Genetic Screens for Enhancers of brahma Reveal Functional Interactions Between the BRM Chromatin-Remodeling Complex and the Delta-Notch Signal Transduction Pathway in Drosophila

Abstract

The Drosophila trithorax group gene brahma (brm) encodes the ATPase subunit of a 2-MDa chromatinremodeling complex. brm was identified in a screen for transcriptional activators of homeotic genes and subsequently shown to play a global role in transcription by RNA polymerase II. To gain insight into the targeting, function, and regulation of the BRM complex, we screened for mutations that genetically interact with a dominant-negative allele of brm (brm K804R). We first screened for dominant mutations that are lethal in combination with a brm K804R transgene under control of the brm promoter. In a distinct but related screen, we identified dominant mutations that modify eye defects resulting from expression of brm K804R in the eye-antennal imaginal disc. Mutations in three classes of genes were identified in our screens: genes encoding subunits of the BRM complex (brm, moira, and osa), other proteins directly involved in transcription (zerknullt and RpII140 ), and signaling molecules (Delta and vein). Expression of brm K804R in the adult sense organ precursor lineage causes phenotypes similar to those resulting from impaired DeltaNotch signaling. Our results suggest that signaling pathways may regulate the transcription of target genes by regulating the activity of the BRM complex.

Baf60c is a nuclear Notch signaling component required for the establishment of left–right asymmetry

“…However, these data collectively do not exclude a requirement for a stabilizing effect of other proteins, because in vitro data solely demonstrate that two proteins can interact sufficiently well under experimental conditions, and immunopurification from cells by default includes other potential cellular components. In the case of the BAF complex, compelling evidence in other organisms suggests that this function may be a general feature of Notch signaling and may extend to invertebrates: in Caenorhabditis elegans, ZK1128.5, encoding a Baf60c ortholog, genetically interacts with Notch signaling (35), and in a screen for genetic interactions with Drosophila Brahma, encoding the Brg1/ Brm homolog, genes encoding Notch signaling components were the predominant class of mutations identified (36). Taken together these results suggest that Baf60c and the BAF complex is a conserved key cellular nuclear component of Notch signaling in several contexts, including the establishment of LR asymmetry in mammals.…”

Investigating the Genetic Circuitry of Mastermind in Drosophila, a Notch Signal Effector

“…Although previous screens uncovered key Notch pathway elements (Fortini and Artavanis-Tsakonas 1994;Verheyenet al 1996;Go and Artavanis-Tsakonas 1998;Armstrong et al 2005;Katic et al 2005;Mahoney et al 2006), they were inevitably of limited genomewide scope as conventional screens cannot escape laborious mapping procedures necessary for identifying gene products for most modifiers. Even for the most comprehensive genetic screen performed to date (Karim et al 1996), relatively few complementation groups were mapped.…”

The Nucleosome Remodeling Factor ISWI Functionally Interacts With an Evolutionarily Conserved Network of Cellular Factors

“…and genes encoding for chromatin covalent modifiers, established that eye-based genetic screens in flies could be a powerful tool for the in vivo dissection of chromatinremodeling signaling pathways occurring in the nucleus Armstrong et al 2005;Burgio et al 2008;Sala and Corona 2009). Moreover, the ISWI K159R screen established that ISWI function could be modulated in vivo by a variety of cellular factors that have escaped previous biochemical analyses .…”