E. Nguyen et al., IMMUNOFLUORESCENT LOCALIZATION OF ACTIN IN RELATION TO TRANSCRIPTION SITES IN MOUSE PRONUCLEI, Molecular reproduction and development, 50(3), 1998, pp. 263-272
Previous biochemical and morphological studies have shown the presence
of actin in the nucleus of different cell types where its role remain
s unclear. In this work, through fluorescence microscopy we studied th
e localization of actin in the nuclei of early mouse embryos with part
icular attention to its possible involvement in the onset of transcrip
tion occurring at the late one-cell stage. Fluorescent labelling of em
bryo sections showed that nuclear actin is abundant, in a non-filament
ous state, in the whole nucleoplasm excluding the nucleolar precursor
bodies. Immunofluorescence on permeabilized embryos revealed that inso
luble nuclear actin accumulates in a few large aggregates in transcrip
tionally inert early one-cell embryos and progressively redistributes
into many small aggregates in transcriptionally active late one-cell e
mbryos. Interestingly, these actin aggregates clearly colocalize with
transcription sites. Treatment of late one-cell embryos with cytochala
sin D induces the formation of actin bundles network in the nucleoplas
m but has no apparent effect on the transcriptional activity. In addit
ion, the inhibition of transcription by oc-amanitin does not modify th
e nuclear actin distribution. Hence, there does not appear to be a dir
ect causal relationship between transcriptional activity and nuclear a
ctin organization at the one-cell stage although nuclear actin aggrega
tes appear associated with transcription sites. (C) 1998 Wiley-Liss, I
nc.