Fig. 6. The dda lineage displays similarities with the dbd lineage. (A) Effects of Notch activation in the PNS at stage 14. Confocal image of C155-GAL4/UAS-Notch^act embryo. (Left) REPO (green), (middle) Nubbin (purple), (right) merged images. Ectopic REPO expression is observed in the dbd neuron (black arrowhead) and the dda neuron (white arrowhead). Nubbin expression is observed in DBDG (arrow) and in the ligament cells (Dick et al., 1991; Lloyd and Sakonju, 1991), but not in the PG3 (asterisk). lig., ligament cells. (B) Developmental sequence of asymmetric cell division in the dda lineage. Double labeling of gcm mRNA (purple) and Nubbin (orange) in stage 12 PNS (single abdominal segment; dorsal up, anterior to left). The dda lineage is boxed. The position of the dbd lineage (out of focus) is indicated by an asterisk. (stage I) Both daughter cells of the dda SOP express Nubbin. The smaller daughter cell (dotted circle) is located apical to the large daughter cell. (stage II) Two symmetrical daughter cells expressing Nubbin are observed. At this stage there is no detectable expression of gcm in the dda lineage. (stage III) One of the daughter cells transiently accumulates gcm mRNA (arrow). (stage IV) Two cells constituting the dda lineage migrate dorsally and are situated anterior to the dbd lineage. Nubbin expression in the presumptive glial cell becomes significantly down-regulated (arrow). Nubbin is never re-expressed in this cell, unlike the presumptive glial cell in the dbd lineage. (stage IV') repo mRNA (purple) and ELAV (orange) expression in ASC mutant at stage IV. In this genetic background the dorsal cluster contains only dda and dbd lineages (Brewster et al., 2001). Weak expression of ELAV is detected in the presumptive dda neuron (white arrowhead) and the dbd neuron (black arrowhead) at this stage. (C) REPO expression in C155-GAL4/UAS- Notch^act, UAS-nub embryo at stage 16. Ectopic REPO expression is observed in the presumptive dbd neuron (black arrowhead), as well as in two cells (black asterisk) that occupy the position dorsal to the glial-transformed dda neuron (white arrowhead). White asterisk indicates PG3 cell; arrow, DBDG. PG3 of the left parasegment is out of focus.

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