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Fig. 4
Motorneuron development is affected in unp mutants. (A) The three primary motorneurons in the ventral half of the spinal cord (sc), CaP, MiP and RoP, occupy unique positions along the antero-posterior axis and extend stereotypic, axonal projections. (B) The antibody znp-1 stains the CaP axons in the ventral and the MiP axons in the dorsal somites of wild-type embryos. (C) In unp mutants MiP axons appear to elongate normally toward dorsal, while axons extending ventrally have abnormal morphology. They form multiple branches (arrowheads) and do not extend as far as in wildtype embryos. Whether these aberrant axons originate from CaP somatas is not clear. CaP, caudal primary motorneuron; MiP, middle primary motorneuron; RoP, rostral primary motorneuron; d, dorsal; v, ventral; sc, spinal cord; n, notochord; hm, horizontal myoseptum.