The step-wise assembly of a functional nucleolus in preimplantation mouse embryos involves the cajal (coiled) body.
After fertilization, ribosomal RNA synthesis is silenced during a period which depends on the species. Data concerning the reassembly of a functional nucleolus remain scarce. We have examined by immunocytochemistry, Western blots, and BrUTP microinjection the dynamics of major nucleolar proteins during the first cycles of mouse embryogenesis, in relation to rDNA transcription sites and coilin, a marker of Cajal bodies. We show that: (1) the reinitiation of rDNA transcription occurs at the two-cell stage, 44-45 h after hCG injection (hphCG), at the surface of the nucleolar precursor bodies (NPBs), where the RNA polymerase I (pol I) transcription complex is recruited 4-5 h before; (2) the NPBs are not equal in their ability to support recruitment of pol I and rDNA transcription; (3) maternally inherited fibrillarin undergoes a dynamic redistribution during the second cell stage, together with coilin, leading to the assembly of the Cajal body around 40 hphCG; and (4) the pol I complex is first recruited to the Cajal body before reaching its rDNA template. We also find that fibrillarin and B23 are both directly assembled around NPBs prior to ongoing pre-rRNA synthesis. Altogether, our results reveal a role of the Cajal bodies in the building of a functional nucleolus.
Zatsepina
Olga
O
A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119992, Moscow, Russia.
Baly
Christine
C
Chebrout
Martine
M
Debey
Pascale
P
D000818:Animals; D015153:Blotting, Western; D002466:Cell Nucleolus; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000235:genetics; D020541:Coiled Bodies; D004275:DNA, Ribosomal / Q000235:genetics; D004622:Embryo, Mammalian / Q000378:metabolism / Q000648:ultrastructure*; D047108:Embryonic Development; D005260:Female; D018392:Genomic Imprinting; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics; D011247:Pregnancy; D012318:RNA Polymerase I / Q000378:metabolism; D012335:RNA, Ribosomal / Q000096:biosynthesis; D014158:Transcription, Genetic
D002868:Chromosomal Proteins, Non-Histone; D004275:DNA, Ribosomal; D009687:Nuclear Proteins; D012335:RNA, Ribosomal; C047458:fibrillarin; C068921:p80-coilin; D012318:RNA Polymerase I