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

Cultures, colleges and the development of ideas about teaching in English Further Education

This article examines the development of new teachers’ practice and conceptions of teaching in English further education (FE). Drawing upon data from observations and interviews involving both trainee and serving teachers at a large FE college, it discusses and applies a restricted conceptualisation of culture to investigate the influence of local cultures on new teachers. The paper concludes that while experiences of sections of teachers within the institution may diverge, they share much greater commonality. Even in the few instances where distinctive and sustainable local cultures existed these did not necessarily lead to distinctive teaching practices, suggesting that the most powerful influences on teaching in FE may derive from dominant ideas in society, not from local workplace settings. The paper argues that research that concentrates on the local, such as the Transforming Learning Cultures in Further Education project, risks understating the significance of wider cultural influences on learning, in this case on learning to teach in FE