Figure 8

Lhx1 confers caudal axonal projection to the caudal dI1 _comm neurons. (A, B) Lhx1 and taumyc were expressed ectopically in dI1 neurons, utilizing the Cre/lox system and the EdI1 enhancer (EdI1::Cre + pCAGG-LoxP-STOP-LoxP-Lhx1-IRES-taumyc). The following dI2-specific axonal cues are assumed by the commissural dI1^Lhx1 neurons: at the lumbosacral levels dI1^Lhx1 axons turn caudally (A, A1); at the thoracic level axons turn either rostrally or caudally, forming a crisscross pattern (A, A2); at the cervical level, axons turn rostrally (A, A3). An illustration of the phenotype of dI1^Lhx1 ectopically expressing neurons is presented in (B). c, cervical level; b, brachial level; FP, floor plate; l, lumbar level, s, sacral level; t, thoracic level. The asterisks represent the level of the limbs. The white arrows point to the rostrally projecting axons. The magenta arrows point to the caudally projecting axons. The crossed arrows point to the crisscross axonal pattern. The arrow-head points to the longitudinal ipsi-lateral axons. Scale bar: 150 μm (A); 75 μm (A1–A3).