Biology subjects

Savitsky, M.

Publications and source records attributed to Savitsky, M..

4 recordsLinked to original sources

bioRxiv2023

Ric8 proteins as the neomorphic partners of G alpha o in GNAO1 encephalopathies

GNAO1 mutated in pediatric encephalopathies encodes the major neuronal G-protein Go. Of >40 pathogenic mutations, most are single amino acid substitutions spreading across Go sequence. We perform extensive characterization of Go mutants showing abnormal GTP uptake and hydrolysis, and deficiencies to bind G{beta}{gamma} and RGS19. Plasma membrane localization of Go is decreased for a subset of mutations that leads to epileptic manifestations. Pathogenic mutants massively gain interaction with Ric8A/B proteins, delocalizing them from cytoplasm to Golgi. Being general G-subunit chaperones and binding multiple other proteins, Ric8A/B likely mediate the disease dominance when engaging in neomorphic interactions with pathogenic Go. As the strength of Go-Ric8B interactions correlates with disease severity, our study further identifies an efficient biomarker and predictor for clinical manifestations in GNAO1 encephalopathies. One-Sentence SummaryNeomorphic mutations in Go gain dominant interactions with Ric8A/B, correlating with severity in pediatric encephalopathies.

cell biology↗

bioRxiv2022

Topological screen identifies hundreds of Cp190 and CTCF dependent Drosophila chromatin insulator elements

Drosophila insulators were the first DNA elements discovered to regulate gene expression by delimiting chromatin contacts. Remarkably, it is still unclear how many of them exist in the Drosophila genome and whether they have a pervasive impact on the genome folding. Contrary to vertebrates, there is no evidence that fly insulators block cohesin-mediated chromatin loop extrusion. Therefore, their mechanism of action remains an open question. To bridge these gaps, we mapped genomic contacts, transcriptomes and binding landscapes of insulator associated proteins in Drosophila cells deficient for CTCF and Cp190. With this approach, we discovered hundreds of chromatin insulator elements. Their study indicates that Drosophila insulators play a minor role in shaping the overall chromosome folding patterns but impact chromatin contacts locally at many individual loci. Our observations argue that Cp190 promotes co-binding of other insulator proteins and that the model, where Drosophila insulators block chromatin contacts by forming loops, needs revision. The extended catalogue of insulator elements presented here provides a significant new resource to study mechanisms that shape the folding of eukaryotic genomes.

genomics↗

bioRxiv2020

Humanization of Drosophila Gαo to model GNAO1 paediatric encephalopathies

Several hundred genes have been identified to contribute to epilepsy - the disease affecting 65 million people worldwide. One of these genes is GNAO1 encoding Go, the major neuronal -subunit of heterotrimeric G proteins. An avalanche of dominant de novo mutations in GNAO1 have been recently described in paediatric epileptic patients, suffering in addition to epilepsy from motor dysfunction and developmental delay. Although occurring in amino acids conserved from humans to Drosophila, these mutations and their functional consequences have only poorly been analysed at the biochemical or neuronal levels. Adequate animal models to study molecular aetiology of GNAO1 encephalopathies have also so far been lacking. As the first step towards modelling the disease in Drosophila, we here describe humanization of the Go locus in the fruit fly. A two-step CRISPR/Cas9-mediated replacement was conducted, first substituting the coding exons 2-3 of Go with respective human GNAO1 sequences. At the next step, the remaining exons 4-7 were similarly replaced, keeping intact the gene Cyp49a1 embedded in-between, as well as the non-coding exon 1 and the surrounding regulatory sequences. The resulting flies, homozygous for the humanized GNAO1 loci, are viable and fertile without any visible phenotypes; their body weight and longevity are also normal. Human Go-specific antibodies confirm the endogenous-level expression of the humanized Go, which fully replaces the Drosophila functions. The genetic model we established will make it easy to incorporate encephalopathic GNAO1 mutations and will permit intensive investigations into the molecular aetiology of the human disease through the powerful toolkit of Drosophila genetics.

genetics↗

bioRxiv2019

Genetic dissection reveals the role of Ash1 domains in counteracting Polycomb repression

Antagonistic functions of Polycomb and Trithorax proteins are essential for proper development of all metazoans. While the Polycomb proteins maintain the repressed state of key developmental genes, the Trithorax proteins ensure that these genes stay active in cells where they have to be expressed. Ash1 is the Trithorax protein that was proposed to counteract Polycomb repression by methylating lysine 36 of histone H3. However, recently it was shown that genetic replacement of Drosophila histone H3 with the variant that carried Arginine instead of Lysine at position 36 did not impair the ability of Ash1 to counteract Polycomb repression. This argues that Ash1 counteracts Polycomb repression by methylating, yet unknown, non-histone proteins. To find these substrates, one may need to look beyond the function of the Ash1 histone methyltransferase SET domain at other evolutionary conserved parts of the protein that received little attention. Here we used Drosophila genetics to demonstrate that Ash1 requires each of the BAH, PHD and SET domains to counteract Polycomb repression, while AT hooks are dispensable. Our findings argue that, in vivo, Ash1 acts as a multimer. Thereby, it can combine the input of the SET domain and PHD-BAH cassette residing in different peptides. Finally, using new loss of function alleles, we show that zygotic Ash1 is required to prevent erroneous repression of homeotic genes.

genetics↗