HP1c regulates development and gut homeostasis by suppressing Notch signaling through Su(H).

Notch signaling and epigenetic factors are known to play critical roles in regulating tissue homeostasis in most multicellular organisms, but how Notch signaling coordinates with epigenetic modulators to control differentiation remains poorly understood. Here, we identify heterochromatin protein 1c (HP1c) as an essential epigenetic regulator of gut homeostasis in Drosophila. Specifically, we observe that HP1c loss-of-function phenotypes resemble those observed after Notch signaling perturbation and that HP1c interacts genetically with components of the Notch pathway. HP1c represses the transcription of Notch target genes by directly interacting with Suppressor of Hairless (Su(H)), the key transcription factor of Notch signaling. Moreover, phenotypes caused by depletion of HP1c in Drosophila can be rescued by expressing human HP1γ, suggesting that HP1γ functions similar to HP1c in Drosophila. Taken together, our findings reveal an essential role of HP1c in normal development and gut homeostasis by suppressing Notch signaling.

Next-generation CRISPR/Cas9 transcriptional activation in Drosophila using flySAM.

CRISPR/Cas9-based transcriptional activation (CRISPRa) has recently emerged as a powerful and scalable technique for systematic overexpression genetic analysis in Drosophila melanogaster We present flySAM, a potent tool for in vivo CRISPRa, which offers major improvements over existing strategies in terms of effectiveness, scalability, and ease of use. flySAM outperforms existing in vivo CRISPRa strategies and approximates phenotypes obtained using traditional Gal4-UAS overexpression. Moreover, because flySAM typically requires only a single sgRNA, it dramatically improves scalability. We use flySAM to demonstrate multiplexed CRISPRa, which has not been previously shown in vivo. In addition, we have simplified the experimental use of flySAM by creating a single vector encoding both the UAS:Cas9-activator and the sgRNA, allowing for inducible CRISPRa in a single genetic cross. flySAM will replace previous CRISPRa strategies as the basis of our growing genome-wide transgenic overexpression resource, TRiP-OE.

Histone H3K27 methylation modulates the dynamics of FANCD2 on chromatin to facilitate NHEJ and genome stability.

Dysregulation of the homeostatic balance of histone H3 di- and tri-methyl lysine 27 (H3K27me2/3) levels caused by the mis-sense mutation of histone H3 (H3K27M) is reported to be associated with various types of cancers. In this study, we found that reduction in H3K27me2/3 caused by H3.1K27M, a mutation of H3 variants found in patients with diffuse intrinsic pontine glioma (DIPG), dramatically attenuated the presence of 53BP1 (also known as TP53BP1) foci and the capability of non-homologous end joining (NHEJ) in human dermal fibroblasts. H3.1K27M mutant cells showed increased rates of genomic insertions/deletions and copy number variations, as well as an increase in p53-dependent apoptosis. We further showed that both hypo-H3K27me2/3 and H3.1K27M interacted with FANCD2, a central player in the choice of DNA repair pathway. H3.1K27M triggered the accumulation of FANCD2 on chromatin, suggesting an interaction between H3.1K27M and FANCD2. Interestingly, knockdown of FANCD2 in H3.1K27M cells recovered the number of 53BP1-positive foci, NHEJ efficiency and apoptosis rate. Although these findings in HDF cells may differ from the endogenous regulation of the H3.1K27M mutant in the specific tumor context of DIPG, our results suggest a new model by which H3K27me2/3 facilitates NHEJ and the maintenance of genome stability.This article has an associated First Person interview with the first author of the paper.

Enhanced Efficiency of flySAM by Optimization of sgRNA Parameters in Drosophila.

The flySAM/CRISPRa system has recently emerged as a powerful tool for gain-of-function studies in Drosophila melanogaster This system includes Gal4/UAS-driven dCas9 activators and U6 promoter-controlled sgRNA. Having established dCas9 activators superior to other combinations, to further enhance the efficiency of the targeting activators we systematically optimized the parameters of the sgRNA. Interestingly, the most efficient sgRNAs were found to accumulate in the region from -150bp to -450bp upstream of the transcription start site (TSS), and the activation efficiency showed a strong positive correlation with the GC content of the sgRNA targeting sequence. In addition, the target region is dominant to the GC content, as sgRNAs targeting areas beyond -600bp from the TSS lose efficiency even when containing 75% GC. Surprisingly, when comparing the activities of sgRNAs targeting to either DNA strand, sgRNAs targeting to the non-template strand outperform those complementary to the template strand, both in cells and in vivo In summary, we define criteria for sgRNA design which will greatly facilitate the application of CRISPRa in gain-of-function studies.

Large-Scale Transgenic Drosophila Resource Collections for Loss- and Gain-of-Function Studies.

The Transgenic RNAi Project (TRiP), a Drosophila melanogaster functional genomics platform at Harvard Medical School, was initiated in 2008 to generate and distribute a genome-scale collection of RNA interference (RNAi) fly stocks. To date, it has generated >15,000 RNAi fly stocks. As this covers most Drosophila genes, we have largely transitioned to development of new resources based on CRISPR technology. Here, we present an update on our libraries of publicly available RNAi and CRISPR fly stocks, and focus on the TRiP-CRISPR overexpression (TRiP-OE) and TRiP-CRISPR knockout (TRiP-KO) collections. TRiP-OE stocks express single guide RNAs targeting upstream of a gene transcription start site. Gene activation is triggered by coexpression of catalytically dead Cas9 fused to an activator domain, either VP64-p65-Rta or Synergistic Activation Mediator. TRiP-KO stocks express one or two single guide RNAs targeting the coding sequence of a gene or genes. Cutting is triggered by coexpression of Cas9, allowing for generation of indels in both germline and somatic tissue. To date, we have generated >5000 TRiP-OE or TRiP-KO stocks for the community. These resources provide versatile, transformative tools for gene activation, gene repression, and genome engineering.

pNP Transgenic RNAi System Manual in Drosophila.

Much of our knowledge about the mechanisms underlying biological processes relies on genetic approaches, whereby gene activity is reduced and the phenotypic consequences of perturbation are analyzed in detail. For functional genomic studies, a specific, systematic, and cost-effective manner is critical. Transgenic RNAi system is the top priority choice to study gene functions due to its simple and practical characteristics in Drosophila. We established a novel system that works well in both soma and germ cells which is efficient and specific. With this system, we can precisely and efficiently modulate highly expressed genes, and simultaneously knock down multiple genes in one step. In this study, we provide a detailed protocol of the pNP system, which replaces other transgenic systems, and expect it can provide some help to researchers who are using this system.

Defining gene networks controlling the maintenance and function of the differentiation niche by an in vivo systematic RNAi screen.

In the Drosophila ovary, escort cells (ECs) extrinsically control germline stem cell (GSC) maintenance and progeny differentiation. However, the underlying mechanisms remain poorly understood. In this study, we identified 173 EC genes for their roles in controlling GSC maintenance and progeny differentiation by using an in vivo systematic RNAi approach. Of the identified genes, 10 and 163 are required in ECs to promote GSC maintenance and progeny differentiation, respectively. The genes required for progeny differentiation fall into different functional categories, including transcription, mRNA splicing, protein degradation, signal transduction and cytoskeleton regulation. In addition, the GSC progeny differentiation defects caused by defective ECs are often associated with BMP signaling elevation, indicating that preventing BMP signaling is a general functional feature of the differentiation niche. Lastly, exon junction complex (EJC) components, which are essential for mRNA splicing, are required in ECs to promote GSC progeny differentiation by maintaining ECs and preventing BMP signaling. Therefore, this study has identified the major regulators of the differentiation niche, which provides important insights into how stem cell progeny differentiation is extrinsically controlled.

An efficient and multiple target transgenic RNAi technique with low toxicity in Drosophila.

Being relatively simple and practical, Drosophila transgenic RNAi is the technique of top priority choice to quickly study genes with pleiotropic functions. However, drawbacks have emerged over time, such as high level of false positive and negative results. To overcome these shortcomings and increase efficiency, specificity and versatility, we develop a next generation transgenic RNAi system. With this system, the leaky expression of the basal promoter is significantly reduced, as well as the heterozygous ratio of transgenic RNAi flies. In addition, it has been first achieved to precisely and efficiently modulate highly expressed genes. Furthermore, we increase versatility which can simultaneously knock down multiple genes in one step. A case illustration is provided of how this system can be used to study the synthetic developmental effect of histone acetyltransferases. Finally, we have generated a collection of transgenic RNAi lines for those genes that are highly homologous to human disease genes.