Fig. 2. Murine Tsh genes rescue the cuticular phenotype of the tsh⁸ null mutant. Both the homeotic transformation and the segment polarity phenotype are restored. (A) Wild-type larval cuticle showing the three thoracic (T1, T2, T3) and the eight abdominal segments. (B) Close-up of the T1-T2 region. Arrows indicate the beard (b) in the T1 segment. (C) Homozygous tsh⁸ loss-of-function cuticular phenotype; the T1-specific denticles are missing (homeotic transformation of the T1 segment into the labial segment) (Röder et al., 1992) and naked and denticled cuticular regions are reduced in the trunk. (D-G) Rescue of tsh⁸ by Tsh genes. Close-up of T1-T3 region is on the right. (D) At 22°C in tsh⁸ homozygotes, 69B>Tsh1 expression results in partial rescue of tsh⁸ phenotype. The T1 segment is weakly restored (denticles form only on one side in this photograph) and the size of naked cuticle is comparable with wild type (compare with A-C). At 22°C, Tsh3 display similar levels of rescue (not shown), whereas Tsh2 has very little effect (see text). (E-G) At 29°C, the three Tsh genes perfectly restore the naked cuticle regions in the trunk although the T1, on the basis of the morphology of the beard and T1 denticle belt, is not completely rescued (compare with B). This defective differentiation was used to distinguish tsh⁸ homozygotes. Homeotic transformation of the labial segment into T1 segment is highlighted by ectopic denticles in the head (additional T1 and arrows). (H,I) Increased dose of mouse Tsh reveals a segment polarity phenotype similar to tsh. (H) 69B>tsh larvae raised at 25°C exhibit ectopic naked cuticle in the trunk (in contrast to 69B>tsh at 18°C in Fig. 1D), particularly along the ventral midline. (I) Combination of two independent insertions of UAS-Tsh1 (69B>2xTsh1) also causes ectopic naked cuticle (similar results were obtained with Tsh2 and Tsh3, data not shown). Most of the denticles of the thoracic and ectopic T1 segments are absent. (J) Combination of UAS-Tsh1 with UAS-Tsh2 (69B>Tsh1;Tsh2) gives similar results (as for UAS-Tsh1 with UAS-Tsh3 and for UAS-Tsh2 with UAS-Tsh3, not shown).