Coprinus cinereus exhibits conspicuous nuclear movement and precise nuclear positioning during its life cycle. Examples include transhyphal migration of nuclei in compatible mating giving rise to a dikaryon, nuclear positioning relative to the hyphal apex in the dikaryon, the close spacing in interphase and conjugate division of the two nuclei in the dikaryon, and the migration of nuclei from the basidium into developing spores. We have investigated the roles of the cytoskeleton in these processes using cytoskeleton mutants as well as fluorescence microscopy. Some of the α1- and β1-tubulin mutations examined blocked nuclear migration in dikaryosis and disturbed nuclear pairing in the dikaryon, demonstrating that microtubules are involved in these processes. The same mutations, however, did not affect the positioning of nuclei in interphase nor in conjugate division in the dikaryon, nor the migration of nuclei into the developing spores. Immunofluorescence microscopy revealed that these mutations inhibit the formation of asters of the mitotic apparatus in conjugate division, providing evidence against direct involvement of astral microtubules in nuclear movement during conjugate division. Actin was concentrated in hyphal regions where the nuclei sit in early phases of conjugate division, suggesting the involvement of actin in conjugate division. Key words: Coprinus cinereus, dikaryon, nuclear movement, microtubules, aster, actin.
Break of symmetry in regenerating tobacco protoplasts is independent of nuclear positioning
