Lilliputian: an AF4/FMR2-related protein that controls cell identity and cell growth

Members of the AF4/FMR2 family of nuclear proteins are involved in human di seases such as acute lymphoblastic leukemia and mental retardation. Here we report the identification and characterization of the Drosophila lilliputi an (lilli) gene, which encodes a nuclear protein related to mammalian AF4 a nd FMR2. Mutations in lilli suppress excessive neuronal differentiation in response to a constitutively active form of Raf in the eye. In the wild typ e, Lilli has a partially redundant function in the Ras/MAPK pathway in diff erentiation but it is essential for normal growth. Loss of Lilli function c auses an autonomous reduction in cell size and partially suppresses the inc reased growth associated with loss of PTEN function. These results suggest that Lilli acts in parallel with the Ras/MAPK and the P13K/PKB pathways in the control of cell identity and cellular growth.