In a recent lab journal club we discussed a very nice paper from Takashi Koyama and Christen Mirth:

Growth-Blocking Peptides As Nutrition-Sensitive Signals for Insulin Secretion and Body Size Regulation. (2016) PLoS Biology

Nutrients promote body growth in Drosophila by stimulating insulin signaling. One main way that this happens involves endocrine signaling between the fat body and the brain – in protein rich diets, amino acid import into fat body cells activates TOR and leads to release of a secreted factor(s) that acts on the brain to stimulate expression and release of insulin-like peptides (ILPs) from neurosecretory cells. However, the nature of the these AA-sensitive fat body factors has remained elusive. In this paper, the authors identify the Growth Blocking Peptides 1 and 2 (GBP1 and 2) as strong candidates. They show that expression of GBP1 and 2 is regulated by AA/TOR signaling and that both GBP1 and 2 are secreted from the fat body and can act directly on the brain to promote ILP release.

We liked this paper a lot. In particular we appreciated the rigorous and comprehensive approach the authors used to establish that both GBP1 and 2 are bona fide fat-body derived factors that respond to TOR signaling and that act directly on the brain to promote insulin release.