Cell and tissue growth can be altered during development by an embryo's nutritional status. Varying nutrient levels cause changes in intracellular amino acid levels and trigger signalling from the insulin receptor (InR)pathway, resulting in the subsequent modulation of intracellular TOR kinase activity. On p. ,Goberdhan et al. report two new Drosophila proton-assisted amino acid transporters (PATs), CG3424 (also called PATH) and CG1139, that modulate tissue growth in many non-endocrine tissues. These PATs genetically interact with TOR and with other InR signalling components. CG3424, which is widely expressed, also activates a TOR target in an amino acid-dependent manner when expressed in a Xenopus oocyte system. Surprisingly, it has a very low capacity for transporting amino acids, but a high affinity compared with CG1139 and other mammalian PATs, suggesting that growth control via this process is conserved but does not require bulk amino acid transport into a cell.
