Tesmin, Metallothionein-Like 5, is Required for Spermatogenesis in Mice†

Mechanisms of meiosis initiation and meiotic prophase progression during spermatogenesis

Meiosis is a critical step for spermatogenesis and oogenesis. Meiosis commences with pre-meiotic S phase that is subsequently followed by meiotic prophase. The meiotic prophase is characterized by the meiosis-specific chromosomal events such as chromosome recombination and homolog synapsis. Meiosis initiator (MEIOSIN) and stimulated by retinoic acid gene 8 (STRA8) initiate meiosis by activating the meiotic genes by installing the meiotic prophase program at pre-meiotic S phase. This review highlights the mechanisms of meiotic initiation and meiotic prophase progression from the point of the gene expression program and its relevance to infertility. Furthermore, upstream pathways that regulate meiotic initiation will be discussed in the context of spermatogenic development, indicating the sexual differences in the mode of meiotic entry.

Evolution of tissue-specific expression of ancestral genes across vertebrates and insects

Regulation of gene expression is arguably the main mechanism underlying the phenotypic diversity of tissues within and between species. Here we assembled an extensive transcriptomic dataset covering 8 tissues across 20 bilaterian species and performed analyses using a symmetric phylogeny that allowed the combined and parallel investigation of gene expression evolution between vertebrates and insects. We specifically focused on widely conserved ancestral genes, identifying strong cores of pan-bilaterian tissue-specific genes and even larger groups that diverged to define vertebrate and insect tissues. Systematic inferences of tissue-specificity gains and losses show that nearly half of all ancestral genes have been recruited into tissue-specific transcriptomes. This occurred during both ancient and, especially, recent bilaterian evolution, with several gains being associated with the emergence of unique phenotypes (for example, novel cell types). Such pervasive evolution of tissue specificity was linked to gene duplication coupled with expression specialization of one of the copies, revealing an unappreciated prolonged effect of whole-genome duplications on recent vertebrate evolution.

Zinc mitigates cadmium-induced sperm dysfunction through regulating Ca2+ and metallothionein expression in the freshwater crab Sinopotamon henanense

Cadmium (Cd) is a highly toxic heavy metal element that might adversely affect sperm function such as the acrosome reaction (AR). Although it is widely recognized that zinc (Zn) plays a crucial role in sperm quality, the complete elucidation of how Zn ameliorates Cd-induced sperm dysfunction is still unclear. In this study, we aimed to explore the protective effects of Zn against the sperm dysfunction induced by Cd in the freshwater crab Sinopotamon henanense. The results demonstrated that Cd exposure not only impaired the sperm ultrastructure, but also caused sperm dysfunction by decreasing the AR induction rate, acrosome enzyme activity, and Ca2+ content in sperm while elevating the activity and transcription expression of key Ca2+ signaling pathway-related proteins Calmodulin (CAM) and Ca2+-ATPase. However, the administration of Zn was found to alleviate Cd-induced sperm morphological and functional disorders by increasing the activity and transcription levels of CaM and Ca2+-ATPase, thereby regulating intracellular Ca2+ homeostasis and reversing the decrease in Ca2+ contents caused by Cd. Furthermore, this study was the first to investigate the distribution of metallothionein (MT) in the AR of S. henanense, and it was found that Zn can reduce the elevated levels of MT in crabs caused by Cd, demonstrating the significance of Zn in inducing MT to participate in the AR process and in metal detoxification in S. henanense. These findings offer novel perspectives and substantiation regarding the utilization of Zn as a protective agent against Cd-induced toxicity and hold significant practical implications for mitigating Cd-induced sperm dysfunction.

Atypical heat shock transcription factor HSF5 is critical for male meiotic prophase under non-stress conditions

Meiotic prophase progression is differently regulated in males and females. In males, pachytene transition during meiotic prophase is accompanied by robust alteration in gene expression. However, how gene expression is regulated differently to ensure meiotic prophase completion in males remains elusive. Herein, we identify HSF5 as a male germ cell-specific heat shock transcription factor (HSF) for meiotic prophase progression. Genetic analyzes and single-cell RNA-sequencing demonstrate that HSF5 is essential for progression beyond the pachytene stage under non-stress conditions rather than heat stress. Chromatin binding analysis in vivo and DNA-binding assays in vitro suggest that HSF5 binds to promoters in a subset of genes associated with chromatin organization. HSF5 recognizes a DNA motif different from typical heat shock elements recognized by other canonical HSFs. This study suggests that HSF5 is an atypical HSF that is required for the gene expression program for pachytene transition during meiotic prophase in males.

A mechanistic insight on how Compromised Hydrolysis of Triacylglycerol 7 (CHT7) restrains the involvement of it's CXC domain from quiescence repression

CHT7 is a regulator of quiescence repression in Chlamydomonas reinhardtii. Initially, CHT7's repression activity was thought to be managed by its DNA-binding CXC domain. Later, it was found that the CHT7-CXC domain is dispensable for CHT7's activities. Rather, CHT7's predicted protein domains were proposed to be involved in regulation activities by binding to other repressors in the cell. Yet, it remains unclear why and how CHT7 refrains its CXC domain from participating in any transcriptional activities. The question becomes more intriguing, since CXC binding regions are available in promoter regions of some of the misregulated genes in CHT7 mutant (cht7). Through biophysical experiments and molecular dynamics approaches, we studied the DNA recognition behavior of CHT7-CXC. The results indicate that this domain possesses sequence selectivity due to the differential binding abilities of its subdomains. Further, to understand if the case is that CXC loses its DNA binding capabilities in the vicinity of other repressors, we examined CHT7-CXC's DNA binding stability under the spatial constraint conditions created through fusing CHT7-CXC with AsLOV2. The results show limited ability of CHT7-CXC to withstand steric forces and provide insights to why and how algal cells may hold back CHT7-CXC's indulgence in quiescence repression. CLASSIFICATIONS: Biological Sciences, Biophysics and Computational Biology.

Clinical Significance and Functional Insights of Tesmin in Hepatocellular Carcinoma

Background

Tesmin, a 60 kDa protein encoded by the metallothionein-like 5 (MTL5) gene, plays a vital role in spermatogenesis and oogenesis. Recent research has unveiled its potential involvement in malignancies, although its impact on HCC remains poorly understood.

Methods

In this study, we sought to elucidate the clinical significance of tesmin in HCC patients. We investigated the relationship between tesmin expression and the prognosis of individuals with hepatocellular carcinoma (HCC), as well as its potential role in tumor proliferation and invasion. Immunohistochemistry (IHC) was employed to assess the expression of tesmin in HCC tissues. Chi-square tests were conducted to analyze the correlation between tesmin expression and various clinicopathological features among HCC patients. For survival analysis, we employed the Kaplan-Meier method and conducted Cox regression analyses. To investigate the functional role of tesmin, we utilized shRNA constructs for transfection-mediated knockdown. Proliferation was assessed using the CCK-8 assay, and invasive capability was determined through Matrigel Transwell assays.

Results

IHC results indicated that tesmin expression was prominently observed in cancerous tissue. Notably, we observed a significant association between tesmin expression and tumor stage and invasion in HCC patients from both our medical center and TCGA dataset. Survival analysis further revealed that tesmin expression emerged as an independent prognostic factor for overall survival among individuals with HCC. Furthermore, cellular experiments demonstrated that knockdown of tesmin led to decreased proliferation and invasion of HCC cells.

Conclusions

Our findings suggest that tesmin may serve as a novel prognostic marker for HCC, highlighting its potential as a target for further research into HCC treatment. Additionally, the functional experiments support the notion that tesmin may participate in promoting the proliferation and invasion of HCC cells, warranting further investigations into its mechanistic involvement in HCC progression.

Proximity-dependent biotin labeling in testicular germ cells identified TESMIN-associated proteins

Characterization of protein-protein interactions (PPI) is a key to understanding the functions of proteins of interest. Recently developed proximity-dependent biotin identification (BioID) has been actively investigated as an alternative PPI mapping method because of its usefulness in uncovering transient PPI. Here, as an example of proximity labeling proteomics application in the testis, we generated two transgenic mouse lines expressing two biotin ligases (BioID2 or TurboID) fused with TESMIN, which translocates from the cytosol to the nucleus during meiotic progression and is required for reproduction. The BioID2 transgene, albeit not the TurboID transgene, rescued fertility defects of the Tesmin KO male mice, indicating that the TESMIN-BioID2 fusion can physiologically replace TESMIN. Furthermore, biotinylated protein pull-down and affinity-purification followed by mass spectrometry using the TESMIN-BioID2 transgenic mice captured components of the MYBL1-MuvB complex that regulate cell-cycle gene expression. Thus, our study shows that proximity labeling proteomics can be applied in male germ cells, although the choice of biotin ligase needs to be carefully tested.

Trim41 is required to regulate chromosome axis protein dynamics and meiosis in male mice

Meiosis is a hallmark event in germ cell development that accompanies sequential events executed by numerous molecules. Therefore, characterization of these factors is one of the best strategies to clarify the mechanism of meiosis. Here, we report tripartite motif-containing 41 (TRIM41), a ubiquitin ligase E3, as an essential factor for proper meiotic progression and fertility in male mice. Trim41 knockout (KO) spermatocytes exhibited synaptonemal complex protein 3 (SYCP3) overloading, especially on the X chromosome. Furthermore, mutant mice lacking the RING domain of TRIM41, required for the ubiquitin ligase E3 activity, phenocopied Trim41 KO mice. We then examined the behavior of mutant TRIM41 (ΔRING-TRIM41) and found that ΔRING-TRIM41 accumulated on the chromosome axes with overloaded SYCP3. This result suggested that TRIM41 exerts its function on the chromosome axes. Our study revealed that Trim41 is essential for preventing SYCP3 overloading, suggesting a TRIM41-mediated mechanism for regulating chromosome axis protein dynamics during male meiotic progression.

Structure and function of MuvB complexes

Proper progression through the cell-division cycle is critical to normal development and homeostasis and is necessarily misregulated in cancer. The key to cell-cycle regulation is the control of two waves of transcription that occur at the onset of DNA replication (S phase) and mitosis (M phase). MuvB complexes play a central role in the regulation of these genes. When cells are not actively dividing, the MuvB complex DREAM represses G1/S and G2/M genes. Remarkably, MuvB also forms activator complexes together with the oncogenic transcription factors B-MYB and FOXM1 that are required for the expression of the mitotic genes in G2/M. Despite this essential role in the control of cell division and the relationship to cancer, it has been unclear how MuvB complexes inhibit and stimulate gene expression. Here we review recent discoveries of MuvB structure and molecular interactions, including with nucleosomes and other chromatin-binding proteins, which have led to the first mechanistic models for the biochemical function of MuvB complexes.

Metallothionein-like 5 expression is correlated with poor prognosis and promotes proliferation of cervical squamous cell carcinoma

Cervical cancer represents one of the most important female genital cancers. Cervical squamous cell carcinoma (CESC) accounts for about 90% of all cervical malignancies and the prognosis are unsatisfied. Here we aimed to investigate the clinical relevance of metallothionein-like 5 (MTL5), a novel metallothionein-like protein, in CESC. RT-qPCR and immunohistochemistry staining showed that MTL5 was upregulated in CESC tissues than nontumorous cervix tissues, which is consistent with the data from TCGA database. Kaplan-Meier survival analysis revealed that higher MTL5 can help predict worse prognosis. In addition, Cox hazard regression analysis verified an independent predictive role of MTL5 in CESC. To further investigate the involvement of MTL5 in CESC, we conducted knockdown experiments in two CESC cell lines. As a result, silencing MTL5g significantly inhibited proliferation of CESC cells. Finally, we validated that silencing MTL5 can suppress CESC tumor growth in vivo using the mice subcutaneous xenografts model. Taken together, higher MTL5 indicates worse survival of CESC after surgical resection. Targeting MTL5 represents a potential therapy of CESC by inhibiting tumor growth, which deserves further investigations.

Nuclear translocation of MTL5 from cytoplasm requires its direct interaction with LIN9 and is essential for male meiosis and fertility

Meiosis is essential for the generation of gametes and sexual reproduction, yet the factors and underlying mechanisms regulating meiotic progression remain largely unknown. Here, we showed that MTL5 translocates into nuclei of spermatocytes during zygotene-pachytene transition and ensures meiosis advances beyond pachytene stage. MTL5 shows strong interactions with MuvB core complex components, a well-known transcriptional complex regulating mitotic progression, and the zygotene-pachytene transition of MTL5 is mediated by its direct interaction with the component LIN9, through MTL5 C-terminal 443–475 residues. Male Mtl5^c-mu/c-mu mice expressing the truncated MTL5 (p.Ser445Arg fs*3) that lacks the interaction with LIN9 and is detained in cytoplasm showed male infertility and spermatogenic arrest at pachytene stage, same as that of Mtl5 knockout mice, indicating that the interaction with LIN9 is essential for the nuclear translocation and function of MTL5 during meiosis. Our data demonstrated MTL5 translocates into nuclei during the zygotene-pachytene transition to initiate its function along with the MuvB core complex in pachytene spermatocytes, highlighting a new mechanism regulating the progression of male meiosis.

Meiosis is essential for spermatogenesis and male fertility. However, the factors regulating the progression of meiosis remain largely unknown. We reported the testis specific protein MTL5 translocated into the nuclei of spermatocytes at the zygotene-pachytene transition by direct interaction with LIN9, which is an essential component of MuvB core complex, to promote meiotic progression beyond the pachytene stage. We also showed that MTL5 pulls down MYBL1 and all of the MuvB core complex (except LIN54) in spermatocytes. Given the known role of the MuvB core complex as a cell cycle regulator in mitotic cells, we suggested that MTL5 promotes meiotic progression along with the MuvB core complex to ensure male fertility. Our results indicated a novel function of the MuvB complex in male meiosis and also shed light on the master regulator proteins that control meiotic progression at the pachytene stage. MTL5 is a novel and germ-cell specific regulator of cell cycle progression to function at a specific stage by nuclear translocation in meiosis.

KCTD19 and its associated protein ZFP541 are independently essential for meiosis in male mice

Meiosis is a cell division process with complex chromosome events where various molecules must work in tandem. To find meiosis-related genes, we screened evolutionarily conserved and reproductive tract-enriched genes using the CRISPR/Cas9 system and identified potassium channel tetramerization domain containing 19 (Kctd19) as an essential factor for meiosis. In prophase I, Kctd19 deficiency did not affect synapsis or the DNA damage response, and chiasma structures were also observed in metaphase I spermatocytes of Kctd19 KO mice. However, spermatocytes underwent apoptotic elimination during the metaphase-anaphase transition. We were able to rescue the Kctd19 KO phenotype with an epitope-tagged Kctd19 transgene. By immunoprecipitation-mass spectrometry, we confirmed the association of KCTD19 with zinc finger protein 541 (ZFP541) and histone deacetylase 1 (HDAC1). Phenotyping of Zfp541 KO spermatocytes demonstrated XY chromosome asynapsis and recurrent DNA damage in the late pachytene stage, leading to apoptosis. In summary, our study reveals that KCTD19 associates with ZFP541 and HDAC1, and that both KCTD19 and ZFP541 are essential for meiosis in male mice.

Meiosis is a fundamental process that consists of one round of genomic DNA replication and two rounds of chromosome segregation, producing four haploid cells. To properly distribute their genetic material, cells need to undergo complex chromosome events such as a physical linkage of homologous chromosomes (termed synapsis) and meiotic recombination. The molecules involved in these events have not been fully characterized yet, especially in mammals. Using a CRISPR/Cas9-screening system, we identified the potassium channel tetramerization domain containing 19 (Kctd19) as an essential factor for meiosis in male mice. Further, we confirmed the association of KCTD19 with zinc finger protein 541 (ZFP541) and histone deacetylase 1 (HDAC1). By observing meiosis of Zfp541 knockout germ cells, we found that Zfp541 was also essential for meiosis. These results show that the KCTD19/ZFP541 complex plays a critical role and is indispensable for male meiosis and fertility.

Cellular and subcellular localization of endogenous phospholipase D6 in seminiferous tubules of mouse testes

Phospholipase D6 (PLD6) plays pivotal roles in mitochondrial dynamics and spermatogenesis, but the cellular and subcellular localization of endogenous PLD6 in testis germ cells is poorly defined. We examined the distribution and subcellular localization of PLD6 in mouse testes using validated specific anti-PLD6 antibodies. Ectopically expressed PLD6 protein was detected in the mitochondria of PLD6-transfected cells, but endogenous PLD6 expression in mouse testes was localized to the perinuclear region of pachytene spermatocytes, and more prominently, to the round (Golgi and cap phases) and elongating spermatids (acrosomal phase); these results suggest that PLD6 is localized to the Golgi apparatus. The distribution of PLD6 in the round spermatids partially overlapped with that of the cis-Golgi marker GM130, indicating that the PLD6 expression corresponded to the GM130-positive subdomains of the Golgi apparatus. Correlative light and electron microscopy revealed that PLD6 expression in developing spermatids was localized almost exclusively to several flattened cisternae, and these structures might correspond to the medial Golgi subcompartment; neither the trans-Golgi networks nor the developing acrosomal system expressed PLD6. Further, we observed that PLD6 interacted with tesmin, a testis-specific transcript necessary for successful spermatogenesis in mouse testes. To our knowledge, these results provide the first evidence of PLD6 as a Golgi-localized protein of pachytene spermatocytes and developing spermatids and suggest that its subcompartment-specific distribution within the Golgi apparatus may be related to the specific functions of this organelle during spermatogenesis.

Prediction and Validation of Mouse Meiosis-Essential Genes Based on Spermatogenesis Proteome Dynamics

The molecular mechanism associated with mammalian meiosis has yet to be fully explored, and one of the main reasons for this lack of exploration is that some meiosis-essential genes are still unknown. The profiling of gene expression during spermatogenesis has been performed in previous studies, yet few studies have aimed to find new functional genes. Since there is a huge gap between the number of genes that are able to be quantified and the number of genes that can be characterized by phenotype screening in one assay, an efficient method to rank quantified genes according to phenotypic relevance is of great importance. We proposed to rank genes by the probability of their function in mammalian meiosis based on global protein abundance using machine learning. Here, nine types of germ cells focusing on continual substages of meiosis prophase I were isolated, and the corresponding proteomes were quantified by high-resolution MS. By combining meiotic labels annotated from the mouse genomics informatics mouse knockout database and the spermatogenesis proteomics dataset, a supervised machine learning package, FuncProFinder (https://github.com/sjq111/FuncProFinder), was developed to rank meiosis-essential candidates. Of the candidates whose functions were unannotated, four of 10 genes with the top prediction scores, Zcwpw1, Tesmin, 1700102P08Rik, and Kctd19, were validated as meiosis-essential genes by knockout mouse models. Therefore, mammalian meiosis-essential genes could be efficiently predicted based on the protein abundance dataset, which provides a paradigm for other functional gene mining from a related abundance dataset.

CRISPR/Cas9-mediated genome-edited mice reveal 10 testis-enriched genes are dispensable for male fecundity

As the world population continues to increase to unsustainable levels, the importance of birth control and the development of new contraceptives are emerging. To date, male contraceptive options have been lagging behind those available to women, and those few options available are not satisfactory to everyone. To solve this problem, we have been searching for new candidate target proteins for non-hormonal contraceptives. Testis-specific proteins are appealing targets for male contraceptives because they are more likely to be involved in male reproduction and their targeting by small molecules is predicted to have no on-target harmful effects on other organs. Using in silico analysis, we identified Erich2, Glt6d1, Prss58, Slfnl1, Sppl2c, Stpg3, Tex33, and Tex36 as testis-abundant genes in both mouse and human. The genes, 4930402F06Rik and 4930568D16Rik, are testis-abundant paralogs of Glt6d1 that we also discovered in mice but not in human, and were also included in our studies to eliminate the potential compensation. We generated knockout (KO) mouse lines of all listed genes using the CRISPR/Cas9 system. Analysis of all of the individual KO mouse lines as well as Glt6d1/4930402F06Rik/4930568D16Rik TKO mouse lines revealed that they are male fertile with no observable defects in reproductive organs, suggesting that these 10 genes are not required for male fertility nor play redundant roles in the case of the 3 Glt6D1 paralogs. Further studies are needed to uncover protein function(s), but in vivo functional screening using the CRISPR/Cas9 system is a fast and accurate way to find genes essential for male fertility, which may apply to studies of genes expressed elsewhere. In this study, although we could not find any potential protein targets for non-hormonal male contraceptives, our findings help to streamline efforts to find and focus on only the essential genes.