Zebrafish lunatic fringe demarcates segmental boundaries

Cell interactions involving Notch signaling are required for the demarcatio n of tissue boundaries in both invertebrate and vertebrate development. Mem bers of the Fringe gene family encode beta -1,3 N-acetyl-glucosaminyltransf erases that function to refine the spatial localization of Notch-receptor s ignaling to tissue boundaries. In this paper we describe the isolation and characterization of the zebrafish (Danio rerio) homologue of the lunatic fr inge gene (lfng). Zebrafish lfng is generally expressed in equivalent struc tures to those reported for the homologous chick and mouse genes. These sit es include expression along the A-P axis of the neural tube, within the lat eral plate mesoderm, in the presomitic mesoderm and the somites and in spec ific rhombomeres of the hindbrain; however, within these general expression domains species-specific differences in lfng expression exist. In mouse, L fng is expressed in odd-numbered rhombomeres, whereas in zebrafish, express ion occurs in even-numbered rhombomeres. In contrast to reports in both mou se and chicken embryos showing a kinematic cyclical expression of Lfng mRNA in the presomitic paraxial mesoderm, we find no evidence for a cyclic patt ern of expression for the zebrafish lfng gene; instead, the zebrafish Lfng is expressed in two static stripes within the presomitic mesoderm. Neverthe less, in zebrafish mutants affecting the correct formation of segment bound aries in the hindbrain and somites, lfng expression is aberrant or lost. (C ) 2001 Published by Elsevier Science Ireland Ltd.