title: beamter/deltaC and the role of Notch ligands in the zebrafish somite segmentation, hindbrain neurogenesis and hypochord differentiation.
abstract: The Tübingen large-scale zebrafish genetic screen completed in 1996 identified a set of five genes required for orderly somite segmentation. Four of them have been molecularly identified and three were found to code for components of the Notch pathway, which are required for the coordinated oscillation of gene expression, known as the segmentation clock, in the presomitic mesoderm (PSM). Here, we show that the final member of the group, beamter (bea), codes for the Notch ligand DeltaC, and we present and characterize two new alleles, including one allele encoding for a protein truncated in the 7th EGF repeat and an allele deleting only the DSL domain which was previously shown to be necessary for ligand function. Interestingly however, when we over-express any of the mutant deltaC mRNAs, we observe antimorphic effects on both hindbrain neurogenesis and hypochord formation. Expression of bea/deltaC oscillates in the PSM, and a triple fluorescent in situ analysis of its oscillation in relation to that of other oscillating genes in the PSM reveals differences in subcellular localization of the oscillating mRNAs in individual cells in different oscillation phases. Mutations in aei/deltaD and bea/deltaC differ in the way they disrupt the oscillating expression of her1 and deltaC. Furthermore, we find that the double mutants have significantly stronger defects in hypochord formation but not in somitogenesis or hindbrain neurogenesis, indicating genetically that the two delta's may function either semi-redundantly or distinctly, depending upon context.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103, USA.
authors.forename: Dörthe
authors.initials: D
authors.lastname: Jülich
authors.forename: Chiaw
authors.initials: C
authors.lastname: Hwee Lim
authors.forename: Jennifer
authors.initials: J
authors.lastname: Round
authors.forename: Claudia
authors.initials: C
authors.lastname: Nicolaije
authors.forename: Joshua
authors.initials: J
authors.lastname: Schroeder
authors.forename: Alexander
authors.initials: A
authors.lastname: Davies
authors.forename: Robert
authors.initials: R
authors.lastname: Geisler
authors.forename: Julian
authors.initials: J
authors.lastname: Lewis
authors.forename: Yun-Jin
authors.initials: YJ
authors.lastname: Jiang
authors.forename: Scott A
authors.initials: SA
authors.lastname: Holley
mesh_terms: D000483:Alleles; D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008565:Membrane Proteins / Q000235:genetics* / Q000502:physiology; D009154:Mutation; D012333:RNA, Messenger / Q000032:analysis; D051880:Receptors, Notch / Q000378:metabolism; D012249:Rhombencephalon / Q000166:cytology / Q000196:embryology* / Q000254:growth & development; D019170:Somites; D015027:Zebrafish / Q000196:embryology*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008565:Membrane Proteins; D012333:RNA, Messenger; D051880:Receptors, Notch; C064045:delta protein