The bHLH-PAS protein Spineless is necessary for the diversification of dendrite morphology of Drosophila dendritic arborization neurons

Abstract

Dendrites exhibit a wide range of morphological diversity, and their arborization patterns are critical determinants of proper neural connectivity. How different neurons acquire their distinct dendritic branching patterns during development is not well understood. Here we report that Spineless (Ss), the Drosophila homolog of the mammalian aryl hydrocarbon (dioxin) receptor (Ahr), regulates dendrite diversity in the dendritic arborization (da) sensory neurons. In loss-of-function ss mutants, class I and II da neurons, which are normally characterized by their simple dendrite morphologies, elaborate more complex arbors, whereas the normally complex class III and IV da neurons develop simpler dendritic arbors. Consequently, different classes of da neurons elaborate dendrites with similar morphologies. In its control of dendritic diversity among da neurons, ss likely acts independently of its known cofactor tango and through a regulatory program distinct from those involving cut and abrupt. These findings suggest that one evolutionarily conserved role for Ahr in neuronal development concerns the diversification of dendrite morphology.[Keywords: Drosophila; neuron; dendrite; axon; aryl hydrocarbon receptor; dioxin] Supplemental material is available at http://www.genesdev.org.

Microtubule nucleation and organization in dendrites

“…4,64 Sensory neuron dendrite patterning is defined by the combinatorial activities of a group of transcription factors, including the homeodomain factor Cut (homolog of Cux1 and 2), the BTB-domain factors Abrupt and Lola, the Kr€ uppellike factor Dar1, the Iroquois factor Mirror, the bHLH-PAS factor Spineless, the PRDM factor Hamlet, and the EBF factor Knot. 41,[68][69][70][71][72][73][74][75][76][77][78] These studies have demonstrated that individual transcription factors control specific aspects of dendrite cytoskeleton organization; for example, Cut and Lola were shown to regulate actin organization, 41,76,78 while Knot, Dar1, and Abrupt regulate microtubule organization. 20,41,77 A complex interacting network of microtubule regulatory events occurs within the differentiating neuron, 7 and consequently, a microtubule regulator that is an effector of a transcription factor need not be under the direct transcriptional control of that factor.…”

spineless provides a little backbone for dendritic morphogenesis: Figure 1.

“…This stereotypy suggests a genetic basis, and has led to experimental approaches to identify molecular regulators of dendrite development and morphology. In this article, we discuss new data published by Kim et al (2006) in this issue of Genes & Development on the role of the Spineless (Ss) basic helix-loop-helix-PAS (bHLH-PAS) transcription factor in controlling dendrite morphogenesis, as well as review the contributions of other regulatory proteins.…”

The Krüppel-Like Factor Dar1 Determines Multipolar Neuron Morphology

“…1H ). Furthermore, neuronal type-specific markers, including Knot (Hattori et al, 2007;Jinushi-Nakao et al, 2007), Cut (Grueber et al, 2003), Abrupt (Sugimura et al, 2004), and Spineless (Kim et al, 2006), were expressed appropriately in dar1 Ϫ / Ϫ da neurons (Fig. 1I and data not shown).…”

“…1 A, B). As a comparison, other transcription factors known to regulate dendritic development in multidendritic (md) neurons, such as Knot, Cut, Abrupt, and Spineless, are expressed either in a subset of or in all PNS and CNS neurons (Grueber et al, 2003;Sugimura et al, 2004;Kim et al, 2006;Hattori et al, 2007;Jinushi-Nakao et al, 2007;Crozatier and Vincent, 2008 and data not shown). The unique and selective expression of Dar1 in multipolar neurons led us to hypothesize that Dar1 determines the multipolar layout of neuronal dendrites.…”

“…Third-instar larvae were dissected and immunostained as described previously (Ye et al, 2011). The primary antibodies include: mouse anti-GFP (Invitrogen, 1:1000), chick anti-GFP (Aves Laboratories, 1:1000), rabbit anti-RFP (Rockland, 1:1000), rat anti-Elav (Developmental Studies Hybridoma Bank, 1:500), guinea pig anti-Dar1 (Ye et al, , 1:1000, guinea pig anti-Knot (gift from Adrian Moore, 1:1000), guinea pig anti-Spineless (Kim et al, 2006(Kim et al, , 1:1000, rabbit anti-Abrupt (gift from Stephen Crews, 1:200), rat antiCut (Blochlinger et al, 1988(Blochlinger et al, , 1:1000, and mouse anti-␤GAL (Developmental Studies Hybridoma Bank, 1:100). Confocal imaging was performed with a Leica TCS SP5 confocal microscope.…”