Presence of permanently activated signal transducers and activators of transcription in nuclear interchromatin granules of unstimulated mouse oocytes and preimplantation embryos.
We previously described that mouse oocytes and preimplantation embryos express the two subunits of interferon-gamma receptor. We now report that, despite the presence of STAT1 (signal transducer and activator of transcription 1) at both the mRNA and protein levels, interferon gamma (IFNgamma) as well as IFNalpha are unable to trigger massive nuclear translocation of STAT1 in these cells, even at high cytokine concentrations. Conversely, nuclear accumulation of STAT1 was readily observed in murine L929 somatic cells under the same conditions. However, in the absence of any stimulation, both tyrosine (Y701p) and serine (S727p) phosphorylated forms of STAT1 were already detected in the nuclei of oocytes and early embryos. Phosphorylated STAT1 appeared concentrated in large nuclear dots, which were identified by indirect immunofluorescence and electron microscopy as clusters of interchromatin granules (IGCs or speckles). A similar distribution was also observed for the serine (S727p) phosphorylated form of STAT3 as well as for tyrosine (Y689p) phosphorylated STAT2. Western blot analysis confirmed that STAT factors present in mouse oocytes are predominantly phosphorylated. In parallel, we showed that the transcription of two IFNgamma-target genes, namely interferon regulatory factor-1 (IRF-1) and suppressor of cytokine signaling-1 (SOCS-1) is indeed increased in two-cell embryos in response to IFNgamma. Altogether, our results suggest that, despite the lack of massive nuclear accumulation of STAT1 in response to exogenous IFNs and the permanent presence of phosphorylated STATs in the nucleus, JAK/ STAT pathways are functional during early development.
Truchet
Sandrine
S
USM 503 MNHN, UMR 8646 CNRS-MNHN, U565 INSERM, Département Régulation, Développement et Diversité Moléculaire, Muséum National d'Histoire Naturelle, 75005 Paris, France. sandrine.truchet@ibpc.fr
Chebrout
Martine
M
Djediat
Chakib
C
Wietzerbin
Juana
J
Debey
Pascale
P
D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D050856:Interferon Regulatory Factor-1; D016898:Interferon-alpha / Q000502:physiology; D007371:Interferon-gamma / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009865:Oocytes / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011247:Pregnancy; D021381:Protein Transport / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D013347:Subcellular Fractions / Q000378:metabolism; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D015533:Transcriptional Activation
D002352:Carrier Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D050856:Interferon Regulatory Factor-1; D016898:Interferon-alpha; C494258:Irf1 protein, mouse; D010750:Phosphoproteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; C491590:Socs1 protein, mouse; C494080:Stat1 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D007371:Interferon-gamma