@article {843271,
	title = {The four-jointed gene is required in the Drosophila eye for ommatidial polarity specification.},
	journal = {Curr Biol},
	volume = {9},
	number = {23},
	year = {1999},
	month = {1999 Dec 2},
	pages = {1363-72},
	abstract = {
	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 {\textquoteright}second signal{\textquoteright}. 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.

},
	keywords = {Animals, Base Sequence, Body Patterning, Cloning, Molecular, DNA-Binding Proteins, Drosophila, Drosophila Proteins, Eye, Frizzled Receptors, Insect Proteins, Janus Kinase 3, Membrane Glycoproteins, Membrane Proteins, Microscopy, Confocal, Molecular Sequence Data, Mutation, Polymerase Chain Reaction, Protein-Tyrosine Kinases, Proto-Oncogene Proteins, Receptors, G-Protein-Coupled, Receptors, Notch, Signal Transduction, STAT1 Transcription Factor, Trans-Activators, Wnt1 Protein},
	issn = {0960-9822},
	author = {Zeidler, M P and Perrimon, N and Strutt, D I}
}
