Mouse Y-Encoded Transcription Factor Zfy2 Is Essential for Sperm Formation and Function in Assisted Fertilization

Analysis of Postnatal Mutant Phenotypes in Mice

Viable homozygous mutant newborn mice may show effects of a mutation at any time during their development by exhibiting abnormal structure, function, or lethality. This overview guides the analysis of postnatal mice through gross anatomical assessment and the detection of visible phenotypes prior to weaning such as altered growth patterns, neurological problems, or abnormalities in movement or coordination. Advice on marking pups for identification purposes and providing adequate nutrition in the event of eating problems is given. After weaning and at the onset of puberty, different phenotypes may become manifest, including compromised growth and vigor and reproductive problems in males and/or females. Assessing infertility in each sex is addressed.

Return of the forgotten hero: the role of Y chromosome-encoded Zfy in male reproduction

The Y-linked zinc finger gene ZFY is conserved across eutherians and is known to be a critical fertility factor in some species. The initial studies of the mouse homologues, Zfy1 and Zfy2, were performed using mice with spontaneous Y chromosome mutations and Zfy transgenes. These studies revealed that Zfy is involved in multiple processes during spermatogenesis, including removal of germ cells with unpaired chromosomes and control of meiotic sex chromosome inactivation during meiosis I, facilitating the progress of meiosis II, promoting spermiogenesis, and improving assisted reproduction outcomes. Zfy was also identified as a key gene in Y chromosome evolution, protecting this chromosome from extinction by serving as the executioner responsible for meiosis surveillance. Studies with targeted Zfy knock-outs revealed that mice lacking both homologues have severe spermatogenic defects and are infertile. Based on protein structure and in vitro assays, Zfy is expected to drive spermatogenesis as a transcriptional regulator. The combined evidence documents that the presence of at least one Zfy homologue is required for male fertility and that Zfy2 plays a more prominent role. This knowledge reinforces the importance of these factors for mouse spermatogenesis and informs our understanding of the human ZFY variants, which are homologous to the mouse Zfy1 and Zfy2.

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.

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.

Update on genetic screening and treatment for infertile men with genetic disorders in the era of assisted reproductive technology

A genetic etiology of male infertility is identified in fewer than 25% of infertile men, while 30% of infertile men lack a clear etiology, resulting in a diagnosis of idiopathic male infertility. Advances in reproductive genetics have provided insights into the mechanisms of male infertility, and a characterization of the genetic basis of male infertility may have broad implications for understanding the causes of infertility and determining the prognosis, optimal treatment, and management of couples. In a substantial proportion of patients with azoospermia, known genetic factors contribute to male infertility. Additionally, the number of identified genetic anomalies in other etiologies of male infertility is growing through advances in whole-genome amplification and next-generation sequencing. In this review, we present an up-to-date overview of the indications for appropriate genetic tests, summarize the characteristics of chromosomal and genetic diseases, and discuss the treatment of couples with genetic infertility by microdissection-testicular sperm extraction, personalized hormone therapy, and in vitro fertilization with pre-implantation genetic testing.

The role of Eif2s3y in mouse spermatogenesis

Eukaryotic translation initiation factor 2 subunit 3 and structural gene Y-linked (Eif2s3y) gene, the gene encoding eIF2γ protein, is located on the mouse Y chromosome short arm. The Eif2s3y gene is globally expressed in all tissues and plays an important role in regulating global and gene-specific mRNA translation initiation. During the process of protein translation initiation, Eif2s3x(its homolog) and Eif2s3y encoded eIF2γ perform similar functions. However, it has been noticed that Eif2s3y plays a crucial role in spermatogenesis, including spermatogonia mitosis, meiosis, and spermiogenesis of spermatids, which may account for infertility. In the period of spermatogenesis, the role of Eif2s3x and Eif2s3y are not equivalent. Importance of Eif2s3y has been observed in ESC and implicated in several aspects, including the pluripotency state and the proliferation rate. Here, we discuss the functional significance of Eif2s3y in mouse spermatogenesis and self-renewal of ESCs.

Distinct roles of haspin in stem cell division and male gametogenesis

The kinase haspin phosphorylates histone H3 at threonine-3 (H3T3ph) during mitosis. H3T3ph provides a docking site for the Chromosomal Passenger Complex at the centromere, enabling correction of erratic microtubule-chromosome contacts. Although this mechanism is operational in all dividing cells, haspin-null mice do not exhibit developmental anomalies, apart from aberrant testis architecture. Investigating this problem, we show here that mouse embryonic stem cells that lack or overexpress haspin, albeit prone to chromosome misalignment during metaphase, can still divide, expand and differentiate. RNA sequencing reveals that haspin dosage affects severely the expression levels of several genes that are involved in male gametogenesis. Consistent with a role in testis-specific expression, H3T3ph is detected not only in mitotic spermatogonia and meiotic spermatocytes, but also in non-dividing cells, such as haploid spermatids. Similarly to somatic cells, the mark is erased in the end of meiotic divisions, but re-installed during spermatid maturation, subsequent to methylation of histone H3 at lysine-4 (H3K4me₃) and arginine-8 (H3R8me₂). These serial modifications are particularly enriched in chromatin domains containing histone H3 trimethylated at lysine-27 (H3K27me₃), but devoid of histone H3 trimethylated at lysine-9 (H3K9me₃). The unique spatio-temporal pattern of histone H3 modifications implicates haspin in the epigenetic control of spermiogenesis.

Y chromosome functions in mammalian spermatogenesis

The mammalian Y chromosome is critical for male sex determination and spermatogenesis. However, linking each Y gene to specific aspects of male reproduction has been challenging. As the Y chromosome is notoriously hard to sequence and target, functional studies have mostly relied on transgene-rescue approaches using mouse models with large multi-gene deletions. These experimental limitations have oriented the field toward the search for a minimum set of Y genes necessary for male reproduction. Here, considering Y-chromosome evolutionary history and decades of discoveries, we review the current state of research on its function in spermatogenesis and reassess the view that many Y genes are disposable for male reproduction.

Y chromosome in health and diseases

Sex differences are prevalent in normal development, physiology and disease pathogeneses. Recent studies have demonstrated that mosaic loss of Y chromosome and aberrant activation of its genes could modify the disease processes in male biased manners. This mini review discusses the nature of the genes on the human Y chromosome and identifies two general categories of genes: those sharing dosage-sensitivity functions with their X homologues and those with testis-specific expression and functions. Mosaic loss of the former disrupts the homeostasis important for the maintenance of health while aberrant activation of the latter promotes pathogenesis in non-gonadal tissues, thereby contributing to genetic predispositions to diseases in men.

Specific expression and alternative splicing of mouse genes during spermatogenesis

Considering the high abundance of spliced RNAs in testis compared to other tissues, it is needed to construct the landscape of alternative splicing during spermatogenesis. However, there is still a lack of the systematic analysis of alternative RNA splicing in spermatogenesis. Here, we constructed a landscape of alternative RNA splicing during mouse spermatogenesis based on integrated RNA-seq data sets. Our results presented several novel alternatively spliced genes (Eif2s3y, Erdr1 Uty and Zfy1) in the Y chromosome with a specific expression pattern. Remarkably, the alternative splicing genes were grouped into co-expression networks involved in the microtubule cytoskeleton organization and post-transcriptional regulation of the gene expression, indicating the potential pathway to germ cell generation. Furthermore, based on the co-expression networks, we identified Atxn2l as a potential key gene in spermatogenesis, which presented dynamic expression patterns in different alternative splicing types. Ultimately, we proposed splicing regulatory networks for understanding novel and innovative alternative splicing regulation mechanisms during spermatogenesis. In summary, our research provides a systematic analysis of alternative RNA splicing and some novel spliced genes related to spermatogenesis.

The Use of RNAi Technology to Interfere with Zfx Gene Increases the Male Rates of Red Deer (Cervus elaphus) Offspring

Zinc finger protein X-linked (Zfx) was regarded to be a sex determination factor and plays a critical role in spermatogenesis. RNAi is an effective method of silencing Zfx mRNA expression. However, there has been little research on the use of RNAi technology to control the sex of the offspring of red deer (Cervus elaphus). The objective of this study was first to explore an efficient method to alter the red deer offspring sex-ratio by silencing the gene Zfx during spermatogenesis. Three recombinant expression vectors pLL3.7/A, pLL3.7/B, and pLL3.7/C were constructed to interrupt the Zfx gene. The results showed that the expression of Zfx mRNA was significantly silenced by pLL3.7/A (P < 0.01), compared with the control group. The group injected with pLL3.7/A produced 94 red deer, including 68 males and 26 females. The male rates (72.34%) were significantly higher than the control groups (P < 0.01). Our result suggests that Zfx siRNA is a useful approach to control offspring sex in red deer. This study further confirms that the Zfx gene plays a significant role in the process of X spermatogenesis.

Mammalian haploid stem cells: establishment, engineering and applications

Haploid embryonic stem cells (haESCs) contain only one set of genomes inherited from the sperm or egg and are termed AG- or PG-haESCs, respectively. Mammalian haESCs show genome-wide hypomethylation and dysregulated imprinting, whereas they can sustain genome integrity during derivation and long-term propagation. In addition, haESCs exhibit similar pluripotency to traditional diploid ESCs but are unique because they function as gametes and have been used to produce semi-cloned animals. More strikingly, unisexual reproduction has been achieved in mice by using haESCs. In combination with a gene editing or screening system, haESCs represent a powerful tool for studies of underlying gene functions and explorations of mechanisms of genetic and epigenetic regulation not only at the cellular level in vitro but also at the animal level in vivo. More importantly, genetically edited AG-haESC lines may further serve as an ideal candidate for the establishment of a sperm bank, which is a highly cost-effective approach, and a wide range of engineered semi-cloned mice have been produced. Here, we review the historical development, characteristics, advantages and disadvantages of haESCs. Additionally, we present an in-depth discussion of the recent advances in haESCs and their potential applications.

Reconstitution of male germline cell specification from mouse embryonic stem cells using defined factors in vitro

In vitro induction of functional haploid cells from embryonic stem cells (ESCs) has been reported by several groups. However, these reports either involve complex induction process with undefined induction factors or show low-induction efficiency. Here, we report complete meiosis in vitro from ESCs with defined induction factors. ESCs were first induced into primordial germ cell-like cells, which were further induced into male germline cells, including spermatogonial stem cell-like cells (SSCLCs) and spermatid-like cells. Importantly, the obtained SSCLCs were functional as infertile male mice sired healthy offspring via SSCLC transplantation. Further, we found that eukaryotic translation initiation factor 2 subunit 3 and structural gene Y-linked (Eif2s3y) was essential for spermatogenesis. Eif2s3y-overexpressing ESCs showed enhanced spermatogenesis in vitro, as demonstrated by higher expression levels of SSC-specific markers during SSCLC induction process, improved reproductive ability recovery of infertile male mice, and increased efficiency of haploid cell induction. Our work provides a convenient and efficient approach to obtain functional male germline cells.

Deep Sequencing of Fosmid Clones Indicates Gene Conversion in the Male-Specific Region of the Giant Panda Y Chromosome

The giant panda (Ailuropoda melanoleuca) is popular around the world and is widely recognized as a symbol of nature conservation. A draft genome of the giant panda is now available, but its Y chromosome has not been sequenced. Y chromosome data are necessary for study of sex chromosome evolution, male development, and spermatogenesis. Thus, in the present study, we sequenced two parts of the giant panda Y chromosome utilizing a male giant panda fosmid library. The sequencing data were assembled into two contigs, each ∼100 kb in length with no gaps, providing high-quality resources for studying the giant panda Y chromosome. Annotation and transposable element comparison indicates varied evolutionary pressure in different regions of the Y chromosome. Two genes, zinc finger protein, Y-linked (ZFY) and lysine demethylase 5D (KDM5D), were annotated and gene conversion was observed for ZFY exon 7. Phylogenetic analysis also revealed that this gene conversion event happened independently in multiple mammalian lineages, indicating a putative mechanism to maintain the function of this particular gene on the Y chromosome. Furthermore, a transposition event, discovered through comparative alignment with the giant panda X chromosome sequence, may be involved in the process of gaining new genes on the Y chromosome. Thus, these newly obtained Y chromosome sequences provide valuable insights into the genomic patterns of the giant panda.

Genetics of the human Y chromosome and its association with male infertility

The human Y chromosome harbors genes that are responsible for testis development and also for initiation and maintenance of spermatogenesis in adulthood. The long arm of the Y chromosome (Yq) contains many ampliconic and palindromic sequences making it predisposed to self-recombination during spermatogenesis and hence susceptible to intra-chromosomal deletions. Such deletions lead to copy number variation in genes of the Y chromosome resulting in male infertility. Three common Yq deletions that recur in infertile males are termed as AZF (Azoospermia Factor) microdeletions viz. AZFa, AZFb and AZFc. As estimated from data of nearly 40,000 Y chromosomes, the global prevalence of Yq microdeletions is 7.5% in infertile males; however the European infertile men are less susceptible to Yq microdeletions, the highest prevalence is in Americans and East Asian infertile men. In addition, partial deletions of the AZFc locus have been associated with infertility but the effect seems to be ethnicity dependent. Analysis of > 17,000 Y chromosomes from fertile and infertile men has revealed an association of gr/gr deletion with male infertility in Caucasians and Mongolian men, while the b2/b3 deletion is associated with male infertility in African and Dravidian men. Clinically, the screening for Yq microdeletions would aid the clinician in determining the cause of male infertility and decide a rational management strategy for the patient. As these deletions are transmitted to 100% of male offspring born through assisted reproduction, testing of Yq deletions will allow the couples to make an informed choice regarding the perpetuation of male infertility in future generations. With the emerging data on association of Yq deletions with testicular cancers and neuropsychiatric conditions long term follow-up data is urgently needed for infertile men harboring Yq deletions. If found so, the information will change the current the perspective of androgenetics from infertility and might have broad implication in men health.

EIF2S3Y suppresses the pluripotency state and promotes the proliferation of mouse embryonic stem cells

Eukaryotic translation initiation factor 2, subunit 3, and structural gene Y-linked (EIF2S3Y) is essential for spermatogenesis in mouse models. However, its effect on embryonic stem (ES) cells remains unknown. In our observation, differentiated ES cells showed higher levels of EIF2S3Y. To further elucidate its role in ES cells, we utilized ES-derived EIF2S3Y-overexpressing cells and found that EIF2S3Y down-regulated the pluripotency state of ES cells, which might be explained by decreased histone methylation levels because of reduced levels of ten-eleven translocation 1 (TET1). Moreover, EIF2S3Y-overexpressing cells showed an enhanced proliferation rate, which might be due to increased Cyclin A and Cyclin E levels. This study highlighted novel roles of EIF2S3Y in the pluripotency maintenance and proliferation control of ES cells, which would provide an efficient model to study germ cell generation as well as cancer development using ES cells, thus providing valuable target for clinical applications of ES cells.

Testicular abnormalities in mice with Y chromosome deficiencies

We recently investigated mice with Y chromosome gene contribution limited to two, one, or no Y chromosome genes in respect to their ability to produce haploid round spermatids and live offspring following round spermatid injection. Here we explored the normalcy of germ cells and Sertoli cells within seminiferous tubules, and the interstitial tissue of the testis in these mice. We performed quantitative analysis of spermatogenesis and interstitial tissue on Periodic acid-Schiff and hematoxylin-stained mouse testis sections. The seminiferous epithelium of mice with limited Y gene contribution contained various cellular abnormalities, the total number of which was higher than in the males with an intact Y chromosome. The distribution of specific abnormality types varied among tested genotypes. The males with limited Y genes also had an increased population of testicular macrophages and internal vasculature structures. The data indicate that Y chromosome gene deficiencies in mice are associated with cellular abnormalities of the seminiferous epithelium and some changes within the testicular interstitium.

Mild reproductive impact of a Y chromosome deletion on a C57BL/6J substrain

A recently reported deletion of about 40 Mb in length between 6.12/6.57 and 46.73/47.31 Mb on the Y chromosome long arm of the C57BL/6JBomTac inbred strain made us closely examine the strain’s breeding history and reproductive characteristics. We verified that the two copies of Rbm31y that are present inside the putative deletion were indeed deleted. This inbred strain presents an expected litter size for a C57BL/6 substrain. In vitro fertilization (IVF) efficiency and breeding efficiencies are comparable to those of the C57BL/6NTac substrain; however, the male/female sex ratio in the C57BL/6JBomTac is mildly skewed towards females. There is an increase in the percentage of sperm shape abnormalities found in C57BL/6JBomTac (35%) versus C57BL/6NTac (11%). The most frequent type of sperm abnormality observed is bent heads (19%). Additionally, there is deregulation of several transcripts expressed in the testes. We determined that this mutation arose in the C57BL/6JBomTac Foundation Colony in 2008, and it was completely fixed in the colony by 2009.

RNAi as a tool to control the sex ratio of mouse offspring by interrupting Zfx/Zfy genes in the testis

The objective of this study was to explore a novel method to alter the sex-ratio balance of mouse offspring by silencing the paralogous genes Zfx/Zfy (Zinc finger X/Y-chromosomal transcription factor gene) during spermatogenesis. Four recombined vectors PRZ1, PRZ2, PRZ3, and PRZ4 (RNAi-Ready-pSIREN-RetroQ-ZsGreen) were constructed for interrupting the Zfx gene. Additionally, a recombined vector Psilencer/Zfy-shRNA was constructed for interrupting the Zfy gene. Male mice were randomly divided into 8 groups, with 20 animals per group. Five groups of mice were injected with PRZ1, PRZ2, PRZ3, PRZ4, and Psilencer/Zfy-shRNA vectors, respectively. The three control groups were injected with an equal volume of physiological saline, empty RNAi-Ready-pSIREN-RetroQ-ZsGreen vector, and empty Psilencer/Zfy-shRNA vector, respectively. All groups were injected every 7 days for a total of four injections. Fourteen days after the fourth injection, 10 male mice from each group were mated individually with 10 females. Testicular tissue of 10 male mice in each group was collected, and the expression level of Zfx/Zfy mRNA was determined by qRT-PCR. Results showed that, compared with the empty RNAi-Ready-pSIREN-RetroQ-ZsGreen vector and the physiological saline group, expression of Zfx mRNA decreased significantly after injection of PRZ1 (p < 0.01), PRZ3 (p < 0.01), and PRZ4 (p < 0.01), and 78.75 ± 7.50% of the offspring were male in PRZ4 group, significantly higher than the offspring derived from the empty RNAi-Ready-pSIREN-RetroQ-ZsGreen vector and physiological saline group (p < 0.01). In the PRZ1 group, the expression of Zfx mRNA was also significantly lower (p < 0.01), but the male rate of offspring was not different (p > 0.05). Conversely, the expression of Zfy mRNA decreased significantly after injection of Psilencer/Zfy-shRNA (p < 0.01) and 31.00 ± 11.00% of the offspring were male, significantly lower than in the physiological saline group (p < 0.01). In conclusion, our findings show that RNAi-mediated disruption of Zfx/Zfy in mouse testis affected X/Y spermatogenesis. Additionally, results suggest that the paralogous genes Zfx/Zfy play an important role in the process of X and Y sperm development. The individual interference of Zfx/Zfy may predict the outcome of X and Y haploid sperms. Presented herein is an advanced method developed to control mouse X/Y spermatogenesis and sex ratio of offspring.

Complementary Critical Functions of Zfy1 and Zfy2 in Mouse Spermatogenesis and Reproduction

The mammalian Y chromosome plays a critical role in spermatogenesis. However, the exact functions of each gene in the Y chromosome have not been completely elucidated, partly owing to difficulties in gene targeting analysis of the Y chromosome. Zfy was first proposed to be a sex determination factor, but its function in spermatogenesis has been recently elucidated. Nevertheless, Zfy gene targeting analysis has not been performed thus far. Here, we adopted the highly efficient CRISPR/Cas9 system to generate individual Zfy1 or Zfy2 knockout (KO) mice and Zfy1 and Zfy2 double knockout (Zfy1/2-DKO) mice. While individual Zfy1 or Zfy2-KO mice did not show any significant phenotypic alterations in fertility, Zfy1/2-DKO mice were infertile and displayed abnormal sperm morphology, fertilization failure, and early embryonic development failure. Mass spectrometric screening, followed by confirmation with western blot analysis, showed that PLCZ1, PLCD4, PRSS21, and HTT protein expression were significantly deceased in spermatozoa of Zfy1/2-DKO mice compared with those of wild-type mice. These results are consistent with the phenotypic changes seen in the double-mutant mice. Collectively, our strategy and findings revealed that Zfy1 and Zfy2 have redundant functions in spermatogenesis, facilitating a better understanding of fertilization failure and early embryonic development failure.

A primer on the use of mouse models for identifying direct sex chromosome effects that cause sex differences in non-gonadal tissues

In animals with heteromorphic sex chromosomes, all sex differences originate from the sex chromosomes, which are the only factors that are consistently different in male and female zygotes. In mammals, the imbalance in Y gene expression, specifically the presence vs. absence of Sry, initiates the differentiation of testes in males, setting up lifelong sex differences in the level of gonadal hormones, which in turn cause many sex differences in the phenotype of non-gonadal tissues. The inherent imbalance in the expression of X and Y genes, or in the epigenetic impact of X and Y chromosomes, also has the potential to contribute directly to the sexual differentiation of non-gonadal cells. Here, we review the research strategies to identify the X and Y genes or chromosomal regions that cause direct, sexually differentiating effects on non-gonadal cells. Some mouse models are useful for separating the effects of sex chromosomes from those of gonadal hormones. Once direct “sex chromosome effects” are detected in these models, further studies are required to narrow down the list of candidate X and/or Y genes and then to identify the sexually differentiating genes themselves. Logical approaches to the search for these genes are reviewed here.

Round Spermatid Injection Rescues Female Lethality of a Paternally Inherited Xist Deletion in Mouse

In mouse female preimplantation embryos, the paternal X chromosome (Xp) is silenced by imprinted X chromosome inactivation (iXCI). This requires production of the noncoding Xist RNA in cis, from the Xp. The Xist locus on the maternally inherited X chromosome (Xm) is refractory to activation due to the presence of an imprint. Paternal inheritance of an Xist deletion (XpΔXist) is embryonic lethal to female embryos, due to iXCI abolishment. Here, we circumvented the histone-to-protamine and protamine-to-histone transitions of the paternal genome, by fertilization of oocytes via injection of round spermatids (ROSI). This did not affect initiation of XCI in wild type female embryos. Surprisingly, ROSI using ΔXist round spermatids allowed survival of female embryos. This was accompanied by activation of the intact maternal Xist gene, initiated with delayed kinetics, around the morula stage, resulting in Xm silencing. Maternal Xist gene activation was not observed in ROSI-derived males. In addition, no Xist expression was detected in male and female morulas that developed from oocytes fertilized with mature ΔXist sperm. Finally, the expression of the X-encoded XCI-activator RNF12 was enhanced in both male (wild type) and female (wild type as well as XpΔXist) ROSI derived embryos, compared to in vivo fertilized embryos. Thus, high RNF12 levels may contribute to the specific activation of maternal Xist in XpΔXist female ROSI embryos, but upregulation of additional Xp derived factors and/or the specific epigenetic constitution of the round spermatid-derived Xp are expected to be more critical. These results illustrate the profound impact of a dysregulated paternal epigenome on embryo development, and we propose that mouse ROSI can be used as a model to study the effects of intergenerational inheritance of epigenetic marks.

The germline-enriched Ppp1r36 promotes autophagy

Spermatogenesis is a highly regulated process during which haploid sperm cells are generated. Although autophagy is involved in the spermatogenesis process, the molecular pathways and regulations of autophagy in germ cell development remain elusive. Here, we showed that Ppp1r36, a regulatory subunit of protein phosphatase 1, is expressed during gonadal development, mainly in testes during spermatogenesis. Autophagy protein LC3 (microtubule associated protein 1 light chain 3), especially its active form LC3-II, had a similar expression pattern to Ppp1r36. Moreover, LC3-II level and puncta analysis showed that autophagy is up-regulated around 21 dpp (day postpartum) in postnatal testis, indicating a potential role of autophagy during the first wave of spermatogenesis. We demonstrated that Ppp1r36 promotes autophagosome formation upon starvation induction. Further autophagy flux analysis using a tandem fluorescent indicator, mCherry-GFP-LC3, confirmed that Ppp1r36 participated in autophagy. We further determined that Ppp1r36 is associated with Atg16L1 (autophagy related 16-like 1) in autophagy of starvation induction. Thus, our results uncover a potential role of the regulatory subunit Ppp1r36 of protein phosphatase 1 in enhancing autophagy during spermatogenesis.