Y chromosome functions in mammalian spermatogenesis

Sex Chromosome Evolution: Hallmarks and Question Marks

Sex chromosomes are widespread in species with separate sexes. They have evolved many times independently and display a truly remarkable diversity. New sequencing technologies and methodological developments have allowed the field of molecular evolution to explore this diversity in a large number of model and nonmodel organisms, broadening our vision on the mechanisms involved in their evolution. Diverse studies have allowed us to better capture the common evolutionary routes that shape sex chromosomes; however, we still mostly fail to explain why sex chromosomes are so diverse. We review over half a century of theoretical and empirical work on sex chromosome evolution and highlight pending questions on their origins, turnovers, rearrangements, degeneration, dosage compensation, gene content, and rates of evolution. We also report recent theoretical progress on our understanding of the ultimate reasons for sex chromosomes' existence.

Vigor King mitigates spermatogenic disorders caused by environmental estrogen zearalenone exposure

Zearalenone (ZEN) has been shown to cause reproductive damage by inducing oxidative stress. Astaxanthin and L-carnitine are widely used to alleviate oxidative stress and promote sperm maturation. However, it remains uncertain whether they are effective in mitigating spermatogenesis disorders induced by ZEN. This study aimed to investigate the therapeutic efficacy and potential mechanisms of Vigor King (Vig), a compound preparation primarily consisting of astaxanthin and L-carnitine, in alleviating ZEN-induced spermatogenesis disorders. In the experiment, mice received continuous oral gavage of ZEN (80 μg/kg) for 35 days, accompanied by a rescue strategy with Vig (200 mg/kg). The results showed that Vig effectively reduced the negative impact on semen quality and improved the structural and functional abnormalities of the seminiferous epithelium caused by ZEN. Additionally, the accumulation of reactive oxygen species (ROS), DNA double-strand breaks, apoptosis, and autophagy abnormalities were all significantly ameliorated. Intriguingly, the GSK3β-dependent BTRC-NRF2 signaling pathway was found to play an important role in this process. Furthermore, testing of offspring indicated that Vig could extend its protective effects to the next generation, effectively combating the transgenerational toxic effects of ZEN. In summary, our research suggests that Vig supplementation holds considerable promise in alleviating spermatogenesis disorders induced by zearalenone.

Identification and functional verification of Y-chromosome-specific gene typo-gyf in Bactrocera dorsalis

Genes on the Y chromosome play important roles in male sex determination and development. The identification of Y-chromosome-specific genes not only provides a theoretical basis for the study of male reproductive development, but also offers genetic control targets for agricultural pests. However, Y-chromosome genes are rarely characterized due to their high repeatability and high heterochromatinization, especially in the oriental fruit fly. In this study, 1 011 Y-chromosome-specific candidate sequences were screened from 2 to 4 h Bactrocera dorsalis embryo datasets with the chromosome quotient method, 6 of which were identified as Y-chromosome-specific sequences by polymerase chain reaction, including typo-gyf, a 19 126-bp DNA sequence containing a 575-amino acid open reading frame. Testicular deformation and a significant reduction in sperm number were observed after typo-gyf knockdown with RNA interference in embryos. After typo-gyf knockout with clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 in the embryonic stage, the sex ratio of the emergent adults was unbalanced, with far more females than males. A genotype analysis of these females with the Y-chromosome gene MoY revealed no sex reversal. Typo-gyf knockout led to the death of XY individuals in the embryonic stage. We conclude that typo-gyf is an essential gene for male survival, and is also involved in testicular development and spermatogenesis. The identification of typo-gyf and its functional verification provide insight into the roles of Y-chromosome genes in male development.

Conserved genes regulating human sex differentiation, gametogenesis and fertilization

The study of the functional genome in mice and humans has been instrumental for describing the conserved molecular mechanisms regulating human reproductive biology, and for defining the etiologies of monogenic fertility disorders. Infertility is a reproductive disorder that includes various conditions affecting a couple's ability to achieve a healthy pregnancy. Recent advances in next-generation sequencing and CRISPR/Cas-mediated genome editing technologies have facilitated the identification and characterization of genes and mechanisms that, if affected, lead to infertility. We report established genes that regulate conserved functions in fundamental reproductive processes (e.g., sex determination, gametogenesis, and fertilization). We only cover genes the deletion of which yields comparable fertility phenotypes in both rodents and humans. In the case of newly-discovered genes, we report the studies demonstrating shared cellular and fertility phenotypes resulting from loss-of-function mutations in both species. Finally, we introduce new model systems for the study of human reproductive biology and highlight the importance of studying human consanguineous populations to discover novel monogenic causes of infertility. The rapid and continuous screening and identification of putative genetic defects coupled with an efficient functional characterization in animal models can reveal novel mechanisms of gene function in human reproductive tissues.

Phased Assembly of Neo-Sex Chromosomes Reveals Extensive Y Degeneration and Rapid Genome Evolution in Rumex hastatulus

Y chromosomes are thought to undergo progressive degeneration due to stepwise loss of recombination and subsequent reduction in selection efficiency. However, the timescales and evolutionary forces driving degeneration remain unclear. To investigate the evolution of sex chromosomes on multiple timescales, we generated a high-quality phased genome assembly of the massive older (<10 MYA) and neo (<200,000 yr) sex chromosomes in the XYY cytotype of the dioecious plant Rumex hastatulus and a hermaphroditic outgroup Rumex salicifolius. Our assemblies, supported by fluorescence in situ hybridization, confirmed that the neo-sex chromosomes were formed by two key events: an X-autosome fusion and a reciprocal translocation between the homologous autosome and the Y chromosome. The enormous sex-linked regions of the X (296 Mb) and two Y chromosomes (503 Mb) both evolved from large repeat-rich genomic regions with low recombination; however, the complete loss of recombination on the Y still led to over 30% gene loss and major rearrangements. In the older sex-linked region, there has been a significant increase in transposable element abundance, even into and near genes. In the neo-sex-linked regions, we observed evidence of extensive rearrangements without gene degeneration and loss. Overall, we inferred significant degeneration during the first 10 million years of Y chromosome evolution but not on very short timescales. Our results indicate that even when sex chromosomes emerge from repetitive regions of already-low recombination, the complete loss of recombination on the Y chromosome still leads to a substantial increase in repetitive element content and gene degeneration.

Where Are the Formerly Y-linked Genes in the Ryukyu Spiny Rat that has Lost its Y Chromosome?

It has been predicted that the highly degenerate mammalian Y chromosome will be lost eventually. Indeed, Y was lost in the Ryukyu spiny rat Tokudaia osimensis, but the fate of the formerly Y-linked genes is not completely known. We looked for all 12 ancestrally Y-linked genes in a draft T. osimensis genome sequence. Zfy1, Zfy2, Kdm5d, Eif2s3y, Usp9y, Uty, and Ddx3y are putatively functional and are now located on the X chromosome, whereas Rbmy, Uba1y, Ssty1, Ssty2, and Sry are missing or pseudogenized. Tissue expressions of the mouse orthologs of the retained genes are significantly broader/higher than those of the lost genes, suggesting that the destinies of the formerly Y-linked genes are related to their original expressions. Interestingly, patterns of gene retention/loss are significantly more similar than by chance across four rodent lineages where Y has been independently lost, indicating a level of certainty in the fate of Y-linked genes even when the chromosome is gone.

Antibody-mediated pathogenesis of chronic GVHD through DBY/HLA class II complexes and induction of a GVL effect

Chronic graft-versus-host disease (cGVHD) is a multiorgan syndrome with clinical features resembling those of autoimmune diseases. Thus, understanding commonalities in the pathophysiology of cGVHD and autoimmune diseases, such as the presence of disease-risk HLA alleles, is imperative for developing novel therapies against cGVHD. Alloantibodies against H-Y antigens encoded on the Y-chromosome are well-described risk factors for cGVHD in female-to-male transplantation. However, because H-Y antigens generally localize intracellularly in the male reproductive organs, how they emerge at affected organ levels remains elusive. Here, by analyzing nationwide registry data stratified per donor-recipient sex, we identified specific HLA class II alleles that contributed to susceptibility to male cGVHD after transplantation from HLA-identical female siblings (HLA-DRB1∗15:02: hazard ratio, 1.28; 95% confidence interval, 1.03-1.58; P = .025). Coexpression of HLA-DRB1∗15:02 efficiently transported full-length H-Y antigens, especially DBY, to the surface. The presence of alloantibodies against DBY/HLA class II complexes significantly predicted the occurrence of cGVHD (68.8% vs 31.7% at 1 year; P = .002). Notably, the ability of HLA class II molecules to transport and present DBY to alloantibodies was closely associated with the susceptibility of HLA class II alleles to cGVHD. DBY specifically colocalized with HLA class II molecules on the dermal vascular endothelium in cGVHD and provoked complement-dependent cytotoxicity. Moreover, these complexes were observed in some male leukemic cells. Altogether, these findings suggest that vascular endothelial cells facilitate alloantibody-mediated cGVHD and highlight that alloantibodies against DBY/HLA class II complexes could be common targets for cGVHD and a graft-versus-leukemia effect.

Identification of Y-SNPs within ovine MSY region and their association with testicular size

The screening of genomic variations within the male-specific region of the mammalian Y chromosome (MSY) is one of the most effective ways to investigate paternal evolutionary history and identify molecular markers related to male fertility. The current study was to identify single nucleotide polymorphisms (SNPs) within single-copy genes of the ovine MSY, and confirm whether they are associated with testicular size. A total of 21 Y-specific gene fragments were successfully amplified to screen Y-SNPs in 956 rams across nine sheep breeds. Three Y-SNPs, including SRY16: g.88 A > G in South African Mutton Merino sheep, ZFY16: g.146 C > T in Suffolk and South African Mutton Merino sheep, and EIF2S3Y2: g.77 C > G in Hu and Tan sheep, were identified using DNA-pooled sequencing and PCR restriction fragment length polymorphism (PCR-RFLP) methods. The investigation of the global distribution for three Y-SNPs showed that the C allele of ZFY16: g.146 C > T co-segregated with haplogroup y-HC, and the C/G allele of EIF2S3Y2: g.77 C > G co-segregated with haplogroup y-HA/y-HB1 in Hu sheep according to data mining from a previous study. In addition, association analysis revealed that ZFY16: g.146 C > T had a significant effect on yearling scrotal circumference in Suffolk sheep, and EIF2S3Y2: g.77 C > G was significantly associated with testicular and epididymis weight in Hu sheep (P ≤ 0.05). The current study concluded that Y-SNPs were associated with testicular size in specific sheep, which provides valuable candidate makers for selecting elite rams at an early age.

PRAMEY: A Bovid-Specific Y-Chromosome Multicopy Gene Is Highly Related to Postnatal Testicular Growth in Hu Sheep

PRAMEY (preferentially expressed antigen in melanoma, Y-linked) belongs to the cancer-testis antigens (CTAs) gene family and is predominantly expressed in testis, playing important roles in spermatogenesis and testicular development. This study cloned the full-length cDNA sequence of ovine PRAMEY using the rapid amplification of cDNA ends (RACE) method and analyzed the expression profile and copy number variation (CNV) of PRAMEY using quantitative real-time PCR (qPCR). The results revealed that the PRAMEY cDNA was 2099 bp in length with an open reading frame (ORF) of 1536 bp encoding 511 amino acids. PRAMEY was predominantly expressed in the testis and significantly upregulated during postnatal testicular development. The median copy number (MCN) of PRAMEY was 4, varying from 2 to 25 in 710 rams across eight sheep breeds. There was no significant correlation between the CNV of PRAMEY and testicular size, while a significant positive correlation was observed between the mRNA expression and testicular size in Hu sheep. The current study suggests that the expression levels of PRAMEY were closely associated with testicular size, indicating that PRAMEY may play an important role in testicular growth.

Two acquired mouse Y chromosome-linked genes, Prssly and Teyorf1, are dispensable for male fertility‡

Prssly (Protease, serine-like, Chr Y) and Teyorf1 (Testis expressed, chromosome Y open reading frame 1) are two acquired single-copy genes located on the distal tip of the non-pairing short arm of the mouse Y chromosome adjacent to telomeric sequence. Both genes lack X chromosome-linked homologues and are expressed in testicular germ cells. We first performed analysis of Prssly and Teyorf1 genomic sequences and demonstrated that previously reported Prssly sequence is erroneous and the true Prssly sequence is longer and encodes a larger protein than previously estimated. We also confirmed that both genes encode pseudogenes that are not expressed in testes. Next, using CRISPR/Cas9 genome targeting, we generated Prssly and Teyorf1 knockout (KO) mice and characterized their phenotype. To create Prssly KO mice, we targeted the conserved exon 5 encoding a trypsin domain typical for serine proteases. The targeting was successful and resulted in a frame shift mutation that introduced a premature stop codon, with the Prssly KO males retaining only residual transcript expression in testes. The Teyorf1 targeting removed the entire open reading frame of the gene, which resulted in no transcript expression in KO males. Both Prssly KO and Teyorf1 KO males were fertile and had normal testis size and normal sperm number, motility, and morphology. Our findings show that Prssly and Teyorf1 transcripts with potential to encode proteins are dispensable for male fertility.

Repetitive DNA Sequences in the Human Y Chromosome and Male Infertility

The male-specific Y chromosome, which is well known for its diverse and complex repetitive sequences, has different sizes, genome structures, contents and evolutionary trajectories from other chromosomes and is of great significance for testis development and function. The large number of repetitive sequences and palindrome structure of the Y chromosome play an important role in maintaining the stability of male sex determining genes, although they can also cause non-allelic homologous recombination within the chromosome. Deletion of certain Y chromosome sequences will lead to spermatogenesis disorders and male infertility. And Y chromosome genes are also involved in the occurrence of reproductive system cancers and can increase the susceptibility of other tumors. In addition, the Y chromosome has very special value in the personal identification and parentage testing of male-related cases in forensic medicine because of its unique paternal genetic characteristics. In view of the extremely high frequency and complexity of gene rearrangements and the limitations of sequencing technology, the analysis of Y chromosome sequences and the study of Y-gene function still have many unsolved problems. This article will introduce the structure and repetitive sequence of the Y chromosome, summarize the correlation between Y chromosome various sequence deletions and male infertility for understanding the repetitive sequence of Y chromosome more systematically, in order to provide research motivation for further explore of the molecules mechanism of Y-deletion and male infertility and theoretical foundations for the transformation of basic research into applications in clinical medicine and forensic medicine.

Loss of mouse Y chromosome gene Zfy1 and Zfy2 leads to spermatogenesis impairment, sperm defects, and infertility

Using mice with Y chromosome deficiencies and supplementing Zfy transgenes, we, and others, have previously shown that the loss of Y chromosome Zfy1 and Zfy2 genes is associated with infertility and spermiogenic defects and that the addition of Zfy transgenes rescues these defects. In these past studies, the absence of Zfy was linked to the loss of other Y chromosome genes, which might have contributed to spermiogenic phenotypes. Here, we used CRISPR/Cas9 to specifically remove open reading frame of Zfy1, Zfy2, or both Zfy1 and Zfy2, and generated Zfy knockout (KO) and double knockout (DKO) mice. Zfy1 KO and Zfy2 KO mice were both fertile, but the latter had decreased litters size and sperm number, and sperm headshape abnormalities. Zfy DKO males were infertile and displayed severe spermatogenesis defects. Postmeiotic arrest largely prevented production of sperm and the few sperm that were produced all displayed gross headshape abnormalities and structural defects within head and tail. Infertility of Zfy DKO mice could be overcome by injection of spermatids or sperm directly to oocytes, and the resulting male offspring had the same spermiogenic phenotype as their fathers. The study is the first describing detailed phenotypic characterization of mice with the complete Zfy gene loss. It provides evidence supporting that the presence of at least one Zfy homolog is essential for male fertility and development of normal sperm functional in unassisted fertilization. The data also show that while the loss of Zfy1 is benign, the loss of Zfy2 is mildly detrimental for spermatogenesis.

Drosophila as a Model System for Studying of the Evolution and Functional Specialization of the Y Chromosome

The Y chromosome is one of the sex chromosomes found in males of animals of different taxa, including insects and mammals. Among all chromosomes, the Y chromosome is characterized by a unique chromatin landscape undergoing dynamic evolutionary change. Being entirely heterochromatic, the Y chromosome as a rule preserves few functional genes, but is enriched in tandem repeats and transposons. Due to difficulties in the assembly of the highly repetitive Y chromosome sequence, deep analyses of Y chromosome evolution, structure, and functions are limited to a few species, one of them being Drosophila melanogaster. Despite Y chromosomes exhibiting high structural divergence between even closely related species, Y-linked genes have evolved convergently and are mainly associated with spermatogenesis-related activities. This indicates that male-specific selection is a dominant force shaping evolution of Y chromosomes across species. This review presents our analysis of current knowledge concerning Y chromosome functions, focusing on recent findings in Drosophila. Here we dissect the experimental and bioinformatics data about the Y chromosome accumulated to date in Drosophila species, providing comparative analysis with mammals, and discussing the relevance of our analysis to a wide range of eukaryotic organisms, including humans.

Human Spermatogenesis: Insights From the Clinical Care of Men With Infertility

Human spermatogenesis is a qualitatively and quantitatively different process than that observed for most other mammals. In contrast with most other mammals, human spermatogenesis is characterized by reduced quantitative production and more abnormal sperm morphology. Until recently, direct evaluation and observations of human sperm production has been limited and the majority of scientific knowledge regarding spermatogenesis was derived from rodent models of study. Unique opportunities to observe human spermatogenesis have occurred as a consequence of the treatment of severe male infertility. These patients have sperm production so limited that no sperm reach the ejaculate so their fertility treatment involves surgical sperm retrieval from the testis, coupled with use of those sperm with advanced assisted reproductive techniques. Treatment of men with severe male infertility has enhanced identification of new genetic abnormalities that may cause this condition, since they now seek medical care. Three key novel concepts have resulted: (a) spermatogenesis is spatially heterogeneous in the human male, especially when sperm production is compromised, (b) genetic abnormalities are common in men with severe male infertility, particularly in men with diffuse maturation arrest and (c) rodent studies may not be an ideal model for understanding human male infertility. Scientific understanding of human spermatogenesis has been enhanced by these clinical observations.