Fig. 1. Analysis of cell divisions in the vmd1a lineage. (A) Diagram of the ventral Cut-positive md neurons and es organs in segments A1-A7. Each vp1-4a organ is composed of an es neuron (large pink circular cell), a sheath cell (green) and a socket/shaft cell pair (yellow). The vmd1a and vmd4a neurons (dark purple diamond-shaped cells) can be distinguished from the vmd1-4 neurons (pink diamond-shaped cells) as they express the B6-2-25 enhancer-trap marker. (B) Md-es lineage (Orgogozo et al., 2001). Numb-inheriting cells are in red. (C-K) Confocal images showing the vmd1a-vp1 region. (C-D) In stage 12 CutA3-lacZ embryos (Jack and DeLotto, 1995) stained for ß-galactosidase in red, Numb in green and DNA in blue, the vmd1a pI cell divides asymmetrically soon after the vp1 pI cell has divided. (E) Stage 12 wild-type embryo stained for Cut in red, Numb in green and DNA in blue. (F-H) Stage 13 wild-type embryo stained for Cut in red, Pros in green and DNA in blue. A small Cut-positive dot is detectable at the pIIa position (arrowhead in F). (I) Late stage 13 wild-type embryo stained for Cut in red, Pros in green and Elav in blue. (J) Late stage 13 B6-2-25 embryo stained for Cut in red and ß-galactosidase in green. (I-J) Cells of the vp1 lineage are indicated by a bracket. (K-K') Same confocal section of a stage 13 CutA3-lacZ embryo stained for Cut (K,K') in red and ß-galactosidase (K') in green. A small Cut-positive and some ß-galactosidase-positive dots are detectable at the position of the pIIa cell (arrowhead in K, K'). In all figures, anterior is left and dorsal is up

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