A. nidulans has substantial advantages over other eukaryotic systems for studying cytoplasmic dynein. Because nuclear migration into the mycelium is an absolute prerequisite for fungal growth, mutants in which nuclear migration is blocked can be easily identified. The mutants can then be used to clone and characterize the genes involved in this process. Four genes, nudA, nudC, nudF, and nudG were previously cloned and characterized. nudA and nudG encode heavy and light chains of cytoplasmic dynein, nudC and nudF encode putative dynein regulatory genes. My colleagues, Dr. Xiang and Dr. Efimov undertook new genetic screens to characterize additional genes that encode proteins involved in dynein mediated motility. Dr. Xiang with the help of Wenshi Chuo identified a large number of new nud-like mutants and sorted them genetically to identify seven new genes. She cloned two of them by DNA-mediated complementation of their growth defect. One encodes a new cytoplasmic dynein intermediate chain. The other encodes the ARP1 actin-related component of dynantin, thereby implicating the dynactin complex as necessary for nuclear migration. 

Although deletion of the nudA gene severely inhibits nuclear migration and colony growth, it is not lethal, suggesting that there may be a backup motility system. To identify genes involved in such a system Dr. Vladimir Efimov carried out a search for mutations synthetically lethal with dynein heavy chain mutations. He found nine such genes (sldA-I) and cloned and characterized four of them. SldA annd sldB encode spindle checkpoint genes, consistent with the fact that cytoplasmic dynein is required for anaphase B in eukaryotes. SldC and sldI encode proteins involved in DNA metabolism. Dr. Efimov has also carried out a screen for multicopy suppressors of a ts nudF mutation that has led to the identification of a new nud gene, nudE, which he is in the process of characterizing. 

NudF resembles the LIS-1 gene required for normal human brain development. Last year in collaboration with Dr. Guy Caldewell, a postdoctoral fellow in Dr. Martin Chalfie's laboratory at Columbia University, Dr. Angus Dawe cloned and characterized a homolog of nudF from the worm C. elegans and showed by complementing a ts nudF mutant of A. nidulans that it is functionally conserved. This year Drs. Dawe and Caldwell cloned a gene, nudCfrom C. elegans that  in mammalian systems interacts with a nudF homolog known as LIS-1 that is required for brain development.  C. elegans GFP-NUDC and GFP-NUDF reporter genes were constructed and introduced into the worm genome. Both genes are expressed in specific C. elegans neurons. Dr. Dawe continues his work to characterize the sndD suppressor of nudD previously identified by Dr. Deborah Willins. 

Dr. Chiyoung Ahn has S-tagged nudF and achieved a two step purification to homogeneity by binding to RNAse I and molecular sieving. Preliminary characterization suggests that the purified protein is either a disulfide-linked homodimer or homotrimer of the NUDF protein. 

Recent Publications
up

Cunniff, J., Chiu, Y.H., Morris, N.R. and Warrior, R. (1997) Characterization of DnudC, the Drosophila homolog of an
Aspergillus gene that functions in nuclear motility. Mech Dev. 66:55-68. 

Chiu, Y.H., Xiang, X., Dawe, A.L. and Morris, N.R. (1997) Deletion of nudC, a nuclear migration gene of Aspergillus
 nidulans, causes morphological and cell wall abnormalities and is lethal. Mol Biol Cell. 8:1735-49. 

Lies CM, et al.(1998) BIMA APC3, a component of the Aspergillus anaphase promoting complex/cyclosome, is required for a G2 checkpoint blocking entry into mitosis in the absence of NIMA function. J Cell Sci. 111:1453-65. 

Efimov, V.P. and Morris, N.R. (1998) A screen for dynein synthetic lethals in Aspergillus nidulans identifies spindle assembly checkpoint genes and other genes involved in mitosis. Genetics 149:101-16. 

Morris N.R, Efimov, V.P. and Xiang X. (1998) Nuclear migration, nucleokinesis  and lissencephaly. Trends Cell Biol. 8:467-70. 

Beckwith, S.M., Roghi, C.H., Liu, B and Morris, N.R. (1998) The "8 kD" cytoplasmic dynein light chain is required for nuclear migration and for dynein heavy chain localization in Aspergillus nidulans. J. Cell Biol. 143:1239-1247 

Xiang, X., Shuo, W., Efimov, V.P., and Morris, N.R. (1999) Isolation of a new set of Aspergillus nidulans mutants defective
in nuclear migration. Curr. Genet. 35:626-630.

Xiang, X. and Morris, N.R. (1999) Hyphal tip growth and nuclear migration. Curr. Opin. Microbiol. 2:636-40.

Morris, N.R. (2000) Nuclear migration: from fungi to the mammalian brain. J. Cell Biol.148:1097-101.

Xiang, X., Winkelmann, D. A., Zhuo, W. and Morris, N. R. (2000) Dynamics of cytoplasmic dynein in living cells and the
effect of a mutation in the dynactin complex actin-related protein arp1. Curr Biol.10:603-6.

Liu, B. and Morris, N.R. (2000) A spindle pole body-associated protein, snaD, affects septation and conidiation in Aspergillus
nidulans. Mol Gen Genet. 263:375-87.

Efimov, V.P. and Morris, N.R. (2000) The LIS1-related NUDF protein of Aspergillus nidulans interacts with the coiled coil
domain of the NUDE/RO11 protein. J Cell Biol.150:681-8.

Ahn, C .and Morris, N.R. (2001) NUDF, a Fungal Homolog of the Human LIS1 lissencephaly protein, functions as a dimer in
vivo. J. Biol. Chem.276:9903-9

Lawrence, C.J., Morris, N.R., Meagher, R.B., Dawe, R..K. (2001) Dyneins have run their course in plant lineage. Traffic
2:362-3.

Gongshe Han, Bo Liu, Jun Zhang, Wenqi Zuo, N. Ronald Morris and Xin Xiang (2001) The Aspergillus cytoplasmic dynein
heavy chain and NUDF localize to microtubule ends and affect microtubule Dynamics. Current Biology 11:719-24.