Molecular basis of the morphogenesis of sperm head and tail in mice

Development of functional spermatozoa in mammalian spermiogenesis

Infertility is a global health problem affecting one in six couples, with 50% of cases attributed to male infertility. Spermatozoa are male gametes, specialized cells that can be divided into two parts: the head and the flagellum. The head contains a vesicle called the acrosome that undergoes exocytosis and the flagellum is a motility apparatus that propels the spermatozoa forward and can be divided into two components, axonemes and accessory structures. For spermatozoa to fertilize oocytes, the acrosome and flagellum must be formed correctly. In this Review, we describe comprehensively how functional spermatozoa develop in mammals during spermiogenesis, including the formation of acrosomes, axonemes and accessory structures by focusing on analyses of mouse models.

Structure and Composition of Spermatozoa Fibrous Sheath in Diverse Groups of Metazoa

The proper functioning and assembly of the sperm flagella structures contribute significantly to spermatozoa motility and overall male fertility. However, the fine mechanisms of assembly steps are poorly studied due to the high diversity of cell types, low solubility of the corresponding protein structures, and high tissue and cell specificity. One of the open questions for investigation is the attachment of longitudinal columns to the doublets 3 and 8 of axonemal microtubules through the outer dense fibers. A number of mutations affecting the assembly of flagella in model organisms are known. Additionally, evolutionary genomics data and comparative analysis of flagella morphology are available for a set of non-model species. This review is devoted to the analysis of diverse ultrastructures of sperm flagellum of Metazoa combined with an overview of the evolutionary distribution and function of the mammalian fibrous sheath proteins.

Golgi associated RAB2 interactor protein family contributes to murine male fertility to various extents by assuring correct morphogenesis of sperm heads

Sperm heads contain not only the nucleus but also the acrosome which is a distinctive cap-like structure located anterior to the nucleus and is derived from the Golgi apparatus. The Golgi Associated RAB2 Interactors (GARINs; also known as FAM71) protein family shows predominant expression in the testis and all possess a RAB2-binding domain which confers binding affinity to RAB2, a small GTPase that is responsible for membrane transport and vesicle trafficking. Our previous study showed that GARIN1A and GARIN1B are important for acrosome biogenesis and that GARIN1B is indispensable for male fertility in mice. Here, we generated KO mice of other Garins, namely Garin2, Garin3, Garin4, Garin5a, and Garin5b (Garin2-5b). Using computer-assisted morphological analysis, we found that the loss of each Garin2-5b resulted in aberrant sperm head morphogenesis. While the fertilities of Garin2-/- and Garin4-/- males are normal, Garin5a-/- and Garin5b-/- males are subfertile, and Garin3-/- males are infertile. Further analysis revealed that Garin3-/- males exhibited abnormal acrosomal morphology, but not as severely as Garin1b-/- males; instead, the amounts of membrane proteins, particularly ADAM family proteins, decreased in Garin3 KO spermatozoa. Moreover, only Garin4 KO mice exhibit vacuoles in the sperm head. These results indicate that GARINs assure correct head morphogenesis and some members of the GARIN family function distinctively in male fertility.

Gene-deficient mouse model established by CRISPR/Cas9 system reveals 15 reproductive organ-enriched genes dispensable for male fertility

Since the advent of gene-targeting technology in embryonic stem cells, mice have become a primary model organism for investigating human gene function due to the striking genomic similarities between the two species. With the introduction of the CRISPR/Cas9 system for genome editing in mice, the pace of loss-of-function analysis has accelerated significantly. This has led to the identification of numerous genes that play crucial roles in male reproductive processes, including meiosis, chromatin condensation, flagellum formation in the testis, sperm maturation in the epididymis, and fertilization in the oviduct. Despite the advancements, the functions of many genes, particularly those enriched in male reproductive tissues, remain largely unknown. In our study, we focused on 15 genes and generated 13 gene-deficient mice [4933411K16Rik, Adam triple (Adam20, Adam25, and Adam39), BC048671, Cfap68, Gm4846, Gm4984, Gm13570, Nt5c1b, Ppp1r42, Saxo4, Sh3d21, Spz1, and Tektl1] to elucidate their roles in male fertility. Surprisingly, all 13 gene-deficient mice exhibited normal fertility in natural breeding experiments, indicating that these genes are not essential for male fertility. These findings have important implications as they may help prevent other research laboratories from duplicating efforts to generate knockout mice for genes that do not demonstrate an apparent phenotype related to male fertility. By shedding light on the dispensability of these genes, our study contributes to a more efficient allocation of research resources in the exploration of male reproductive biology.

Map-1a regulates Sertoli cell BTB dynamics through the cytoskeletal organization of microtubule and F-actin

Microtubule-associated protein 1a (Map1a) is a microtubule (MT) regulatory protein that binds to the MT protofilaments in mammalian cells to promote MT stabilization. Maps work with MT cleavage proteins and other MT catastrophe-inducing proteins to confer MT dynamics to support changes in the Sertoli cell shape to sustain spermatogenesis. However, no functional studies are found in the literature to probe its role in spermatogenesis. Using an RNAi approach, coupled with the use of toxicant-induced testis (in vivo)- and Sertoli cell (in vitro)-injury models, RNA-Seq analysis, transcriptome profiling, and relevant bioinformatics analysis, immunofluorescence analysis, and pertinent biochemical assays for cytoskeletal organization, we have delineated the functional role of Map1a in Sertoli cells and testes. Map1a was shown to support MT structural organization, and its knockdown (KD) also perturbed the structural organization of actin, vimentin, and septin cytoskeletons as these cytoskeletons are intimately related, working in concert to support spermatogenesis. More importantly, cadmium-induced Sertoli cell injury that perturbed the MT structural organization across the cell cytoplasm was associated with disruptive changes in the distribution of Map1a and a surge in p-p38-MAPK (phosphorylated p38-mitogen-activated protein kinase) expression but not total p38-MAPK. These findings thus support the notion that p-p38-MAPK activation is involved in cadmium-induced Sertoli cell injury. This conclusion was supported by studies using doramapimod, a specific p38-MAPK phosphorylation (activation) inhibitor, which was capable of restoring the cadmium-induced disruptive structural organization of MTs across the Sertoli cell cytoplasm. In summary: this study provides mechanistic insights regarding restoration of toxicant-induced Sertoli cell and testis injury and male infertility.

Bi-allelic variants in DNAH3 cause male infertility with asthenoteratozoospermia in humans and mice

STUDY QUESTION

Are there other pathogenic genes for asthenoteratozoospermia (AT)?

SUMMARY ANSWER

DNAH3 is a novel candidate gene for AT in humans and mice.

WHAT IS KNOWN ALREADY

AT is a major cause of male infertility. Several genes underlying AT have been reported; however, the genetic aetiology remains unknown in a majority of affected men.

STUDY DESIGN SIZE DURATION

A total of 432 patients with AT were recruited in this study. DNAH3 mutations were identified by whole-exome sequencing (WES). Dnah3 knockout mice were generated using the genome editing tool. The morphology and motility of sperm from Dnah3 knockout mice were investigated. The entire study was conducted over 3 years.

PARTICIPANTS/MATERIALS SETTING METHODS

WES was performed on 432 infertile patients with AT. In addition, two lines of Dnah3 knockout mice were generated. Haematoxylin and eosin (H&E) staining, transmission electron microscopy (TEM), immunostaining, and computer-aided sperm analysis (CASA) were performed to investigate the morphology and motility of the spermatozoa. ICSI was used to overcome the infertility of one patient and of the Dnah3 knockout mice.

MAIN RESULTS AND THE ROLE OF CHANCE

DNAH3 biallelic variants were identified in three patients from three unrelated families. H&E staining revealed various morphological abnormalities in the flagella of sperm from the patients, and TEM and immunostaining further showed the loss of the central pair of microtubules, a dislocated mitochondrial sheath and fibrous sheath, as well as a partial absence of the inner dynein arms. In addition, the two Dnah3 knockout mouse lines demonstrated AT. One patient and the Dnah3 knockout mice showed good treatment outcomes after ICSI.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

This is a preliminary report suggesting that defects in DNAH3 can lead to asthenoteratozoospermia in humans and mice. The pathogenic mechanism needs to be further examined in a future study.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings show that DNAH3 is a novel candidate gene for AT in humans and mice and provide crucial insights into the biological underpinnings of this disorder. The findings may also be beneficial for counselling affected individuals.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants from National Natural Science Foundation of China (82201773, 82101961, 82171608, 32322017, 82071697, and 81971447), National Key Research and Development Program of China (2022YFC2702604), Scientific Research Foundation of the Health Committee of Hunan Province (B202301039323, B202301039518), Hunan Provincial Natural Science Foundation (2023JJ30716), the Medical Innovation Project of Fujian Province (2020-CXB-051), the Science and Technology Project of Fujian Province (2023D017), China Postdoctoral Science Foundation (2022M711119), and Guilin technology project for people's benefit (20180106-4-7). The authors declare no competing interests.

Roles of Y-27632 on sheep sperm metabolism

To investigate the effect of Y-27632 on low-temperature metabolism of sheep sperm, different concentrations of Y-27632 were added to sheep semen at 4 °C in this experiment to detect indicators such as sperm motility, plasma membrane, acrosome, antioxidant performance, mitochondrial membrane potential (MMP), and metabolomics. The results showed that the addition of 20 µM Y-27632 significantly increased sperm motility, plasma membrane integrity rate, acrosome integrity rate, antioxidant capacity, MMP level, significantly increased sperm adenosine triphosphate (ATP) and total cholesterol content, and significantly reduced sperm Ca2+ content. In metabolomics analysis, compared with the control group, the 20 µM Y-27632 group screened 20 differential metabolites, mainly involved in five metabolic pathways, with the most significant difference in Histidine metabolism (P = 0.001). The results confirmed that Y-27632 significantly improved the quality of sheep sperm preservation under low-temperature conditions.

Zinc oxide nanoparticles-induced testis damage at single-cell resolution: Depletion of spermatogonia reservoir and disorder of Sertoli cell homeostasis

The widespread application of zinc oxide nanoparticles (ZnO NPs) in our daily life has initiated an enhanced awareness of their biosafety concern. An incredible boom of evidence of organismal disorder has accumulated for ZnO NPs, yet there has been no relevant study at the single-cell level. Here, we profiled > 28,000 single-cell transcriptomes and assayed > 25,000 genes in testicular tissues from two healthy Sprague Dawley (SD) rats and two SD rats orally exposed to ZnO NPs. We identified 10 cell types in the rat testis. ZnO NPs had more deleterious effects on spermatogonia, Sertoli cells, and macrophages than on the other cell types. Cell-cell communication analysis indicated a sharp decrease of interaction intensity for all cell types except macrophages in the ZnO NPs group than in the control group. Interestingly, two distinct maturation states of spermatogonia were detected during pseudotime analysis, and ZnO NPs induced reservoir exhaustion of undifferentiated spermatogonia. Mechanically, ZnO NPs triggered fatty acid accumulation in GC-1 cells through protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling and peroxisome proliferator-activated receptor alpha (PPARα)/acyl-CoA oxidase 1 (Acox1) axis, contributing to cell apoptosis. In terms of Sertoli cells, downregulated genes were highly enriched for tight junction. In vitro and in vivo experiments verified that ZnO NPs disrupted blood-testis barrier formation and growth factors synthesis, which subsequently inhibited the proliferation and induced the apoptosis of spermatogonia. As for the macrophages, ZnO NPs activated oxidative stress of Raw264.7 cells through nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway and promoted cell apoptosis through extracellular signal-regulated kinase (ERK) 1/2 pathway. Collectively, our work reveals the cell type-specific and cellularly heterogenetic mechanism of ZnO NPs-induced testis damage and paves the path for identifying putative biomarkers and therapeutics against this disorder.

TTC6-Mediated Stabilization of the Flagellum Annulus Ensures the Rapid and Directed Motion of Sperm

Sperm motility and structural integrity are essential for successful fertilization in vivo, and any hindrance of the correct assembly of the axoneme and peri-axonemal structures in the sperm flagellum can lead to fertility problems. While there has been considerable advancement in studying diseases related to the flagellum, the underlying mechanisms that control sperm movement are not yet fully understood. In this study, we reveal that the tetratricopeptide repeat protein 6 (Ttc6) gene, expressed mainly in the testes, plays a crucial role in maintaining male fertility in mice. We further demonstrate that the knockout of Ttc6 in mice results in decreased sperm motility and induces an abnormal circular swimming pattern, consequently leading to male subfertility. Morphological analysis showed an atypical hairpin-like appearance of the spermatozoa, and ultrastructural studies showed unsheathed flagella at the juncture between the midpiece and principal piece. Collectively, these findings suggest that TTC6 plays an essential role in maintaining the stability of the annulus region of the sperm flagellum, thus ensuring the swift and directed motion of sperm.

Role of Macroautophagy in Mammalian Male Reproductive Physiology

Physiologically, autophagy is an evolutionarily conserved and self-degradative process in cells. Autophagy carries out normal physiological roles throughout mammalian life. Accumulating evidence shows autophagy as a mechanism for cellular growth, development, differentiation, survival, and homeostasis. In male reproductive systems, normal spermatogenesis and steroidogenesis need a balance between degradation and energy supply to preserve cellular metabolic homeostasis. The main process of autophagy includes the formation and maturation of the phagophore, autophagosome, and autolysosome. Autophagy is controlled by a group of autophagy-related genes that form the core machinery of autophagy. Three types of autophagy mechanisms have been discovered in mammalian cells: macroautophagy, microautophagy, and chaperone-mediated autophagy. Autophagy is classified as non-selective or selective. Non-selective macroautophagy randomly engulfs the cytoplasmic components in autophagosomes that are degraded by lysosomal enzymes. While selective macroautophagy precisely identifies and degrades a specific element, current findings have shown the novel functional roles of autophagy in male reproduction. It has been recognized that dysfunction in the autophagy process can be associated with male infertility. Overall, this review provides an overview of the cellular and molecular basics of autophagy and summarizes the latest findings on the key role of autophagy in mammalian male reproductive physiology.

Expression of RSPH6A in the first wave of rat spermatogenesis and oxidative stress conditions: Attenuation by melatonin

Purpose

Here, we report, for the first time, the temporal expression and localization of axonemal radial spoke head homolog A (RSPH6A) protein during the first wave of rat spermatogenesis and in oxidative stress conditions.

Methods

For the developmental study, testes were collected from rats at different developmental stages (7, 14, 21, 28, 35, 42, and 60 postnatal days); for in vivo treatment, 24 rats were treated with cadmium and/or melatonin. From each sample, western blot (WB) and immunofluorescence (IF) analyses for RSPH6A were performed.

Results

RSPH6A expression starts at 21 PND alongside the appearance of I spermatocytes (SPC) with a significant increase up to 60 PND. Data were confirmed by IF analysis, showing that RPSH6A expression is restricted to I and II SPC, spermatids, and mature sperm. In vivo experiments showed that the expression and localization of RSPH6A in the testis and epididymal spermatozoa of adult rats treated with cadmium were impaired. Interestingly, melatonin (an antioxidant), given together with Cd, can counteract its damaging effects.

Conclusions

All combined data confirm that RSPH6A contributes to the onset of fertility by acting on sperm motility, raising the possibility of using RSPH6A as a marker for normal fertility in the general population.