Fig. 1. Gcm protein distribution, spindle orientation and cell migration in neural precursor lineages. (A) NGB 6-4T divides along the apical-basal axis and expresses Gcm before its first division. In the left column are schematic representations; in the right column are paired confocal images (each pair from the same focal plane) corresponding to the diagrammed cells. Ventral view. Anterior is upwards; midline is towards the left. Gcm is expressed in the pre-divisional NGB 6-4T (6-4T). NGB 6-4T divides along the apical-basal axis (n>60 mitotic NGB 6-4T). Both the daughter cell (G) and the post-divisional NGB 6-4T are Gcm positive, and Gcm is localized to the nucleus (a different focal plane is shown for each of these cells). The G cell (arrow) next undergoes a migration to a position just medial to NGB 6-4T (arrowhead; note that NGB 6-4T and G are in the same focal plane at this stage). By the end of this migration, Gcm protein is no longer detectable in NGB 6-4T. The G cell divides twice to generate three glia (one medial cell body glia, m-CBG; and two medial-most cell body glia, mm-CBG), which migrate toward the midline. Subsequent divisions of NGB 6-4T (dotted circle in bottom confocal image) are along the apical-basal axis, and generate neuron-producing daughter cells (n). (B) GB 6-4A divides along the apical-basal axis and expresses Gcm before its first division (oriented as in A). Gcm is expressed in the predivisional GB 6-4A (6-4A). GB 6-4A divides along the apical-basal axis (a different focal plane is shown for each cell), and both daughter cells are Gcm-positive. The G cell next rapidly migrates to a position medial to GB 6-4A (note that these cells are in the same focal plane at this stage); both G and GB 6-4A maintain Gcm expression and differentiate as glia. The gray circle in the diagram and the dotted circle in the confocal image approximate the position of the predivisional GB 6-4A. (C) Glial progeny of NGB 7-4. The position of NGB 7-4 (which is just out of the focal plane) is indicated by the dotted circle in the confocal image. Ventral glia: at the ventral surface of the CNS, two glial progeny of NGB 7-4 migrate to the midline and become channel glia (CG, arrowheads); three glia remain close to NGB 7-4 and become cell body glia (CBG, arrows). Dorsal glia: one to two glia migrate laterally and dorsally and become lateral subperineurial glia (l-SPG, large arrows).
