Hydronephrosis, the dilation of kidneys due to abnormal urine retention, occurs spontaneously in certain inbred mouse strains. In humans, its occurrence is often attributed to acquired urinary tract obstructions in adults, whereas in children, it can be congenital. However, the genetic factors underlying hydronephrosis pathogenesis remain unclear. We investigated the cause of hydronephrosis by analyzing tetraspanin 7 (Tspan7) gene-modified mice, which had shown a high incidence of hydronephrosis-like symptoms. We found that these mice were characterized by low liver weights relative to kidney weights and elevated blood ammonia levels, suggesting liver involvement in hydronephrosis. Gene expression analysis of the liver suggested that dysfunction of ornithine transcarbamylase (OTC), encoded by the X chromosome gene Otc and involved in the urea cycle, may contribute as a congenital factor in hydronephrosis. This OTC dysfunction may be caused by genomic mutations in X chromosome genes contiguous to Otc, such as Tspan7, or via the genomic manipulations used to generate transgenic mice, including the introduction of Cre recombinase DNA cassettes and cleavage of loxP by Cre recombinase. Therefore, caution should be exercised in interpreting the hydronephrosis phenotype observed in transgenic mice as solely a physiological function of the target gene.

Analyses of ancient DNA typically involve sequencing the surviving short oligonucleotides and aligning to genome assemblies from related, modern species. Here, we report that skin from a female woolly mammoth (†Mammuthus primigenius) that died 52,000 years ago retained its ancient genome architecture. We use PaleoHi-C to map chromatin contacts and assemble its genome, yielding 28 chromosome-length scaffolds. Chromosome territories, compartments, loops, Barr bodies, and inactive X chromosome (Xi) superdomains persist. The active and inactive genome compartments in mammoth skin more closely resemble Asian elephant skin than other elephant tissues. Our analyses uncover new biology. Differences in compartmentalization reveal genes whose transcription was potentially altered in mammoths vs. elephants. Mammoth Xi has a tetradic architecture, not bipartite like human and mouse. We hypothesize that, shortly after this mammoth\'s death, the sample spontaneously freeze-dried in the Siberian cold, leading to a glass transition that preserved subfossils of ancient chromosomes at nanometer scale.

Statin drugs lower blood cholesterol levels for cardiovascular disease prevention. Women are more likely than men to experience adverse statin effects, particularly new-onset diabetes (NOD) and muscle weakness. Here we find that impaired glucose homeostasis and muscle weakness in statin-treated female mice are associated with reduced levels of the omega-3 fatty acid, docosahexaenoic acid (DHA), impaired redox tone, and reduced mitochondrial respiration. Statin adverse effects are prevented in females by administering fish oil as a source of DHA, by reducing dosage of the X chromosome or the Kdm5c gene, which escapes X chromosome inactivation and is normally expressed at higher levels in females than males. As seen in female mice, we find that women experience more severe reductions than men in DHA levels after statin administration, and that DHA levels are inversely correlated with glucose levels. Furthermore, induced pluripotent stem cells from women who developed NOD exhibit impaired mitochondrial function when treated with statin, whereas cells from men do not. These studies identify X chromosome dosage as a genetic risk factor for statin adverse effects and suggest DHA supplementation as a preventive co-therapy.

The sex chromosomes of skinks are usually poorly differentiated and hardly distinguished by cytogenetic methods. Therefore, identifying sex chromosomes in species lacking easily recognizable heteromorphic sex chromosomes is necessary to fully understand sex chromosome diversity. In this paper, we employed cytogenetics, sex quantification of genes, and transcriptomic approaches to characterize the sex chromosomes in Plestiodon elegans. Cytogenetic examination of metaphases revealed a diploid number of 2n = 26, consisting of 12 macrochromosomes and 14 microchromosomes, with no significant heteromorphic chromosome pairs, speculating that the sex chromosomes may be homomorphic or poorly differentiated. The results of the sex quantification of genes showed that Calumenin (calu), COPI coat complex subunit γ 2 (copg2), and Smoothened (smo) were at half the dose in males as in females, suggesting that they are on the X chromosome. Transcriptomic data analysis from the gonads yielded the excess expression male-specific genes (n = 16), in which five PCR molecular markers were developed. Restricting the observed heterozygosity to males suggests the presence of homomorphic sex chromosomes in P. elegans, XX/XY. This is the first breakthrough in the study of the sex chromosomes of Plestiodon.

The tree shrew (Tupaia belangeri) is a promising emerging model organism in biomedical studies, notably due to their evolutionary proximity to primates. To enhance our understanding of how DNA methylation is implicated in regulation of gene expression and the X chromosome inactivation (XCI) in tree shrew brains, here we present their first genome-wide, single-base-resolution methylomes integrated with transcriptomes from prefrontal cortices. We discovered both divergent and conserved features of tree shrew DNA methylation compared to that of other mammals. DNA methylation levels of promoter and gene body regions are negatively correlated with gene expression, consistent with patterns in other mammalian brains studied. Comparing DNA methylation patterns of the female and male X chromosomes, we observed a clear and significant global reduction (hypomethylation) of DNA methylation across the entire X chromosome in females. Our data suggests that the female X hypomethylation does not directly contribute to the gene silencing of the inactivated X chromosome nor does it significantly drive sex-specific gene expression of tree shrews. However, we identified a putative regulatory region in the 5\' end of the X inactive specific transcript (Xist) gene, a key gene for XCI, whose pattern of differential DNA methylation strongly relate to its differential expression between male and female tree shrews. We show that differential methylation of this region is conserved across different species. Moreover, we provide evidence suggesting that the observed difference between human and tree shrew X-linked promoter methylation is associated with the difference in genomic CpG contents. Our study offers novel information on genomic DNA methylation of tree shrews, as well as insights into the evolution of X chromosome regulation in mammals.

Vertebrates exhibit sexual dimorphism in response to infectious diseases and in morbidity and mortality rates to various pathogens. Females are generally more immunocompetent than males, despite their increased reproductive burden and the immunosuppressive effects of gestation. In addition, females generally have lower incidences of cancer compared to males; however, they have higher rates of autoimmune disorders. These sex differences may be a result of life history differences, sexual selection, genetics, and/or the physiological effects of hormones. As highly social mammals with complex life histories, primates offer a unique opportunity to investigate the evolution of enhanced female immunocompetence. This review aims to examine the evidence of this immunity gap, understand current hypotheses for its evolution, and explore the potential role of X chromosome specific genes and heterozygosity within this framework.

CRISPR-Cas9 technology has facilitated development of strategies that can potentially provide more humane and effective methods to control invasive vertebrate species, such as mice. One promising strategy is X chromosome shredding which aims to bias offspring towards males, resulting in a gradual and unsustainable decline of females. This method has been explored in insects with encouraging results. Here, we investigated this strategy in Mus musculus by targeting repeat DNA sequences on the X chromosome with the aim of inducing sufficient DNA damage to specifically eliminate X chromosome-bearing sperm during gametogenesis. We tested three different guide RNAs (gRNAs) targeting different repeats on the X chromosome, together with three male germline-specific promoters for inducing Cas9 expression at different stages of spermatogenesis. A modest bias towards mature Y-bearing sperm was detected in some transgenic males, although this did not translate into significant male-biasing of offspring. Instead, cleavage of the X chromosome during meiosis typically resulted in a spermatogenic block, manifest as small testes volume, empty tubules, low sperm concentration, and sub/infertility. Our study highlights the importance of controlling the timing of CRISPR-Cas9 activity during mammalian spermatogenesis and the sensitivity of spermatocytes to X chromosome disruption.

Engineered sex ratio distorters (SRDs) have been proposed as a powerful component of genetic control strategies designed to suppress harmful insect pests. Two types of CRISPR-based SRD mechanisms have been proposed: X-shredding, which eliminates X-bearing sperm, and X-poisoning, which eliminates females inheriting disrupted X-chromosomes. These differences can have a profound impact on the population dynamics of SRDs when linked to the Y-chromosome: an X-shredder is invasive, constituting a classical meiotic Y-drive, whereas X-poisoning is self-limiting, unable to invade but also insulated from selection. Here, we establish X-poisoning strains in the malaria vector Anopheles gambiae targeting three X-linked genes during spermatogenesis, resulting in male bias. We find that sex distortion is primarily driven by a loss of X-bearing sperm, with limited evidence for postzygotic lethality of female progeny. By leveraging a Drosophila melanogaster model, we show unambiguously that engineered SRD traits can operate differently in these two insects. Unlike X-shredding, X-poisoning could theoretically operate at early stages of spermatogenesis. We therefore explore premeiotic Cas9 expression to target the mosquito X-chromosome. We find that, by pre-empting the onset of meiotic sex chromosome inactivation, this approach may enable the development of Y-linked SRDs if mutagenesis of spermatogenesis-essential genes is functionally balanced.

Klinefelter syndrome (47,XXY) causes infertility with a testicular histology comprising two types of Sertoli cell-only tubules, representing mature and immature-like Sertoli cells, and occasionally focal spermatogenesis. Here, we show that the immature-like Sertoli cells highly expressed XIST and had two X-chromosomes, while the mature Sertoli cells lacked XIST expression and had only one X-chromosome. Sertoli cells supporting focal spermatogenesis also lacked XIST expression and the additional X-chromosome, while the spermatogonia expressed XIST despite having only one X-chromosome. XIST was expressed in Sertoli cells until puberty, where a gradual loss was observed. Our results suggest that a micro-mosaic loss of the additional X-chromosome is needed for Sertoli cells to mature and to allow focal spermatogenesis.

Most vertebrates develop distinct females and males, where sex is determined by repeatedly evolved environmental or genetic triggers. Undifferentiated sex chromosomes and large genomes have caused major knowledge gaps in amphibians. Only a single master sex-determining gene, the dmrt1-paralogue (dm-w) of female-heterogametic clawed frogs (Xenopus; ZW♀/ZZ♂), is known across >8740 species of amphibians. In this study, by combining chromosome-scale female and male genomes of a non-model amphibian, the European green toad, Bufo(tes) viridis, with ddRAD- and whole genome pool-sequencing, we reveal a candidate master locus, governing a male-heterogametic system (XX♀/XY♂). Targeted sequencing across multiple taxa uncovered structural X/Y-variation in the 5\'-regulatory region of the gene bod1l, where a Y-specific non-coding RNA (ncRNA-Y), only expressed in males, suggests that this locus initiates sex-specific differentiation. Developmental transcriptomes and RNA in-situ hybridization show timely and spatially relevant sex-specific ncRNA-Y and bod1l-gene expression in primordial gonads. This coincided with differential H3K4me-methylation in pre-granulosa/pre-Sertoli cells, pointing to a specific mechanism of amphibian sex determination.