Considerable progress has been made in understanding how combinatorially ex
pressed transcription factors control the development of neuronal subtypes
in the fly and vertebrate central nervous systems. The mode of action of ma
ny of these factors has been conserved from invertebrates to vertebrates th
roughout evolution, such as the formation and regulation of specific transc
riptional complexes, the utilization of repressors for maintaining specific
ity, and the use of phosphorylation as an important means for transiently a
ltering transcriptional activity.