Biology subjects

Brehm, A.

Publications and source records attributed to Brehm, A..

4 recordsLinked to original sources

bioRxiv2025

Targeted degradation of Drosophila FOG homolog U-shaped mimics macrophage transdifferentiation in S2 cells

The highly plastic cellular component of the Drosophila immune system consists of three main blood cell types - plasmatocytes, crystal cells and lamellocytes - that together allow effective responses to various insults. Infection with parasitic wasp eggs results in a rapid increase in highly specialized lamellocytes that are generated by differentiation from hemocyte precursors as well as by transdifferentiation from plasmatocytes. How differentiation and transdifferentiation are regulated at the molecular level is not well understood. Here, we show that inducible degradation of the Friend of GATA (FOG) homolog U-shaped (Ush) in the plasmatocyte-like S2 cell line results in downregulation of plasmatocyte marker genes and subsequent upregulation of lamellocyte marker genes. This transcriptional shift is accompanied by morphological and functional changes consistent with lamellocyte cell identity, including increased cell spreading and adhesion, driven by enhanced integrin expression associated with increased focal adhesions. Our findings demonstrate that targeted Ush depletion is sufficient to reprogramme plasmatocyte-like S2 cells toward a lamellocyte-like state, thereby providing the first in vitro model for studying processes involved in macrophage transdifferentiation.

cell biology↗

bioRxiv2025

Hangover regulates gene expression by limiting NSL-mediated H4K16 acetylation

The RNA-binding protein hangover is essential for several stress responses in Drosophila melanogaster. Here, we discover a novel function of hangover in the regulation of gene expression. Hangover binds to more than 2.000 genes in the Drosophila genome and modulates transcription. We identify a diverse set of chromatin regulators as hangover interactors, including NSL, dMec, Sin3A, dREAM and Ino80. Among these, the non-specific lethal complex (NSL) is the most prominent one. We show that hangover attenuates NSL-mediated H4K16 acetylation at transcriptional start sites to downregulate gene expression. Our work uncovers novel roles for hangover in epigenetic gene regulation and suggests that it coordinates the function of multiple chromatin regulators. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=83 SRC="FIGDIR/small/649938v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@193e682org.highwire.dtl.DTLVardef@1028cb2org.highwire.dtl.DTLVardef@632bdforg.highwire.dtl.DTLVardef@d57617_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2021

RNA inhibits dMi-2/CHD4 chromatin binding and nucleosome remodelling

The ATP-dependent nucleosome remodeller Mi-2/CHD4 broadly modulates epigenetic landscapes to repress transcription and to maintain genome integrity. Here we use individual nucleotide resolution crosslinking and immunoprecipitation (iCLIP) to show that Drosophila Mi-2 associates with thousands of mRNA molecules in vivo. Biochemical data reveal that recombinant dMi-2 preferentially binds to G-rich RNA molecules using two intrinsically disordered regions of previously undefined function. Pharmacological inhibition of transcription and RNase digestion approaches establish that RNA inhibits the association of dMi-2 with chromatin. We also show that RNA inhibits dMi-2-mediated nucleosome mobilization by competing with the nucleosome substrate. Importantly, this activity is shared by CHD4, the human homolog of dMi-2, strongly suggesting that RNA-mediated regulation of remodeller activity is an evolutionary conserved mechanism. Our data support a model in which RNA serves to protect actively transcribed regions of the genome from dMi-2/CHD4- mediated establishment of repressive chromatin structures.

molecular biology↗

bioRxiv2020

Ush regulates hemocyte-specific gene expression, fatty acid metabolism and cell cycle progression and cooperates with dNuRD to orchestrate hematopoiesis

The generation of lineage-specific gene expression programmes that alter proliferation capacity, metabolic profile and cell type-specific functions during differentiation from multipotent stem cells to specialised cell types is crucial for development. During differentiation gene expression programmes are dynamically modulated by a complex interplay between sequence-specific transcription factors, associated cofactors and epigenetic regulators. Here, we study U-shaped (Ush), a multi-zinc finger protein that maintains the multipotency of stem cell-like hemocyte progenitors during Drosophila hematopoiesis. Using genomewide approaches we reveal that Ush binds to promoters and enhancers and that it controls the expression of three gene classes that encode proteins relevant to stem cell-like functions and differentiation: cell cycle regulators, key metabolic enzymes and proteins conferring specific functions of differentiated hemocytes. We employ complementary biochemical approaches to characterise the molecular mechanisms of Ush-mediated gene regulation. We uncover distinct Ush isoforms one of which binds the Nucleosome Remodeling and Deacetylation (NuRD) complex using an evolutionary conserved peptide motif. Remarkably, the Ush/NuRD complex specifically contributes to the repression of lineage-specific genes but does not impact the expression of cell cycle regulators or metabolic genes. This reveals a mechanism that enables specific and concerted modulation of functionally related portions of a wider gene expression programme. Finally, we use genetic assays to demonstrate that Ush and NuRD regulate enhancer activity during hemocyte differentiation in vivo and that both cooperate to suppress the differentiation of lamellocytes, a highly specialised blood cell type. Our findings reveal that Ush coordinates proliferation, metabolism and cell type-specific activities by isoform-specific cooperation with an epigenetic regulator.

molecular biology↗