title: The intracellular domain of X-Serrate-1 is cleaved and suppresses primary neurogenesis in Xenopus laevis.
abstract: The Notch ligands, Delta/Serrate/Lag-2 (DSL) proteins, mediate the Notch signaling pathway in a numerous developmental processes in multicellular organisms. Although the ligands induce the activation of the Notch receptor, the intracellular domain-deleted forms of the ligands cause dominant-negative phenotypes, implying that the intracellular domain is necessary for the Notch signal transduction. Here we examined the role of the intracellular domain of Xenopus Serrate (XSICD) in Xenopus embryos. X-Serrate-1 has the putative nuclear localization sequence (NLS) in downstream of the transmembrane domain. Biochemical analysis revealed that XSICD fragments are cleaved from the C-terminus side of X-Serrate-1. Fluorescence microscopic analysis showed that the nuclear localization of XSICD occurs in the neuroectoderm of the embryo injected with the full-length X-Serrate-1/GFP. Overexpression of XSICD showed the inhibitory effect on primary neurogenesis. However, a point mutation in the NLSs of XSICD inhibited the nuclear localization of XSICD, which caused the induction of a neurogenic phenotype. The animal cap assay revealed that X-Serrate-1 suppresses primary neurogenesis in neuralized animal cap, but X-Delta-1 does not. Moreover, XSICD could not activate the expression of the canonical Notch target gene, XESR-1 in contrast to the case of full-length X-Serrate-1. These results suggest that the combination of XSICD-mediated intracellular signaling and the extracellular domain of Notch ligands-mediated activation of Notch receptor is involved in the primary neurogenesis. Moreover, we propose a bi-directional signaling pathway mediated by X-Serrate-1 in Notch signaling.
authors.affiliation: Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kiyota
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kinoshita
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004475:Ectoderm / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D047468:Immunoprecipitation; D036341:Intercellular Signaling Peptides and Proteins; D000072100:Jagged-1 Protein; D008024:Ligands; D008565:Membrane Proteins; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D009420:Nervous System / Q000196:embryology*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism; D010641:Phenotype; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D000072099:Serrate-Jagged Proteins; D015398:Signal Transduction; D013997:Time Factors; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: D002135:Calcium-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D000072100:Jagged-1 Protein; D008024:Ligands; D008565:Membrane Proteins; D011506:Proteins; D000072099:Serrate-Jagged Proteins; D029867:Xenopus Proteins; C000606280:jag1 protein, Xenopus; D049452:Green Fluorescent Proteins; D004247:DNA