Figure 8.

Split Gal4 applications in neurodevelopment and technical spinoffs. (A–C) Split Gal4 has been used to target neurons in specific neuronal lineages. (A) Larval neurons, some of which persist into adulthood, are born embryonically from neural stem cells called neuroblasts (NBs). Each hemisegment in the ventral nerve cord (VNC), has a similar complement of identified NBs, arranged in rows and columns. (B) Diagram of the arrangement of the NBs in a VNC hemisegment, with NB1–2 highlighted in green. (C) Two CRM-Gal4 lines (left panels) overlap in expression in NB1–2, as indicated by the Split Gal4 driver made using the two CRMs (right panel). Neuronal progeny of NB1–2 is labeled with GFP (green). (D–F) The Split LexA system uses the same heterodimerizing leucine zippers as Split Gal4. (D) Using a UAS-Zip⁻-LexADBD, a Gal4 expression pattern can be converted into a Split LexA expression pattern. Where this pattern intersects with the expression pattern of a Zip⁺-VP16AD driven by its own enhancer (P2), a functional LexA::VP16AD transcriptional activator is produced and LexA_op-mediated transgene expression occurs. (E) The 9–9-Gal4 driver expresses in multiple subsets of optic lobe neurons, including the Ort-positive, L3 neurons of the lamina (somata, arrowhead; axon terminals, arrow). (F) The L3 neurons can be isolated by using 9–9-Gal4 to drive UAS- Zip⁻-LexADBD in combination with an ort-driven Zip⁺-VP16AD hemidriver. Red, 24B10 immunolabeling. Panel (A) from Luan et al. (2020); panel (C) adapted from Lacin and Truman (2016); panels (D–F) from Ting et al. (2011).