Background: Mammalian early embryogenesis is characterized by drastic alterations of gene expression patterns due to a course of metabolic and structural changes known as the zygotic gene activation. This crucial period of early development was studied in detail on the molecular but not on the ultrastructural level. Nuclear distribution of some essential components of gene expression machinery including mRNA export factors is poorly known.
Methods: In the present work, the distribution of Y14, Aly and NXF1/TAP and the colocalization of these proteins with actin were studied in mouse embryo nuclei during ZGA using double indirect immunofluorescent microscopy.
Results: Redistribution of studied proteins between the nuclei and cytoplasm as well as within the nucleoplasm occurs during ZGA progress. Colocalization of these proteins with nuclear actin is being intensified while ZGA is carried out. We revealed two types of colocalization zones between actin and mRNA export factors: (i) RNase-sensitive zones in the nucleoplasm and (ii) DNase-sensitive zones in the vicinity of nucleolus precursor bodies. The latter zones increased in number and size after artificial suppression of transcription. We suggest these different areas of colocalization between actin and mRNA export factors correspond to the molecular pools with different functions. Some molecules may be involved in mRNA posttranscriptional metabolism, whereas other molecules disengaged from this process are deposited at the periphery of nucleolar precursor bodies.
Conclusions: Distribution patterns of studied mRNA export factors depend on the transcriptional status of the embryo.
Keywords: cell nucleus, mouse embryos, mRNA export, nuclear actin, zygotic gene activation