SummaryThe role of the complex network of the ubiquitin-like modifier SumO in fungal development was analysed. SumO is not only required for sexual development but also for accurate induction and light stimulation of asexual development. The Aspergillus nidulans COMPASS complex including its subunits CclA and the methyltransferase SetA connects the SumO network to histone modification. SetA is required for correct positioning of aerial hyphae for conidiophore and asexual spore formation. Multicellular fungal development requires sumoylation and desumoylation. This includes the SumO processing enzyme UlpB, the E1 SumO activating enzyme AosA/UbaB, the E2 conjugation enzyme UbcN and UlpA as major SumO isopeptidase. Genetic suppression analysis suggests a connection between the genes for the Nedd8 isopeptidase DenA and the SumO isopeptidase UlpA and therefore a developmental interplay between neddylation and sumoylation in fungi. Biochemical evidence suggests an additional connection of the fungal SumO network with ubiquitination. Members of the cellular SumO network include histone modifiers, components of the transcription, RNA maturation and stress response machinery, or metabolic enzymes. Our data suggest that the SumO network controls specific temporal and spatial steps in fungal differentiation.

Nuclear migration depends on microtubules, the dynein motor complex, and regulatory components like LIS1 and NUDC. We sought to identify new binding partners of the fungal LIS1 homolog NUDF to clarify its function in dynein regulation. We therefore analyzed the association between NUDF and NUDC in Aspergillus nidulans. NUDF and NUDC directly interacted in yeast two-hybrid experiments via NUDF's WD40 domain. NUDC-green fluorescent protein (NUDC-GFP) was localized to immobile dots in the cytoplasm and at the hyphal cortex, some of which were spindle pole bodies (SPBs). We showed by bimolecular fluorescence complementation microscopy that NUDC directly interacted with NUDF at SPBs at different stages of the cell cycle. Applying tandem affinity purification, we isolated the NUDF-associated protein BNFA (for binding to NUDF). BNFA was dispensable for growth and for nuclear migration. GFP-BNFA fusions localized to SPBs at different stages of the cell cycle. This localization depended on NUDF, since the loss of NUDF resulted in the cytoplasmic accumulation of BNFA. BNFA did not bind to NUDC in a yeast two-hybrid assay. These results show that the conserved NUDF and NUDC proteins play a concerted role at SPBs at different stages of the cell cycle and that NUDF recruits additional proteins specifically to the dynein complex at SPBs.Nuclear movement is a precisely regulated developmental process that is of special importance in highly elongated cells, like neurons or the linear hyphae of filamentous fungi. These cell types grow by apical extension and the subsequent longrange translocation of nuclei into the leading process. In neurons, this nuclear movement can be followed by the retraction of the trailing process so that active cell migration, so-called nucleokinesis, is achieved (37).Important aspects of nuclear migration were elucidated by genetic analyses performed with the amenable fungal model organism Aspergillus nidulans. In a screen for nuclear migration mutant strains, the genes nudA, nudC, nudF, and nudG were discovered (60). The human homolog to nudF is Lis1, the haploinsufficiency of which causes autosomal-dominant lissencephaly type 1 (10). Mutations of Lis1 lead to retarded neuronal migration to the cerebral cortex, creating disorganized cortical layers. This defective brain development causes mental retardation, epilepsy, and early death. The characterization of LIS1-interacting proteins showed that LIS1 also plays a role in other diseases, like schizophrenia and neuronal degeneration (45). While during the nucleokinesis of neurons a single nucleus is transported through the cytoplasm, fungal growth is characterized by the distribution of multiple nuclei along filamentous hyphae. Mutations of nudF prevent the active transport of nuclei out of the spore into the growing hyphae, leading to the accumulation of nuclei near the spore remnant and only incidental nuclear motion, which leads to slow growth and excessive hyphal branching (61). In addition, nuclear migration is important for the development of asex...