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Fig. 3. The XMLC2 promoter recapitulates expression of the endogenous gene in
transgenic embryos. Expression of XMLC2-GFP transgenes, assayed by
fluorescence (A,E-G) or whole-mount in situ hybridisation for GFP RNA (B-D).
Arrowheads indicate the tadpole heart. A GFP transgene containing 2990 bp of
promoter sequence directs strong, consistent and uniform expression of GFP
protein in the tadpole heart (A). Variation in fluorescence intensity reflects
differences in myocardial wall thickness between heart chambers and the stage
of contraction. (B) Transverse section through the forming heart tube heart
(stage 30), showing that staining for GFP RNA is restricted to the myocardium.
Heart-specific expression is retained after 5' truncation of the
promoter to –675 (C) or –249 (D); truncation to –159 retains
heart-specific expression, although the level is much reduced (E). Further
truncation to –127 yields occasional, weak expression of GFP to the
heart and more frequently in ectopic locations (e.g. branchial arches,
pronephros, blood island; small arrows). GFP activity in the eyes and
hindbrain (F,G) is from the 
-crystallin co-transgene.
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