Fig. 1. The pattern of CaP cell bodies before and after axonogenesis. (A) Optical sections at different focal levels of an nrp1a:gfp transgenic embryo at the 28-somite stage (23 hpf). CaPs are labeled with anti-GFP antibody. Position of CaP cell bodies was not related to the corresponding somites. Also, two distinct and discrete cell bodies were observed at the 25th somite level. Arrows (lower panel) indicate the somite boundaries. (B) Irregular patterns of CaP cell bodies were also observed as the pattern of isl2-expressing cells (stars) during the pre-axonogenesis period in wild-type embryos. Two separate CaP cells were observed at the 11th somite level. (C) Appearance ratio of spinal hemisegments with two discrete CaPs. The two discrete CaPs were only seen in caudal segments where CaPs did not begin axonogenesis. Position 0 is defined as the most caudal segment in which a CaP axon was formed. Thirty-three pairs of separate CaPs from 26 embryos at the 26- to 29-somite stages were sorted by relative somite levels and scored for spinal hemisegments with two separated CaPs. (D) A transgenic embryo at the 29-somite stage (23.5 hpf). Although CaP cell bodies with axons were ellipsoid (20th, 21st), more caudal CaP cells appeared triangular or trapezoid (23rd, 24th). (E) Side view of a transgenic embryo at the 27-somite stage (22.5 hpf). (F) CaP cell bodies with axons were regularly spaced in the middle of overlying somites. Stars and triangles show mAb Sv2-labeled CaP/VaP cell bodies. Blue lines denote somite borders. Unless noted otherwise, embryos are oriented as rostral to the left and dorsal up. Sc, spinal cord; Nc, notochord. The numbers in the panels indicate the segmental order. Scale bars: 50 mm.