Selection and maintenance of sexual identity in the Drosophila germline.

Unlike sex determination in the soma, which is an autonomous process, sex determination in the germline of Drosophila has both inductive and autonomous components. In this paper, we examined how sexual identity is selected and maintained in the Drosophila germline. We show that female-specific expression of genes in the germline is dependent on a somatic signaling pathway. This signaling pathway requires the sex-non-specific transformer 2 gene but, surprisingly, does not appear to require the sex-specific genes, transformer and doublesex. Moreover, in contrast to the soma where pathway initiation and maintenance are independent processes, the somatic signaling pathway appears to function continuously from embryogenesis to the larval stages to select and sustain female germline identity. We also show that the primary target for the somatic signaling pathway in germ cells can not be the Sex-lethal gene

Pseudomonas aeruginosa Induced Airway Epithelial Injury Drives Fibroblast Activation:A Mechanism in Chronic Lung Allograft Dysfunction

Bacterial infections after lung transplantation cause airway epithelial injury and are associated with an increased risk of developing bronchiolitis obliterans syndrome. The damaged epithelium is a source of alarmins that activate the innate immune system, yet their ability to activate fibroblasts in the development of bronchiolitis obliterans syndrome has not been evaluated. Two epithelial alarmins were measured longitudinally in bronchoalveolar lavages from lung transplant recipients who developed bronchiolitis obliterans syndrome and were compared to stable controls. In addition, conditioned media from human airway epithelial cells infected with Pseudomonas aeruginosa was applied to lung fibroblasts and inflammatory responses were determined. Interleukin‐1 alpha (IL‐1α) was increased in bronchoalveolar lavage of lung transplant recipients growing P. aeruginosa (11.5 [5.4–21.8] vs. 2.8 [0.9–9.4] pg/mL, p < 0.01) and was significantly elevated within 3 months of developing bronchiolitis obliterans syndrome (8.3 [1.4–25.1] vs. 3.6 [0.6–17.1] pg/mL, p < 0.01), whereas high mobility group protein B1 remained unchanged. IL‐1α positively correlated with elevated bronchoalveolar lavage IL‐8 levels (r(2) = 0.6095, p < 0.0001) and neutrophil percentage (r(2) = 0.25, p = 0.01). Conditioned media from P. aeruginosa infected epithelial cells induced a potent pro‐inflammatory phenotype in fibroblasts via an IL‐1α/IL‐1R‐dependent signaling pathway. In conclusion, we propose that IL‐1α may be a novel therapeutic target to limit Pseudomonas associated allograft injury after lung transplantation

Requirement of Male-Specific Dosage Compensation in Drosophila Females—Implications of Early X Chromosome Gene Expression

Dosage compensation equates between the sexes the gene dose of sex chromosomes that carry substantially different gene content. In Drosophila, the single male X chromosome is hypertranscribed by approximately two-fold to effect this correction. The key genes are male lethal and appear not to be required in females, or affect their viability. Here, we show these male lethals do in fact have a role in females, and they participate in the very process which will eventually shut down their function—female determination. We find the male dosage compensation complex is required for upregulating transcription of the sex determination master switch, Sex-lethal, an X-linked gene which is specifically activated in females in response to their two X chromosomes. The levels of some X-linked genes are also affected, and some of these genes are used in the process of counting the number of X chromosomes early in development. Our data suggest that before the female state is set, the ground state is male and female X chromosome expression is elevated. Females thus utilize the male dosage compensation process to amplify the signal which determines their fate

Cooperative and Antagonistic Contributions of Two Heterochromatin Proteins to Transcriptional Regulation of the Drosophila Sex Determination Decision

Eukaryotic nuclei contain regions of differentially staining chromatin (heterochromatin), which remain condensed throughout the cell cycle and are largely transcriptionally silent. RNAi knockdown of the highly conserved heterochromatin protein HP1 in Drosophila was previously shown to preferentially reduce male viability. Here we report a similar phenotype for the telomeric partner of HP1, HOAP, and roles for both proteins in regulating the Drosophila sex determination pathway. Specifically, these proteins regulate the critical decision in this pathway, firing of the establishment promoter of the masterswitch gene, Sex-lethal (Sxl). Female-specific activation of this promoter, SxlPe, is essential to females, as it provides SXL protein to initiate the productive female-specific splicing of later Sxl transcripts, which are transcribed from the maintenance promoter (SxlPm) in both sexes. HOAP mutants show inappropriate SxlPe firing in males and the concomitant inappropriate splicing of SxlPm-derived transcripts, while females show premature firing of SxlPe. HP1 mutants, by contrast, display SxlPm splicing defects in both sexes. Chromatin immunoprecipitation assays show both proteins are associated with SxlPe sequences. In embryos from HP1 mutant mothers and Sxl mutant fathers, female viability and RNA polymerase II recruitment to SxlPe are severely compromised. Our genetic and biochemical assays indicate a repressing activity for HOAP and both activating and repressing roles for HP1 at SxlPe

Sex determination in the Drosophila germline is dictated by the sexual identity of the surrounding soma.

It has been suggested that sexual identity in the germline depends upon the combination of a nonautonomous somatic signaling pathway and an autonomous X chromosome counting system. In the studies reported here, we have examined the role of the sexual differentiation genes transformer (tra) and doublesex (dsx) in regulating the activity of the somatic signaling pathway. We asked whether ectopic somatic expression of the female products of the tra and dsx genes could feminize the germline of XY animals. We find that Tra(F) is sufficient to feminize XY germ cells, shutting off the expression of male-specific markers and activating the expression of female-specific markers. Feminization of the germline depends upon the constitutively expressed transformer-2 (tra-2) gene, but does not seem to require a functional dsx gene. However, feminization of XY germ cells by Tra(F) can be blocked by the male form of the Dsx protein (Dsx(M)). Expression of the female form of dsx, Dsx(F), in XY animals also induced germline expression of female markers. Taken together with a previous analysis of the effects of mutations in tra, tra-2, and dsx on the feminization of XX germ cells in XX animals, our findings indicate that the somatic signaling pathway is redundant at the level tra and dsx. Finally, our studies call into question the idea that a cell-autonomous X chromosome counting system plays a central role in germline sex determination