title: Overexpression of S-adenosylmethionine decarboxylase (SAMDC) in Xenopus embryos activates maternal program of apoptosis as a "fail-safe" mechanism of early embryogenesis.
abstract: In Xenopus, injection of S-adenosylmethionine decarboxylase (SAMDC) mRNA into fertilized eggs or 2-cell stage embryos induces massive cell dissociation and embryo-lysis at the early gastrula stage due to activation of the maternal program of apoptosis. We injected SAMDC mRNA into only one of the animal side blastomeres of embryos at different stages of cleavage, and examined the timing of the onset of the apoptotic reaction. In the injection at 4- and 8-cell stages, a considerable number of embryos developed into tadpoles and in the injection at 16- and 32-cell stages, all the embryos became tadpoles, although tadpoles obtained were sometimes abnormal. However, using GFP as a lineage tracer, we found that descendant cells of the blastomere injected with SAMDC mRNA at 8- to 32-cell stages are confined within the blastocoel at the early gastrula stage and undergo apoptotic cell death within the blastocoel, in spite of the continued development of the injected embryos. These results indicate that cells overexpressed with SAMDC undergo apoptotic cell death consistently at the early gastrula stage, irrespective of the timing of the mRNA injection. We assume that apoptosis is executed in Xenopus early gastrulae as a "fail-safe" mechanism to eliminate physiologically-severely damaged cells to save the rest of the embryo.
authors.affiliation: Laboratory of Molecular Embryology, Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan. m.kai@ucl.ac.uk
authors.forename: Masatake
authors.initials: M
authors.lastname: Kai
authors.forename: Chikara
authors.initials: C
authors.lastname: Kaito
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fukamachi
authors.forename: Takayasu
authors.initials: T
authors.lastname: Higo
authors.forename: Eiji
authors.initials: E
authors.lastname: Takayama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hara
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ohya
authors.forename: Kazuei
authors.initials: K
authors.lastname: Igarashi
authors.forename: Koichiro
authors.initials: K
authors.lastname: Shiokawa
mesh_terms: D012437:Adenosylmethionine Decarboxylase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D036703:Blastula / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian / Q000378:metabolism* / Q000648:ultrastructure; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D049452:Green Fluorescent Proteins; D006801:Humans; D007814:Larva / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D008954:Models, Biological; D012333:RNA, Messenger / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014981:Xenopus
chemical_list: D008164:Luminescent Proteins; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins; D012437:Adenosylmethionine Decarboxylase