The Steroid Hormone 20-Hydroxyecdysone Enhances Neurite Growth ofDrosophilaMushroom Body Neurons Isolated during Metamorphosis

Abstract

Mushroom bodies (MBs) are symmetrically paired neuropils in the insect brain that are of critical importance for associative olfactory learning and memory. In Drosophila melanogaster, the MB intrinsic neurons (Kenyon cells) undergo extensive reorganization at the onset of metamorphosis. A phase of rapid axonal degeneration without cell death is followed by axonal regeneration. This re-elaboration occurs as levels of the steroid hormone 20-hydroxyecdysone (20E) are rising during the pupal stage. Based on the known role of 20E in directing many features of CNS remodeling during insect metamorphosis, we hypothesized that the outgrowth of MB axonal processes is promoted by 20E. Using a GAL4 enhancer trap line (201Y) that drives MB-restricted reporter gene expression, we identified Kenyon cells in primary cultures dissociated from early pupal CNS. Paired cultures derived from single brains isolated before the 20E pupal peak were incubated in medium with or without 20E for 2-4 d. Morphometric analysis demonstrated that MB neurons exposed to 20E had significantly greater total neurite length and branch number compared with that of MB neurons grown without hormone. The relationship between branch number and total neurite length remained constant regardless of hormone treatment in vitro, suggesting that 20E enhances the rate of outgrowth from pupal MB neurons in a proportionate manner and does not selectively increase neuritic branching. These results implicate 20E in enhancing axonal outgrowth of Kenyon cells to support MB remodeling during metamorphosis.

Ecdysone signaling regulates the formation of long-term courtship memory in adult Drosophila melanogaster

“…Given that genetically programmed ecdysone signaling is known to control neuronal remodeling during development (47)(48)(49), it is interesting to speculate that certain experiences may recapture the ecdysone-mediated developmental processes in the adult brain and lead to structural and functional modifications to the nervous system that facilitate the formation of stable, LTM. The ability of ecdysone to remodel the nervous system is known not to be limited to developmental stages.…”

Mental retardation genes in drosophila: New approaches to understanding and treating developmental brain disorders

“…We developed culture methods for genetically marked Drosophila mushroom body neurons harvested at specific developmental times. In vitro, these developmentally plastic neurons grow a neurite arbor with distinctive morphometric features and respond with greater outgrowth to physiological levels of an endogenous steroid hormone [Kraft et al, 1998]. Moreover, mutant neuronal phenotypes, including stunted growth, excessive growth, and altered branching structure, can be detected [Kraft R, Escobar M, Kurtis J, Restifo L, manuscript in preparation].…”

Identification of 20-Hydroxyecdysone-Inducible Genes from Larval Brain of the Silkworm, Bombyx mori, and Their Expression Analysis

“…PTTH signals the prothoracic glands (PGs) to trigger production and release of ecdysone, the precursor of its active metabolite 20-hydroxyecdysone (20E) (Kawakami et al, 1990;Gilbert et al, 2002). 20E governs morphological changes of the brain (Champlin and Truman, 1998;Kraft et al, 1998) by regulating gene expression cascades associated with ecdysteroidogenesis and metamorphosis (Beckstead et al, 2005).…”