Sequence and embryonic expression of three zebrafish fringe genes: lunatic fringe, radical fringe, and manic fringe.

Drosophila fringe and its homologues in vertebrates code for glycosyltransferases that modify Notch, altering the sensitivity of this receptor protein to its ligands Delta and Serrate and, thereby, playing an essential part in the demarcation of tissue boundaries. We describe the isolation and characterization of three zebrafish (Danio rerio) fringe homologues: lunatic fringe (lfng), radical fringe (rfng), and manic fringe (mfng). In addition to the sites previously described (Prince et al. [2001] Mech. Dev. 105:175-180; Leve et al. [ 2001] Dev. Genes Evol. 211:493-500), lfng is also expressed in the sensory patches of the inner ear. The newly described rfng is expressed in adaxial cells, tectum, rhombomere boundaries, and formed somites, but the expression of mfng is only detectable by reverse transcription-polymerase chain reaction and not by whole-mount in situ hybridization (WISH) during early embryonic development; later, it is expressed in the sensory patches of the ear. In mib mutants, where Notch signaling is defective and rhombomere boundaries fail to form, the rfng expression in hindbrain is almost completely lost. None of the three zebrafish fringe genes is detectably expressed in the posterior presomitic mesoderm, suggesting that, in contrast with chick and mouse, the somitogenesis oscillator in this tissue in the zebrafish does not depend on Fringe activity.