Cis-regulation of achaete and scute: shared enhancer-like elements drive their coexpression in proneural clusters of the imaginal discs.

Abstract

The pattern of bristles and other sensory organs on the adult cuticle of Drosophila is prefigured in the imaginal discs by the pattern of expression of the proneural achaete (ac) and scute (sc) genes, two members of the ac-sc complex (AS-C). These genes are simultaneously expressed by groups of cells (the proneural clusters) located at constant positions in discs. Their products {transcription factors of the basic-helix-loop-helix family) allow cells to become sensory organ mother cells (SMCs), a fate normally realized by only one or a few cells per cluster. Here we show that the highly complex pattern of proneural clusters is constructed piecemeal, by the action on ac and sc of site-specific, enhancer-like elements distributed along most of the AS-C (-90 kb). Fragments of AS-C DNA containing these enhancers drive reporter lacZ genes in only one or a few proneural clusters. This expression is independent of the ac and sc endogenous genes, indicating that the enhancers respond to local combinations of factors (prepattern). We show further that the cross-activation between ac and sc, discovered by means of transgenes containing either ac or sc promoter fragments linked to lacZ and thought to explain the almost identical patterns of ac and sc expression, does not occur detectably between the endogenous ac and sc genes in most proneural clusters. Our data indicate that coexpression is accomplished by activation of both ac and sc by the same set of position-specific enhancers.

An endogenous Suppressor of Hairy-wing insulator separates regulatory domains in Drosophila

“…43). This complex contains multiple enhancer regions distributed over a Ϸ90-kb region (44). We postulate that enhancers from the AS-C drive transcription in the bristles and tarsal claws of the y ϩ660gin flies because these elements are active at the same time and in the same tissues as the yellow intronic enhancers.…”

The Complex Tale of the achaete–scute Complex: A Paradigmatic Case in the Analysis of Gene Organization and Function During Development

“…Similarly, the complex and puzzling complementation patterns among sc mutations came to be understood as a consequence of the existence of cis-regulatory regions directing gene expression in individual proneural clusters (Ghysen and DamblyChaudiere 1988;Campuzano and Modolell 1992;Modolell and Campuzano 1998). Interestingly, the same enhancers control the expression of ac and sc, and therefore both genes are expressed in the same pattern of proneural clusters (Ruiz-Gomez and Ghysen 1993;Gomez-Skarmeta et al 1995). If the specific effects of ac and sc mutations involved only the enhancers they each affect, why do the two sets remove complementary subsets of bristles?…”

Dual role for Drosophila lethal of scute in CNS midline precursor formation and dopaminergic neuron and motoneuron cell fate

“…Drosophila strains used included: sc M6 (Gomez-Skarmeta et al, 1995), Df(1)ase-1 (Gonzalez et al, 1989), Df(1)sc10-1 (Villares and Cabrera, 1987), Df(1)sc19 (Campuzano et al, 1985), Df(1)sc-B57 (Jimenez and Campos-Ortega, 1990), SoxN GA1192 (Buescher et al, 2002), tup 1 (Thor and Thomas, 1997) and tup isl-1 (Thor and Thomas, 1997). Gal4 and UAS lines employed were: sim-Gal4 (Xiao et al, 1996), UAS-tau-GFP (Wheeler et al, 2006), UAS-l(1)sc (Parras et al, 1996), UAS-sc (Parras et al, 1996) and UAS-elav (Koushika et al, 1996).…”