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Fig. 1. The E(spl)m
PNC enhancer drives strong expression in
non-SOPs but is directly repressed by Su(H) in SOPs. (A) Diagram of reporter
constructs in which wild-type and mutant versions of the
E(spl)m PNC cis-regulatory module drive expression of GFP or
RFP via a minimal Hsp70 promoter. Positions of the five Su(H)-binding
sites (S) and single proneural (PN) protein-binding site (E box) are
indicated; mutant sites are indicated by a red cross. (1) Wild-type module;
(2) module with E box mutated (Em); (3) Su(H)-binding sites mutated
(Sm); (4) E box and Su(H) sites mutated (EmSm). (B-D,F-H)
Single wing disc from a late third-instar larva carrying one copy each of
E(spl)m-RFP and E(spl)m
Sm-GFP and stained with anti-Hindsight (Hnt) antibody (C) to mark
SOPs. Insets show higher-magnification views of the boxed region of the wing
disc. (B'-D',F'-H') Microchaete row (adjacent to the
dorsal midline) on the notum of a single pupa of the same genotype 14 hours
after puparium formation (APF), also stained with anti-Hnt (C').
(B,B') RFP signal driven by the wild-type module is strong in most
non-SOP cells but minimal or absent in SOPs (B,D,B',D'). (E)
Mutation of the E box (Em) causes severe loss of PNC expression;
expression is retained at the wing margin and in a small subset of PNC cells.
(F,G,F',G') Mutation of the Su(H)-binding sites (Sm)
abolishes or severely lowers reporter expression in non-SOP cells of the PNCs
but causes strong ectopic expression in SOPs. (H,H') Overlay of B
(B') and F (F') highlights dramatic change in the pattern of
reporter gene activity when Su(H) sites are mutated. (I) Mutation of both the
E box and the Su(H) sites (EmSm) demonstrates that ectopic SOP
expression of the Sm mutant (F) is dependent on direct input from the
proneural proteins.
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