Figure 4
Axonal projection pattern of contra-laterally projecting dI2 neurons. Chick embryos were electroporated at stage 16 (left side) with (A) EdI2/V1 and (B) EdI1/2 enhancers along with a Cre-dependent GFP plasmid (EdI2/V1::Cre or EdI1/2::Cre + pCAGG-LoxP-STOP-LoxP-GFP). At E6, spinal cords were removed, fixed and analyzed as an open-book preparation. Whole neural tubes (sacral to cervical) are presented. Confocal images were taken and photomerged utilizing Photoshop software. Rostral is up in the image and the schematics. At the sacral level at the contra-lateral side dI2caud axons turn caudally (A, A1, B, B1, magenta arrows); at the caudal thoracic level axons turn either caudally or rostrally, forming a crisscross pattern (A, A2, B, B2, white and magenta crossed arrows). At the rostral two-thirds of the thoracic level, the brachial and cervical levels dI2rost axons turn rostrally (A, A3, B, B3, white arrows). At the sacral and cervical levels axons turn from the ventral funiculus (VF) to the lateral funiculus (LF) (A, A1, A3, B). c, cervical level; b, brachial level; FP, floor plate; l, lumbar level, s, sacral level; t, thoracic level. Asterisks represent the level of the limbs. Scale bar: 200 μm (A); 50 μm (A1–A3); 150 μm (B); 30 μm (B1–B3).