Motor neuron development in embryonic mouse neural tube. Fluorescence images of embryonic (E10.5) mouse neural tube, after immunolabelling for Olig2 (green), Islet1 (red), Hb9/MNR2 (red), Ki67 (green) and DAPI for nuclei (blue). Scale bars 50 μm. The schematic of the neural tube shows the dorsal (d1-d6) and ventral domains (v0-v3, MN) of the neural tube and corresponding expression markers. RP: roof plate, FP: floor plate, VZ: ventricular zone, MZ: mantle zone, d: dorsal, v: ventral, MN: motor neuron. Olig2+ cells are restricted to the VZ, the region of proliferating progenitor cells in the developing neural tube. Islet1+ and Hb9/MNR2+ cells are found at the peripheral mantle zone of the neural tube representing post-mitotic neurons. A small number of Olig2+/Hb9+ cells, or Olig2+/Islet1+ cells represent progenitor cells that are making the transition towards Hb9/MNR2+ neurons as they migrate away from the medial VZ to the peripheral MZ.