Observation of EGFP-visualized nuclei and distribution of vacuoles in Aspergillus oryzae arpA null mutant.

The arpA gene encoding Arp1 (actin-related protein) was previously cloned and characterized from Aspergillus oryzae. Phenotypes of the arpA null mutant indicate its requirement for normal nuclear distribution and morphology of conidiophores. In this study, we further characterized the function of the arpA gene in distribution of organelles. For further analysis of nuclear migration in living cells, an expression system consisting of a fusion protein of Aspergillus nidulans histone H2B and EGFP (H2B::EGFP) was used. This demonstrated diminished hyphal-tip growth rate and inefficient nuclear transport to apical regions in the arpA null mutant. Expression of H2B::EGFP also revealed an increase in the nuclear number of each conidium in the arpA null mutant, implicating a role for the arpA gene in controlling the nuclear movement into conidia. Furthermore, staining of vacuoles of the arpA null mutant with CMAC (cell tracker blue) suggested that the arpA gene is required for proper vacuolar distribution in addition to its role in normal nuclear distribution.