Fig. 2

On E13.5, Islet 1/2 positive neurons migrate across the midline independent of the existing commissure, with a small number of Islet positive neurons found in fibers projecting away from the nucleus. A-D. Transverse sections through the oculomotor nucleus on E13.5, shown anterior (A) to posterior (D), were antibody labeled for the motor neuron-specific transcription factor Islet1/2. The ventral tegmental commissure traveling through the floor plate is indicated (brackets in A-D). A In anterior sections, Islet1/2+ oculomotor neurons were located in distinct nuclei on either side of the floor plate, with no midline cell bodies visible (only non-specific blood vessel labeling is seen in the midline). B-D Large numbers of oculomotor neurons were located in the floor plate in a distinct stream above the commissure in intermediate (B) through posterior sections (C, D). In posterior sections, a subset of Islet1/2+ cells formed a stream toward the pial surface, moving outside of the bounds of the nucleus (marked with dashed white lines), apparently along the nerve fibers projecting to the ventral exit point (arrows in C, D). E Islet 1/2+ neurons were located in fibers projecting from the oculomotor nucleus toward the pial surface of the neural tube (arrows point to fibers projecting away from the oculomotor nucleus). F Sagittal section through the oculomotor nerve, projecting from ventral exit points (asterisks) toward the eye (arrow head points to peripheral oculomotor nerve fibers), shows Islet 1/2 positive cells located within the peripheral oculomotor nerve (arrows in F). G Schematic indicating the location of Islet1/2+ cell bodies in anterior to posterior sections. Right and left oculomotor nuclei are indicated by green and red colors respectively. The tegmental commissure is shown as blue curved lines traveling through the floor plate (gray color). Islet positive cells are located above the commissure. Abbrev: Tegmental commissure (TC). Scale bar100 μm