title: Effects of S-adenosylmethionine decarboxylase, polyamines, amino acids, and weak bases (amines and ammonia) on development and ribosomal RNA synthesis in Xenopus embryos.
abstract: We have been studying control mechanisms of gene expression in early embryogenesis in a South African clawed toad Xenopus laevis, especially during the period of midblastula transition (MBT), or the transition from the phase of active cell division (cleavage stage) to the phase of extensive morphogenesis (post-blastular stages). We first found that ribosomal RNA synthesis is initiated shortly after MBT in Xenopus embryos and those weak bases, such as amines and ammonium ion, selectively inhibit the initiation and subsequent activation of rRNA synthesis. We then found that rapidly labeled heterogeneous mRNA-like RNA is synthesized in embryos at pre-MBT stage. We then performed cloning and expression studies of several genes, such as those for activin receptors, follistatin and aldolases, and then reached the studies of S-adenosylmethionine decarboxylase (SAMDC), a key enzyme in polyamine metabolism. Here, we cloned a Xenopus SAMDC cDNA and performed experiments to overexpress the in vitro-synthesized SAMDC mRNA in Xenopus early embryos, and found that the maternally preset program of apoptosis occurs in cleavage stage embryos, which is executed when embryos reach the stage of MBT. In the present article, we first summarize results on SAMDC and the maternal program of apoptosis, and then describe our studies on small-molecular-weight substances like polyamines, amino acids, and amines in Xenopus embryos. Finally, we summarize our studies on weak bases, especially on ammonium ion, as the specific inhibitor of ribosomal RNA synthesis in Xenopus embryonic cells.
authors.affiliation: Department of Judo Therapy, Faculty of Medical Technology, Teikyo University, 1-1 Toyosatodai, Utsunomiya, Tochigi, 320-8551, Japan. shiokawa@nasu.bio.teikyo-u.ac.jp
authors.forename: Koichiro
authors.initials: K
authors.lastname: Shiokawa
authors.forename: Mai
authors.initials: M
authors.lastname: Aso
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kondo
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Takai
authors.forename: Junki
authors.initials: J
authors.lastname: Yoshida
authors.forename: Takamichi
authors.initials: T
authors.lastname: Mishina
authors.forename: Kota
authors.initials: K
authors.lastname: Fuchimukai
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Ogasawara
authors.forename: Taro
authors.initials: T
authors.lastname: Kariya
authors.forename: Kosuke
authors.initials: K
authors.lastname: Tashiro
authors.forename: Kazuei
authors.initials: K
authors.lastname: Igarashi
mesh_terms: D012437:Adenosylmethionine Decarboxylase / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001679:Biogenic Amines / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D008969:Molecular Sequence Data; D011073:Polyamines / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000235:genetics; D014981:Xenopus / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D001679:Biogenic Amines; D011073:Polyamines; D012335:RNA, Ribosomal; D029867:Xenopus Proteins; D000641:Ammonia; D012437:Adenosylmethionine Decarboxylase