Ecdysone and 20-hydroxyecdysone are not required to activate glycolytic gene expression in Drosophila melanogaster embryos

Abstract

Many of the Drosophila enzymes involved in carbohydrate metabolism are coordinately up-regulated approximately midway through embryogenesis. Previous studies have demonstrated that this metabolic transition is controlled by the Drosophila Estrogen-Related Receptor (dERR), which is stabilized and activated immediately prior to onset of glycolytic gene expression. The mechanisms that promote dERR activity, however, are poorly understood and other transcriptional regulators could control this metabolic transition, independent of dERR. In this regard, the steroid hormone 20-hydroxyecdysone (20E) represents an intriguing candidate for regulating glycolytic gene expression in embryos - not only does the embryonic 20E pulse immediately precede transcriptional up-regulation of glycolytic metabolism, but 20E is also known to promote Lactate dehydrogenase gene expression. Here I test the hypothesis that embryonic 20E signaling is required to activate glycolytic gene expression. Using developmental northern blots, I demonstrate that the transcriptional up-regulation of glycolytic genes during embryogenesis still occurs in shadow mutants, which are unable to synthesize either ecdysone or 20E. My finding indicates that ecdysone and 20E signaling are not required for this mid-embryonic metabolic transition.

Figure 1. Timecourse northern blots examining glycolytic gene expression in control and shadow mutant embryos

Total RNA from stage w¹¹¹⁸ control embryos and and w¹¹¹⁸; shadow^10D104/5F45 mutantembryos were analyzed by northern blot hybridization to detect transcripts encoding DHR3, Pgi, Pfk, Pglym78, and Ldh. The Ldh short exposure represents a 6-hour long film exposure. The Ldh long exposure is the same blot exposed for 24 hours. Hybridization to detect rp49 mRNA is included as a loading control.