NUCLEAR TRANSLOCATION AND CARBOXYL-TERMINAL DOMAIN PHOSPHORYLATION OFRNA-POLYMERASE-II DELINEATE THE 2 PHASES OF ZYGOTIC GENE ACTIVATION IN MAMMALIAN EMBRYOS
S. Bellier et al., NUCLEAR TRANSLOCATION AND CARBOXYL-TERMINAL DOMAIN PHOSPHORYLATION OFRNA-POLYMERASE-II DELINEATE THE 2 PHASES OF ZYGOTIC GENE ACTIVATION IN MAMMALIAN EMBRYOS, EMBO journal, 16(20), 1997, pp. 6250-6262
In mammalian embryos, zygotic gene transcription initiates after a lim
ited number of cell divisions through a two-step process termed the zy
gotic gene activation (ZGA), Here we report that RNA polymerase IT und
ergoes major changes in mouse and rabbit preimplantation embryos durin
g the ZGA, Tn transcriptionally inactive unfertilized oocytes, the RNA
polymerase II largest subunit is predominantly hyperphosphorylated on
its carboxy-terminal domain (CTD), The CTD is markedly dephosphorylat
ed several hours after fertilization, before the onset of a period cha
racterized by a weak transcriptional activity. The largest subunit of
RNA polymerase II then lacks immunological and drug-sensitivity charac
teristics related to its phosphorylation by the TFIIH-associated kinas
e and gradually translocates into the nuclei independently of DNA repl
ication and mitosis, A phosphorylation pattern of the largest subunit,
close to that observed in somatic cells, is established in both mouse
and rabbit embryos at the stage when transcription becomes a requirem
ent for further development (respectively at the 2- and 8/16-cell stag
e), As these events occurred in the presence of actinomycin D, the nuc
lear translocation of RNA polymerase II and the phosphorylation of the
CTD might be major determinants of ZGA.