Given their copy number differences and unique modes of inheritance, the evolved gene content and expression of sex chromosomes is unusual. In many organisms the X and Y chromosomes are inactivated in spermatocytes, possibly as a defense mechanism against insertions into unpaired chromatin. In addition to current sex chromosomes, Drosophila has a small gene-poor X-chromosome relic (4th) that re-acquired autosomal status. Here we use single cell RNA-Seq on fly larvae to demonstrate that the single X and pair of 4th chromosomes are specifically inactivated in primary spermatocytes, based on measuring all genes or a set of broadly expressed genes in testis we identified. In contrast, genes on the single Y chromosome become maximally active in primary spermatocytes. Reduced X transcript levels are due to failed activation of RNA-Polymerase-II by phosphorylation of Serine 2 and 5.
Experts demonstrate that oceanic plastic pollution is increasing at astounding rates (Eriksen et al., 2014;Geyer et al., 2017). Research indicates harmful levels of toxicity in everyday plastic items (SCP/RAC, 2020). Scientists find this issue so important that they have recommended plastics be classified as a pollutant on par with hazardous waste (Mouat et al., 2010;Rochman et al., 2013) or that single use plastics should be banned (Telesetsky, 2019). For many years, experts have noted that increasing plastic manufacturing and use will worsen the condition in the marine environment (Carpenter and Smith, 1972;Azzarello and Van Vleet, 1987;Gregory, 2009) and yet the global plastic industry continues to increase production, cumulatively producing 368 million tons in 2019 (PlasticsEurope, 2020). If current growth trajectories continue, by 2050 plastic could account for 20% of global oil production (Giacovelli, 2018) and the world could have four times the amount of plastic waste that we generate today (Geyer et al., 2017). Plastic debris contributes to a comprehensive global environmental problem that -if current trends continue-will worsen significantly (Borrelle et al., 2020;Silva et al., 2020). The COVID-19 crisis only exacerbates the problem, as it has led to an increase in the use of single use plastics in the form of personal protection equipment, which researchers have already begun to see in the environment at high levels (Ammendolia et al., 2021;Mejjad et al., 2021).The majority of the plastic pollution problem falls disproportionately on the global south, especially in south and southeast Asia (Jambeck et al., 2015;Lebreton et al., 2017), creating an issue of slow violence (Homer-Dixon, 2000) and environmental injustice. While plastic pollution is universal, some consequences such as clogged drainage systems, increases in vector-borne diseases, and reduction in tourism are particularly felt in poorer communities, where solid waste management systems are not in place (
Sex chromosome gene content and expression is unusual. In many organisms the X and Y chromosomes are inactivated in spermatocytes, possibly as a defense mechanism against insertions into unpaired chromatin. In addition to current sex chromosomes, Drosophila has a small gene-poor X-chromosome relic (4 th ) that re-acquired autosomal status. Using single cell RNA-Seq, we demonstrate that the single X and pair of 4 th chromosomes are specifically inactivated in primary spermatocytes. In contrast, genes on the single Y chromosome become maximally active in primary spermatocytes. Reduced X steady-state transcript levels are due to failed activation of RNA-Polymerase-II by phosphorylation of Serine 2 and 5.
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