Fig. 4. Hb specifies the identity of the first two GMCs. (A-L) Flat preparations of embryos at stage 15 (except E', which is stage 13); one hemineuromere; dorsal view; anterior is towards the left; arrowheads indicate GW neuron. (A,D,G,J,M) Wild type, (B,E,H,K,N) hb12 and (C,F,I,L,O) egGal4::hb. Eg is red; double stained neurons are yellow. (A-C) NB7-3 lineage as revealed by anti-Eg staining. In hb mutant embryos at stage 15 (B), only two Eg-positive neurons are detected when compared with wild type (A). (C) Ectopic hb expression in the late sublineage leads to additional Eg-positive neurons. Shown is an NB 7-3 lineage consisting of seven Eg-positive cells (arrows). (D-F) Zfh1 (green) within the NB7-3 lineage. (D) In wild type, only the motorneuron (GW) of the NB7-3 lineage is Zfh1 positive (arrowhead). (E) In hb mutant embryos at stage 13, this Zfh1-positive neuron can still be detected in those hemisegments that show three Eg positive neurons (arrowhead, E'). At a later stage (stage 15, E''), this Eg-positive neuron has disappeared. (F) In egGal4::hb embryos, often two or more Zfh1-positive neurons can be found in the NB 7-3 lineage (arrowheads). (G-I) Zfh2 (green) within the NB7-3 lineage. (G) In wild type, Zfh2 labels exclusively the late born neurons EW2 and EW3 (arrows). (H) In hb mutant embryos, the remaining two neurons express Zfh2. (I) Ectopic expression of hb in the late part of the lineage results in absence of zfh2 expression in all neurons of the NB7-3 lineage. (J-L) dSerT mRNA expression. (J) In wild type, each abdominal hemisegment except the last shows two dSerT-positive neurons (EW1 and EW2). (K) In hb mutant embryos, only one dSerT-positive neuron (EW2) is left, whereas after ectopic hb expression, up to four dSerT positive neurons (EW1) are obtained (L). (M-O) Summaries of the result obtained in A,D,G,J, B,E',E'',H,K and C,F,I,L, respectively.
