Baboon/dSmad2 TGF-β signaling is required during late larval stage for development of adult-specific neurons

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Abstract
The intermingling of larval functional neurons with adult‐specific neurons during metamorphosis contributes to the development of the adult Drosophila brain. To better understand this process, we characterized the development of a dorsal cluster (DC) of Atonal‐positive neurons that are born at early larval stages but do not undergo extensive morphogenesis until pupal formation. We found that Baboon(Babo)/dSmad2‐mediated TGF‐β signaling, known to be essential for remodeling of larval functional neurons, is also indispensable for proper morphogenesis of these adult‐specific neurons. Mosaic analysis reveals slowed development of mutant DC neurons, as evidenced by delays in both neuronal morphogenesis and atonal expression. We observe similar phenomena in other adult‐specific neurons. We further demonstrate that Babo/dSmad2 operates autonomously in individual neurons and specifically during the late larval stage. Our results suggest that Babo/dSmad2 signaling prior to metamorphosis may be widely required to prepare neurons for the dynamic environment present during metamorphosis.