title: Zar1 represses translation in Xenopus oocytes and binds to the TCS in maternal mRNAs with different characteristics than Zar2.
abstract: Maternal mRNAs are translationally regulated during early development. Zar1 and its closely related homolog, Zar2, are both crucial in early development. Xenopus laevis Zygote arrest 2 (Zar2) binds to the Translational Control Sequence (TCS) in maternal mRNAs and regulates translation. The molecular mechanism of Zar1 has not been described. Here we report similarities and differences between Xenopus Zar1 and Zar2. Analysis of Zar sequences in vertebrates revealed two Zar family members with conserved, characteristic amino acid differences in the C-terminal domain. The presence of only two vertebrate Zar proteins was supported by analyzing Zar1 synteny. We propose that the criteria for naming Zar sequences are based on the characteristic amino acids and the chromosomal context. We also propose reclassification of some Zar sequences. We found that Zar1 is expressed throughout oogenesis and is stable during oocyte maturation. The N-terminal domain of Zar1 repressed translation of a reporter construct in immature oocytes. Both Zar1 and Zar2 bound to the TCS in the Wee1 and Mos 3' UTRs using a zinc finger in the C-terminal domain. However, Zar1 had much higher affinity for RNA than Zar2. To show the functional significance of the conserved amino acid substitutions, these residues in Zar2 were mutated to those found in Zar1. We show that these residues contributed to the different RNA binding characteristics of Zar1 compared to Zar2. Our study shows that Zar proteins have generally similar molecular functions in the translational regulation of maternal mRNAs, but they may have different roles in early development.
authors.affiliation: Department of Integrative Biology, University of Colorado Denver, Denver, CO, USA. Electronic address: tomomi.yamamoto@ucdenver.edu.
authors.forename: Tomomi M
authors.initials: TM
authors.lastname: Yamamoto
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Cook
authors.forename: Cassandra V
authors.initials: CV
authors.lastname: Kotter
authors.forename: Terry
authors.initials: T
authors.lastname: Khat
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Silva
authors.forename: Michael
authors.initials: M
authors.lastname: Ferreyros
authors.forename: Justin W
authors.initials: JW
authors.lastname: Holt
authors.forename: Jefferson D
authors.initials: JD
authors.lastname: Knight
authors.forename: Amanda
authors.initials: A
authors.lastname: Charlesworth
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D018507:Gene Expression Regulation, Developmental; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D009866:Oogenesis / Q000502:physiology; D014176:Protein Biosynthesis; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D023121:RNA, Messenger, Stored / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D023121:RNA, Messenger, Stored; D029867:Xenopus Proteins; C547737:Zar2 protein, Xenopus; C530005:WEE1 protein, Xenopus; D011505:Protein-Tyrosine Kinases
keywords: CPE; CPEB; EMSA; MBE; Musashi binding element; RNA binding protein; TCS; Translational Control Sequence; Translational control; UTR; Xenopus oocyte; Zygote arrest; cytoplasmic polyadenylation element; cytoplasmic polyadenylation element binding protein; electrophoretic mobility shift assay; untranslated region