Dynamic Sex Chromosome Expression in Drosophila Male Germ Cells

Abstract

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.

Single-cell RNA-sequencing reveals pre-meiotic X-chromosome dosage compensation inDrosophila testis

“…In this work, we directly observe dosage compensation in terms of X:autosome count ratios and differential gene activity around CE sites. These lines of evidence point to adult pre-meiotic dosage compensation for the X chromosome, consistent with recent findings in larval testis (Mahadevaraju et al, 2020). After meiosis, the X chromosome is downregulated to an extent that would be expected from incomplete dosage compensation.…”

“…In some cases it may be difficult to distinguish the effect of X chromosome inactivation from the loss of dosage compensation, however, the multiple transgenic insertions in X and autosomes made by the Parsch group (Hense et al, 2007;Kemkemer et al, 2011) show that X inactivation exceeds that expected for loss of dosage compensation. Recent evidence supports spermatogonial dosage compensation in single-cell sequencing from larval testis (Mahadevaraju et al, 2020). We asked if the same is true in adult testis by analyzing gene expression from somatic, pre-meiotic, meiotic, and post-meiotic cells.…”

“…The spatial and temporal patterns of dosage compensation are key to understanding gene expression regulation and its roles in development. Single-cell sequencing has been successfully used to study dosage compensation during development (Mahadevaiah et al, 2020;Mahadevaraju et al, 2020), but has not yet been applied to adult spermatogenesis.…”

Trajectory Mapping of the Early Drosophila Germline Reveals Controls of Zygotic Activation and Sex Differentiation

“…The observation that expression of many X-chromosome genes are higher in female germ cells than males brings to our mind the issue of dosage compensation. Previous reports have suggested that usage and expression of the X chromosome in the germline could be stage-dependent (Gan et al 2010;Shi et al 2020;Mahadevaraju et al 2020;Hense et al 2007;Kemkemer et al 2011;Meiklejohn et al 2011). and male germ cells prior to the bifurcation point of the germline cluster from the sexed dataset.…”

“…The emergence of single-cell RNA-sequencing techniques has opened a new window to investigating critical early germline developmental events especially since germ cells exist in small numbers at these stages. Multiple studies have analyzed transcriptomes of germ cells at the single-cell level, but mostly at later stages of development (Slaidina et al 2020;Jevitt et al 2020;Mahadevaraju et al 2020;Rust et al 2019;Li et al 2017;Niu and Spradling 2020). Here we profile the transcriptomes of fruit fly germ cells after specification and before they have coalesced with somatic cells, and we perform this survey for both male and female germ cells.…”