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Fig. 4 Knockdown of Sema3ab causes the double exit phenotype of CaP axons similar to Nrp1a knockdown. (A) The position of CaP cell bodies after axonogenesis was examined using isl2 expression. Separate isl2+ CaP cell bodies were detected in Sema3ab-knockdown embryos (11th segment of a 25-somite stage embryo). (B) The double exit phenotype of CaP axons was observed in a Sema3ab-knockdown embryo. CaP axons and cell bodies were labeled with mAb Sv2. (C) sema3ab was expressed in the posterior halves of somites, and CaP cell bodies (detected by isl2 expression) were observed around the margin of the sema3ab expressing region. The inset shows the 21st segment of the same embryo at the focal plane of the CaP cell bodies. In older segments in which CaP axonogenesis had begun, expression of sema3ab was downregulated (17th segment of a 25-somite stage embryo). The numbers indicate the segmental order, and the stars indicate the positions of the CaP cell bodies. Scale bar: 50 μm.