Fig. 5

Trunk/tail phenotype of 18-h-old embryos treated with geldanamycin beginning at 50% epiboly (5–5.5 h). (A, C, and E) Control. (B, D, and F) GA. (A–D) Lateral view of whole embryos. (E and F) Longitudinally oblique sections through the four most recently formed somites and the unsegmented paraxial mesoderm. (A, B, E, and F) Unstained. (C and D) In situ hybridization detection of α-tropomyosin mRNA. Anterior is to the left in all. Seventy-eight percent of the GA-treated embryos exhibited a shortened trunk/tail phenotype and the somites did not form their characteristic full chevron shape as described under Results (compare arrows in C and D, which indicate somites at comparable positions along the anterior–posterior axis). In addition, somites of treated embryos typically assumed a block-like shape and varied significantly in size within any one embryo (compare somites indicated by asterisks in E and F, which are the four most recently fully formed in both cases). The closely related benzoquinone ansamycin geldampicin, which is ineffective as an Hsp90-binding agent, had no detectable effect on embryonic development. In contrast to embryos treated with GA beginning at gastrulation, treatment initiated at the blastula stage was rapidly lethal. Scale bar in A–D, 100 μm. Scale bar in E and F, 25 μm.