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.

Effects of the Sex Chromosome Complement, XX, XO, or XY, on the Transcriptome and Development of Mouse Oocytes During Follicular Growth

The sex chromosome complement, XX or XY, determines sexual differentiation of the gonadal primordium into a testis or an ovary, which in turn directs differentiation of the germ cells into sperm and oocytes, respectively, in eutherian mammals. When the X monosomy or XY sex reversal occurs, XO and XY females exhibit subfertility and infertility in the mouse on the C57BL/6J genetic background, suggesting that functional germ cell differentiation requires the proper sex chromosome complement. Using these mouse models, we asked how the sex chromosome complement affects gene transcription in the oocytes during follicular growth. An oocyte accumulates cytoplasmic components such as mRNAs and proteins during follicular growth to support subsequent meiotic progression, fertilization, and early embryonic development without de novo transcription. However, how gene transcription is regulated during oocyte growth is not well understood. Our results revealed that XY oocytes became abnormal in chromatin configuration, mitochondria distribution, and de novo transcription compared to XX or XO oocytes near the end of growth phase. Therefore, we compared transcriptomes by RNA-sequencing among the XX, XO, and XY oocytes of 50–60 µm in diameter, which were still morphologically comparable. The results showed that the X chromosome dosage limited the X-linked and autosomal gene transcript levels in XO oocytes whereas many genes were transcribed from the Y chromosome and made the transcriptome in XY oocytes closer to that in XX oocytes. We then compared the transcript levels of 3 X-linked, 3 Y-linked and 2 autosomal genes in the XX, XO, and XY oocytes during the entire growth phase as well as at the end of growth phase using quantitative RT-PCR. The results indicated that the transcript levels of most genes increased with oocyte growth while largely maintaining the X chromosome dosage dependence. Near the end of growth phase, however, transcript levels of some X-linked genes did not increase in XY oocytes as much as XX or XO oocytes, rendering their levels much lower than those in XX oocytes. Thus, XY oocytes established a distinct transcriptome at the end of growth phase, which may be associated with abnormal chromatin configuration and mitochondria distribution.

The contribution of the Y chromosome to hybrid male sterility in house mice

Hybrid sterility in the heterogametic sex is a common feature of speciation in animals. In house mice, the contribution of the Mus musculus musculus X chromosome to hybrid male sterility is large. It is not known, however, whether F1 male sterility is caused by X-Y or X-autosome incompatibilities or a combination of both. We investigated the contribution of the M. musculus domesticus Y chromosome to hybrid male sterility in a cross between wild-derived strains in which males with a M. m. musculus X chromosome and M. m. domesticus Y chromosome are partially sterile, while males from the reciprocal cross are reproductively normal. We used eight X introgression lines to combine different X chromosome genotypes with different Y chromosomes on an F1 autosomal background, and we measured a suite of male reproductive traits. Reproductive deficits were observed in most F1 males, regardless of Y chromosome genotype. Nonetheless, we found evidence for a negative interaction between the M. m. domesticus Y and an interval on the M. m. musculus X that resulted in abnormal sperm morphology. Therefore, although F1 male sterility appears to be caused mainly by X-autosome incompatibilities, X-Y incompatibilities contribute to some aspects of sterility.

Brief report: chimeric pigs produced from induced pluripotent stem cells demonstrate germline transmission and no evidence of tumor formation in young pigs

The recent development of porcine induced pluripotent stem cells (piPSCs) capable of generating chimeric animals, a feat not previously accomplished with embryonic stem cells or iPSCs in a species outside of rodents, has opened the doors for in-depth study of iPSC tumorigenicity, autologous transplantation, and other key aspects to safely move iPSC therapies to the clinic. The study of iPSC tumorigenicity is critical as previous research in the mouse showed that iPSC-derived chimeras possessed large numbers of tumors, rising significant concerns about the safety of iPSC therapies. Additionally, piPSCs capable of generating germline chimeras could revolutionize the transgenic animal field by enabling complex genetic manipulations (e.g., knockout or knockin of genes) to produce biomedically important large animal models or improve livestock production. In this study, we demonstrate for the first time in a nonrodent species germline transmission of iPSCs with the live birth of a transgenic piglet that possessed genome integration of the human POU5F1 and NANOG genes. In addition, gross and histological examination of necropsied porcine chimeras at 2, 7, and 9 months showed that these animals lacked tumor formation and demonstrated normal development. Tissue samples positive for human POU5F1 DNA showed no C-MYC gene expression, further implicating C-MYC as a cause of tumorigenicity. The development of germline-competent porcine iPSCs that do not produce tumors in young chimeric animals presents an attractive and powerful translational model to study the efficacy and safety of stem cell therapies and perhaps to efficiently produce complex transgenic animals.

Promoter ChIP-chip analysis in mouse testis reveals Y chromosome occupancy by HSF2

The mammalian Y chromosome is essential for spermatogenesis, which is characterized by sperm cell differentiation and chromatin condensation for acquisition of correct shape of the sperm. Deletions of the male-specific region of the mouse Y chromosome long arm (MSYq), harboring multiple copies of a few genes, lead to sperm head defects and impaired fertility. Using chromatin immunoprecipitation on promoter microarray (ChIP-chip) on mouse testis, we found a striking in vivo MSYq occupancy by heat shock factor 2 (HSF2), a transcription factor involved in spermatogenesis. HSF2 was also found to regulate the transcription of MSYq resident genes, whose transcriptional regulation has been unknown. Importantly, disruption of Hsf2 caused a similar phenotype as the 2/3 deletion of MSYq, i.e., altered expression of the multicopy genes and increased mild sperm head abnormalities. Consequently, aberrant levels of chromatin packing proteins and more frequent DNA fragmentation were detected, implying that HSF2 is required for correct chromatin organization in the sperm. Our findings define a physiological role for HSF2 in the regulation of MSYq resident genes and the quality of sperm.

The influence of the deletion on the long arm of the Y chromosome on sperm motility in mice

The multicopy region on the long arm of the mouse Y chromosome contains four known genes. There are evidences that deletions in this region lead to decrease of sperm quality in mutant mice. Male mice completely lacking this region are infertile. Here we report results obtained by using the computer assisted semen analysis system (CASA), describing the movement parameters of spermatozoa from mutant males with partial deletion on the long arm of the Y chromosome (B10. BR-Y(del)). First we have determined that genes necessary for spermiogenesis and located in this region are still active in mutants, than we have compared the sperm movement of mutants and control animals. This analysis revealed that the Yq deletion affects: velocity parameters (VAP, VCL, VSL), parameters describing sperm head activity during movement (ALH and BCF) and linearity (LIN) of movement. Our findings indicate that sperm movement is controlled by genes located in the long arm of the Y chromosome.