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In both vertebrate and invertebrate development, cells are often programmed to adopt fates distinct from their neighbors. Genetic analyses in Drosophila melanogaster have highlighted the importance of cell surface and secreted proteins in these cell fate decisions. Homologues of these proteins have been identified and shown to play similar roles in vertebrate development. Fringe, a novel signalling protein, has been shown to induce wing margin formation in Drosophila. Fringe shares significant sequence homology and predicted secondary structure similarity with bacterial glycosyltransferases. Thus fringe may control wing development by altering glycosylation of cell surface and/or secreted molecules. Recently, two fringe genes were isolated from Xenopus laevis. We report here the cloning and characterization of three murine fringe genes (lunatic fringe, manic fringe and radical fringe). We find in several tissues that fringe expression boundaries coincide with Notch-dependent patterning centres and with Notch-ligand expression boundaries. Ectopic expression of murine manic fringe or radical fringe in Drosophila results in phenotypes that resemble those seen in Notch mutants.

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In this work, we modify the multisite Stern-Volmer (MSV) equation for fitting fluorescence titration curves. Under the condition of a static quenching mechanism, the MSV postulates an underlying 1:1 fulvic acid (FA)/copper coordination ratio at multisites. Approximates of six fitting parameters characterize the stability constants (K1 and K2) of FA ligands with Cu2+, micromolar ligand site concentrations (CL1 and CL2), the unquenched, steady-state fractional fluorescence contributions (fx), and the residual fluorescence intensity (IRES). Prior to its application to actual FA titration data, the MSV function is simulated, and its predictive ability is confirmed by titrating a mixture of model fluorophores, glycyl-L-tryptophan and L-tryptophan with Cu2+ at pH 6. Molecular fluorescence measurements of FA are acquired at a fixed spectral position (lambda(ex) = 335 nm; lambda(em) = 450 nm), and FA is titrated with copper in triplicate at three pH values-5, 6, and 7. An objective analysis of log K(1) and K(2) values supports several site organization schemes, including (i) subtle, cooperative interaction, (ii) interfering molecular conformations, and (iii) aggregate forms. Site densities (CL1 and CL2) are consistent across varied pH. The f(1) is indicative of a pH-induced spectral shift of a fluorophore and convincingly associates with a transect in the Deltalambda = 25 synchronous fluorescence spectrum and with the preexponential terms describing the time-dependent fluorescence decay. The MSV and its parent one-site version are equivalent for data fitting but are only simple approximations of a FA ligand system with more complex molecular fundamentals.