Fig. 5. Bmp signals are received by Tv neurons. (A) A single plane of focus showing P-Mad accumulation in subsets of neurons in the thoracic region of the ventral ganglion. Two Tv neurons are highlighted with yellow arrows. (B) The same image as in A except FMRFa expression is overlaid to highlight the two Tv neuron cell bodies. (C) A compressed stack of optical images through the thoracic region of the ventral ganglion showing all P-Mad accumulating cells. Most of these are motoneurons as revealed by double staining with other markers (data not shown). (D) An equivalent stack to that in C but through a wit^B11/wit^A12 mutant animal. Note the absence of P-Mad accumulation in all cells of the ventral ganglion. (E) FMRFa expression in a sax³/sax^{Df Hr–1} mutant animal. (F) Rescue of FMRFa expression in the Tv neurons (yellow arrows) and the NHO (white arrows) of wit^A12/wit^B11 animals ubiquitously expressing the Wit^EC/Tkv^IC and Tkv^EC/Wit^IC pair of chimeric receptors. The schematic above F depicts, from left to right, the situation in wild-type animals in which a heterodimer of Wit (black) and Tkv (red) binds Gbb (blue) resulting in activation of the pathway (red arrow); wit mutants in which there is no ligand binding nor pathway activation; and wit mutants supplemented with the reciprocal chimeras. In this case, the intracellular domains of Wit and Tkv are brought together by Gbb binding to the extracellular domains of the receptors, resulting in pathway activation analogous to the wild-type situation. See Feng et al. (Feng et al., 1995) for more details. (G) FMRFa/lacZ expression in the brain and ventral ganglia of a babo^P1164 homozygous larva. Scale bars: in A, 50 µm for A-D; in E, 50 µm for E-G.