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1. Induction and inhibition of Drosophila X chromosome gene expression are both impeded by the dosage compensation complex

   https://doi.org/10.1093/g3journal/jkac165  

   Meisel, Richard P.; Asgari, Danial; Schlamp, Florencia; Unckless, Robert L.; Betran, ed., E. (July 2022, G3 Genes|Genomes|Genetics)

   Abstract Sex chromosomes frequently differ from the autosomes in the frequencies of genes with sexually dimorphic or tissue-specific expression. Multiple hypotheses have been put forth to explain the unique gene content of the X chromosome, including selection against male-beneficial X-linked alleles, expression limits imposed by the haploid dosage of the X in males, and interference by the dosage compensation complex on expression in males. Here, we investigate these hypotheses by examining differential gene expression in Drosophila melanogaster following several treatments that have widespread transcriptomic effects: bacterial infection, viral infection, and abiotic stress. We found that genes that are induced (upregulated) by these biotic and abiotic treatments are frequently under-represented on the X chromosome, but so are those that are repressed (downregulated) following treatment. We further show that whether a gene is bound by the dosage compensation complex in males can largely explain the paucity of both up- and downregulated genes on the X chromosome. Specifically, genes that are bound by the dosage compensation complex, or close to a dosage compensation complex high-affinity site, are unlikely to be up- or downregulated after treatment. This relationship, however, could partially be explained by a correlation between differential expression and breadth of expression across tissues. Nonetheless, our results suggest that dosage compensation complex binding, or the associated chromatin modifications, inhibit both up- and downregulation of X chromosome gene expression within specific contexts, including tissue-specific expression. We propose multiple possible mechanisms of action for the effect, including a role of Males absent on the first, a component of the dosage compensation complex, as a dampener of gene expression variance in both males and females. This effect could explain why the Drosophila X chromosome is depauperate in genes with tissue-specific or induced expression, while the mammalian X has an excess of genes with tissue-specific expression. 

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2. Condensin I ^DC , H4K20me1, and perinuclear tethering maintain X chromosome repression in C. elegans

   https://doi.org/10.1101/2024.04.05.588224  

   Trombley, Jessica; Rakozy, Audry I; Jash, Eshna; Csankovszki, Györgyi (April 2024, bioRxiv)

   Abstract Dosage compensation inCaenorhabditis elegansequalizes X-linked gene expression between XX hermaphrodites and XO males. The process depends on a condensin- containing dosage compensation complex (DCC), which binds the X chromosomes in hermaphrodites to repress gene expression. Condensin I^DCand an additional five DCC components must be present on the X during early embryogenesis in hermaphrodites to establish dosage compensation. However, whether the DCC’s continued presence is required to maintain the repressed state once established is unknown. Beyond the role of condensin I^DCin X chromosome compaction, additional mechanisms contribute to X- linked gene repression. DPY-21, a non-condensin I^DCDCC component, is an H4K20me2/3 demethylase whose activity enriches the repressive histone mark, H4 lysine 20 monomethylation, on the X chromosomes. In addition, CEC-4 tethers H3K9me3-rich chromosomal regions to the nuclear lamina, which also contributes to X- linked gene repression. To investigate the necessity of condensin I^DCduring the larval and adult stages of hermaphrodites, we used the auxin-inducible degradation system to deplete the condensin I^DCsubunit DPY-27. While DPY-27 depletion in the embryonic stages resulted in lethality, DPY-27 depleted larvae and adults survive. In these DPY-27 depleted strains, condensin I^DCwas no longer associated with the X chromosome, the X became decondensed, and the H4K20me1 mark was gradually lost, leading to X-linked gene derepression. These results suggest that the stable maintenance of dosage compensation requires the continued presence of condensin I^DC. A loss-of-function mutation incec-4, in addition to the depletion of DPY-27 or the genetic mutation ofdpy- 21, led to even more significant increases in X-linked gene expression, suggesting that tethering heterochromatic regions to the nuclear lamina helps stabilize repression mediated by condensin I^DCand H4K20me1. Author SummaryIn some organisms, whether an individual becomes male, female, or hermaphrodite is determined by the number of their sex chromosomes. In the nematodeCaenorhabditis elegans, males have one X chromosome, whereas hermaphrodites have two X chromosomes. This difference in the number of X chromosomes is crucial for deciding whether an individual becomes a hermaphrodite or a male. However, having two X chromosomes can lead to problems because it results in different gene expression levels, resulting in hermaphrodite lethality. To solve this issue, many organisms undergo a process called dosage compensation. Dosage compensation inC. elegansis achieved by a group of proteins known as the dosage compensation complex (DCC), which includes a protein called DPY-27. The function of DPY-27 is essential during early embryonic development. This study shows that in contrast to early embryonic development, larvae and adults can still survive when DPY-27 is missing. In these worms, all known mechanisms involved in dosage compensation are disrupted and the X is no longer repressed. Our results suggest that the maintenance of dosage compensation in nematodes is an active process, and that it is essential for survival when the organism is developing, but once fully developed, the process becomes dispensable. 

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3. KDM6A facilitates Xist upregulation at the onset of X inactivation

   https://doi.org/10.1186/s13293-024-00683-3  

   Lin, Josephine; Zhang, Jinli; Ma, Li; Fang, He; Ma, Rui; Groneck, Camille; Filippova, Galina_N; Deng, Xinxian; Kinoshita, Chizuru; Young, Jessica_E; et al (January 2025, Biology of Sex Differences)

   Abstract BackgroundX chromosome inactivation (XCI) is a female-specific process in which one X chromosome is silenced to balance X-linked gene expression between the sexes. XCI is initiated in early development by upregulation of the lncRNAXiston the future inactive X (Xi). A subset of X-linked genes escape silencing and thus have higher expression in females, suggesting female-specific functions. One of these genes is the highly conserved geneKdm6a, which encodes a histone demethylase that removes methyl groups at H3K27 to facilitate gene expression.KDM6Amutations have been implicated in congenital disorders such as Kabuki Syndrome, as well as in sex differences in development and cancer. MethodsKdm6awas knocked out (KO) using CRISPR/Cas9 gene editing in hybrid female mouse embryonic stem (ES) cells derived either from a 129 × Mus castaneus(cast) cross or a BL6 xcastcross. In one of the lines a transcriptional stop signal inserted inTsixresults in completely skewed X silencing upon differentiation. The effects of both homozygous and heterozygousKdm6aKO onXistexpression during the onset of XCI were measured by RT-PCR and RNA-FISH. Changes in gene expression and in H3K27me3 enrichment were investigated using allele-specific RNA-seq and Cut&Run, respectively. KDM6A binding to theXistgene was characterized by Cut&Run. ResultsWe observed impaired upregulation ofXistand reduced coating of the Xi during early stages of differentiation inKdm6aKO cells, both homozygous and heterozygous, suggesting a threshold effect of KDM6A. This was associated with aberrant overexpression of genes from the Xi after differentiation, indicating loss of X inactivation potency. Consistent with KDM6A having a direct role inXistregulation, we found that the histone demethylase binds to theXistpromoter and KO cells show an increase in H3K27me3 atXist, consistent with reduced expression. ConclusionsThese results reveal a novel female-specific role for the X-linked histone demethylase, KDM6A in the initiation of XCI through histone demethylase-dependent activation ofXistduring early differentiation. Plain language summaryX chromosome inactivation is a female-specific mechanism that evolved to balance sex-linked gene dosage between females (XX) and males (XY) by silencing one X chromosome in females. X inactivation begins with the upregulation of the long noncoding RNAXiston the future inactive X chromosome. While most genes become silenced on the inactive X chromosome some genes escape inactivation and thus have higher expression in females compared to males, suggesting that escape genes may have female-specific functions. One such gene encodes the histone demethylase KDM6A which function is to turn on gene expression by removing repressive histone modifications. In this study, we investigated the role of KDM6A in the regulation ofXistexpression during the onset of X inactivation. We found that KDM6A binds to theXistgene to remove repressive histone marks and facilitate its expression in early development. Indeed, depletion of KDM6A prevents upregulation ofXistdue to abnormal persistence of repressive histone modifications. In turn, this results in aberrant overexpression of genes from the inactive X chromosome. Our findings point to a novel mechanism ofXistregulation during the initiation of X inactivation, which may lead to new avenues of treatment to alleviate congenital disorders such as Kabuki syndrome and sex-biased immune disorders where X-linked gene dosage is perturbed. 

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4. Sex-biased Transcriptome in in vitro Produced Bovine Early Embryos

   https://doi.org/10.1101/2025.03.04.641446  

   Shi, Meihong; Li, Guangsheng; Araujo, Hannah Marie; Lee, Angie S; Zhang, Jingzhi; Lee, Yoke Lee; Cheong, Soon Hon; Duan, Jingyue Ellie (March 2025, bioRxiv)

   Abstract BackgroundMorphologic sex differences between males and females typically emerge after the primordial germ cell migration and gonad formation, although sex is determined at fertilization based on chromosome composition. A key debated sexual difference is the embryonic developmental rate, within vitroproduced male embryos often developing faster. However, the molecular mechanisms driving early embryonic sex differences remain unclear. ResultsTo investigate the transcriptional sex difference during early development,in vitroproduced bovine blastocysts were collected and sexed by PCR. A significant male-biased development was observed in expanded blastocysts. Ultra-low input RNA-seq analysis identified 837 DEGs, with 231 upregulated and 606 downregulated in males. Functional enrichment analysis revealed male-biased DEGs were associated with metabolic regulation, whereas female-biased DEGs were related to female gonad development, sex differentiation, inflammatory pathways, and TGF-beta signaling. Comparing X chromosome and autosome expression ratio, we found that female-biased DEGs contributed to the higher X-linked gene dosage, a phenomenon not observed in male embryos. Moreover, we identified the sex-biased transcription factors and RNA-bind proteins, including pluripotent factors such asSOX21andPRDM14, and splicing factorsFMR1andHNRNPH2. Additionally, we revealed 1,555 significantly sex-biased differential alternative splicing (AS), predominantly skipped exons, mapped to 906 genes, with 59 overlapping with DEGs enriched in metabolic and autophagy pathways. By incorporating novel isoforms from long reads sequencing, we identified 1,151 sex-biased differentially expressed isoforms (DEIs) associated with 1,017 genes. Functional analysis showed that female-biased DEIs were involved in the negative regulation of transcriptional activity, while male-biased DEIs were related to energy metabolism. Furthermore, we identified sex-biased differential exon usage inDENND1B, DIS3L2, DOCK11, IL1RAPL2,andZRSR2Y,indicating their sex-specific regulation in early embryo development. ConclusionThis study provided a comprehensive analysis of transcriptome differences between male and female bovine blastocysts, integrating sex-biased gene expression, alternative splicing, and isoform dynamics. Our findings indicate that enriched metabolism processes in male embryos may contribute to the faster developmental pace, providing insights into sex-specific regulatory mechanisms during early embryogenesis. Plain English summaryMale and female early embryos develop at different speeds, with male embryos often developing faster than female embryos. However, the reasons behind these early differences remain unclear. In this study, we examined gene activity in bovine embryos to uncover the biological factors regulating these early sex differences. We collected in vitro-produced bovine blastocysts, examined their sex, and confirmed that male embryos develop faster. By analyzing global gene activity, including alternative splicing, which allows one gene to code for multiple RNA isoforms and proteins, we found distinct gene expression profiles between male and female embryos. Male embryos showed higher activity in genes related to metabolism and cellular functions, while female embryos had increased activity in genes associated with female-specific gonad development and gene expression regulation. We also examined differences in how genes on the X chromosome were expressed. Female embryos had higher X-linked gene expression, which may contribute to sex-specific developmental regulation. Additionally, we identified sex-specific transcription factors and RNA-binding proteins that regulate early embryo development, some of which are known to control pluripotency and gene splicing. Overall, our study provides new insights into how gene activity shapes early sex differences, suggesting that enhanced metabolism in male embryos may be a key driver of their faster developmental rate. HighlightsMale embryos develop faster due to increased gene expression in metabolism pathwaysFemale embryos exhibit higher X-linked gene expression, suggesting X-dosage compensation plays a role in early developmentSex-biased alternative splicing events contribute to embryonic metabolism, autophagy, and transcriptional regulation in embryosSex-biased isoform diversity contributes to distinct developmental regulation in male and female embryosKey pluripotency factors (SOX21, PRDM14) and splicing regulators (FMR1, HNRNPH2) drive sex-specific gene expression 

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5. Evaluation of Additional Drosophila suzukii Male-Only Strains Generated Through Remobilization of an FL19 Transgene

   https://doi.org/10.3389/fbioe.2022.829620  

   Yamamoto, Akihiko; Yadav, Amarish K.; Scott, Maxwell J. (March 2022, Frontiers in Bioengineering and Biotechnology)

   Drosophila suzukii (D. suzukii) (Matsumura, 1931; Diptera: Drosophilidae), also known as spotted wing Drosophila , is a worldwide pest of fruits with soft skins such as blueberries and cherries. Originally from Asia, D. suzukii is now present in the Americas and Europe and has become a significant economic pest. Growers largely rely on insecticides for the control of D. suzukii . Genetic strategies offer a species-specific environmentally friendly way for suppression of D. suzukii populations. We previously developed a transgenic strain of D. suzukii that produced only males on a diet that did not contain tetracycline. The strain carried a single copy of the FL19 construct on chromosome 3. Repeated releases of an excess of FL19 males led to suppression of D. suzukii populations in laboratory cage trials. Females died as a consequence of overexpression of the tetracycline transactivator (tTA) and tTA-activated expression of the head involution defective proapoptotic gene. The aim of this study was to generate additional male-only strains that carried two copies of the FL19 transgene through crossing the original line with a piggyBac jumpstarter strain. Males that carried either two chromosome 3 or a singleX-linked transgene were identified through stronger expression of the red fluorescent protein marker gene. The brighter fluorescence of the X-linked lines was likely due to dosage compensation of the red fluorescent protein gene. In total, four X-linked lines and eleven lines with two copies on chromosome 3 were obtained, of which five were further examined. All but one of the strains produced only males on a diet without tetracycline. When crossed with wild type virgin females, all of the five two copy autosomal strains examined produced only males. However, the single copy X-linked lines did not show dominant female lethality. Five of the autosomal lines were further evaluated for productivity (egg to adult) and male competition. Based on these results, the most promising lines have been selected for future population suppression experiments with strains from different geographical locations. 

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