Multiple roles for four-jointed in planar polarity and limb patterning

Insect cuticles have been a model system for the study of planar polarity f or many years and a number of genes required for this process have been ide ntified. These genes organise the polarised arrangement of hairs on the leg s, wings, thorax, and abdomen of adult Drosophila. It has previously been s hown that four-jointed is involved in planar polarity decisions in the eye as well as proximal distal leg and wing development. We now present evidenc e that four-jointed is expressed in a gradient through the developing wing and show that it is required for planar polarity determination in both the wing and the abdomen. Clones of cells either lacking or ectopically express ing four-jointed cause both autonomous and nonautonomous repolarisation of hairs in these tissues. We propose that the inferred four-jointed expressio n gradient is important for planar polarity establishment and that local in versions of the gradient by the clones are the probable cause of the observ ed polarity phenotypes. In addition we observe defects in wing vein develop ment. The subtle phenotypes of mutant flies, and the diverse patterning pro cesses in which it is involved, suggest that four-jointed may act as a modi fier of the activity of multiple other signalling factors. (C) 2000 Academi c Press.