Abstract
Drosophila Tribbles (Trbl) is the founding member of a family of pseudokinases with conserved roles in antagonizing cell division, tissue growth and cell differentiation. In humans, three Tribbles isoforms serve as adaptor proteins, binding targets such as Cdc25 phosphatase, Akt kinase or the transcription factor C/EBP to block their activity or direct their proteosomal degradation. Mutations in Tribbles family members are associated with susceptibility to diabetes and cancer, notably Notch-induced tumor growth. Trbl misexpression in the fly wing disk leads to a block in mitosis associated with decreased levels of String/Cdc25 and increased levels of Cyclin B leading to reduced overall wing size and reduced trichome density. We show these Trbl growth-restricting phenotypes can be suppressed by manipulating levels of known Trbl targets, and use this sensitized wing system to screen a collection of growth regulating open reading frames (ORFs) to search for enhancers and suppressors affecting cell and tissue size. By precisely measuring morphometric changes in wing phenotypes using a computer-based tool, we detected synthetic interactions with several E3 ubiquitin ligases, and focused our analysis on the Notch pathway components Neuralized (Neur) and Mindbomb1 (Mib1). In the wing, notum and egg chamber epithelia, Trbl misexpression suppressed Neur and Mib1 activities and stabilized the accumulation of both proteins. To understand these interactions, we used yeast two-hybrid assays to show Trbl physically bound to both Neur and Mib1. Our data are consistent with published reports that mammalian Tribbles3 modulates Notch responses by binding and stabilizing Mindbomb and indicate that a wing misexpression approach is useful to identify novel components in a conserved Tribbles signaling pathway.
Footnotes
authorship order fixed from first submission
