Seven-up acts in neuroblasts to specify adult central complex neuron identity and initiate neuroblast decommissioning

ABSTRACT An unanswered question in neurobiology is how are diverse neuron cell types generated from a small number of neural stem cells? In the Drosophila larval central brain, there are eight bilateral Type 2 neuroblast (T2NB) lineages that express a suite of early temporal factors followed by a different set of late temporal factors and generate the majority of the central complex (CX) neurons. The early-to-late switch is triggered by the orphan nuclear hormone receptor Seven-up (Svp), yet little is known about how this Svp-dependent switch is involved in specifying CX neuron identities. Here, we: (1) birth date the CX neurons P-EN and P-FN (early and late, respectively); (2) show that Svp is transiently expressed in all early T2NBs; and (3) show that loss of Svp expands the population of early born P-EN neurons at the expense of late born P-FN neurons. Furthermore, in the absence of Svp, T2NBs fail decommissioning and abnormally extend their lineage into week-old adults. We conclude that Svp is required to specify CX neuron identity, as well as to initiate T2NB decommissioning.

(A-H) In all images, Svp mRNA is in white and T2NBs identified with Pnt-Gal4>GFP.
Svp mRNA is detected at high levels in the T2NB nucleus and at very low levels in the cytoplasm, possibly due to our probe labeling a large intronic region of the svp RC

Development • Supplementary information
Table S2.Genetic crosses for each experiment.S3.Antibodies used.

Fig. S1 .
Fig. S1.Svp mRNA is expressed early in all larval T2NB lineages similar to protein expression.

Fig. S3 .
Fig. S3.Adult P-EN and P-FN neurons do not express Svp.(A-B'') P-EN and P-FN neurons labeled by LexA driver lines express Runt but do not Svp.(C) Quantification of molecular expression in P-EN and P-FN neurons.P-EN and P-FN, n = 6 brains.In all panels, LexA+ neurons in green, Runt in magenta, and Svp in cyan.Yellow outline, neurons of interest.Scale bars: 10 m.