Fine-tuning of secondary arbor development: the effects of the ecdysone receptor on the adult neuronal lineages of theDrosophilathoracic CNS

Abstract

The adult central nervous system (CNS) of Drosophila is largely composed of relatively homogenous neuronal classes born during larval life. These adult-specific neuron lineages send out initial projections and then arrest development until metamorphosis, when intense sprouting occurs to establish the massive synaptic connections necessary for the behavior and function of the adult fly. In this study, we identified and characterized specific lineages in the adult CNS and described their secondary branch patterns. Because prior studies show that the outgrowth of incumbent remodeling neurons in the CNS is highly dependent on the ecdysone pathway, we investigated the role of ecdysone in the development of the adult-specific neuronal lineages using a dominant-negative construct of the ecdysone receptor (EcR-DN). When EcR-DN was expressed in clones of the adult-specific lineages, neuroblasts persisted longer, but we saw no alteration in the initial projections of the lineages. Defects were observed in secondary arbors of adult neurons, including clumping and cohesion of fine branches, misrouting, smaller arbors and some defasciculation. The defects varied across the multiple neuron lineages in both appearance and severity. These results indicate that the ecdysone receptor complex influences the fine-tuning of connectivity between neuronal circuits, in conjunction with other factors driving outgrowth and synaptic partnering.

Role of Notch signaling in establishing the hemilineages of secondary neurons in Drosophila melanogaster

“…By contrast, the secondary neurons produced during the postembryonic neurogenic phase are much more homogeneous (Truman et al, 2004;Pereanu and Hartenstein, 2006;Brown and Truman, 2009;Zhou et al, 2009). As seen in Fig.…”

“…Lineage 15 makes exclusively motoneurons that project to the leg imaginal disc (Truman et al, 2004;Baek and Mann, 2009;Brown and Truman, 2009;Brierley et al, 2009). Removal of Notch results in a doubling in the size of this neuron cluster from 28±2 (n10) cells in control clones to 57±2 (n7) neurons in Notch null clones.…”

“…We have concluded that the majority of lineage 15 motoneurons arise as the 'B' sibling, but a few may arise as part of the 'A' portion of the lineage. A second, smaller motor lineage that was missed in Truman et al (Truman et al, 2004) is lineage 24 (Brown and Truman, 2009), which makes the motoneurons for the proximal leg muscles (Baek and Mann, 2009) (D. J. Brierley and D.W.W., unpublished). These motoneurons arise as the 'B' fate in lineage 24 (Fig.…”

Dual role for Hox genes and Hox co-factors in conferring leg motoneuron survival and identity in Drosophila

“…Wild-type LinA MNs mainly target the femur and tibia and have a complex dendritic morphology in the neuropil (Fig. 4A) (Baek and Mann, 2009;Brierley et al, 2009;Brown and Truman, 2009). In either Hox (Scr Antp Ubx) or hth mutant LinA clones, the surviving MN axons targeted the same region of the leg as did wild-type LinA clones.…”

Beyond molting-roles of the steroid molting hormone ecdysone in regulation of memory and sleep in adult Drosophila

“…With regard to this possibility, it is noteworthy that developmental studies have demonstrated a significant role for EcR-mediated ecdysone signaling in neuronal remodeling during formation of the adult nervous system. [31][32][33][34] For example, when EcR-mediated ecdysone signaling is blocked during the remodeling of neurosecretory Tv neurons, filipodial activity and axonal sprouting are severely inhibited, resulting in adult Tv neurons with a significantly reduced, misshapen axonal arbor. 35 Thus, 20E is able to trigger and coordinate the molecular processes necessary for proper neuronal remodeling during development.…”