Spag4, a novel sperm protein, binds outer dense-fiber protein Odf1 and localizes to microtubules of manchette and axoneme

Life at the crossroads: the nuclear LINC complex and vascular mechanotransduction

Vascular endothelial cells line the inner surface of all blood vessels, where they are exposed to polarized mechanical forces throughout their lifespan. Both basal substrate interactions and apical blood flow-induced shear stress regulate blood vessel development, remodeling, and maintenance of vascular homeostasis. Disruption of these interactions leads to dysfunction and vascular pathologies, although how forces are sensed and integrated to affect endothelial cell behaviors is incompletely understood. Recently the endothelial cell nucleus has emerged as a prominent force-transducing organelle that participates in vascular mechanotransduction, via communication to and from cell-cell and cell-matrix junctions. The LINC complex, composed of SUN and nesprin proteins, spans the nuclear membranes and connects the nuclear lamina, the nuclear envelope, and the cytoskeleton. Here we review LINC complex involvement in endothelial cell mechanotransduction, describe unique and overlapping functions of each LINC complex component, and consider emerging evidence that two major SUN proteins, SUN1 and SUN2, orchestrate a complex interplay that extends outward to cell-cell and cell-matrix junctions and inward to interactions within the nucleus and chromatin. We discuss these findings in relation to vascular pathologies such as Hutchinson-Gilford progeria syndrome, a premature aging disorder with cardiovascular impairment. More knowledge of LINC complex regulation and function will help to understand how the nucleus participates in endothelial cell force sensing and how dysfunction leads to cardiovascular disease.

A framework for identifying fertility gene targets for mammalian pest control

Fertility-targeted gene drives have been proposed as an ethical genetic approach for managing wild populations of vertebrate pests for public health and conservation benefit. This manuscript introduces a framework to identify and evaluate target gene suitability based on biological gene function, gene expression and results from mouse knockout models. This framework identified 16 genes essential for male fertility and 12 genes important for female fertility that may be feasible targets for mammalian gene drives and other non-drive genetic pest control technology. Further, a comparative genomics analysis demonstrates the conservation of the identified genes across several globally significant invasive mammals. In addition to providing important considerations for identifying candidate genes, our framework and the genes identified in this study may have utility in developing additional pest control tools such as wildlife contraceptives.

Deficiency of the Tmem232 Gene Causes Male Infertility with Morphological Abnormalities of the Sperm Flagellum in Mice

The axoneme and accessory structures of flagella are critical for sperm motility and male fertilization. Sperm production needs precise and highly ordered gene expression to initiate and sustain the many cellular processes that result in mature spermatozoa. Here, we identified a testis enriched gene transmembrane protein 232 (Tmem232), which is essential for the structural integrity of the spermatozoa flagella axoneme. Tmem232 knockout mice were generated for in vivo analyses of its functions in spermatogenesis. Phenotypic analysis showed that deletion of Tmem232 in mice causes male-specific infertility. Transmission electron microscopy together with scanning electron microscopy were applied to analyze the spermatozoa flagella and it was observed that the lack of TMEM232 caused failure of the cytoplasm removal and the absence of the 7th outer microtubule doublet with its corresponding outer dense fiber (ODF). Co-IP assays further identified that TMEM232 interacts with ODF family protein ODF1, which is essential to maintain sperm motility. In conclusion, our findings indicate that TMEM232 is a critical protein for male fertility and sperm motility by regulating sperm cytoplasm removal and maintaining axoneme integrity.

A framework for identifying fertility gene targets for mammalian pest control

Fertility-targeted gene drives have been proposed as an ethical genetic approach for managing wild populations of vertebrate pests for public health and conservation benefit.This manuscript introduces a framework to identify and evaluate target gene suitability based on biological gene function, gene expression, and results from mouse knockout models.This framework identified 16 genes essential for male fertility and 12 genes important for female fertility that may be feasible targets for mammalian gene drives and other non-drive genetic pest control technology. Further, a comparative genomics analysis demonstrates the conservation of the identified genes across several globally significant invasive mammals.In addition to providing important considerations for identifying candidate genes, our framework and the genes identified in this study may have utility in developing additional pest control tools such as wildlife contraceptives.

Morphological and Molecular Bases of Male Infertility: A Closer Look at Sperm Flagellum

Infertility is a major health problem worldwide without an effective therapy or cure. It is estimated to affect 8-12% of couples in the reproductive age group, equally affecting both genders. There is no single cause of infertility, and its knowledge is still far from complete, with about 30% of infertile couples having no cause identified (named idiopathic infertility). Among male causes of infertility, asthenozoospermia (i.e., reduced sperm motility) is one of the most observed, being estimated that more than 20% of infertile men have this condition. In recent years, many researchers have focused on possible factors leading to asthenozoospermia, revealing the existence of many cellular and molecular players. So far, more than 4000 genes are thought to be involved in sperm production and as regulators of different aspects of sperm development, maturation, and function, and all can potentially cause male infertility if mutated. In this review, we aim to give a brief overview of the typical sperm flagellum morphology and compile some of the most relevant information regarding the genetic factors involved in male infertility, with a focus on sperm immotility and on genes related to sperm flagellum development, structure, or function.

Development of the Connecting Piece in ODF1-Deficient Mouse Spermatids

ODF1 is a major protein of the accessory fibres of the mammalian sperm tail. In addition, ODF1 is found in the connecting piece, a complex structure located at the posterior end of the nucleus that connects the sperm head and tail. The tight coupling of the sperm head and tail is critical for the progressive motility of the sperm to reach the oocyte for fertilisation. The depletion of ODF1 by homologous recombination in mice led to male infertility. Although sperm tails were present in the epididymis, no intact spermatozoa were found. Instead, the depletion of ODF1 resulted in sperm decapitation, suggesting that ODF1 is essential for the formation of the coupling apparatus and the tight linkage of the sperm head and tail. However, the development of the linkage complex in the absence of ODF1 has never been investigated. Here, I analysed the fine structure of the developing connecting piece by transmission electron microscopy. I show that the connecting piece develops as in wild-type spermatids. Structural abnormalities were not observed when ODF1 was absent. Thus, ODF1 is dispensable for the development of the connecting piece. However, the decapitation of ODF1-deficient spermatozoa indicates that the heads and tails of the spermatozoa are not linked, so that they separate when force is applied.

Novel mutations of PMFBP1 in a man with acephalic spermatozoa defects

BACKGROUND

Acephalic spermatozoa (AS) is a serious but rare reproductive genetic disorder that causes infertility in men. To date, only a few genes associated with AS defects have been identified, including the polyamine modulated factor 1 binding protein 1 (PMFBP1) gene. Consistent with this, PMFBP1 localizes to the head-neck connection, which bridges the implantation fossa and basal body.

METHODS

A male patient was diagnosed as having an AS defect. Blood samples from all family members and a sample of the patient's semen were collected to determine the genetic causes of his infertility.

RESULTS

Compound heterozygote mutation in the PMFBP1 gene, which is associated with AS defects in the present case: two loss-of-function mutations, with one a nonsense mutation c.361C > T p.Gln121Ter, and another a splice donor mutation c.414 + 1G > T. The current study, together with previous studies, suggests that the nonsense mutation is responsible for a truncated PMFBP1 protein during its formation; a splice donor mutation c.414 + 1G > T might lead to new open reading frames, from which the dysfunction of an abnormal PMFBP1 protein might be predicted. Additionally, the expression of outer dense fiber 1 (ODF1) and ODF2 proteins has been experimentally shown to be regulated by the truncated PMFBP1 protein.

CONCLUSION

We herein present a case with AS defects associated with heterozygote mutations of PMFBP1, which have been shown to be rare and pathogenic; the association with an AS defect is a monogenic disorder with a recessive inherited pattern in the patient's family.

Sperm associated antigen 4 promotes SREBP1-mediated de novo lipogenesis via interaction with lamin A/C and contributes to tumor progression in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly malignant tumor and its progression is associated with altered lipid metabolism in precancerous lesions, such as non-alcoholic fatty liver disease. Here, we identified sperm associated antigen 4 (SPAG4), and explored its oncogenic role in HCC progression. Database analysis and immunohistochemistry indicated increased level of SPAG4 in HCC tissues which was of prognostic value. Gain/loss-of-function experiments showed that SPAG4 exerted oncogenic roles in HCC growth both in vitro and in vivo. RNA sequencing revealed activation of a lipogenic state and SREBP1-mediated pathway following SPAG4 overexpression. Mechanistically, the N-terminal region of SPAG4 bound to lamin A/C, which increased SREBP1 expression, nuclear translocation, and transcriptional activity. Treatment with orlistat, a lipid synthesis inhibitor, reversed SPAG4-mediated oncogenic effects, and its efficacy varied with SPAG4 level. The effect of orlistat was further amplified when combined with sorafenib in tumor xenograft mouse models. Our study provides evidence that SPAG4 mediates HCC progression by affecting lipid metabolism. Administration of orlistat combined with sorafenib reverses SPAG4-mediated oncogenesis in HCC cells and ectopic xenograft tumors in mice, suggesting that this pathway represents a potential target for HCC treatment.

Insights on Human Small Heat Shock Proteins and Their Alterations in Diseases

The family of the human small Heat Shock Proteins (HSPBs) consists of ten members of chaperones (HSPB1-HSPB10), characterized by a low molecular weight and capable of dimerization and oligomerization forming large homo- or hetero-complexes. All HSPBs possess a highly conserved centrally located α-crystallin domain and poorly conserved N- and C-terminal domains. The main feature of HSPBs is to exert cytoprotective functions by preserving proteostasis, assuring the structural maintenance of the cytoskeleton and acting in response to cellular stresses and apoptosis. HSPBs take part in cell homeostasis by acting as holdases, which is the ability to interact with a substrate preventing its aggregation. In addition, HSPBs cooperate in substrates refolding driven by other chaperones or, alternatively, promote substrate routing to degradation. Notably, while some HSPBs are ubiquitously expressed, others show peculiar tissue-specific expression. Cardiac muscle, skeletal muscle and neurons show high expression levels for a wide variety of HSPBs. Indeed, most of the mutations identified in HSPBs are associated to cardiomyopathies, myopathies, and motor neuropathies. Instead, mutations in HSPB4 and HSPB5, which are also expressed in lens, have been associated with cataract. Mutations of HSPBs family members encompass base substitutions, insertions, and deletions, resulting in single amino acid substitutions or in the generation of truncated or elongated proteins. This review will provide an updated overview of disease-related mutations in HSPBs focusing on the structural and biochemical effects of mutations and their functional consequences.

The Transformation of the Centrosome into the Basal Body: Similarities and Dissimilarities between Somatic and Male Germ Cells and Their Relevance for Male Fertility

The sperm flagellum is essential for the transport of the genetic material toward the oocyte and thus the transmission of the genetic information to the next generation. During the haploid phase of spermatogenesis, i.e., spermiogenesis, a morphological and molecular restructuring of the male germ cell, the round spermatid, takes place that includes the silencing and compaction of the nucleus, the formation of the acrosomal vesicle from the Golgi apparatus, the formation of the sperm tail, and, finally, the shedding of excessive cytoplasm. Sperm tail formation starts in the round spermatid stage when the pair of centrioles moves toward the posterior pole of the nucleus. The sperm tail, eventually, becomes located opposed to the acrosomal vesicle, which develops at the anterior pole of the nucleus. The centriole pair tightly attaches to the nucleus, forming a nuclear membrane indentation. An articular structure is formed around the centriole pair known as the connecting piece, situated in the neck region and linking the sperm head to the tail, also named the head-to-tail coupling apparatus or, in short, HTCA. Finally, the sperm tail grows out from the distal centriole that is now transformed into the basal body of the flagellum. However, a centriole pair is found in nearly all cells of the body. In somatic cells, it accumulates a large mass of proteins, the pericentriolar material (PCM), that together constitute the centrosome, which is the main microtubule-organizing center of the cell, essential not only for the structuring of the cytoskeleton and the overall cellular organization but also for mitotic spindle formation and chromosome segregation. However, in post-mitotic (G1 or G0) cells, the centrosome is transformed into the basal body. In this case, one of the centrioles, which is always the oldest or mother centriole, grows the axoneme of a cilium. Most cells of the body carry a single cilium known as the primary cilium that serves as an antenna sensing the cell's environment. Besides, specialized cells develop multiple motile cilia differing in substructure from the immotile primary cilia that are essential in moving fluids or cargos over the cellular surface. Impairment of cilia formation causes numerous severe syndromes that are collectively subsumed as ciliopathies. This comparative overview serves to illustrate the molecular mechanisms of basal body formation, their similarities, and dissimilarities, in somatic versus male germ cells, by discussing the involved proteins/genes and their expression, localization, and function. The review, thus, aimed to provide a deeper knowledge of the molecular players that is essential for the expansion of clinical diagnostics and treatment of male fertility disorders.

LINCking the Nuclear Envelope to Sperm Architecture

Nuclear architecture undergoes an extensive remodeling during spermatogenesis, especially at levels of spermatocytes (SPC) and spermatids (SPT). Interestingly, typical events of spermiogenesis, such as nuclear elongation, acrosome biogenesis, and flagellum formation, need a functional cooperation between proteins of the nuclear envelope and acroplaxome/manchette structures. In addition, nuclear envelope plays a key role in chromosome distribution. In this scenario, special attention has been focused on the LINC (linker of nucleoskeleton and cytoskeleton) complex, a nuclear envelope-bridge structure involved in the connection of the nucleoskeleton to the cytoskeleton, governing mechanotransduction. It includes two integral proteins: KASH- and SUN-domain proteins, on the outer (ONM) and inner (INM) nuclear membrane, respectively. The LINC complex is involved in several functions fundamental to the correct development of sperm cells such as head formation and head to tail connection, and, therefore, it seems to be important in determining male fertility. This review provides a global overview of the main LINC complex components, with a special attention to their subcellular localization in sperm cells, their roles in the regulation of sperm morphological maturation, and, lastly, LINC complex alterations associated to male infertility.

Pathogenesis of acephalic spermatozoa syndrome caused by SUN5 variant

Acephalic spermatozoa syndrome (ASS) is a rare teratozoospermia that leads to male infertility. Previous work suggested a genetic origin. Variants of Sad1 and UNC84 domain containing 5 (SUN5) are the main genetic cause of ASS; however, its pathogenesis remains unclear. Here, we performed whole-exome sequencing in 10 unrelated ASS and identified 2 homozygous variants, c.381delA[p.V128Sfs7*] and c.675C>A[p.Y225X], and 1 compound variant, c.88 C > T[p.R30X] and c.381 delA [p.V128Sfs7*], in SUN5 in 4 patients. The c.381delA variant had been identified as pathogenic in previous reports, while c.675C>A and c.88 C > T were two novel variants which could lead to a premature termination codon (PTC) and resulted in loss of SUN5, and may also be pathogenic. SUN5 mRNA and protein were present at very low levels in ASS patients with SUN5 nonsense mutation. Furthermore, the distribution of outer dense fiber protein 1 (ODF1) and Nesprin3 was altered in sperm of ASS patients with SUN5 variants. The co-immunoprecipitation analysis indicated that SUN5 and ODF1, SUN5 and Nesprin3, and ODF1 and Nesprin3 interacted with each other in transfected HEK293T cells. Thus, we propose that SUN5, Nesprin3, and ODF1 may form a 'triplet' structure through interactions at neck of sperm. When gene variants resulted in a loss of SUN5, the 'triplet' structure disappears and then the head-tail junction becomes fragile, leading to the occurrence of ASS.

The SUN2-nesprin-2 LINC complex and KIF20A function in the Golgi dispersal

The morphology of the Golgi complex is influenced by the cellular context, which strictly correlates with nuclear functions; however, the mechanism underlying this association remains elusive. The inner nuclear membrane SUN proteins, SUN1 and SUN2, have diverse functions together with the outer nuclear membrane nesprin proteins, which comprise the LINC complex. We found that depletion of SUN1 leads to Golgi complex dispersion with maintenance of ministacks and retained function for vesicle transport through the Golgi complex. In addition, SUN2 associates with microtubule plus-end-directed motor KIF20A, possibly via nesprin-2. KIF20A plays a role in the Golgi dispersion in conjunction with the SUN2-nesprin-2 LINC complex in SUN1-depleted cells, suggesting that SUN1 suppresses the function of the SUN2-nesprin-2 LINC complex under a steady-state condition. Further, SUN1-knockout mice, which show impaired cerebellar development and cerebellar ataxia, presented altered Golgi morphology in Purkinje cells. These findings revealed a regulation of the Golgi organization by the LINC complex.

Expression profile analysis of a new testis-specifically expressed gene C17ORF64 and its association with cell apoptosis in MCF-7 cells

With the increasing incidence of male infertility, identification and investigation the functions of new genes related to spermatogenesis are effective avenues to elucidate the decline of testicular function. In this study, a new gene, C17ORF64 (chromosome 17 open reading frame 64), was identified from mouse testes and its potential function was studied.RT-PCR and qRT-PCR assay showed that C17ORF64 mRNA was expressed exclusively in mouse testes and up-regulated from the 3-week old to 6-month old testes during postpartum development, which is consistent with C17ORF64 protein expression profile by western blotting analysis. Immunohistochemical analysis revealed that C17ORF64 protein was mainly localized in the cytoplasm of spermatogonia and spermatocytes, which is verified by GFP- labeled C17ORF64 gene expressed in GC-1 cells. C17ORF64 overexpression not only promoted cell apoptosis in MCF-7 cells, but also significantly decreased cell viability via MTT assay. Flow cytometric assay showed that C17ORF64 overexpression could inhibit cell cycle progression by arresting G1/S transition. Western blot and qRT-PCR analysis revealed that C17ORF64 overexpression inhibited the expression of anti-apoptotic protein bcl-2 and increased the expressions of pro-apoptotic protein caspase-3, caspase-8, caspase-9, Bax, P21 and P53. Taken together, our results confirmed C17ORF64 testis-specific expression pattern and, for the first time, demonstrated that C17ORF64 could inhibit cell viability and accelerate apoptosis in MCF-7 cells through caspase-3 regulatory pathways.

The Role of the LINC Complex in Sperm Development and Function

The LINC (LInker of Nucleoskeleton and Cytoskeleton) complex is localized within the nuclear envelope and consists of SUN (Sad1/UNc84 homology domain-containing) proteins located in the inner nuclear membrane and KASH (Klarsicht/Anc1/Syne1 homology domain-containing) proteins located in the outer nuclear membrane, hence linking nuclear with cytoplasmic structures. While the nucleoplasm-facing side acts as a key player for correct pairing of homolog chromosomes and rapid chromosome movements during meiosis, the cytoplasm-facing side plays a pivotal role for sperm head development and proper acrosome formation during spermiogenesis. A further complex present in spermatozoa is involved in head-to-tail coupling. An intact LINC complex is crucial for the production of fertile sperm, as mutations in genes encoding for complex proteins are known to be associated with male subfertility in both mice and men. The present review provides a comprehensive overview on our current knowledge of LINC complex subtypes present in germ cells and its central role for male reproduction. Future studies on distinct LINC complex components are an absolute requirement to improve the diagnosis of idiopathic male factor infertility and the outcome of assisted reproduction.

Fertility Relevance Probability Analysis Shortlists Genetic Markers for Male Fertility Impairment

Impairment of male fertility is one of the major public health issues worldwide. Nevertheless, genetic causes of male sub- and infertility can often only be suspected due to the lack of reliable and easy-to-use routine tests. Yet, the development of a marker panel is complicated by the large quantity of potentially predictive markers. Actually, hundreds or even thousands of genes could have fertility relevance. Thus, a systematic method enabling a selection of the most predictive markers out of the many candidates is required. As a criterion for marker selection, we derived a gene-specific score, which we refer to as fertility relevance probability (FRP). For this purpose, we first categorized 2,753 testis-expressed genes as either candidate markers or non-candidates, according to phenotypes in male knockout mice. In a parallel approach, 2,502 genes were classified as candidate markers or non-candidates based on phenotypes in men. Subsequently, we conducted logistic regression analyses with evolutionary rates of genes (dN/dS), transcription levels in testis relative to other organs, and connectivity of the encoded proteins in a protein-protein interaction network as covariates. In confirmation of the procedure, FRP values showed the expected pattern, thus being overall higher in genes with known relevance for fertility than in their counterparts without corresponding evidence. In addition, higher FRP values corresponded with an increased dysregulation of protein abundance in spermatozoa of 37 men with normal and 38 men with impaired fertility. Present analyses resulted in a ranking of genes according to their probable predictive power as candidate markers for male fertility impairment. Thus, AKAP4, TNP1, DAZL, BRDT, DMRT1, SPO11, ZPBP, HORMAD1, and SMC1B are prime candidates toward a marker panel for male fertility impairment. Additional candidate markers are DDX4, SHCBP1L, CCDC155, ODF1, DMRTB1, ASZ1, BOLL, FKBP6, SLC25A31, PRSS21, and RNF17. FRP inference additionally provides clues for potential new markers, thereunder TEX37 and POU4F2. The results of our logistic regression analyses are freely available at the PreFer Genes website (https://prefer-genes.uni-mainz.de/).

Genetic loss of importin α4 causes abnormal sperm morphology and impacts on male fertility in mouse

Importin α proteins play a central role in the transport of cargo from the cytoplasm to the nucleus. In this study, we observed that male knock-out mice for importin α4, which is encoded by the Kpna4 gene (Kpna4^-/- ), were subfertile and yielded smaller litter sizes than those of wild-type (WT) males. In contrast, mice lacking the closely related importin α3 (Kpna3^-/- ) were fertile. In vitro fertilization and sperm motility assays demonstrated that sperm from Kpna4^-/- mice had significantly reduced quality and motility. In addition, acrosome reaction was also impaired in Kpna4^-/- mice. Transmission electron microscopy revealed striking defects, including abnormal head morphology and multiple axoneme structures in the flagella of Kpna4^-/- mice. A five-fold increase in the frequency of abnormalities in Kpna4^-/- mice compared to WT mice indicates the functional importance of importin α4 in normal sperm development. Moreover, Nesprin-2, which is a component of the linker of nucleus and cytoskeleton complex, was expressed at lower levels in sperm from Kpna4^-/- mice and was localized with abnormal axonemes, suggesting incorrect formation of the nuclear membrane-cytoskeleton structure during spermiogenesis. Proteomics analysis of Kpna4^-/- testis showed significantly altered expression of proteins related to sperm formation, which provided evidence that genetic loss of importin α4 perturbed chromatin status. Collectively, these findings indicate that importin α4 is critical for establishing normal sperm morphology in mice, providing new insights into male germ cell development by highlighting the requirement of importin α4 for normal fertility.

The SUN1 splicing variants SUN1_888 and SUN1_916 differentially regulate nucleolar structure

The nucleolar structure is highly dynamic and strictly regulated in response to internal cues, such as metabolic rates, and to external cues, such as mechanical forces applied to cells. Although the multilayered nucleolar structure is largely determined by the liquid-like properties of RNA and proteins, the mechanisms regulating the morphology and number of nucleoli remain elusive. The linker of the nucleoskeleton and cytoskeleton (LINC) complex comprises inner nuclear membrane Sad1/UNC-84 (SUN) proteins and outer nuclear membrane-localized nesprins. We previously showed that the depletion of SUN1 proteins affects nucleolar morphologies. This study focuses on the function of SUN1 splicing variants in determining nucleolar morphology. An RNA interference strategy showed that the predominantly expressed variants, SUN1_888 and SUN1_916, were crucial for nucleolar morphology but functionally distinct. In addition, the depletion of either SUN1_888 or SUN1_916 altered the chromatin structure and affected the distribution of histone modifications. Based on these results, we propose a model in which the LINC complex plays a role in modulating nucleolar morphology and numbers via chromatin.

The WD40-protein CFAP52/WDR16 is a centrosome/basal body protein and localizes to the manchette and the flagellum in male germ cells

Development of spermatozoa requires remodelling and formation of particular structures. In elongating spermatids, the transient microtubular manchette contributes to the formation of the head-tail coupling apparatus (HTCA) and the sperm tail. The HTCA derives from the centrosome in that the proximal centriole inserts into the nuclear indentation and the distal centriole gives rise to the sperm flagellum. Although impairments in the formation of HTCA and sperm tail cause male infertility their molecular constituents are only partially known. The WD40-protein CFAP52 is implicated in motile cilia, but its relevance for male germ cell differentiation is not known. Here we show that CFAP52 is widespread expressed and localizes to a subset of microtubular structures. In male germ cells, CFAP52 is a component of the transient manchette and the sperm tail. However, expression of Cfap52 is not restricted to motile cilia-bearing cells. In NIH3T3 cells, CFAP52 localizes to the centrosome, the basal body, and the mitotic spindle poles, but not to the primary cilium. Our results demonstrate that CFAP52 is not restricted to motile cilia but instead most likely functions in constituting the centrosome/basal body matrix and the sperm tail.

The testis-specific LINC component SUN3 is essential for sperm head shaping during mouse spermiogenesis

Sperm head shaping is a key event in spermiogenesis and is tightly controlled via the acrosome-manchette network. Linker of nucleoskeleton and cytoskeleton (LINC) complexes consist of Sad1 and UNC84 domain-containing (SUN) and Klarsicht/ANC-1/Syne-1 homology (KASH) domain proteins and form conserved nuclear envelope bridges implicated in transducing mechanical forces from the manchette to sculpt sperm nuclei into a hook-like shape. However, the role of LINC complexes in sperm head shaping is still poorly understood. Here we assessed the role of SUN3, a testis-specific LINC component harboring a conserved SUN domain, in spermiogenesis. We show that CRISPR/Cas9-generated Sun3 knockout male mice are infertile, displaying drastically reduced sperm counts and a globozoospermia-like phenotype, including a missing, mislocalized, or fragmented acrosome, as well as multiple defects in sperm flagella. Further examination revealed that the sperm head abnormalities are apparent at step 9 and that the sperm nuclei fail to elongate because of the absence of manchette microtubules and perinuclear rings. These observations indicate that Sun3 deletion likely impairs the ability of the LINC complex to transduce the cytoskeletal force to the nuclear envelope, required for sperm head elongation. We also found that SUN3 interacts with SUN4 in mouse testes and that the level of SUN4 proteins is drastically reduced in Sun3-null mice. Altogether, our results indicate that SUN3 is essential for sperm head shaping and male fertility, providing molecular clues regarding the underlying pathology of the globozoospermia-like phenotype.

Human sperm-associated antigen 4 as a potential biomarker of glioblastoma progression and prognosis

Glioblastoma (GBM) is a highly lethal brain tumor, refractory to current therapies. Sperm-associated antigen 4 (SPAG4) is a novel cancer marker with unclear roles in GBM progression. This study aimed to explore the specific effects of SPAG4 on the pathogenesis of GBM. We first investigated the expression level and prognostic power of SPAG4 in patients with GBM using The Cancer Genome Atlas cohort, and then SPAG4 knockdown by RNA interference was performed to reveal the effects of SPAG4 on GBM cells. mRNA and protein expression levels were determined by real-time PCR and western blot. MTT assay was used to examine cell proliferation, and a wound healing assay was performed to detect cell migration. SPAG4 was significantly overexpressed in patients with GBM, and high expression of SPAG4 was associated with a poor prognosis. Silencing of SPAG4 significantly suppressed the proliferation and migration of GBM cells. Meanwhile, decreased expression and phosphorylation of MEK and ERK were identified after SPAG4 knockdown, suggesting that SPAG4 might regulate GBM progression by activating MEK/ERK signaling pathway. Our study revealed that SPAG4 was identified as a cancer biomarker for GBM and might be a promising target for clinical diagnosis and intervention of GBM.

Pathogenic mutations in genes encoding nuclear envelope proteins and defective nucleocytoplasmic connections

Mutations in genes encoding nuclear lamins and associated nuclear envelope proteins have been linked to a broad range of inherited diseases affecting different tissues and organs. These diseases are often referred to as laminopathies. Scientists have yet to elucidate exactly how pathogenic mutations leading to alteration of a nuclear envelope protein cause disease. Our relatively recent research has shown that pathogenic mutations in genes encoding nuclear envelope proteins lead to defective nucleocytoplasmic connections that disrupt proper functioning of the linker of nucleoskeleton and cytoskeleton complex in the establishment of cell polarity. These defects may explain, at least in part, pathogenic mechanisms underlying laminopathies.

Impact statement

Mutations in genes encoding nuclear lamins and associated nuclear envelope proteins have been linked to several diseases affecting different tissues and organs. The pathogenic mechanisms underlying these diseases, often called laminopathies, remain poorly understood. Increased knowledge of the functions of different nuclear envelope proteins and the interactions between them is crucial to elucidate these disease mechanisms. Our research has shown that pathogenic mutations in genes encoding nuclear envelope proteins lead to defective nucleocytoplasmic connections that disrupt proper functioning of the linker of nucleoskeleton and cytoskeleton (LINC) complex in the establishment of cell polarity. These defects may contribute to the pathogenesis of laminopathies and provide novel targets for therapeutics.

SPAG4L/SPAG4Lβ interacts with Nesprin2 to participate in the meiosis of spermatogenesis

SUN domain proteins are identified as a novel family of nuclear envelope proteins which are involved in spermatogenesis. SPAG4L is identified as the fifth member of this family. Previous studies have revealed that SPAG4L is involved in spermatogenesis and the mutations occurring in SPAG4L will lead to male infertility. However, the transcriptions of SPAG4L and its interacting proteins in the testis are still unclear. In this study, we identified a shorter transcript variant of SPAG4L, named SPAG4Lβ, in human testis by northern blot and reverse transcription-polymerase chain reaction. Bioinformatics analysis showed that it encodes a protein consisting of 311 amino acids, and subcellular localization analysis revealed that it is mainly expressed in the cytoplasm. In situ hybridization and immunofluorescence assay revealed that SPAG4L/SPAG4Lβ is involved in meiosis. Furthermore, co-IP results demonstrated that SPAG4L/SPAG4Lβ interacts with Nesprin2, a KASH domain protein to form the LINC (linker of nucleoskeleton and cytoskeleton) complexes. Immunofluorescence results revealed that the LINC complexes of Spag4l/Nesprin2 in mouse are involved in spermatocyte division. Our data indicated that SPAG4L/SPAG4Lβ may play an important role in the meiotic process.

Testis-Specific SEPT12 Expression Affects SUN Protein Localization and is Involved in Mammalian Spermiogenesis

Male infertility is observed in approximately 50% of all couples with infertility. Intracytoplasmic sperm injection (ICSI), a conventional artificial reproductive technique for treating male infertility, may fail because of a severe low sperm count, immotile sperm, immature sperm, and sperm with structural defects and DNA damage. Our previous studies have revealed that mutations in the septin (SEPT)-coding gene SEPT12 cause teratozoospermia and severe oligozoospermia. These spermatozoa exhibit morphological defects in the head and tail, premature chromosomal condensation, and nuclear damage. Sperm from Sept12 knockout mice also cause the developmental arrest of preimplantation embryos generated through in vitro fertilization and ICSI. Furthermore, we found that SEPT12 interacts with SPAG4, a spermatid nuclear membrane protein that is also named SUN4. Loss of the Spag4 allele in mice also disrupts the integration nuclear envelope and reveals sperm head defects. However, whether SEPT12 affects SPAG4 during mammalian spermiogenesis remains unclear. We thus conducted this study to explore this question. First, we found that SPAG4 and SEPT12 exhibited similar localizations in the postacrosomal region of elongating spermatids and at the neck of mature sperm through isolated murine male germ cells. Second, SEPT12 expression altered the nuclear membrane localization of SPAG4, as observed through confocal microscopy, in a human testicular cancer cell line. Third, SEPT12 expression also altered the localizations of nuclear membrane proteins: LAMINA/C in the cells. This effect was specifically due to the expression of SEPT12 and not that of SEPT1, SEPT6, SEPT7, or SEPT11. Based on these results, we suggest that SEPT12 is among the moderators of SPAG4/LAMIN complexes and is involved in the morphological formation of sperm during mammalian spermiogenesis.

Signal Transduction across the Nuclear Envelope: Role of the LINC Complex in Bidirectional Signaling

The primary functions of the nuclear envelope are to isolate the nucleoplasm and its contents from the cytoplasm as well as maintain the spatial and structural integrity of the nucleus. The nuclear envelope also plays a role in the transfer of various molecules and signals to and from the nucleus. To reach the nucleus, an extracellular signal must be transmitted across three biological membranes: the plasma membrane, as well as the inner and outer nuclear membranes. While signal transduction across the plasma membrane is well characterized, signal transduction across the nuclear envelope, which is essential for cellular functions such as transcriptional regulation and cell cycle progression, remains poorly understood. As a physical entity, the nuclear envelope, which contains more than 100 proteins, functions as a binding scaffold for both the cytoskeleton and the nucleoskeleton, and acts in mechanotransduction by relaying extracellular signals to the nucleus. Recent results show that the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, which is a conserved molecular bridge that spans the nuclear envelope and connects the nucleoskeleton and cytoskeleton, is also capable of transmitting information bidirectionally between the nucleus and the cytoplasm. This short review discusses bidirectional signal transduction across the nuclear envelope, with a particular focus on mechanotransduction.

It takes two (centrioles) to tango

Cells that divide during embryo development require precisely two centrioles during interphase and four centrioles during mitosis. This precise number is maintained by allowing each centriole to nucleate only one centriole per cell cycle (i.e. centriole duplication). Yet, how the first cell of the embryo, the zygote, obtains two centrioles has remained a mystery in most mammals and insects. The mystery arose because the female gamete (oocyte) is thought to have no functional centrioles and the male gamete (spermatozoon) is thought to have only one functional centriole, resulting in a zygote with a single centriole. However, recent studies in fruit flies, beetles and mammals, including humans, suggest an alternative explanation: spermatozoa have a typical centriole and an atypical centriole. The sperm typical centriole has a normal structure but distinct protein composition, whereas the sperm atypical centriole is distinct in both. During fertilization, the atypical centriole is released into the zygote, nucleates a new centriole and participates in spindle pole formation. Thus, the spermatozoa's atypical centriole acts as a second centriole in the zygote. Here, we review centriole biology in general and especially in reproduction, we describe the discovery of the spermatozoon atypical centriole, and we provide an updated model for centriole inherence during sexual reproduction. While we focus on humans and other non-rodent mammals, we also provide a broader evolutionary perspective.

Nuclear envelope dynamics during mammalian spermatogenesis: new insights on male fertility

The production of highly specialized spermatozoa from undifferentiated spermatogonia is a strictly organized and programmed process requiring extensive restructuring of the entire cell. One of the most remarkable cellular transformations accompanying the various phases of spermatogenesis is the profound remodelling of the nuclear architecture, in which the nuclear envelope (NE) seems to be crucially involved. In recent years, several proteins from the distinct layers forming the NE (i.e. the inner and outer nuclear membranes as well as the nuclear lamina) have been associated with meiosis and/or spermiogenesis in different mammalian species. Among these are A- and B-type lamins, Dpy-19-like protein 2 (DPY19L2), lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), LAP2/emerin/MAN1 (LEM) domain-containing proteins, spermatogenesis-associated 46 (SPATA46) and diverse elements of the linker of nucleoskeleton and cytoskeleton (LINC) complex, namely Sad-1/UNC-84 homology (SUN) and Klarsicht/ANC-1/Syne-1 homology (KASH) domain-containing proteins. Herein, we summarize the current state of the art on the cellular and subcellular distribution of NE proteins expressed during mammalian spermatogenesis, and discuss the latest research developments regarding their testis-specific functions. This review provides a comprehensive and innovative overview of the NE network as a regulatory platform and as an essential determinant of efficient meiotic chromosome recombination as well as spermiogenesis-associated nuclear remodelling and differentiation in mammalian male germline cells. Thus, this review provides important novel insights on the biological relevance of NE proteins for male fertility.

Molecular evolution of SUN-domain containing proteins in diverse plant species and their expression profiling in response to developmental and perturbation stimuli

SUN (Sad1/UNC-84) domain-containing proteins are highly conserved throughout evolution. They are localized to the inner membrane of the nuclear envelope and are involved in nuclear migration and nucleoskeleton formation. In the present study, a genome-wide investigation was performed in three dicotyledonous (Arabidopsis thaliana, Glycine max and Medicago truncatula) and three monocotyledonous (Oryza sativa, Zea mays and Sorghum bicolor) plants. A total of 56 SUN proteins encoded by 30 genes were identified. Based on their length, transmembrane topology, conserved domains and phylogenetic relationships, they could be divided into two previously defined groups- Cter-SUN and mid-SUN proteins. Expression of these genes was analyzed in different developmental stages, tissues and various unfavorable conditions such as salinity, drought, and hormonal treatment. Analyses indicated that the expression of SUN1/2 transcripts are ubiquitous; that of SUN3/4 are development/tissue regulated, and SUN5 are inflorescence stage-specific. This study provides an initial framework for the characterization and functional validation of the plant SUN family.

Protein oligomerization and mobility within the nuclear envelope evaluated by the time-shifted mean-segmented Q factor

Analysis of fluorescence fluctuation experiments by the mean-segmented Q (MSQ) method was recently used to successfully characterize the oligomeric state and mobility of proteins within the nuclear envelope (NE) of living cells. However, two significant shortcomings of MSQ were recognized. Non-ideal detector behavior due to dead-time and afterpulsing as well as the lack of error analysis currently limit the potential of MSQ. This paper presents time-shifted MSQ (tsMSQ), a new formulation of MSQ that is robust with respect to dead-time and afterpulsing. In addition, a protocol for performing error analysis on tsMSQ data is introduced to assess the quality of fit models and estimate the uncertainties of fit parameters. Together, these developments significantly simplify and improve the analysis of fluorescence fluctuation data taken within the NE. To demonstrate these new developments, tsMSQ was used to characterize the oligomeric state and mobility of the luminal domains of two inner nuclear membrane SUN proteins. The results for the luminal domain of SUN2 obtained through tsMSQ without correction for non-ideal detector effects agree with a recent study that was conducted using the original MSQ formulation. Finally, tsMSQ was applied to characterize the oligomeric state and mobility of the luminal domain of the germline-restricted SUN3.

Detection of SUN1 Splicing Variants at the mRNA and Protein Levels in Cancer

The linker of nucleoskeleton and cytoskeleton (LINC) complex, containing the proteins SUN and nesprin, is the fundamental structural unit of the nuclear envelope. The neoplastic-based regulation of the LINC complex in cancer tissues has become increasingly recognized in recent years, including the altered expression, somatic mutation, and methylation of genes. However, precisely how mutations and deregulated expression of the LINC complex contribute to the pathogenic mechanisms of tumorigenesis remain to be elucidated, mainly because of several technical difficulties. First, both the SUN and SYNE (encoding nesprin) genes give rise to a vast number of splicing variants. Second, immunoprecipitation experiments of endogenous SUN and nesprin proteins are difficult owing to the lack of suitable reagents as well as the limited solubility of these proteins in mild extraction conditions. Here, we describe three protocols to investigate these aspects: (1) immunohistochemistry to determine the expression levels and localization of the LINC complex in cancer tissue, (2) detection of SUN1 splicing variants at the mRNA level, and (3) detection of SUN1 splicing variants and binding partners at the protein level.

Ultra-structure of the sperm head-to-tail linkage complex in the absence of the spermatid-specific LINC component SPAG4

Tight connection between sperm head and tail is crucial for the transport of the male genome and fertilization. The linkage complex, the sperm head-to-tail coupling apparatus (HTCA), originates from the centrosome and anchors to the nuclear membrane. In contrast to its ultra-structural organization, which is already well known for decades, its protein composition largely still awaits future deciphering. SUN-domain proteins are essential components of a complex that links the cytoskeleton to the peripheral nucleoskeleton, which is the nuclear lamina. Here, we studied the impact of the SUN protein SPAG4/SUN4 on the formation of the HTCA. SPAG4/SUN4 is specifically expressed in haploid male germ cells showing a polarized distribution towards the posterior pole in late spermatids that corresponds to the tail attachment site. SPAG4-deficient male mice are infertile with compromised manchette formation and malformed sperm heads. Nonetheless, sperm tails are present demonstrating dispensability of a proper manchette for their formation. Ultra-structural analyses revealed that the development of the sperm head-to-tail linkage complex in the absence of SPAG4 resembles that in the wild type. However, in SPAG4-deficient sperm, the attachment site is diminished with obvious lateral detachment of the HTCA from the nucleus. Our results thus indicate that SPAG4, albeit not essential for the formation of the HTCA per se, is, nevertheless, required for tightening the sperm head-to-tail anchorage by provoking the correct attachment of the lateral parts of the basal plate to the implantation fossa.

Nuclear Envelope-Associated Chromosome Dynamics during Meiotic Prophase I

Chromosome dynamics during meiotic prophase I are associated with a series of major events such as chromosomal reorganization and condensation, pairing/synapsis and recombination of the homologs, and chromosome movements at the nuclear envelope (NE). The NE is the barrier separating the nucleus from the cytoplasm and thus plays a central role in NE-associated chromosomal movements during meiosis. Previous studies have shown in various species that NE-linked chromosome dynamics are actually driven by the cytoskeleton. The linker of nucleoskeleton and cytoskeleton (LINC) complexes are important constituents of the NE that facilitate in the transfer of cytoskeletal forces across the NE to individual chromosomes. The LINCs consist of the inner and outer NE proteins Sad1/UNC-84 (SUN), and Klarsicht/Anc-1/Syne (KASH) domain proteins. Meiosis-specific adaptations of the LINC components and unique modifications of the NE are required during chromosomal movements. Nonetheless, the actual role of the NE in chromosomic dynamic movements in plants remains elusive. This review summarizes the findings of recent studies on meiosis-specific constituents and modifications of the NE and corresponding nucleoplasmic/cytoplasmic adaptors being involved in NE-associated movement of meiotic chromosomes, as well as describes the potential molecular network of transferring cytoplasm-derived forces into meiotic chromosomes in model organisms. It helps to gain a better understanding of the NE-associated meiotic chromosomal movements in plants.

Outer dense fibers stabilize the axoneme to maintain sperm motility

Outer dense fibers (ODFs), as unique accessory structures in mammalian sperm, are considered to play a role in the protection of the sperm tail against shear forces. However, the role and relevant mechanisms of ODFs in modulating sperm motility and its pathological involvement in asthenozoospermia were unknown. Here, we found that the percentage of ODF defects was higher in asthenozoospermic samples than that in control samples and was significantly correlated with the percentage of axoneme defects and non-motile sperm. Furthermore, the expression levels of ODF major components (Odf1, 2, 3, 4) were frequently down-regulated in asthenozoospermic samples. Intriguingly, the positive relationship between ODF size and sperm motility existed across species. The conditional disruption of Odf2 expression in mice led to reduced sperm motility and the characteristics of asthenozoospermia. Meanwhile, the expression of acetylated α-tubulin was decreased in sperm from both Odf2 conditional knockout (cKO) mice and asthenozoospermic men. Immunofluorescence and biochemistry analyses showed that Odf2 could bind to acetylated α-tubulin and protect the acetylation level of α-tubulin in HEK293T cells in a cold environment. Finally, we found that lithium elevated the expression levels of Odf family proteins and acetylated α-tubulin, elongated the midpiece length and increased the percentage of rapidly moving sperm in mice. Our results demonstrate that ODFs are beneficial for sperm motility via stabilization of the axoneme and that hypo-expression of Odf family proteins is involved in the pathogenesis of asthenozoospermia. The lithium administration assay will provide valuable insights into the development of new treatments for asthenozoospermia.

Essential role for SUN5 in anchoring sperm head to the tail

SUN (Sad1 and UNC84 domain containing)-domain proteins are reported to reside on the nuclear membrane playing distinct roles in nuclear dynamics. SUN5 is a new member of the SUN family, with little knowledge regarding its function. Here, we generated Sun5^−/− mice and found that male mice were infertile. Most Sun5-null spermatozoa displayed a globozoospermia-like phenotype but they were actually acephalic spermatozoa. Additional studies revealed that SUN5 was located in the neck of the spermatozoa, anchoring sperm head to the tail, and without functional SUN5 the sperm head to tail coupling apparatus was detached from nucleus during spermatid elongation. Finally, we found that healthy heterozygous offspring could be obtained via intracytoplasmic injection of Sun5-mutated sperm heads for both male mice and patients. Our studies reveal the essential role of SUN5 in anchoring sperm head to the tail and provide a promising way to treat this kind of acephalic spermatozoa-associated male infertility.

Comparative and Experimental Studies on the Genes Altered by Chronic Hypoxia in Human Brain Microendothelial Cells

Background : Hypoxia inducible factor 1 alpha (HIF1A) is a master regulator of acute hypoxia; however, with chronic hypoxia, HIF1A levels return to the normoxic levels. Importantly, the genes that are involved in the cell survival and viability under chronic hypoxia are not known. Therefore, we tested the hypothesis that chronic hypoxia leads to the upregulation of a core group of genes with associated changes in the promoter DNA methylation that mediates the cell survival under hypoxia. Results : We examined the effect of chronic hypoxia (3 days; 0.5% oxygen) on human brain micro endothelial cells (HBMEC) viability and apoptosis. Hypoxia caused a significant reduction in cell viability and an increase in apoptosis. Next, we examined chronic hypoxia associated changes in transcriptome and genome-wide promoter methylation. The data obtained was compared with 16 other microarray studies on chronic hypoxia. Nine genes were altered in response to chronic hypoxia in all 17 studies. Interestingly, HIF1A was not altered with chronic hypoxia in any of the studies. Furthermore, we compared our data to three other studies that identified HIF-responsive genes by various approaches. Only two genes were found to be HIF dependent. We silenced each of these 9 genes using CRISPR/Cas9 system. Downregulation of EGLN3 significantly increased the cell death under chronic hypoxia, whereas downregulation of ERO1L, ENO2, adrenomedullin, and spag4 reduced the cell death under hypoxia. Conclusions : We provide a core group of genes that regulates cellular acclimatization under chronic hypoxic stress, and most of them are HIF independent.

SUN1 splice variants, SUN1_888, SUN1_785, and predominant SUN1_916, variably function in directional cell migration

The LINC complex is a multifunctional protein complex that is involved in various processes at the nuclear envelope, such as nuclear migration, mechanotransduction and chromatin tethering in the meiotic phase. However, it remains unknown how these functions are regulated in different cell contexts. An inner nuclear membrane component of the LINC complex, SUN1, is ubiquitously expressed. The human SUN1 gene produces over 10 variants by alternative splicing. Although functions of SUN1 are relatively well characterized, functional differences among SUN1 splice variants are poorly characterized. LINC complex components are associated with a wide range of human diseases; therefore, it is important to understand the functional diversity among SUN1 splice variants. Here, we identified a novel human SUN1 splice variant, SUN1_888. overexpression of the SUN1 splice variants, SUN1_888 or SUN1_785, but not the predominant isoform, SUN1_916, activated directional cell migration. Knockdown of SUN1_888 suppressed cell migration; in contrast depletion of SUN1_916 activated cell migration. In addition, all of investigated SUN1 splicing variants rescued cell migration in SUN1 knock out cell. These results indicate that redundant and non-redundant functions of SUN1 splice variant in directional cell migration and suggest that variable LINC complexes with distinct task may exit. Furthermore, in contrast to previous studies, we showed association between SUN1 and B-type lamins. Interestingly, B-type lamin preferentially interacts with SUN1 but not SUN2. These results suggest that tissue-specific SUN1 variants variably interact with nucleoplasmic partners and allow variable assembly of LINC complexes that can be assigned to distinct tasks.

Gene expression of behaviorally relevant genes in the cerebral hemisphere changes after selection for tameness in Red Junglefowl

The process of domestication in animals has led to alterations in behavior, physiology and phenotypic traits, changes that may be driven by correlations with reduced fear of humans. We used Red Junglefowl, ancestors of all domesticated chickens selected for either high or low fear of humans for five generations to study the effects of selection on gene transcription in the cerebral hemisphere, which is heavily involved in behaviour control. A total of 24 individuals from the parental generation as well as from the fifth selected generation were used. Twenty-two genes were significantly differentially expressed at p < 0.05 after false discovery rate (FDR) correction. Those genes that were upregulated in the low fearful animals were found to be involved in neural functions. Gene ontology and pathway analysis revealed enrichment for terms associated with behavioural processes. We conclude that five generations of divergent selection for high or low tameness has significantly changed gene expression patterns in the cerebral hemisphere in the Red Junglefowl population used here, which could underlie a range of changes in the domestic phenotype.

Implications for Diverse Functions of the LINC Complexes Based on the Structure

The linker of nucleoskeleton and cytoskeleton (LINC) complex is composed of the outer and inner nuclear membrane protein families Klarsicht, Anc-1, and Syne homology (KASH), and Sad1 and UNC-84 (SUN) homology domain proteins. Increasing evidence has pointed to diverse functions of the LINC complex, such as in nuclear migration, nuclear integrity, chromosome movement and pairing during meiosis, and mechanotransduction to the genome. In metazoan cells, the nuclear envelope possesses the nuclear lamina, which is a thin meshwork of intermediate filaments known as A-type and B-type lamins and lamin binding proteins. Both of lamins physically interact with the inner nuclear membrane spanning SUN proteins. The nuclear lamina has also been implicated in various functions, including maintenance of nuclear integrity, mechanotransduction, cellular signalling, and heterochromatin dynamics. Thus, it is clear that the LINC complex and nuclear lamins perform diverse but related functions. However, it is unknown whether the LINC complex-lamins interactions are involved in these diverse functions, and their regulation mechanism has thus far been elusive. Recent structural analysis suggested a dynamic nature of the LINC complex component, thus providing an explanation for LINC complex organization. This review, elaborating on the integration of crystallographic and biochemical data, helps to integrate this research to gain a better understanding of the diverse functions of the LINC complex.

Cryopreservation of bull semen is associated with carbonylation of sperm proteins

Artificial insemination with cryopreserved semen enables affordable, large-scale dissemination of gametes with superior genetics. However, cryopreservation can cause functional and structural damage to spermatozoa that is associated with reactive oxygen species (ROS) production, impairment of sperm motility and decreased fertilizing potential, but little attention has been paid to protein changes. The goal of this study was to investigate the oxidative modifications (measured as carbonylation level changes) of bull spermatozoa proteins triggered by the cryopreservation process. Flow cytometry and computer-assisted sperm analysis were used to evaluate changes in viability, ROS level and motility of spermatozoa. Western blotting, in conjunction with two-dimensional electrophoresis (2D-oxyblot) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight spectrometry, was employed to identify and quantify the specifically carbonylated spermatozoa proteins. Cryopreservation decreased motility and viability but increased the number of ROS-positive cells. We identified 11 proteins (ropporin-1, outer dense fiber protein 2, glutathione S-transferase, triosephosphate isomerase, capping protein beta 3 isoform, actin-related protein M1, actin-related protein T2, NADH dehydrogenase, isocitrate dehydrogenase, cilia- and flagella-associated protein 161, phosphatidylethanolamine-binding protein 4) showing differences in protein carbonylation in response to cryopreservation. The identified proteins are associated with cytoskeleton and flagella organization, detoxification and energy metabolism. Moreover, almost all of the identified carbonylated proteins are involved in capacitation. Our results indicate for the first time that cryopreservation induces oxidation of selected sperm proteins via carbonylation. We suggest that carbonylation of sperm proteins could be a direct result of oxidative stress and potentially lead to disturbances of capacitation-involved proteins or could indicate cryopreservation-induced premature capacitation.

A Disulfide Bond Is Required for the Transmission of Forces through SUN-KASH Complexes

Numerous biological functions of a cell, including polarization, differentiation, division, and migration, rely on its ability to endure mechanical forces generated by the cytoskeleton on the nucleus. Coupling of the cytoskeleton and nucleoskeleton is ultimately mediated by LINC complexes that are formed via a strong interaction between SUN- and KASH-domain-containing proteins in the nuclear envelope. These complexes are mechanosensitive and essential for the transmission of forces between the cytoskeleton and nucleoskeleton, and the progression of cellular mechanotransduction. Herein, using molecular dynamics, we examine the effect of tension on the human SUN2-KASH2 complex and show that it is remarkably stable under physiologically relevant tensile forces and large strains. However, a covalent disulfide bond between two highly conserved cysteine residues of SUN2 and KASH2 is crucial for the stability of this interaction and the transmission of forces through the complex.

TMF/ARA160 Governs the Dynamic Spatial Orientation of the Golgi Apparatus during Sperm Development

TMF/ARA160 is known to be a TATA element Modulatory Factor (TMF). It was initially identified as a DNA-binding factor and a coactivator of the Androgen receptor. It was also characterized as a Golgi-associated protein, which is essential for acrosome formation during functional sperm development. However, the molecular roles of TMF in this intricate process have not been revealed. Here, we show that during spermiogenesis, TMF undergoes a dynamic change of localization throughout the Golgi apparatus. Specifically, TMF translocates from the cis-Golgi to the trans-Golgi network and to the emerging vesicles surface, as the round spermatids develop. Notably, lack of TMF led to an abnormal spatial orientation of the Golgi and to the deviation of the trans-Golgi surface away from the nucleus of the developing round spermatids. Concomitantly, pro-acrosomal vesicles derived from the TMF-/- Golgi lacked targeting properties and did not tether to the spermatid nuclear membrane thereby failing to form the acrosome anchoring scaffold, the acroplaxome, around the cell-nucleus. Absence of TMF also perturbed the positioning of microtubules, which normally lie in proximity to the Golgi and are important for maintaining Golgi spatial orientation and dynamics and for chromatoid body formation, which is impaired in TMF-/- spermatids. In-silico evaluation combined with molecular and electron microscopic analyses revealed the presence of a microtubule interacting domain (MIT) in TMF, and confirmed the association of TMF with microtubules in spermatogenic cells. Furthermore, the MIT domain in TMF, along with microtubules integrity, are required for stable association of TMF with the Golgi apparatus. Collectively, we show here for the first time that a Golgi and microtubules associated protein is crucial for maintaining proper Golgi orientation during a cell developmental process.

Making the LINC: SUN and KASH protein interactions

Cell nuclei are physically integrated with the cytoskeleton through the linker of nucleoskeleton and cytoskeleton (LINC) complex, a structure that spans the nuclear envelope to link the nucleoskeleton and cytoskeleton. Outer nuclear membrane KASH domain proteins and inner nuclear membrane SUN domain proteins interact to form the core of the LINC complex. In this review, we provide a comprehensive analysis of the reported protein-protein interactions for KASH and SUN domain proteins. This critical structure, directly connecting the genome with the rest of the cell, contributes to a myriad of cellular functions and, when perturbed, is associated with human disease.

The LINC complex component Sun4 plays a crucial role in sperm head formation and fertility

LINC complexes are evolutionarily conserved nuclear envelope bridges, physically connecting the nucleus to the peripheral cytoskeleton. They are pivotal for dynamic cellular and developmental processes, like nuclear migration, anchoring and positioning, meiotic chromosome movements and maintenance of cell polarity and nuclear shape. Active nuclear reshaping is a hallmark of mammalian sperm development and, by transducing cytoskeletal forces to the nuclear envelope, LINC complexes could be vital for sperm head formation as well. We here analyzed in detail the behavior and function of Sun4, a bona fide testis-specific LINC component. We demonstrate that Sun4 is solely expressed in spermatids and there localizes to the posterior nuclear envelope, likely interacting with Sun3/Nesprin1 LINC components. Our study revealed that Sun4 deficiency severely impacts the nucleocytoplasmic junction, leads to mislocalization of other LINC components and interferes with the formation of the microtubule manchette, which finally culminates in a globozoospermia-like phenotype. Together, our study provides direct evidence for a critical role of LINC complexes in mammalian sperm head formation and male fertility.

SUN proteins and nuclear envelope spacing

The nuclear envelope consists of 2 membranes separated by 30–50 nm, but how the 2 membranes are evenly spaced has been an open question in the field. Nuclear envelope bridges composed of inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins have been proposed to set and regulate nuclear envelope spacing. We tested this hypothesis directly by examining nuclear envelope spacing in Caenorhabditis elegans animals lacking UNC-84, the sole somatic SUN protein. SUN/KASH bridges are not required to maintain even nuclear envelope spacing in most tissues. However, UNC-84 is required for even spacing in body wall muscle nuclei. Shortening UNC-84 by 300 amino acids did not narrow the nuclear envelope space. While SUN proteins may play a role in maintaining nuclear envelope spacing in cells experiencing forces, our data suggest they are dispensable in most cells.

LINC'ing form and function at the nuclear envelope

The nuclear envelope is an amazing piece of engineering. On one hand it is built like a mediaeval fortress with filament systems reinforcing its membrane walls and its double membrane structure forming a lumen like a castle moat. On the other hand its structure can adapt while maintaining its integrity like a reed bending in a river. Like a fortress it has guarded drawbridges in the nuclear pore complexes, but also has other mechanical means of communication. All this is enabled largely because of the LINC complex, a multi-protein structure that connects the intermediate filament nucleoskeleton across the lumen of the double membrane nuclear envelope to multiple cytoplasmic filament systems that themselves could act simultaneously both like mediaeval buttresses and like lines on a suspension bridge. Although many details of the greater LINC structure remain to be discerned, a number of recent findings are giving clues as to how its structural organization can yield such striking dynamic yet stable properties. Combining double- and triple-helical coiled-coils, intrinsic disorder and order, tissue-specific components, and intermediate filaments enables these unique properties.

SEPT12/SPAG4/LAMINB1 complexes are required for maintaining the integrity of the nuclear envelope in postmeiotic male germ cells

Male infertility affects approximately 50% of all infertile couples. The male-related causes of intracytoplasmic sperm injection failure include the absence of sperm, immotile or immature sperm, and sperm with structural defects such as those caused by premature chromosomal condensation and DNA damage. Our previous studies based on a knockout mice model indicated that SEPT12 proteins are critical for the terminal morphological formation of sperm. SEPT12 mutations in men result in teratozospermia and oligozospermia. In addition, the spermatozoa exhibit morphological defects of the head and tail, premature chromosomal condensation, and nuclear damage. However, the molecular functions of SEPT12 during spermatogenesis remain unclear. To determine the molecular functions of SEPT12, we applied a yeast 2-hybrid system to identify SEPT12 interactors. Seven proteins that interact with SEPT12 were identified: SEPT family proteins (SEPT4 and SEPT6), nuclear or nuclear membrane proteins (protamine 2, sperm-associated antigen 4, and NDC1 transmembrane nucleoproine), and sperm-related structural proteins (pericentriolar material 1 and obscurin-like 1). Sperm-associated antigen 4 (SPAG4; also known as SUN4) belongs to the SUN family of proteins and acts as a linker protein between nucleoskeleton and cytoskeleton proteins and localizes in the nuclear membrane. We determined that SEPT12 interacts with SPAG4 in a male germ cell line through coimmunoprecipitation. During human spermiogenesis, SEPT12 is colocalized with SPAG4 near the nuclear periphery in round spermatids and in the centrosome region in elongating spermatids. Furthermore, we observed that SEPT12/SPAG4/LAMINB1 formed complexes and were coexpressed in the nuclear periphery of round spermatids. In addition, mutated SEPT12, which was screened from an infertile man, affected the integration of these nuclear envelope complexes through coimmunoprecipitation. This was the first study that suggested that SEPT proteins link to the SUN/LAMIN complexes during the formation of nuclear envelopes and are involved in the development of postmeiotic germ cells.

Dynamics of Sun5 localization during spermatogenesis in wild type and Dpy19l2 knock-out mice indicates that Sun5 is not involved in acrosome attachment to the nuclear envelope

The acrosome is an organelle that is central to sperm physiology and a defective acrosome biogenesis leads to globozoospermia, a severe male infertility. The identification of the actors involved in acrosome biogenesis is therefore particularly important to decipher the molecular pathogeny of globozoospermia. We recently showed that a defect in the DPY19L2 gene is present in more than 70% of globozoospermic men and demonstrated that Dpy19l2, located in the inner nuclear membrane, is the first protein involved in the attachment of the acrosome to the nuclear envelope (NE). SUN proteins serve to link the nuclear envelope to the cytoskeleton and are therefore good candidates to participate in acrosome-nucleus attachment, potentially by interacting with DPY19L2. In order to characterize new actors of acrosomal attachment, we focused on Sun5 (also called Spag4l), which is highly expressed in male germ cells, and investigated its localization during spermatogenesis. Using immunohistochemistry and Western blot experiments in mice, we showed that Sun5 transits through different cellular compartments during meiosis. In pachytene spermatocytes, it is located in a membranous compartment different to the reticulum. In round spermatids, it progresses to the Golgi and the NE before to be located to the tail/head junction in epididymal sperm. Interestingly, we demonstrate that Sun5 is not, as initially reported, facing the acrosome but is in fact excluded from this zone. Moreover, we show that in Dpy19l2 KO spermatids, upon the detachment of the acrosome, Sun5 relocalizes to the totality of the NE suggesting that the acrosome attachment excludes Sun5 from the NE facing the acrosome. Finally, Western-blot experiments demonstrate that Sun5 is glycosylated. Overall, our work, associated with other publications, strongly suggests that the attachment of the acrosome to the nucleus does not likely depend on the formation of SUN complexes.