Capicua DNA-binding sites are general response elements for RTK signaling inDrosophila

Abstract

SUMMARYRTK/Ras/MAPK signaling pathways play key functions in metazoan development, but how they control expression of downstream genes is not well understood. In Drosophila, it is generally assumed that most transcriptional responses to RTK signal activation depend on binding of Ets-family proteins to specific cis-acting sites in target enhancers. Here, we show that several Drosophila RTK pathways control expression of downstream genes through common octameric elements that are binding sites for the HMGbox factor Capicua, a transcriptional repressor that is downregulated by RTK signaling in different contexts. We show that Torso RTK-dependent regulation of terminal gap gene expression in the early embryo critically depends on Capicua octameric sites, and that binding of Capicua to these sites is essential for recruitment of the Groucho co-repressor to the huckebein enhancer in vivo. We then show that subsequent activation of the EGFR RTK pathway in the neuroectodermal region of the embryo controls dorsal-ventral gene expression by downregulating the Capicua protein, and that this control also depends on Capicua octameric motifs. Thus, a similar mechanism of RTK regulation operates during subdivision of the anterior-posterior and dorsal-ventral embryonic axes. We also find that identical DNA octamers mediate Capicua-dependent regulation of another EGFR target in the developing wing. Remarkably, a simple combination of activator-binding sites and Capicua motifs is sufficient to establish complex patterns of gene expression in response to both Torso and EGFR activation in different tissues. We conclude that Capicua octamers are general response elements for RTK signaling in Drosophila.

Minibrain and Wings apart control organ growth and tissue patterning through down-regulation of Capicua

“…Previous studies have shown that phosphorylation of Cic by ERK can result in downregulation of Cic by lowering its repressor activity, protein level, or nuclear localization (5,6,17). We hypothesized that Mnb may exert similar effects.…”

“…To assess whether Mnb could similarly affect Cic repressor activity, we used a reporter, CUASC-lacZ, which contains five GAL4 binding sites flanked on either side by two Cic binding motifs (Fig. 3A) (6). This reporter is only responsive to GAL4 in areas where Cic activity is inhibited, e.g., by RTK signaling (Fig.…”

“…In Drosophila, Cic controls anteroposterior and dorsoventral embryonic polarity, the subdivision of the lateral ectoderm, and pattern formation in several tissues (1,(3)(4)(5)(6). In addition, Cic negatively regulates the growth of imaginal discs and the midgut (7,8).…”

“…In both Drosophila and mammals, Cic functions as a primary sensor of signaling downstream of the receptor tyrosine kinase (RTK)/extracellular signal-regulated kinase (ERK) pathway (2,(5)(6)(7)(8)(13)(14)(15)(16). According to the current model, activation of RTK signaling results in the accumulation of doubly phosphorylated activated ERK, which directly binds to and phosphorylates Cic (5).…”

Mapping the binding interface of ERK and transcriptional repressor Capicua using photocrosslinking

“…Cic represses genes by binding directly to their regulatory regions and recruiting global corepressors. Both the DNA-binding domain of Cic and the Cic-binding sites within the regulatory DNA sequences are highly conserved across species (3)(4)(5). Another aspect of Cic regulation that appears to be conserved is its sensitivity to signaling by receptor tyrosine kinases (RTKs), which can antagonize gene repression by Cic (4-7) (Fig.…”