The steroid hormone-regulated gene Broad Complex is required for dendritic growth of motoneurons during metamorphosis of Drosophila.
Dendrites are subject to subtle modifications as well as extensive remodeling during the assembly and maturation of neural circuits in a wide variety of organisms. During metamorphosis, Drosophila flight motoneurons MN1-MN4 undergo dendritic regression, followed by regrowth, whereas MN5 differentiates de novo (Consoulas et al. [2002] J. Neurosci. 22:4906-4917). Many cellular changes during metamorphosis are triggered and orchestrated by the steroid hormone 20-hydroxyecdysone, which initiates a cascade of coordinated gene expression. Broad Complex (BRC), a primary response gene in the ecdysone cascade, encodes a family of transcription factors (BRC-Z1-Z4) that are essential for metamorphic reorganization of the central nervous system (CNS). Using neuron-filling techniques that reveal cellular morphology with very high resolution, we tested the hypothesis that BRC is required for metamorphic development of MN1-MN5. Through a combination of loss-of-function mutant analyses, genetic mapping, and transgenic rescue experiments, we found that 2Bc function, mediated by BRC-Z3, is required selectively for motoneuron dendritic regrowth (MN1-MN4) and de novo outgrowth (MN5), as well as for soma expansion of MN5. In contrast, larval development and dendritic regression of MN1-MN4 are BRC-independent. Surprisingly, BRC proteins are not expressed in the motoneurons, suggesting that BRC-Z3 exerts its effect in a non-cell-autonomous manner. The 2Bc mutants display no gross defects in overall thoracic CNS structure, or in peripheral structures such as target muscles or sensory neurons. Candidates for mediating the effect of BRC-Z3 on dendritic growth of MN1-MN5 include their synaptic inputs and non-neuronal CNS cells that interact with them through direct contact or diffusible factors.
Consoulas
Christos
C
ARL Division of Neurobiology, University of Arizona, Tucson, Arizona 85721, USA. cconsoul@med.uoa.gr
Levine
Richard B
RB
Restifo
Linda L
LL
D000818:Animals; D030801:Animals, Genetically Modified; D003712:Dendrites / Q000235:genetics / Q000502:physiology*; D004330:Drosophila / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D004441:Ecdysterone / Q000096:biosynthesis* / Q000235:genetics; D008675:Metamorphosis, Biological / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D009154:Mutation; D014157:Transcription Factors / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics
C102117:Br protein, Drosophila; D029721:Drosophila Proteins; D014157:Transcription Factors; D004441:Ecdysterone