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Although it is generally accepted that nuclear
architecture is an important determinant of nuclear activity, it is
not clear whether cytoplasmic events, such as transcript localization
and cell polarity, are affected by this architecture. Characterization
of the nuclear architecture of the single-cell alga Chlamydomonas reinhardtii
revealed a polarized nucleus, with nuclear pore complexes preferentially
concentrated at the posterior side of the nucleus. Nuclear asymmetry
was greatly exaggerated during the upregulation of genes encoding flagellar
proteins, when nuclear pore complexes (NPCs) were observed to hyperpolarize
to the posterior side of the nucleus while heterochromatin polarized
to the anterior side. Interestingly, prior to deflagellation, the beta2-tubulin
gene was preferentially located in the posterior region of the nucleus,
and following deflagellation, beta2-tubulin transcripts accumulated
posteriorly in polysome-rich cytoplasmic regions adjacent to the highest
concentration of NPCs, suggesting a connection between nuclear architecture
and cytoplasmic transcript localization.
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