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Fig. 5. In situ detection of engrailed and maxillopedia
(mxp, ortholog of Dm'probiscipedia) in wild type (A,I) and
in embryos depleted for Tc'giant by RNAi (B-H,J). Black arrowheads in
A-H indicate the labial segment. The proctodeum (p) indicates completion of
segmentation in D-H. (A) Wild-type germ band shortly before formation of the
last (tenth) abdominal engrailed stripe. (B-H) In all germ bands
analyzed, the first three segments were unaffected, suggesting, that in the
head Tc'giant has a homeotic function. The T1 stripe was often
disturbed or deleted in young embryos (stars in B and C), leading to an
enlarged segment. By the end of segmentation, no defects are evident in the
anterior thorax (D-H), suggesting that the embryo corrects for these early
patterning defects. In some cases, the superfluous cells became assigned to
the appendages that then appeared enlarged (white arrowheads in D and the
close-up E). In cuticles, enlarged appendages were not observed, suggesting
further correction. Segmentation is disturbed in a variable pattern in the
region between T1 and A9. In germ bands with proctodeum formed (p), the number
of deleted segments can be determined (D, 7; F and G, 8; H,4). (I) The Hox
gene maxillopedia (red) is expressed in the appendages of the
maxillary and labial segments (arrowheads). (J) In Tc'giant RNAi
embryos, this expression is reduced or absent (arrowheads), confirming that
Tc'giant knock down interferes with proper Hox gene regulation.
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