%0 Journal Article %J Curr Biol %D 1999 %T The four-jointed gene is required in the Drosophila eye for ommatidial polarity specification. %A Zeidler, M P %A Perrimon, N %A Strutt, D I %K Animals %K Base Sequence %K Body Patterning %K Cloning, Molecular %K DNA-Binding Proteins %K Drosophila %K Drosophila Proteins %K Eye %K Frizzled Receptors %K Insect Proteins %K Janus Kinase 3 %K Membrane Glycoproteins %K Membrane Proteins %K Microscopy, Confocal %K Molecular Sequence Data %K Mutation %K Polymerase Chain Reaction %K Protein-Tyrosine Kinases %K Proto-Oncogene Proteins %K Receptors, G-Protein-Coupled %K Receptors, Notch %K Signal Transduction %K STAT1 Transcription Factor %K Trans-Activators %K Wnt1 Protein %X

BACKGROUND: The Drosophila eye is composed of about 800 ommatidia, each of which becomes dorsoventrally polarised in a process requiring signalling through the Notch, JAK/STAT and Wingless pathways. These three pathways are thought to act by setting up a gradient of a signalling molecule (or molecules) often referred to as the 'second signal'. Thus far, no candidate for a second signal has been identified. RESULTS: The four-jointed locus encodes a type II transmembrane protein that is expressed in a dorsoventral gradient in the developing eye disc. We have analysed the function and regulation of four-jointed during eye patterning. Loss-of-function clones or ectopic expression of four-jointed resulted in strong non-autonomous defects in ommatidial polarity on the dorsoventral axis. Ectopic expression experiments indicated that localised four-jointed expression was required at the time during development when ommatidial polarity was being determined. In contrast, complete removal of four-jointed function resulted in only a mild ommatidial polarity defect. Finally, we found that four-jointed expression was regulated by the Notch, JAK/STAT and Wingless pathways, consistent with it mediating their effects on ommatidial polarity. CONCLUSIONS: The clonal phenotypes, time of requirement and regulation of four-jointed are consistent with it acting in ommatidial polarity determination as a second signal downstream of Notch, JAK/STAT and Wingless. Interestingly, it appears to act redundantly with unknown factors in this process, providing an explanation for the previous failure to identify a second signal.

%B Curr Biol %V 9 %P 1363-72 %8 1999 Dec 2 %G eng %N 23 %1 http://www.ncbi.nlm.nih.gov/pubmed/10607560?dopt=Abstract