Microscopic analysis of Neurospora ropy mutants defective in nuclear distribution

Movement and distribution of nuclei in fungi has been shown to be dependent on microtubules and the microtubule-associated motor cytoplasmic dynein, N eurospora crassa mutants known as ropy are defective in nuclear distributio n. We have shown that three of the ro genes, ro-1, ro-3, and ro-4, encode s ubunits of either cytoplasmic dynein or the dynein activator complex, dynac tin, Three other ro genes, ro-7, ro-10, and ro-ll, are required for the int egrity or localization of cytoplasmic dynein or dynactin, In this report, w e describe a microscopic analysis of N, crassa ro mutants. Our results reve al that defects in germination of conidia, placement of septa, and mitochon drial morphology are typical of ro mutants. Two classes of cytoplasmic micr otubules are identified in wild-type and ro mutants. One class of microtubu les has no obvious association with nuclei while the other class of microtu bules connects spindle pole bodies of adjacent nuclei. The possible role of internuclear microtubule tracts in the movement and distribution of nuclei is discussed, (C) 1999 Academic Press.