Dosage compensation (DC) in Drosophila equalizes X chromosome–linked gene expression via the male-specific lethal complex, which acetylates histone 4 lysine-16 on the male X chromosome. How DC is established during early embryogenesis remains obscure, largely due to the difficulty of obtaining sufficient sex-specific material at early embryonic stages. Here, we developed a high-throughput embryo sorting strategy and combined newly synthesized RNA-sequencing and RNA polymerase II (Pol II) profiling to investigate the mechanisms underlying the onset of DC in vivo. We found that changes in transcription initiation occur before detectable differences in transcriptional pausing or elongation and represent the primary determinant of enhanced mRNA output during DC establishment. It had hitherto been unclear whether DC establishment and maintenance exerted similar or distinct effects on transcriptional kinetics. Extending genome-wide profiling to S2 cells, we uncovered Pol II initiation as a general principle underlying both inception and perpetuation of DC-driven transcriptional up-regulation.
Ronald Oellers, A. Alexiadis, Yidan Sun et al.· Science Advances· 0 citations
To systematically map cellular factors constraining nonviral genome editing, influencing uptake and intracellular trafficking, we develop a genome-wide CRISPR screening platform linking perturbation of 19,114 genes to editing outcomes in human cells. We identify six negative regulators of delivery whose depletion increases editing efficiency by up to six-fold across diverse payloads, loci, and cell types. We test the top two factors, GJB2 and BET1L, in two distinct human models: correction of a pathogenic adenine base mutation in KCNJ13 and introduction of a cytosine base mutation in the GABAA receptor gene. Depletion of either improves base-editing outcomes by 6-fold, potentially through effects on delivery. In a patient-derived model of retinal channelopathy, knockdown of either gene improves lipid nanoparticle base editing efficiency by over 3.5-fold. This enables functional restoration of Kir7.1 ion channels in a subset of edited cells, highlighting cellular barriers as actionable targets to enhance the potency of genetic therapies. Low editing efficiency of nonviral delivery in post mitotic tissues presents a challenge to the field of gene therapy. Here, authors dissect the genetic regulators of nonviral delivery in post mitotic retinal epithelial cells describe strategies for improved base editor delivery and editing.
Shivani Saxena, Meha Kabra, Amr A. Abdeen et al.· Nature Communications· 0 citations
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