Fig. 2. The BMP pathway is active in many peptidergic cells, but only a subset is responsive to the ap/sqz Fmrf code. (A) The Drosophila VNC contains 150 peptidergic neurons, as revealed by c929-GAL4/UAS-nls-myc-EGFP expression. (B,C) pMad immunoreactivity in c929-GAL4+ neurons reveals that some peptidergic cells, such as Corazonin neurons, do not have active BMP signaling (arrowhead in B), whereas others, such as the peptidergic lateral cluster (Plc) do (arrow in C). (D) Based upon their responsiveness to sqz/ap co-misexpression (Allan et al., 2003), the pMad+, peptidergic cells of the VNC can be subdivided into a responsive and a non-responsive `compartment'.