Chlamydomonas is a highly polarized cell that offers a unique system to study changes in nuclear shape. Loss of this algae's flagella (after certain chemical or mechanical stresses) causes the nucleus to adopt a pear-like shape and take an anterior position in the cell, nearer where the flagella once sat.
García-Blanco wondered whether sites of transcription of the β tubulin gene, which is strongly up-regulated upon deflagellation, move closer to the flagella to expedite their rebuilding. Immunocytochemistry and electron microscopy revealed that the β tubulin gene did not move from its posterior nuclear position. But the experiments did uncover an unexpected asymmetry of nuclear pore complex distribution.
Even in flagellated cells, the complexes were preferentially located at the posterior side of the nucleus, near a polysome-rich portion of the cytoplasm. Deflagellation further exaggerated the asymmetry. The changes correlated with accumulation of β tubulin transcripts near the concentrated translation machinery. Says García-Blanco, “what we don't know yet is what causes what.” He hopes to find mutants that uncouple events following deflagellation to determine whether nuclear architecture directly targets mRNA cytoplasmic localization. ▪