Fig. 4. Determination of the critical period sensitive to HH and WG signals, using hh^ts (hh^9K/hh^13C) and wg^ts (wg^IL114) mutants. (A,F) Black boxes, permissive temperature (18°C); white boxes, non-permissive temperature (29°C). Developmental time in this and subsequent sections is shown by time after egg laying (AEL) at 25°C. tin, con and VM-hh expression was examined at late stage 11 to early stage 12. +, normal or virtually normal expression; -, no expression; a), abnormal restriction of expression area (see L-N). Horizontal lines show metameric expression of VM-hh (yellow), con (red), VM-bnl (blue) and tin (green) in wild type. Gray bars associated with thick gray broken lines, deduced critical periods when VM-hh, con and tin are sensitive to HH (A) or WG (F). (B-E,G-N) Examples of shift-up/down effects on expression of three VM-metameric genes. hh^ts (B-E) and wg^ts (G-N) embryos were shifted down (D,J) or up (B,C,E,G-I,L-N) at indicated time AEL. (B-E,G-J) Lateral views of late stage 11 to early stage 12 embryos stained as indicated. (K-N) Ventral views of mid-stage 11 VM. Asterisks indicate expression of TIN (K,L) and bnl (M). (K) Wild type. a and p indicate a and p regions of VM-PSs, respectively. (L,M) Elimination of wg activity from early stage 11 on caused TIN/bnl expression only in posterior halves of the presumptive expression domains, which correspond to the anterior terminal region of each VM-PS. (N) Elimination of TIN activity from mid-stage 10 in response to absence of wg activity from mid-stage 10. (O) Ventrolateral views of wild-type early stage 11 VM. O2 is slightly younger than O3. Asterisks indicate tin RNA expression. Arrows in B-E,G-J indicate VM; arrows in K-O3 indicate VM-PS boundaries.

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