Engineered Truncations in the Drosophila Mastermind Protein Disrupt Notch Pathway Function

Abstract

The phenotypes and genetic interactions associated with mutations in the Drosophila mastermind (mam) gene have implicated it as a component of the Notch signaling pathway. However, its function and site of action within many tissues requiring Notch signaling have not been thoroughly investigated. To address these questions, we have constructed truncated versions of the Mam protein that elicit dominant phenotypes when expressed in imaginal tissues under GAL4-UAS regulation. By several criteria, these effects appear to phenocopy loss of function for the Notch pathway. When expressed in the notum, truncated Mam results in failure of lateral inhibition within proneural clusters and perturbations in cell fate specification within the sensory organ precursor cell lineage. Expression in the wing is associated with vein thickening and margin defects, including nicking and bristle loss. The truncation-associated wing margin phenotypes are modified by mutations in Notch and Wg pathway genes and are correlated with depressed expression of wg, cut, and vg. These data support the idea that Mam truncations have lost key effector domains and therefore behave as dominant-negative proteins. Coexpression of Delta or an activated form of Notch suppresses the effects of the Mam truncation, suggesting that Mam can function upstream of ligand-receptor interaction in the Notch pathway. This system should prove useful for the investigation of the role of Mam within the Notch pathway.

Mastermind-like transcriptional co-activators: emerging roles in regulating cross talk among multiple signaling pathways

“…This screen took advantage of a Drosophila mutant (C96-MamN) that displays a fully penetrant wingmargin phenotype associated with the expression of the N-terminal Mastermind protein, MamN (Helms et al, 1999). The screen searched for mutations in the Exelixis collection that dominantly modified the wing-margin phenotype of C96-MamN.…”

A male‐specific effect of dominant‐negative Fos

“…We examined this by assaying expression of Wingless (Wg) and Cut expression across the dorsal-ventral margin in wing discs expressing UASFbz under C96-Gal4 or vg-Gal4 control. Both Wg and Cut are well-described targets of the Notch pathway (Neumann and Cohen, 1996;Helms et al, 1999). In wild-type wing discs both Wg and Cut are evident at high levels at the margin ( Fig.…”

“…We crossed UAS-Fbz to a strain that expresses a mutant form of the Notch pathway effector Mastermind (UASMamH) across the dorsal-ventral wing margin under regulation of the C96-Gal4 transgene (Helms et al, 1999;Hall et al, 2004). Males and females expressing the UAS-MamH construct exhibit multiple wing nicks along the margin (Fig.…”

“…Moreover, such effects could in principle arise from either naturally occurring mutations, or alternatively, in vitro-produced transgenic constructs. C96-Gal4, blk-Gal4, glass-Gal4, pnrGal4, C96-MamH, EP 3084, w 1118 , Delta BX9 /TM6c, mam IL115 /Cy, and nd 1 were described previously (Schmid et al, 1996;Helms et al, 1999;Hall et al, 2004). vg-Gal4 was obtained from the Artavanis-Tsakonas lab (Harvard).…”

“…C96-MamH is a recombinant chromosome that contains the C96-Gal4 driver and a UAS-MamH transgene. The latter transgene encodes a truncated form of the Notch pathway effector Mastermind (Helms et al, 1999) (Lucchesi et al, 2005). hsmsl-1 ⌬84, hs-msl-1 (1-265HA), hsmsl-2 (1-193Flag) and hs-msl-2 (490-773Flag) were obtained from M. Scott (Massey University).…”