Fig. 1. Receptor constructs tested in vivo. (A) Representation of a tracheal segment indicating the six different primary tracheal branches: DB, dorsal branch; DT, dorsal trunk; VB, visceral branch; LTa and LTp, lateral trunk anterior and posterior; GB, ganglionic branch. (B,C) Wild-type Btl and Htl constructs, and the chimeric receptor constructs. The extracellular domain of Btl is composed from left to right of a N-terminal signal peptide, three Ig domains, an acidic region, a CAM binding domain, two Ig domains and a transmembrane domain. The intracellular domain consists of the juxtamembrane domain followed by the split tyrosine kinase catalytic domain and a short C-terminal domain. Htl contains only two Ig extracellular domains; all the other domains are homologous to Btl. (B) The extracellular and transmenbrane domain of Btl were fused to the intracellular domain of the following RTKs: Htl, Tor and EGFR. (C) Additionally, the extracellular domain and the transmembrane domain of Htl were fused to the intracellular domain of Btl, Tor and EGFR.