Pumilio1 phosphorylation precedes translational activation of its target mRNA in zebrafish oocytes

• Published in: Zygote (Cambridge) Vol. 26; no. 5; pp. 372 - 380
• Main Authors: Saitoh, Atsushi, Takada, Yuki, Horie, Mayu, Kotani, Tomoya
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.10.2018
• Subjects: Actin; Actin Cytoskeleton - metabolism; Activation; Animals; Animals, Genetically Modified; Cell cycle; Cyclin B1; Cyclin B1 - genetics; Cytoplasmic Granules - genetics; Cytoplasmic Granules - metabolism; Danio rerio; Depolymerization; Dismantling; Female; Filaments; Gel electrophoresis; Gene Expression Regulation, Developmental; Granular materials; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Insects; Kinases; Maturation; mRNA; N-Terminus; Oocytes; Oocytes - physiology; Phosphorylation; Polyadenylation; Protein Biosynthesis; Protein synthesis; Proteins; Ribonucleic acid; RNA; RNA, Messenger - genetics; RNA, Messenger - metabolism; Sodium lauryl sulfate; Studies; Translation; Zebrafish; Zebrafish - genetics; Zebrafish Proteins - genetics; Zebrafish Proteins - metabolism; Japan; Translation; Cytoplasmic polyadenylation; Vertebrate; RNA granule; Oocyte maturation
• DOI: 10.1017/S0967199418000369
• ISSN: 0967-1994

Translational regulation of mRNAs is crucial for promoting various cellular and developmental processes. Pumilio1 (Pum1) has been shown to play key roles in translational regulation of target mRNAs in many systems of diverse organisms. In zebrafish immature oocytes, Pum1 was shown to bind to cyclin B1 mRNA and promote the formation of cyclin B1 RNA granules. This Pum1-mediated RNA granule formation seemed critical to determine the timing of translational activation of cyclin B1 mRNA during oocyte maturation, leading to activation of maturation/M-phase-promoting factor (MPF) at the appropriate timing. Despite its fundamental importance, the mechanisms of translational regulation by Pum1 remain elusive. In this study, we examined the phosphorylation of Pum1 as a first step to understand the mechanisms of Pum1-mediated translation. SDS-PAGE analyses and phosphatase treatments showed that Pum1 was phosphorylated at multiple sites during oocyte maturation. This phosphorylation began in an early period after induction of oocyte maturation, which preceded the polyadenylation of cyclin B1 mRNA. Interestingly, depolymerization of actin filaments in immature oocytes caused phosphorylation of Pum1, disassembly of cyclin B1 RNA granules, and polyadenylation of cyclin B1 mRNA but not translational activation of the mRNA. Overexpression of the Pum1 N-terminus prevented the phosphorylation of Pum1, disassembly of cyclin B1 RNA granules, and translational activation of the mRNA even after induction of oocyte maturation. These results suggest that Pum1 phosphorylation in the early period of oocyte maturation is one of the key processes for promoting the disassembly of cyclin B1 RNA granules and translational activation of target mRNA.