where expression of genes and different visualisation methods can be explored ( https://testis.cells.ucsc.edu/ ).

Abnormal fertility, acrosome formation, IFT20 expression and localization in conditional Gmap210 knockout mice

GMAP210 (TRIP11) is a cis-Golgi network-associated protein and a Golgi membrane receptor for IFT20, an intraflagellar transport component essential for male fertility and spermiogenesis in mice. To investigate the role of GMAP210 in male fertility and spermatogenesis, floxed Gmap210 mice were bred with Stra8-iCre mice so that the Gmap210 gene is disrupted in spermatocytes and spermatids in this study. The Gmap210flox/flox: Stra8-iCre mutant mice showed no gross abnormalities and survived to adulthood. In adult males, testis and body weights showed no difference between controls and mutant mice. Low-magnification histological examination of the testes revealed normal seminiferous tubule structure, but sperm counts and fertility were significantly reduced in mutant mice compared with controls. Higher resolution examination of the mutant seminiferous epithelium showed that nearly all sperm had more oblong, abnormally shaped heads, while the sperm tails appeared to have normal morphology. Electron microscopy also revealed abnormally shaped sperm heads but normal axoneme core structure; some sperm showed membrane defects in the midpiece. In mutant mice, expression levels of IFT20 and other selective acrosomal proteins were significantly reduced, and their localization was also affected. Peanut-lectin, an acrosome maker, was almost absent in the spermatids and epididymal sperm. Mitochondrion staining was highly concentrated in the heads of sperm, suggesting that the midpieces were coiling around or aggregating near the heads. Defects in acrosome biogenesis were further confirmed by electron microscopy. Collectively, our findings suggest that GMAP210 is essential for acrosome biogenesis, normal mitochondrial sheath formation, and male fertility, and it determines expression levels and acrosomal localization of IFT20 and other acrosomal proteins.

Architecture and Life History of Female Germ-Line Cysts in Clitellate Annelids

Animal female and male germ-line cells often form syncytial units termed cysts, clusters, or clones. Within these cysts, the cells remain interconnected by specific cell junctions known as intercellular bridges or ring canals, which enable cytoplasm to be shared and macromolecules and organelles to be exchanged between cells. Numerous analyses have shown that the spatial organization of cysts and their functioning may differ between the sexes and taxa. The vast majority of our knowledge about the formation and functioning of germ-line cysts comes from studies of model species (mainly Drosophila melanogaster); the other systems of the cyst organization and functioning are much less known and are sometimes overlooked. Here, we present the current state of the knowledge of female germ-line cysts in clitellate annelids (Clitellata), which is a monophyletic taxon of segmented worms (Annelida). The organization of germ-line cysts in clitellates differs markedly from that of the fruit fly and vertebrates. In Clitellata, germ cells are not directly connected one to another, but, as a rule, each cell has one ring canal that connects it to an anuclear central cytoplasmic core, a cytophore. Thus, this pattern of cell distribution is similar to the germ-line cysts of Caenorhabditis elegans. The last decade of studies has revealed that although clitellate female germ-line cysts have a strong morphological plasticity, e.g., cysts may contain from 16 to as many as 2500 cells, the oogenesis always shows a meroistic mode, i.e., the interconnected cells take on different fates; a few (sometimes only one) become oocytes, whereas the rest play the role of supporting (nurse) cells and do not continue oogenesis.This is the first comprehensive summary of the current knowledge on the organization and functioning of female germ-line cysts in clitellate annelids.

Dynamic cytoplasmic projections connect mammalian spermatogonia in vivo

Throughout the male reproductive lifespan, spermatogonial stem cells (SSCs) produce committed progenitors that proliferate and then remain physically connected in growing clones via short cylindrical intercellular bridges (ICBs). These ICBs, which enlarge in meiotic spermatocytes, have been demonstrated to provide a conduit for postmeiotic haploid spermatids to share sex chromosome-derived gene products. In addition to ICBs, spermatogonia exhibit multiple thin cytoplasmic projections. Here, we have explored the nature of these projections in mice and find that they are dynamic, span considerable distances from their cell body (≥25 μm), either terminate or physically connect multiple adjacent spermatogonia, and allow for sharing of macromolecules. Our results extend the current model that subsets of spermatogonia exist as isolated cells or clones, and support a model in which spermatogonia of similar developmental fates are functionally connected through a shared dynamic cytoplasm mediated by thin cytoplasmic projections.

Low mitochondrial activity within developing earthworm male germ-line cysts revealed by JC-1

The male germ-line cysts that occur in annelids appear to be a very convenient model for spermatogenesis studies. Germ-line cysts in the studied earthworm are composed of two compartments: (1) germ cells, where each cell is connected via one intercellular bridge to (2) an anuclear central cytoplasmic mass, the cytophore. In the present paper, confocal and transmission electron microscopy were used to follow the changes in the mitochondrial activity and ultrastructure within the cysts during spermatogenesis. JC-1 was used to visualize the populations of mitochondria with a high and low membrane potential. We used the spot detection Imaris software module to obtain the quantitative data. We counted and compared the 'mitochondrial spots' - the smallest detectable signals from mitochondria. It was found that in all of the stages of cyst development, the majority of mitochondria spots showed a green fluorescence, thus indicating a low mitochondrial membrane potential (MMP). Moreover, the number of active mitochondria spots that were visualized by red JC-1 fluorescence (high MMP) drastically decreased as spermatogenesis progressed. As much as 26% of the total number of mitochondrial spots in the spermatogonial cysts showed a high MMP - 19% in the spermatocytes, 24% in the isodiametric spermatids and 3% and 6%, respectively, in the cysts that were holding early and late elongate spermatids. The mitochondria were usually thread-like and had an electron-dense matrix and lamellar cristae. Then, during spermiogenesis, the mitochondria within both the spermatids and the cytophore had a tendency to form aggregates in which the mitochondria were cemented by an electron-dense material.

Content of testis-specific isoform of Na/K-ATPase (ATP1A4) is increased during bovine sperm capacitation through translation in mitochondrial ribosomes

Capacitation comprises a series of structural and functional modifications of sperm that confer fertilizing ability. We previously reported that the testis-specific isoform of Na/K-ATPase (ATP1A4) regulated bovine sperm capacitation through signaling mechanisms involving kinases. During subsequent investigations to elucidate mechanisms by which ATP1A4 regulates sperm capacitation, we observed that ATP1A4 was localised in both raft and non-raft fractions of the sperm plasma membrane and that its total content was increased in both membrane fractions during capacitation. The objective of the present study was to investigate mechanism(s) of capacitation-associated increase in the content of ATP1A4. Despite the widely accepted dogma of transcriptional/translational quiescence, incubation of sperm with either ouabain (specific ligand for ATP1A4) or heparin increased ATP1A4 content in raft and non-raft sperm membrane fractions, total sperm protein extracts (immunoblotting) and fixed sperm (flow cytometry), with a concurrent increase in Na/K-ATPase enzyme activity. This capacitation-associated increase in ATP1A4 content was partially decreased by chloramphenicol (mitochondrial translation inhibitor) but not affected by actinomycin D (transcription inhibitor). To demonstrate de novo ATP1A4 synthesis, we evaluated incorporation of bodipy conjugated lysine in this protein during capacitation. A partial decrease in bodipy-lysine incorporation occurred in ATP1A4 from sperm capacitated in the presence of chloramphenicol. Therefore, increased ATP1A4 content during capacitation was attributed to mitochondrial translation of ATP1A4 mRNA present in ejaculated sperm, rather than gene transcription. To our knowledge, this is the first report demonstrating ATP1A4 synthesis during bovine sperm capacitation.

Analysis of the cytoskeleton organization and its possible functions in male earthworm germ-line cysts equipped with a cytophore

We studied the organization of F-actin and the microtubular cytoskeleton in male germ-line cysts in the seminal vesicles of the earthworm Dendrobaena veneta using light, fluorescent and electron microscopy along with both chemically fixed tissue and life cell imaging. Additionally, in order to follow the functioning of the cytoskeleton, we incubated the cysts in colchicine, nocodazole, cytochalasin D and latrunculin A. The male germ-line cells of D. veneta are interconnected via stable intercellular bridges (IB), and form syncytial cysts. Each germ cell has only one IB that connects it to the anuclear central cytoplasmic mass, the cytophore. During the studies, we analyzed the cytoskeleton in spermatogonial, spermatocytic and spermatid cysts. F-actin was detected in the cortical cytoplasm and forms distinct rings in the IBs. The arrangement of the microtubules changed dynamically during spermatogenesis. The microtubules are distributed evenly in whole spermatogonial and spermatocytic cysts; however, they primarily accumulate within the IBs in spermatogonia. In early spermatids, microtubules pass through the IBs and are present in whole cysts. During spermatid elongation, the microtubules form a manchette while they are absent in the cytophore and in the IBs. Use of cytoskeletal drugs did not alter the general morphology of the cysts. Detectable effects—the occurrence of nuclei in the late spermatids and manchette fragments in the cytophore—were observed only after incubation in nocodazole. Our results suggest that the microtubules are responsible for cytoplasmic/organelle transfer between the germ cells and the cytophore during spermatogenesis and for the positioning of the spermatid nuclei.

Movement of regulatory RNA between animal cells

Recent studies suggest that RNA can move from one cell to another and regulate genes through specific base-pairing. Mechanisms that modify or select RNA for secretion from a cell are unclear. Secreted RNA can be stable enough to be detected in the extracellular environment and can enter the cytosol of distant cells to regulate genes. Mechanisms that import RNA into the cytosol of an animal cell can enable uptake of RNA from many sources including other organisms. This role of RNA is akin to that of steroid hormones, which cross cell membranes to regulate genes. The potential diagnostic use of RNA in human extracellular fluids has ignited interest in understanding mechanisms that enable the movement of RNA between animal cells. Genetic model systems will be essential to gain more confidence in proposed mechanisms of RNA transport and to connect an extracellular RNA with a specific biological function. Studies in the worm C. elegans and in other animals have begun to reveal parts of this novel mechanism of cell-to-cell communication. Here, I summarize the current state of this nascent field, highlight the many unknowns, and suggest future directions.

Genome-wide single-nucleotide polymorphism analysis revealed SUFU suppression of acute graft-versus-host disease through downregulation of HLA-DR expression in recipient dendritic cells

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). To identify recipient risk factors, a genome-wide study was performed including 481,820 single-nucleotide polymorphisms (SNPs). Two GVHD susceptibility loci (rs17114803 and rs17114808) within the SUFU gene were identified in the discovery cohort (p = 2.85 × 10⁻⁵). The incidence of acute GVHD among patients homozygous for CC at SUFU rs17114808 was 69%, which was significantly higher than the 8% rate observed in CT heterozygous patients (p = 0.0002). In an independent validation cohort of 100 patients, 50% of the patients with the CC genotype developed GVHD compared to 8% of the patients with either CT or TT genotype (p = 0.01). In comparison to CC dendritic cells, those from CT expressed higher levels of SUFU mRNA and protein, had lower levels of surface HLA-DR, and induced less allogeneic mixed leukocyte response (MLR). Ectopic expression of SUFU in THP-1 derived DCs reduced HLA-DR expression and suppressed MLR, whereas silencing of SUFU enhanced HLA-DR expression and increased MLR. Thus our findings provide novel evidence that recipient SUFU germline polymorphism is associated with acute GVHD and is a novel molecular target for GVHD prevention and treatment.

Intercellular bridges are essential for human parthenogenetic cell survival

Parthenogenetic cells, obtained from in vitro activated mammalian oocytes, display multipolar spindles, chromosome malsegregation and a high incidence of aneuploidy, probably due to the lack of paternal contribution. Despite this, parthenogenetic cells do not show high rates of apoptosis and are able to proliferate in a way comparable to their biparental counterpart. We hypothesize that a series of adaptive mechanisms are present in parthenogenetic cells, allowing a continuous proliferation and ordinate cell differentiation both in vitro and in vivo. Here we identify the presence of intercellular bridges that contribute to the establishment of a wide communication network among human parthenogenetic cells, providing a mutual exchange of missing products. Silencing of two molecules essential for intercellular bridge formation and maintenance demonstrates the key function played by these cytoplasmic passageways that ensure normal cell functions and survival, alleviating the unbalance in cellular component composition.

Pre-spermiogenic initiation of flagellar growth and correlative ultrastructural observations on nuage, nuclear and mitochondrial developmental morphology in the zebrafish Danio rerio

The microstructural and ultrastructural changes of germ cells during spermatogenesis of zebrafish (Danio rerio) were examined using light microscopy (LM) and transmission electron microscopy (TEM). Generally the process of spermatogenesis in zebrafish is similar to that of other teleosts, however, here we describe some peculiar features of zebrafish spermatogenic cells which have a limited report in this species. (1) The basic events of spermiogenesis are asynchronous, location of flagellum finished in initial stage, while chromatin condensation sharply occurred in intermediate stage and elimination of excess cytoplasm mainly taken place in final stages. (2) Surprisingly, the cilia or initial flagellae are created in spermatocytes, approach toward the nucleus of early stage spermatids, and then the centrioles depress into nuclear fossa and change their orientation to each other from right angle to obtuse angle about 125°. (3) During spermatogenesis, the chromatin compaction performs in a distinctive pattern, condensed heterogeneously from granular into chromatin clumps with central electron-lucent areas, round or long, which diminished to small nuclear vacuoles in spermatozoa. This finding demonstrates the origin of nuclear vacuoles in zebrafish spermatozoa for the first time. (4) Nuages are observed in both spermatogonia and spermatocytes. They are connected with the mitochondria and nuclear membrane, and are even located in the perinuclear spaces of spermatogonia nuclei. (5) Mitochondrial morphology and distribution shows diversity in different germ cells. The condensed mitochondria appear in pachytene spermatocytes, and mitochondria including membrane conglomerate exist in both spermatocytes and spermatids. This study was undertaken in order to disclose specific spermatogenic cells features in zebrafish that could be helpful for understanding the correlative function in this model species.

AKAP3 synthesis is mediated by RNA binding proteins and PKA signaling during mouse spermiogenesis

Mammalian spermatogenesis is regulated by coordinated gene expression in a spatiotemporal manner. The spatiotemporal regulation of major sperm proteins plays important roles during normal development of the male gamete, of which the underlying molecular mechanisms are poorly understood. A-kinase anchoring protein 3 (AKAP3) is one of the major components of the fibrous sheath of the sperm tail that is formed during spermiogenesis. In the present study, we analyzed the expression of sperm-specific Akap3 and the potential regulatory factors of its protein synthesis during mouse spermiogenesis. Results showed that the transcription of Akap3 precedes its protein synthesis by about 2 wk. Nascent AKAP3 was found to form protein complex with PKA and RNA binding proteins (RBPs), including PIWIL1, PABPC1, and NONO, as revealed by coimmunoprecipitation and protein mass spectrometry. RNA electrophoretic gel mobility shift assay showed that these RBPs bind sperm-specific mRNAs, of which proteins are synthesized during the elongating stage of spermiogenesis. Biochemical and cell biological experiments demonstrated that PIWIL1, PABPC1, and NONO interact with each other and colocalize in spermatids' RNA granule, the chromatoid body. In addition, NONO was found in extracytoplasmic granules in round spermatids, whereas PIWIL1 and PABPC1 were diffusely localized in cytoplasm of elongating spermatids, indicating their participation at different steps of mRNA metabolism during spermatogenesis. Interestingly, type I PKA subunits colocalize with PIWIL1 and PABPC1 in the cytoplasm of elongating spermatids and cosediment with the RBPs in polysomal fractions on sucrose gradients. Further biochemical analyses revealed that activation of PKA positively regulates AKAP3 protein synthesis without changing its mRNA level in elongating spermatids. Taken together, these results indicate that PKA signaling directly participates in the regulation of protein translation in postmeiotic male germ cells, underscoring molecular mechanisms that regulate protein synthesis during mouse spermiogenesis.

Bridging the divide: illuminating the path of intercellular exchange through ring canals

Ring canals are made from arrested cleavage furrows, and provide direct cytoplasmic connections among sibling cells. They are well documented for their participation in Drosophila oogenesis, but little is known about their role in several somatic tissues in which they are also found. Using a variety of genetic tools in live and fixed tissue, we recently demonstrated that rapid intercellular exchange occurs through somatic ring canals by diffusion, and presented evidence that ring canals permit equilibration of protein among transcriptionally mosaic cells. We also used a novel combination of markers to evaluate the extent of protein movement within and across mitotic clones in follicle cells and imaginal discs, providing evidence of robust movement of GFP between the 2 sides of mitotic clones and frequently into non-recombined cells. These data suggest that, depending on the experimental setup and proteins of interest, inter-clonal diffusion of protein may alter the interpretation of clonal data in follicle cells. Here, we discuss these results and provide additional insight into the impact of ring canals in Drosophila somatic tissues.

Conformational transitions in human translin enable nucleic acid binding

Translin is a highly conserved RNA- and DNA-binding protein that plays essential roles in eukaryotic cells. Human translin functions as an octamer, but in the octameric crystallographic structure, the residues responsible for nucleic acid binding are not accessible. Moreover, electron microscopy data reveal very different octameric configurations. Consequently, the functional assembly and the mechanism of nucleic acid binding by the protein remain unclear. Here, we present an integrative study combining small-angle X-ray scattering (SAXS), site-directed mutagenesis, biochemical analysis and computational techniques to address these questions. Our data indicate a significant conformational heterogeneity for translin in solution, formed by a lesser-populated compact octameric state resembling the previously solved X-ray structure, and a highly populated open octameric state that had not been previously identified. On the other hand, our SAXS data and computational analyses of translin in complex with the RNA oligonucleotide (GU)₁₂ show that the internal cavity found in the octameric assemblies can accommodate different nucleic acid conformations. According to this model, the nucleic acid binding residues become accessible for binding, which facilitates the entrance of the nucleic acids into the cavity. Our data thus provide a structural basis for the functions that translin performs in RNA metabolism and transport.

Intercellular communication: diverse structures for exchange of genetic information

An emerging concept is that cellular communication in mammals can be mediated by the exchange of genetic information, mainly in the form of microRNAs. This can occur when extracellular vesicles, such as exosomes, secreted by a donor cell are taken up by an acceptor cell. Transfer of genetic material can also occur through intimate membrane contacts between donor and acceptor cells. Specialized cell-cell contacts, such as synapses, have the potential to combine these modes of genetic transfer.

Germ cell intercellular bridges

Stable intercellular bridges are a conserved feature of gametogenesis in multicellular animals observed more than 100 years ago, but their function was unknown. Many of the components necessary for this structure have been identified through the study of cytokinesis in Drosophila; however, mammalian intercellular bridges have distinct properties from those of insects. Mammalian germ cell intercellular bridges are composed of general cytokinesis components with additional germ cell-specific factors including TEX14. TEX14 is an inactive kinase essential for the maintenance of stable intercellular bridges in gametes of both sexes but whose loss specifically impairs male meiosis. TEX14 acts to impede the terminal steps of abscission by competing for essential component CEP55, blocking its interaction in nongerm cells with ALIX and TSG101. Additionally, TEX14-interacting protein RBM44, whose localization in stabile intercellular bridges is limited to pachytene and secondary spermatocytes, may participate in processes such as RNA transport but is nonessential to the maintenance of intercellular bridge stability.

Structure and functions of stable intercellular bridges formed by incomplete cytokinesis during development

Cytokinesis, the final step of cell division, normally proceeds to completion in living organisms, so that daughter cells physically separate by abscission. In certain tissues and developmental stages, on the other hand, the cytokinesis process is incomplete, giving rise to cells interconnected in syncytia by stable intercellular bridges. This evolutionarily conserved physiological process occurs in the female and male germline in species ranging from insects to humans, and has also been observed in some somatic tissues in invertebrates. Stable intercellular bridges have fascinated cell biologists ever since they were first described more than 50 years ago, and even though substantial progress has been made concerning their ultrastructure and molecular composition, much remains to be understood about their biological functions. Another major question is by which mechanisms complete versus incomplete cytokinesis is determined. In this mini-review we will try to give an overview of the current knowledge about the structure, composition and functions of stable intercellular bridges, and discuss recent insights into the molecular control of the incomplete cytokinesis process.

Biological roles of translin and translin-associated factor-X: RNA metabolism comes to the fore

Translin, and its binding partner protein TRAX (translin-associated factor-X) are a paralogous pair of conserved proteins, which have been implicated in a broad spectrum of biological activities, including cell growth regulation, mRNA processing, spermatogenesis, neuronal development/function, genome stability regulation and carcinogenesis, although their precise role in some of these processes remains unclear. Furthermore, translin (with or without TRAX) has nucleic-acid-binding activity and it is apparent that controlling nucleic acid metabolism and distribution are central to the biological role(s) of this protein and its partner TRAX. More recently, translin and TRAX have together been identified as enhancer components of an RNAi (RNA interference) pathway in at least one organism and this might provide critical insight into the biological roles of this enigmatic partnership. In the present review we discuss the biological and the biochemical properties of these proteins that indicate that they play a central and important role in eukaryotic cell biology.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Mapping of interaction sites of the Schizosaccharomyces pombe protein Translin with nucleic acids and proteins: a combined molecular genetics and bioinformatics study

Translin is a single-stranded RNA- and DNA-binding protein, which has been highly conserved in eukaryotes, from man to Schizosaccharomyces pombe. TRAX is a Translin paralog associated with Translin, which has coevolved with it. We generated structural models of the S. pombe Translin (spTranslin), based on the solved 3D structure of the human ortholog. Using several bioinformatics computation tools, we identified in the equatorial part of the protein a putative nucleic acids interaction surface, which includes many polar and positively charged residues, mostly arginines, surrounding a shallow cavity. Experimental verification of the bioinformatics predictions was obtained by assays of nucleic acids binding to amino acid substitution variants made in this region. Bioinformatics combined with yeast two-hybrid assays and proteomic analyses of deletion variants, also identified at the top of the spTranslin structure a region required for interaction with spTRAX, and for spTranslin dimerization. In addition, bioinformatics predicted the presence of a second protein-protein interaction site at the bottom of the spTranslin structure. Similar nucleic acid and protein interaction sites were also predicted for the human Translin. Thus, our results appear to generally apply to the Translin family of proteins, and are expected to contribute to a further elucidation of their functions.

Functional transformation of the chromatoid body in mouse spermatids requires testis-specific serine/threonine kinases

The cytoplasmic chromatoid body (CB) organizes mRNA metabolism and small regulatory RNA pathways, in relation to haploid gene expression, in mammalian round spermatids. However, little is known about functions and fate of the CB at later steps of spermatogenesis, when elongating spermatids undergo chromatin compaction and transcriptional silencing. In mouse elongating spermatids, we detected accumulation of the testis-specific serine/threonine kinases TSSK1 and TSSK2, and the substrate TSKS, in a ring-shaped structure around the base of the flagellum and in a cytoplasmic satellite, both corresponding to structures described to originate from the CB. At later steps of spermatid differentiation, the ring is found at the caudal end of the newly formed mitochondrial sheath. Targeted deletion of the tandemly arranged genes Tssk1 and Tssk2 in mouse resulted in male infertility, with loss of the CB-derived ring structure, and with elongating spermatids possessing a collapsed mitochondrial sheath. These results reveal TSSK1- and TSSK2-dependent functions of a transformed CB in post-meiotic cytodifferentiation of spermatids.

Docosahexaenoic acid supplementation fully restores fertility and spermatogenesis in male delta-6 desaturase-null mice

Delta-6 desaturase-null mice ((-/-)) are unable to synthesize highly unsaturated fatty acids (HUFAs): arachidonic acid (AA), docosahexaenoic acid (DHA), and n6-docosapentaenoic acid (DPAn6). The (-/-) males exhibit infertility and arrest of spermatogenesis at late spermiogenesis. To determine which HUFA is essential for spermiogenesis, a diet supplemented with either 0.2% (w/w) AA or DHA was fed to wild-type ((+/+)) and (-/-) males at weaning until 16 weeks of age (n = 3-5). A breeding success rate of DHA-supplemented (-/-) was comparable to (+/+). DHA-fed (-/-) showed normal sperm counts and spermiogenesis. Dietary AA was less effective in restoring fertility, sperm count, and spermiogenesis than DHA. Testis fatty acid analysis showed restored DHA in DHA-fed (-/-), but DPAn6 remained depleted. In AA-fed (-/-), AA was restored at the (+/+) level, and 22:4n6, an AA elongated product, accumulated in testis. Cholesta-3,5-diene was present in testis of (+/+) and DHA-fed (-/-), whereas it diminished in (-/-) and AA-fed (-/-), suggesting impaired sterol metabolism in these groups. Expression of spermiogenesis marker genes was largely normal in all groups. In conclusion, DHA was capable of restoring all observed impairment in male reproduction, whereas 22:4n6 formed from dietary AA may act as an inferior substitute for DHA.

The tumor suppressor gene TRC8/RNF139 is disrupted by a constitutional balanced translocation t(8;22)(q24.13;q11.21) in a young girl with dysgerminoma

Background

RNF139/TRC8 is a potential tumor suppressor gene with similarity to PTCH, a tumor suppressor implicated in basal cell carcinomas and glioblastomas. TRC8 has the potential to act in a novel regulatory relationship linking the cholesterol/lipid biosynthetic pathway with cellular growth control and has been identified in families with hereditary renal (RCC) and thyroid cancers. Haploinsufficiency of TRC8 may facilitate development of clear cell-RCC in association with VHL mutations, and may increase risk for other tumor types. We report a paternally inherited balanced translocation t(8;22) in a proposita with dysgerminoma.

Methods

The translocation was characterized by FISH and the breakpoints cloned, sequenced, and compared. DNA isolated from normal and tumor cells was checked for abnormalities by array-CGH. Expression of genes TRC8 and TSN was tested both on dysgerminoma and in the proposita and her father.

Results

The breakpoints of the translocation are located within the LCR-B low copy repeat on chromosome 22q11.21, containing the palindromic AT-rich repeat (PATRR) involved in recurrent and non-recurrent translocations, and in an AT-rich sequence inside intron 1 of the TRC8 tumor-suppressor gene at 8q24.13. TRC8 was strongly underexpressed in the dysgerminoma. Translin is underexpressed in the dysgerminoma compared to normal ovary.

TRC8 is a target of Translin (TSN), a posttranscriptional regulator of genes transcribed by the transcription factor CREM-tau in postmeiotic male germ cells.

Conclusion

A role for TRC8 in dysgerminoma may relate to its interaction with Translin. We propose a model in which one copy of TRC8 is disrupted by a palindrome-mediated translocation followed by complete loss of expression through suppression, possibly mediated by miRNA.

Society for Reproductive Biology Founders' Lecture 2007. Insights into germ cell biology: from the bench to the clinic

The germline is unique among tissues in being the only lineage that is transmitted through generations. The gonadal somatic cells that interact with male and female germ cells are equally important for their juxtacrine and paracrine signalling pathways that lead to the formation of functionally mature gametes and healthy progeny. The present review summarises exciting new studies that our group and others have achieved at the frontier of male and female germ cell biology and in studying transforming growth factor-beta signalling pathways in oocyte-somatic cell interactions and gonadal growth and differentiation. In the process, we have produced over 70 transgenic and knockout models to study reproduction in vivo. These models have helped us identify novel and unexplored areas of germ cell biology and translate this work into the fertility clinic.

Noncoding RNAs of the mammalian testis: the meiotic transcripts Nct1 and Nct2 encode piRNAs

In eukaryotic cells, the vast majority of transcribed sequences are extragenic with no known functions. Translin is a DNA/RNA-binding protein involved in mRNA transport and translation in postmeiotic male germ cells. In an effort to identify meiotic target RNAs of Translin, reversible RNA protein cross-linking and immunoprecipitations with an affinity purified antibody to Translin were performed. Four new meiotically expressed mRNAs and one noncoding RNA with Translin binding sites were identified. Following sequencing, the noncoding RNA, Nct1, was 100% identical to a site on mouse chromosome 2. A second partially homologous sequence, Nct2, was detected nearby. Nct 1 and 2 contained sequences identical to piRNAs. Nct1 and 2 appear to be male germ cell-specific transcripts and are predominantly detected in pachytene spermatocytes. Focusing on the abundant single-copy PIWI-interacting RNA (piRNA), germline small RNA (gsRNA10) (the gsRNA10 sequence is identical to 29 nt in Nct1), we find that gsRNA10 increases greatly as spermatogenesis proceeds with concomitant decreases in Nct1 and 2. The piRNA gsRNA10 binds to the germ cell-specific Y-box protein, MSY2, but not to Translin. Although the size of the primary transcript(s) encoding the piRNAs in the locus on chromosome 2 is not known, we propose that Nct1 and 2 are part of a piRNA precursor.

Polypyrimidine tract binding protein 2 stabilizes phosphoglycerate kinase 2 mRNA in murine male germ cells by binding to its 3'UTR

The mRNA that encodes the testis-specific protein phosphoglycerate kinase (PGK2) is a long-lived mRNA that is transcribed in meiotic and postmeiotic male germ cells. Pgk2 mRNA is present in germ cells for up to 2 wk before its protein product is detected. Using affinity chromatography with the 3'-UTR of the Pgk2 mRNA, several proteins, including the RNA-binding protein, polypyrimidine tract binding protein 2 (PTBP2), were identified in mouse testis extracts. Coimmunoprecipitation experiments confirmed that PTBP2 binds to Pgk2 mRNA in the testis and RNA gel shifts demonstrated that PTBP2, but not PTBP1, binds to a specific region of the Pgk2 3'-UTR. Recombinant PTBP2 increased the stability of reporter constructs that contained the 3'-UTR Pgk2 sequence element in both testis extracts and transfected HeLa cells. We propose that PTBP2 is a trans-acting factor that helps to stabilize Pgk2 mRNA in male mouse germ cells.

Molecular biological features of male germ cell differentiation

Somatic cell differentiation is required throughout the life of a multicellular organism to maintain homeostasis. In contrast, germ cells have only one specific function; to preserve the species by conveying the parental genes to the next generation. Recent studies of the development and molecular biology of the male germ cell have identified many genes, or isoforms, that are specifically expressed in the male germ cell. In the present review, we consider the unique features of male germ cell differentiation. (Reprod Med Biol 2007; 6: 1-9).

Expression pattern of Drosophila translin and behavioral analyses of the mutant

Translin is an evolutionarily conserved approximately 27-kDa protein that binds to specific DNA and RNA sequences and has diverse cellular functions. Here, we report the cloning and characterization of the translin orthologue from the fruit fly Drosophila melanogaster. Under protein-denaturing conditions, purified Drosophila translin exists as a mixture of dimers and monomers just like human translin. In contrast to human translin, the Drosophila translin dimers do not appear to be stabilized by disulfide interactions. Drosophila translin shows a ubiquitous cytoplasmic localization in early embryonal syncytial stage, with an enhanced staining in ventral neuroblasts at later stages (8-9), which are probably at metaphase. An elevated expression was seen in several other cell types, such as cells around the tracheal pits in the embryo and oenocytes in the third instar larva. RNA in situ hybridization showed an increased expression in the ventral midline cells of the larval brain, suggesting a neuronal expression, which was corroborated by protein immunostaining. In adult flies, Drosophila translin is localized in the brain neuronal cell bodies and in early spermatocytes. Interestingly, Drosophila translin mutants exhibit an impaired motor response which is sex specific. Taken together, the multiple cellular localizations, the high neuronal expression and the attendant locomotor defect of the Drosophila translin mutant suggest that Drosophila translin may have roles in neuronal development and behavior analogous to that of mouse translin.

Altered protamine expression and diminished spermatogenesis: what is the link?

During the elongating spermatid stage of spermiogenesis, human sperm chromatin undergoes a complex transition in which histones are extensively replaced by protamines in a carefully regulated transition including histone modifications and intermediate and temporary replacement of the histones by sperm-specific transition proteins. The replacement of most histones by protamines 1 and 2 facilitates a high order of chromatin packaging necessary for normal sperm function and may also be necessary for DNA silencing and imprinting changes within the sperm cell. Protamines 1 and 2 are usually expressed in nearly equal quantities, but elevated or diminished protamine 1/protamine 2 ratios are observed in some infertile men and is often associated with severe spermatogenesis defects. Human and animal studies demonstrate that expression of the protamine proteins is uniquely regulated by transcription/translation factors, including storage of the mRNA in ribonucleoprotein (RNP) particles composed of the mRNA, transcription factors and a kinesin molecule necessary for transport of the RNP to the cytoplasm and removal of transcriptional activators from the nucleus. Recent studies indicate that most patients with abnormal protamine protein levels have elevated levels of protamine transcript in the mature sperm cell, indicating a possible defect in transcription or translation. The regulation of protamine expression is unique and includes several possible mechanisms which may be responsible for dysregulation of protamine expression and concurrent broad spectrum defects in spermatogenesis. We suggest two hypotheses: (i) that abnormal protamine expression is indicative of a generalized defect in mRNA storage and/or translation which affects other mRNA transcripts or (ii) that protamines may act as a checkpoint of spermatogenesis.