Bonus is maternally required for Dorsal nuclear translocation and zygotically for Dpp responsiveness in dorsal-ventral axis formation. Janine Quijano, Michael Stinchfield, Stuart Newfeld. School of Life Sciences, Arizona State Univ, Tempe, AZ.

   bonus is the fly counterpart to vertebrate Tif1/TRIM family members and is best known from studies of its post-embryonic mutant phenotypes. Analyses of larval and pupal functions revealed that it is a chromatin remodeling protein with roles such as nuclear receptor co-factor and transcription regulator. Here we provide the first report of bonus zygotic and maternal functions. In zygotic bonus mutant embryos we observed roughly 40% lethality with cuticles that were ventralized like dpp mutants. Further experiments revealed a loss of Dpp responsiveness, as shown by reduction in expression of the amnioserosa marker Hindsight. Our investigation also revealed that maternally supplied Bonus translocates to the nucleus synchronously with Dorsal and that its nuclear translocation depends upon Toll. Experiments utilizing bonus null germ line clones revealed that maternal bonus is required for Dorsal nuclear translocation. Overall, the data suggest that bonus has two distinct roles during embryonic dorsal-ventral patterning: first a maternal cytoplasmic requirement that facilitates Dorsal nuclear translocation that is unprecedented for any Tif1 protein and second a zygotic nuclear requirement for proper Dpp responsiveness. To our knowledge bon is the first identified gene required on both sides of the maternal to zygotic transition with different roles on each side. Further our data suggest a more intimate connection between signal transduction and chromatin remodeling, one whose disregulation may have a role in tumorigenesis.