Spermatogenesis

piRNAs are crucial for transposon silencing, germ cell maturation, and fertility in male mice. Here, we report on the genetic landscape of piRNA dysfunction in humans and present 39 infertile men carrying biallelic variants in 14 different piRNA pathway genes, including PIWIL1, GTSF1, GPAT2, MAEL, TDRD1, and DDX4. In some affected men, the testicular phenotypes differ from those of the respective knockout mice and range from complete germ cell loss to the production of a few morphologically abnormal sperm. A reduced number of pachytene piRNAs was detected in the testicular tissue of variant carriers, demonstrating impaired piRNA biogenesis. Furthermore, LINE1 expression in spermatogonia links impaired piRNA biogenesis to transposon de-silencing and serves to classify variants as functionally relevant. These results establish the disrupted piRNA pathway as a major cause of human spermatogenic failure and provide insights into transposon silencing in human male germ cells.

Male reproductive health, particularly the regulation of spermatogenesis, is controlled by a complex combination of factors, including luteinizing hormone (LH) and its effects on Leydig cells (LCs). LH stimulates testosterone synthesis in LCs, which is critical for maintaining spermatogenesis and male fertility. This review examines the pathways through which LH regulates testosterone production, LC proliferation, differentiation, and circadian rhythm in human and non-human species. In particular, the signaling pathways of luteinizing hormone involved in testosterone production are discussed. Additionally, we explore LH's role in sperm maturation and quality, emphasizing its clinical implications in treating hypogonadotropic hypogonadism and diagnosing gonadal dysfunctions such as androgen insensitivity syndrome and precocious puberty. Furthermore, the potential of LH in assisted reproductive technologies for improving sperm quality is discussed. By highlighting key molecular mechanisms, this work provides insights into the therapeutic potential of LH in addressing male infertility and conditions of LC dysfunction.

Spermatogenesis is a complex and highly regulated process involving the proliferation, differentiation, and apoptosis of germ cells. This process is controlled by various hormonal, genetic, and environmental factors, including temperature. In hormonal regulation, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T) are essential for correct spermatogenesis development from the early stages and spermatogonia proliferation to germ cell maturation. Other hormones, like inhibin and activin, finely participate tuning the process of spermatogenesis. Genetic regulation involves various transcription factors, such as SOX9, SRY, and DMRT1, which are crucial for the development and maintenance of the testis and germ cells. MicroRNAs (miRNAs) play a significant role by regulating gene expression post-transcriptionally. Epigenetic modifications, including DNA methylation, histone modifications, and chromatin remodelling, are also vital. Temperature regulation is another critical aspect, with the testicular temperature maintained around 2-4 °C below body temperature, essential for efficient spermatogenesis. Heat shock proteins (HSPs) protect germ cells from heat-induced damage by acting as molecular chaperones, ensuring proper protein folding and preventing the aggregation of misfolded proteins during thermal stress. Elevated testicular temperature can impair spermatogenesis, increasing germ cell apoptosis and inducing oxidative stress, DNA damage, and the disruption of the blood-testis barrier, leading to germ cell death and impaired differentiation. The cellular mechanisms of germ cell proliferation, differentiation, and death include the mitotic divisions of spermatogonia to maintain the germ cell pool and produce spermatocytes. Spermatocytes undergo meiosis to produce haploid spermatids, which then differentiate into mature spermatozoa. Apoptosis, or programmed cell death, ensures the removal of defective germ cells and regulates the germ cell population. Hormonal imbalance, genetic defects, and environmental stress can trigger apoptosis during spermatogenesis. Understanding these mechanisms is crucial for addressing male infertility and developing therapeutic interventions. Advances in molecular biology and genetics continue to uncover the intricate details of how spermatogenesis is regulated at multiple levels, providing new insights and potential targets for treatment.

BackgroundRNA-binding proteins (RBPs) are indispensable for transcriptional and post-transcriptional processes during spermatogenesis, orchestrating germ cell proliferation, differentiation, and maturation. Despite their established importance, the contributions of RBPs in male infertility remain underexplored. Recently, a seminal Science publication reported an RBP atlas of 1744 murine testicular RBPs, 22 loss-of-function variants, and 137 deleterious missense variants identified in 1046 infertile patients, providing unprecedented opportunities to investigate their molecular and clinical relevance. Variants in RBP-related genes associated with azoospermia, oligozoospermia, teratozoospermia, and asthenozoospermia highlight their potential as diagnostic biomarkers and therapeutic targets. However, comprehensive analyses that integrate genetic, functional, and clinical insights are still lacking.Objective and rationaleThis review aims to systematically analyze the roles of RBPs in male infertility. Leveraging state-of-the-art datasets and experimental insights, it examines pathogenic variants and variants of uncertain significance (VUS), and elucidates the gene-disease relationships (GDRs). Furthermore, it explores known RBP functions across spermatogenesis stages and identifies candidate RBP genes. By integrating these findings, this work provides a comprehensive framework to advance the genetic understanding of RBPs, and their potential as clinical biomarkers and therapeutic targets in male infertility.Search methodsWe searched the PubMed database for articles until 13 July 2025, using the keywords 'RNA-binding protein', 'male infertility', 'spermatogenesis', 'sperm', 'genetic variant', 'functional analyses', and 'knockout mouse model'. Pathogenic variants and VUS in 1744 RBP-coding genes, retrieved from the ClinVar and PubMed databases, were systematically analyzed to classify GDRs by the International Male Infertility Genomics Consortium database. Functional data from RBP knockout mouse models were assessed to elucidate stage-specific roles in spermatogenesis. Candidate RBP genes lacking knockout mouse models were identified by mining the RBP atlas, alongside data from the Genotype-Tissue Expression, Human Protein Atlas, and Uniprot databases. The clinical potential of RBPs as diagnostic biomarkers and therapeutic targets was also discussed.OutcomesOur search generated ∼2000 records, and 331 relevant articles were ultimately included in the final text. Firstly, this review identified 177 pathogenic variants in 62 RBP genes and 91 VUS in 35 RBP genes, 15 of which have been confidently linked to human male infertility. Secondly, functional analyses of 124 RBP knockout mouse models revealed their stage-specific regulatory roles in spermatocytogenesis, spermatidogenesis, and spermiogenesis, offering insights into key processes such as piwi-interacting RNA biogenesis, chromatin remodeling, and RNA stability. Thirdly, 38 RBP genes lacking knockout mouse models were screened as candidate RBP genes in male infertility, underscoring their potential for future functional investigations. Finally, this review discusses the clinical potential of RBPs as biomarkers and therapeutic targets, including RNA-based drugs, small molecules, and gene editing technologies as innovative strategies to address RBP-related male infertility.Wider implicationsThis review highlights the role of RBPs in male infertility and offers a framework for integrating genetic, functional, and clinical data. By identifying candidate RBPs and their therapeutic potential, it lays the groundwork for future diagnostic advancements and personalized treatments in reproductive medicine.Registration numberN/A.