The Drosophila epidermis is characterized by a dramatic planar or tissue polarity. The frizzled pathway has been shown to be a key regulator of planarpolarity for hairs on the wing, ommatidia in the eye and sensory bristles on the notum. We have investigated the genetic relationships between putative frizzledpathway downstream genes inturned, fuzzy and multiple wing hairs (inturned-likegenes) and upstream genes such as frizzled, prickle and starry night(frizzled-like genes).  Previous data showed that the inturned-like genes wereepistatic to the frizzled-like genes when the entire wing was mutant. Weextended those experiments and examined the behavior of frizzled clones inmutant wings. We found the domineering nonautonomy of frizzled clones was notaltered when the clone cells were simultaneously mutant for inturned, multiplewing hairs or dishevelled but it was blocked when the entire wing was mutant forinturned, fuzzy, multiple wing hairs or dishevelled. Thus, for the domineeringnonautonomy phenotype of frizzled, inturned and multiple wing hairs are neededin the responding cells but not in the clone itself. Expressing a number of frizzled pathway genes in a gradient across part of the wing repolarizes wingcells in that region. We found inturned, fuzzy and multiple wing hairs wererequired for a gradient of frizzled, starry night, prickle or spiny-legs expression to repolarize wing cells. These data argue that inturned, fuzzy andmultiple wing hairs are downstream components of the frizzled pathway. Tofurther probe the relationship between the frizzled-like and inturned-like geneswe determined the consequences of altering the activity of frizzled-like genesin wings that carried weak alleles of inturned or fuzzy. Interestingly bothincreasing and decreasing the activity of frizzled and other upstream genesenhanced the phenotypes of hypomorphic inturned and fuzzy mutants.

We also examined the relationship between the frizzled-like and inturned-like genes in other regions of the fly. For some body regions and cell types (e.g. abdomen) the inturned-like genes were epistatic to the frizzled-like genes, but in other body regions (e.g. eye) that was not the case. Thus, the genetic control of tissue polarity is body region specific.