The molecular underpinnings of body size regulation: Transcriptional changes in foxo and mTor in Drosophila melanogaster selected for fast development

Abstract

One of biology's most perplexing ideas is the biological control of an organism's size. Even if many questions remain unanswered, it can be logically implied that the size of an individual is clearly correlated with its cell number and cell size. Size regulation, which happens through the control of cell size and number, is crucial for the development of multicellular organisms. Long term selection of Drosophila melanogaster for fast development has led to reduction in body size. In this study, we compared three types of D. melanogaster populations- the first were selected for fast development and short effective lifespan (FEJs), second were selected for fast development and longer effective lifespan (FLJs) and the third were their ancestral control populations (JBs), and answered whether up-regulation of foxo (forkhead box, subgroup-o) and/or down regulation of mTor (mechanistic Target of rapamycin) is responsible for reduction in organismal size in fast developing D. melanogaster. Our results show that upregulation of foxo might be responsible for reduction in size in both FLJs and FEJs. Further, higher mTor in FEJs but no change in mTor in FLJs in comparison to JBs confirms that selection for fast development does not lead to starvation like phenotype or stress like conditions in D. melanogaster. Furthermore, this difference in mTor in FEJs and FLJs might be due to selection for short effective lifespan and long effective lifespan respectively, as suppression or blocking mTor expression has been reported to extend lifespan. These results suggest that potentially deleterious allele for late life is under positive selection in FEJs but not in FLJs.