Figure 4. tal Is Required for Embryonic Development.

(A–D) Expression of tal RNA throughout embryogenesis. (A) Expression of tal starts in seven blastodermal stripes and a cluster of cells in the anterior part of the embryo. (B) This expression refines to the tracheal precursors by the extended germ band stage. (C and D) Later, tal is present in the dorsal tracheal trunks (dt), posterior spiracles (ps), pharynx (ph), hindgut (hg), and presumptive denticle belts (db).

(E) Dorsal tracheal trunks (dt) in a stage 16 wild-type embryo (dorsal view) revealed by the detection of the chitin binding protein.

(F) Gaps in the dorsal tracheal trunks of a tal mutant.

(G) Wild-type embryo cuticle: cephalopharyngeal skeleton (cps), ventral denticle belts (db), and posterior spiracles (ps).

(H) In tal null mutants, these cuticular structures are missing or reduced.

(I) Ectopic tal expression in the head produces extra cephalopharyngeal skeleton (ventral view; inset shows lateral view).

(J) Wg protein distribution in the epidermis is normal in an extended germ band tal mutant embryo.

(K) Expression of a shaven-baby reporter gene in ventral epidermis is not affected in a stage 17 tal mutant embryo. tal expression is not affected either in svb mutants (unpublished data).

(L) Ventral view of the anterior-most segments of a stage 16 wild-type embryo. The denticle cells of the epidermis accumulate tubulin bundles prior to any denticle cuticle structures being observed.

(M) In tal mutants, these tubulin bundles do not form.