Dynamic expression of the RNA-binding protein Sam68 during mouse pre-implantation development.
The STAR protein Sam68 (KHDRBS1) is involved in several aspects of post-transcriptional mRNA metabolism. Herein, we have investigated the expression and subcellular localization of Sam68 during early mouse embryogenesis. We found that mouse oocytes express high levels of Sam68 mRNA, low levels of the transcript for Khdrbs2 (current symbol for Slm-1) and no Khdrbs3 (current symbol for Slm-2), two highly homologous STAR genes. Sam68 protein is expressed throughout oocyte meiotic maturation and early embryogenesis. It is released in the cytoplasm upon meiotic resumption and it slowly accumulates in the nucleus after fertilization. Unlike what was observed for other RNA-binding proteins, nuclear accumulation of Sam68 was independent of de novo mRNA transcription. However, we found that inhibition of mRNA translation by either cycloheximide or puromycin in one-cell embryos caused the accumulation of Sam68 in cytoplasmic granules. Analysis of these granules by deconvolution microscopy demonstrated that they are sites of accumulation for proteins involved in the initiation of mRNA translation, such as eIF4A1, eIF4E and eIF4G. These granules contained RNA and were dissolved by treatment with RNase A. Other proteins expressed by the zygote, like the splicing factor SC35 or the cytoplasmic kinase ERK2, did not accumulate in such structures after treatment with inhibitors of mRNA translation, indicating that the localization of Sam68 and of the translation initiation factors in these granules is a specific event. These results indicate that Sam68 is involved in translational regulation of maternal mRNAs in the zygote and in the early signaling events triggered by fertilization.
Paronetto
Maria Paola
MP
Department of Public Health and Cell Biology, Section of Anatomy, University of Rome Tor Vergata, Via Montpellier 1, 00133 Rome, Italy.
Bianchi
Enrica
E
Geremia
Raffaele
R
Sette
Claudio
C
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D053959:Alpha-Amanitin / Q000494:pharmacology; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D010064:Embryo Implantation; D004622:Embryo, Mammalian / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006801:Humans; D051379:Mice; D008815:Mice, Inbred Strains; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D010053:Ovary / Q000166:cytology; D011247:Pregnancy; D014176:Protein Biosynthesis / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011691:Puromycin / Q000494:pharmacology; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012102:Reproductive Control Agents / Q000494:pharmacology; D012259:Ribonuclease, Pancreatic / Q000494:pharmacology; D046509:Tissue Culture Techniques; D015053:Zygote / Q000166:cytology / Q000187:drug effects
D048868:Adaptor Proteins, Signal Transducing; D053959:Alpha-Amanitin; D006063:Chorionic Gonadotropin; C513253:Khdrbs1 protein, mouse; D019384:Nucleic Acid Synthesis Inhibitors; D011500:Protein Synthesis Inhibitors; D016601:RNA-Binding Proteins; D012102:Reproductive Control Agents; D003609:Dactinomycin; D011691:Puromycin; D004004:Dichlororibofuranosylbenzimidazole; D003513:Cycloheximide; D012259:Ribonuclease, Pancreatic