Fig. 1. Toll^10b mutant embryos differentiate largely as somatic mesoderm. Anterior is to the left and dorsal up unless otherwise noted. All stages are according to Campos-Ortega and Hartenstein (Campos-Ortega and Hartenstein, 1985). All views are lateral except for those shown in G,H,U,V,AA,BB, which are ventral. Wild-type and Toll^10b mutant embryos were stained with the indicated antibodies, subjected to in situ hybridization (E,F) or processed to reveal the larval cuticle (U,V), as described in Materials and methods. (A-L) The somatic mesoderm is the chief mesodermal tissue present in Toll^10b mutant embryos. All embryos were 5- to 9-hour AEL except for those shown in A,B and K,L, which were stage 5 and stage 16, respectively. (A,B) Arrowhead denotes lack of dorsal Twist staining in a wild-type embryo (A) and ubiquitous expression of Twist in Toll^10b mutant embryos (B). (C,D) Tinman was expressed in heart precursors (straight arrow, C), dorsal somatic muscle and foregut (bent arrow, C). Only some putative foregut expression remained in Toll^10b mutant embryos (bent arrow, D). (E,F) bagpipe transcripts were expressed in circular visceral mesoderm precursors (straight arrow, E), foregut and hindgut precursors (bent arrow, E). Only the expression in putative hindgut precursors was maintained in Toll^10b mutant embryos (bent arrow, F). Straight arrow in F denotes lack of the circular visceral mesoderm marker bagpipe expression in the trunk. (G,H) Fasciclin III, a marker for differentiated visceral mesoderm, labeled the muscle sheet surrounding midgut (arrow, G) and pharyngeal muscles (arrowhead, G). Toll^10b embryos showed expression in the putative remains of the pharyngeal musculature (arrowhead, H). Arrow in H denotes the absence of Fasciclin III expression in the trunk where the visceral mesoderm would have developed. (I,J) A serpent-lacZ reporter revealed that pro-hematocytes migrating from the head mesoderm (arrowhead, I) were also present in Toll^10b mutant embryos (arrowhead, J). (K,L) Myosin heavy chain staining of wild-type (K) and Toll^10b mutant (L) embryos. The final muscle pattern was disrupted in Toll^10b mutant embryos but there was an abundance of Myosin-positive myoblasts and muscle fibers (arrow, L). (M-V) Ectodermally derived tissues were missing from Toll^10b mutant embryos. All embryos were 5- to 9-hour AEL, except for those shown in Q,R, which were 7.5- to 10.5-hour AEL, and those shown in U,V, which were first instar larvae. (M,N) Single-minded expression, an early mesectoderm marker, was maintained in the Toll^10b mutant background but showed an aberrant pattern. However, further mesectoderm differentiation did not occur, as antibodies to neuronal markers such as HRP failed to detect differentiated neurons (not shown). (O,P) Crumbs, a marker for apical-basal polarization of epidermal cells, was expressed in ectodermal stripes (arrow) and in foregut ectoderm in wild-type embryos (O). All the ectodermal stripe expression was absent in Toll^10b mutant embryos (arrow) but foregut ectoderm expression remained (arrow, P). (Q,R) The anti-22C10 antibody labeled all neurons in the peripheral nervous system in wildtype embryos (Q) but was almost completely absent in Toll^10b mutant embryos (R). (S,T) Anti-Trachealess, a marker for tracheal cell fate, revealed invaginating ectodermal cells (arrowhead in S) in wild-type embryos but showed only marginal posterior expression in Toll^10b mutant embryos (arrowhead, T). (U,V) A terminal ectodermal specialization, the larval cuticle, was readily detected in wild-type larvae (U) but was completely absent in Toll^10b mutant larvae. Image shows vitelline membrane and absence of cuticle (V). (W,X) An endoderm-specific enhancer-trap line crossed into the Toll^10b mutant background revealed that the endodermal cell fate was readily specified in these mutant embryos. Panels show 5- to 9-hour AEL embryos. (Y-BB) Several paracrine signaling pathways remain active in Toll^10b mutant embryos. All embryos were 5- to 9-hour AEL. (Y-Z) Htl expression in wild-type stage 12 embryos was restricted to clusters of myoblasts (arrow, Y). Toll^10b mutant embryos similarly aged also showed expression in clusters (arrow, Z). (AA,BB) Wg expression in Toll^10b mutant embryos was found in stripes reminiscent of wild-type expression.