Stage-dependent Dishevelled-1 expression during mouse spermatogenesis suggests a role in regulating spermatid morphological changes

Planar cell polarity (PCP) proteins support spermatogenesis through cytoskeletal organization in the testis

Few reports are found in the literature regarding the role of planar cell polarity (PCP) in supporting spermatogenesis in the testis. Yet morphological studies reported decades earlier have illustrated the directional alignment of polarized developing spermatids, most notably step 17-19 spermatids in stage V-early VIII tubules in the testis, across the plane of the epithelium in seminiferous tubules of adult rats. Such morphological features have unequivocally demonstrated the presence of PCP in developing spermatids, analogous to the PCP noted in hair cells of the cochlea in mammals. Emerging evidence in recent years has shown that Sertoli and germ cells express numerous PCP proteins, mostly notably, the core PCP proteins, PCP effectors and PCP signaling proteins. In this review, we discuss recent findings in the field regarding the two core PCP protein complexes, namely the Van Gogh-like 2 (Vangl2)/Prickle (Pk) complex and the Frizzled (Fzd)/Dishevelled (Dvl) complex. These findings have illustrated that these PCP proteins exert their regulatory role to support spermatogenesis through changes in the organization of actin and microtubule (MT) cytoskeletons in Sertoli cells. For instance, these PCP proteins confer PCP to developing spermatids. As such, developing haploid spermatids can be aligned and orderly packed within the limited space of the seminiferous tubules in the testes for the production of sperm via spermatogenesis. Thus, each adult male in the mouse, rat or human can produce an upward of 30, 50 or 300 million spermatozoa on a daily basis, respectively, throughout the adulthood. We also highlight critical areas of research that deserve attention in future studies. We also provide a hypothetical model by which PCP proteins support spermatogenesis based on recent studies in the testis. It is conceivable that the hypothetical model shown here will be updated as more data become available in future years, but this information can serve as the framework by investigators to unravel the role of PCP in spermatogenesis.

SPATS1 (spermatogenesis-associated, serine-rich 1) is not essential for spermatogenesis and fertility in mouse

SPATS1 (spermatogenesis-associated, serine-rich 1) is an evolutionarily conserved, testis-specific protein that is differentially expressed during rat male meiotic prophase. Some reports have suggested a link between SPATS1 underexpression/mutation and human pathologies such as male infertility and testicular cancer. Given the absence of functional studies, we generated a Spats1 loss-of-function mouse model using CRISPR/Cas9 technology. The phenotypic analysis showed no overt phenotype in Spats1^-/- mice, with both males and females being fertile. Flow cytometry and histological analyses did not show differences in the testicular content and histology between WT and knockout mice. Moreover, no significant differences in sperm concentration, motility, and morphology, were observed between WT and KO mice. These results were obtained both for young adults and for aged animals. Besides, although an involvement of SPATS1 in the Wnt signaling pathway has been suggested, we did not detect changes in the expression levels of typical Wnt pathway-target genes in mutant individuals. Thus, albeit Spats1 alteration might be a risk factor for male testicular health, we hereby show that this gene is not individually essential for male fertility and spermatogenesis in mouse.

Vangl2 regulates spermatid planar cell polarity through microtubule (MT)-based cytoskeleton in the rat testis

During spermatogenesis, developing elongating/elongated spermatids are highly polarized cells, displaying unique apico-basal polarity. For instance, the heads of spermatids align perpendicular to the basement membrane with their tails pointing to the tubule lumen. Thus, the maximal number of spermatids are packed within the limited space of the seminiferous epithelium to support spermatogenesis.  Herein, we reported findings that  elongating/elongated spermatids displayed planar cell polarity (PCP) in adult rat testes in which the proximal end of polarized spermatid heads were aligned uniformly across the plane of the seminiferous epithelium based on studies  using confocal microscopy and 3-dimensional (D) reconstruction of the seminiferous tubules.  We also discovered  that spermatid PCP was regulated by PCP protein Vangl2 (Van Gogh-like protein 2) since Vangl2 knockdown by RNAi was found to perturb spermatid PCP. More important, Vangl2 exerted its regulatory effects through changes in the organization of the microtubule (MT)-based cytoskeleton in the seminiferous epithelium. These changes were mediated via the downstream signaling proteins atypical protein kinase C ξ (PKCζ) and MT-associated protein (MAP)/microtubule affinity-regulating kinase 2 (MARK2). These findings thus provide new insights regarding the biology of spermatid PCP during spermiogenesis.

Cell polarity and planar cell polarity (PCP) in spermatogenesis

In adult mammalian testes, spermatids, most notably step 17-19 spermatids in stage IV-VIII tubules, are aligned with their heads pointing toward the basement membrane and their tails toward the tubule lumen. On the other hand, these polarized spermatids also align across the plane of seminiferous epithelium, mimicking planar cell polarity (PCP) found in other hair cells in cochlea (inner ear). This orderly alignment of developing spermatids during spermiogenesis is important to support spermatogenesis, such that the maximal number of developing spermatids can be packed and supported by a fixed population of differentiated Sertoli cells in the limited space of the seminiferous epithelium in adult testes. In this review, we provide emerging evidence to demonstrate spermatid PCP in the seminiferous epithelium to support spermatogenesis. We also review findings in the field regarding the biology of spermatid cellular polarity (e.g., head-tail polarity and apico-basal polarity) and its inter-relationship to spermatid PCP. Furthermore, we also provide a hypothetical concept on the importance of PCP proteins in endocytic vesicle-mediated protein trafficking events to support spermatogenesis through protein endocytosis and recycling.

Does murine spermatogenesis require WNT signalling? A lesson from Gpr177 conditional knockout mouse models

Wingless-related MMTV integration site (WNT) proteins and several other components of the WNT signalling pathway are expressed in the murine testes. However, mice mutant for WNT signalling effector β-catenin using different Cre drivers have phenotypes that are inconsistent with each other. The complexity and overlapping expression of WNT signalling cascades have prevented researchers from dissecting their function in spermatogenesis. Depletion of the Gpr177 gene (the mouse orthologue of Drosophila Wntless), which is required for the secretion of various WNTs, makes it possible to genetically dissect the overall effect of WNTs in testis development. In this study, the Gpr177 gene was conditionally depleted in germ cells (Gpr177^flox/flox, Mvh-Cre; Gpr177^flox/flox, Stra8-Cre) and Sertoli cells (Gpr177^flox/flox, Amh-Cre). No obvious defects in fertility and spermatogenesis were observed in these three Gpr177 conditional knockout (cKO) mice at 8 weeks. However, late-onset testicular atrophy and fertility decline in two germ cell-specific Gpr177 deletion mice were noted at 8 months. In contrast, we did not observe any abnormalities of spermatogenesis and fertility, even in 8-month-old Gpr177^flox/flox, Amh-Cre mice. Elevation of reactive oxygen species (ROS) was detected in Gpr177 cKO germ cells and Sertoli cells and exhibited an age-dependent manner. However, significant increase in the activity of Caspase 3 was only observed in germ cells from 8-month-old germ cell-specific Gpr177 knockout mice. In conclusion, GPR177 in Sertoli cells had no apparent influence on spermatogenesis, whereas loss of GPR177 in germ cells disrupted spermatogenesis in an age-dependent manner via elevating ROS levels and triggering germ cell apoptosis.

First Evidence of DAAM1 Localization During the Post-Natal Development of Rat Testis and in Mammalian Sperm

Dishevelled-associated activator of morphogenesis 1 (DAAM1) is a formin-family protein involved in nucleation of unbranched actin filaments and in cytoskeletal organization through Wnt-Dishevelled PCP pathway, which participates in essential biological processes, such as cell polarity, movement, and adhesion during morphogenesis and organogenesis. While its role has been investigated during development and in somatic cells, its potential association with the germinal compartment and reproduction is still unexplored. In this work, we assessed the possible association of DAAM1 with the morphogenesis of rat testis. We studied its expression and profiled its localization versus actin and tubulin, during the first wave of spermatogenesis and in the adult gonad (from 7 to 60 dpp). We show that, in mitotic phases, DAAM1 shares its localization with actin in Sertoli cells, gonocytes, and spermatogonia. Later, during meiosis, both proteins are found in spermatocytes, while only actin is detectable at the forming blood-testis barrier. DAAM1, then, follows the development of the acrosome system throughout spermiogenesis, and it is finally retained inside the cytoplasmic droplet in mature gametes, as corroborated by additional immunolocalization data on both rat and human sperm. Unlike the DAAM1, actin keeps its localization in Sertoli cells, and tubulin is associated with their protruding cytoplasm during the process. Our data support, for the first time, the hypothesis of a role for DAAM1 in cytoskeletal organization during Mammalian testis morphogenesis and gamete progression, while also hinting at its possible investigation as a morphological marker of germ cell and sperm physiology. J. Cell. Physiol. 231: 2172-2184, 2016. © 2016 Wiley Periodicals, Inc.

Transcriptome profiling of the developing postnatal mouse testis using next-generation sequencing

Mammalian testis development is a complex and highly sophisticated process. To study the dynamic change of normal testis development at the transcriptional level, we investigated mouse testes at three postnatal ages: 6 days postnatal, 4 weeks old, and 10 weeks old, representing infant (PN1), juvenile (PN2), and adult (PN3) stages, respectively. Using ultra high-throughput RNA sequencing (RNA-seq) technology, we obtained 211 million reads with a length of 35 bp. We identified 18837 genes that were expressed in mouse testes, and found that genes expressed at the highest level were involved in spermatogenesis. The gene expression pattern in PN1 was distinct from that in PN2 and PN3, which indicates that spermatogenesis has commenced in PN2. We analyzed a large number of genes related to spermatogenesis and somatic development of the testis, which play important roles at different developmental stages. We also found that the MAPK, Hedgehog, and Wnt signaling pathways were significantly involved at different developmental stages. These findings further our understanding of the molecular mechanisms that regulate testis development. Our study also demonstrates significant advantages of RNA-seq technology for studying transcriptome during development.

A unique combination of male germ cell miRNAs coordinates gonocyte differentiation

The last 100 years have seen a concerning decline in male reproductive health associated with decreased sperm production, sperm function and male fertility. Concomitantly, the incidence of defects in reproductive development, such as undescended testes, hypospadias and testicular cancer has increased. Indeed testicular cancer is now recognised as the most common malignancy in young men. Such cancers develop from the pre-invasive lesion Carcinoma in Situ (CIS), a dysfunctional precursor germ cell or gonocyte which has failed to successfully differentiate into a spermatogonium. It is therefore essential to understand the cellular transition from gonocytes to spermatogonia, in order to gain a better understanding of the aetiology of testicular germ cell tumours. MicroRNA (miRNA) are important regulators of gene expression in differentiation and development and thus highly likely to play a role in the differentiation of gonocytes. In this study we have examined the miRNA profiles of highly enriched populations of gonocytes and spermatogonia, using microarray technology. We identified seven differentially expressed miRNAs between gonocytes and spermatogonia (down-regulated: miR-293, 291a-5p, 290-5p and 294*, up-regulated: miR-136, 743a and 463*). Target prediction software identified many potential targets of several differentially expressed miRNA implicated in germ cell development, including members of the PTEN, and Wnt signalling pathways. These targets converge on the key downstream cell cycle regulator Cyclin D1, indicating that a unique combination of male germ cell miRNAs coordinate the differentiation and maintenance of pluripotency in germ cells.

Transcriptome profiling of testis during sexual maturation stages in Eriocheir sinensis using Illumina sequencing

The testis is a highly specialized tissue that plays dual roles in ensuring fertility by producing spermatozoa and hormones. Spermatogenesis is a complex process, resulting in the production of mature sperm from primordial germ cells. Significant structural and biochemical changes take place in the seminiferous epithelium of the adult testis during spermatogenesis. The gene expression pattern of testis in Chinese mitten crab (Eriocheir sinensis) has not been extensively studied, and limited genetic research has been performed on this species. The advent of high-throughput sequencing technologies enables the generation of genomic resources within a short period of time and at minimal cost. In the present study, we performed de novo transcriptome sequencing to produce a comprehensive transcript dataset for testis of E. sinensis. In two runs, we produced 25,698,778 sequencing reads corresponding with 2.31 Gb total nucleotides. These reads were assembled into 342,753 contigs or 141,861 scaffold sequences, which identified 96,311 unigenes. Based on similarity searches with known proteins, 39,995 unigenes were annotated based on having a Blast hit in the non-redundant database or ESTscan results with a cut-off E-value above 10⁻⁵. This is the first report of a mitten crab transcriptome using high-throughput sequencing technology, and all these testes transcripts can help us understand the molecular mechanisms involved in spermatogenesis and testis maturation.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

SIRT1 regulates Dishevelled proteins and promotes transient and constitutive Wnt signaling

Sirtuin 1 (SIRT1) is a class III histone deacetylase that deacetylates histone and nonhistone proteins to regulate gene transcription and protein function. Because SIRT1 regulates very diverse responses such as apoptosis, insulin sensitivity, autophagy, differentiation, and stem cell pluripotency, it has been a challenge to reconcile how it orchestrates such pleiotropic effects. Here we show that SIRT1 serves as an important regulator of Wnt signaling. We demonstrate that SIRT1 loss of function leads to a significant decrease in the levels of all three Dishevelled (Dvl) proteins. Furthermore, we demonstrate that SIRT1 and Dvl proteins complex in vivo and that inhibition of SIRT1 leads to changes in gene expression of Wnt target genes. Finally, we demonstrate that Wnt-stimulated cell migration is inhibited by a SIRT1 inhibitor. Because the three mammalian Dvl proteins serve as key messengers for as many as 19 Wnt ligands, SIRT1-mediated regulation of Dvl proteins may explain the diverse physiological responses observed in different cellular contexts. Previously, SIRT1 had only been shown to mediate the epigenetic silencing of Wnt antagonists. In contrast, here we report that SIRT1 regulates Dvl protein levels and Wnt signaling in several cellular contexts. These findings demonstrate that SIRT1 is a regulator of transient and constitutive Wnt signaling.

Constitutive WNT/beta-catenin signaling in murine Sertoli cells disrupts their differentiation and ability to support spermatogenesis

Sertoli and germ cell interactions are essential for spermatogenesis and, thus, male fertility. Sertoli cells provide a specialized microenvironment for spermatogonial stem cells to divide, allowing both self-renewal and spermatogenesis. In the present study, we used mice with a conditional activated allele of the beta-catenin gene (Ctnnb1(tm1Mmt)(/+)) in Sertoli cells expressing Cre recombinase driven by the anti-Müllerian hormone (AMH; also known as Müllerian-inhibiting substance) type II receptor promoter (Amhr2(tm3(cre)Bhr)(/+)) to show that constitutively activated beta-catenin leads to their continuous proliferation and compromised differentiation. Compared to controls, Sertoli cells in mature mutant mice continue to express high levels of both AMH and glial cell-derived neurotrophic factor (GDNF), which normally are expressed only in immature Sertoli cells. We also show evidence that LiCl treatment, which activates endogenous nuclear beta-catenin activity, regulates both AMH and GDNF expression at the transcriptional level. The epididymides were devoid of sperm in the Amhr2(tm3(cre)Bhr)(/+);Ctnnb1(tm1Mmt)(/+) mice at all ages examined. We show that the mutant mice are infertile because of defective differentiation of germ cells and increased apoptosis, both of which are characteristic of GDNF overexpression in Sertoli cells. Constitutive activation of beta-catenin in Amhr2-null mice showed the same histology, suggesting that the phenotype was the result of persistent overexpression of GDNF. These results show that dysregulated wingless-related MMTV integration site/beta-catenin signaling in Sertoli cells inhibits their postnatal differentiation, resulting in increased germ cell apoptosis and infertility.

Wnt signaling promotes proliferation and stemness regulation of spermatogonial stem/progenitor cells

Spermatogonial stem cells (SSCs) self-renew throughout life to produce progenitor cells that are able to differentiate into spermatozoa. However, the mechanisms underlying the cell fate determination between self-renewal and differentiation have not yet been delineated. Culture conditions and growth factors essential for self-renewal and proliferation of mouse SSCs have been investigated, but no information is available related to growth factors that affect fate determination of human spermatogonia. Wnts form a large family of secreted glycoproteins, the members of which are involved in cell proliferation, differentiation, organogenesis, and cell migration. Here, we show that Wnts and their receptors Fzs are expressed in mouse spermatogonia and in the C18-4 SSC line. We demonstrate that WNT3A induces cell proliferation, morphological changes, and cell migration in C18-4 cells. Furthermore, we show that beta-catenin is activated during testis development in 21-day-old mice. In addition, our study demonstrates that WNT3A sustained adult human embryonic stem (ES)-like cells derived from human germ cells in an undifferentiated stage, expressing essential human ES cell transcription factors. These results demonstrate for the first time that Wnt/beta-catenin pathways, especially WNT3A, may play an important role in the regulation of mouse and human spermatogonia.

Actin-based dynamics during spermatogenesis and its significance

Actin can be found in all kinds of eukaryotic cells, maintaining their shapes and motilities, while its dynamics in sperm cells is understood less than their nonmuscle somatic cell counterparts. Spermatogenesis is a complicated process, resulting in the production of mature sperm from primordial germ cell. Significant structural and biochemical changes take place in the seminiferous epithelium of the adult testis during spermatogenesis. It was proved that all mammalian sperm contain actin, and that F-actin may play an important role during spermatogenesis, especially in nuclear shaping. Recently a new model for sperm head elongation based on the acrosome-acroplaxome-manchette complex has been proposed. In Drosophila, F-actin assembly is supposed to be very crucial during individualization. In this mini-review, we provide an overview of the structure, function, and regulation characteristics of actin cytoskeleton, and a summary of the current status of research of actin-based structure and movement is also provided, with emphasis on the role of actins in sperm head shaping during spermiogenesis and the cell junction dynamics in the testis. Research of the Sertoli ectoplasmic specialization is in the spotlight, which is a testis-specific actin-based junction very important for the movement of germ cells across the epithelium. Study of the molecular architecture and the regulating mechanism of the Sertoli ectoplasmic specialization has become an intriguing field. All this may lead to a new strategy for male infertility and, at the same time, a novel idea may result in devising much safer contraception with high efficiency. It is hoped that the advances listed in this review would give developmental and morphological researchers a favorable investigating outline and could help to enlarge the view of new strategies and models for actin dynamics during spermatogenesis.