Figure 2.

The proximal somite induces motoneuron death in spinal explants. A, Dissection of an E12 asymmetric explant. som, Somite; DRG, dorsal root ganglia; O, ventral horn opposite to the somite; A, ventral horn adjacent to the somite (red arrowhead). B, Transverse section of an E12 asymmetric explant cultured for 2 d in vitro. The explant section is immunolabeled with an anti-neurofilament antibody to show the position of the somite (red arrowhead). C, The section adjacent to that shown in B was double-labeled with TUNEL (green) and islet1/2 immunostaining (red). Note that there are numerous TUNEL- and fewer islet1/2-stained nuclei in the motor area (dotted) close to the somite (red arrowhead). Although some apoptotic nuclei are observed outside the motor area, most of them appear confined to the motor region (dotted). D, Quantification of surviving motoneurons (MNs) opposite (O) and adjacent (A) to the somite compared with control (Ct) E12 explants cultured for 2 d in vitro (8 explants quantified in each condition). ^**p < 0.01; ^***p < 0.0001 (O and A vs Ct), Student's t test. Scale bars, 100 μm.