Ras2, the TC21/R-Ras2 Drosophila homologue, contributes to insulin signalling but is not required for organism viability

Highlights

• We generated mutations in the Drosophila Ras2 gene, orthologous to human RRas1, RRas2/TC21 and RRas3.

• Loss of Ras2 function does not compromise organism viability, but cause reduced wing size and expanded life span.

• Ras2 interact with the InR transducer PI3K.

• Activated and overexpressed Ras2 can supply for Ras1 function.

• Ras2 participates in one of several complementary mechanisms downstream to InR.

Abstract

Ras1 (Ras85D) and Ras2 (Ras64B) are the Drosophila orthologs of human H-Ras/N-Ras/K-Ras and R-Ras1-3 genes, respectively. The function of Ras1 has been thoroughly characterised during Drosophila embryonic and imaginal development, and it is associated with coupling activated trans-membrane receptors with tyrosine kinase activity to their downstream effectors. In this capacity, Ras1 binds and is required for the activation of Raf. Ras1 can also interact with PI3K, and it is needed to achieve maximal levels of PI3K signalling in specific cellular settings. In contrast, the function of the unique Drosophila R-Ras member (Ras2/Ras64B), which is more closely related to vertebrate R-Ras2/TC21, has been only studied through the use of constitutively activated forms of the protein. This pioneering work identified a variety of phenotypes that were related to those displayed by Ras1, suggesting that Ras1 and Ras2 might have overlapping activities. Here we find that Ras2 can interact with PI3K and Raf and activate their downstream effectors Akt and Erk. However, and in contrast to mutants in Ras1, which are lethal, null alleles of Ras2 are viable in homozygosis and only show a phenotype of reduced wing size and extended life span that might be related to reduced Insulin receptor signalling.