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Many Routes Lead to the Pole Nidulans and the Fission Yeast Schizo.Mc­ Charomyces Pombe, Genes Required for the Caroline E

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Many Routes Lead to the Pole Nidulans and the Fission Yeast Schizo.Mc­ Charomyces Pombe, Genes Required for the Caroline E NEWS AND VIEWS remaining material. One intriguing pro­ planets and under the sea, and especially One of the most surprising has emerged posal (R. F. Scott, California Institute of of the artificially triggered Soviet geo­ from the study of genes concerned with Technology) was that a 10-m diameter, technical landslides, will shed new light another process associated with the pole 1,000 g geotechnical centrifuge would on this vexing question. It is clear that body, namely, the movement of nuclei permit model experiments on dynam­ Western geoscientists have much to gain towards one another during karyogamy. ically scaled analogues of natural large from cooperation with our Soviet counter­ One of these, KARI, encodes a pole-body landslides. parts in the new spirit of glasnost. D component of unknown function 111 but In spite of the flood of new data on giant another, KAR3, has been shown to landslides, the fundamental cause of their H. J. Me/ash is in the Lunar and Planetary encode a homologue of the microtubule 11 mobility is still far from understood. It is Laboratory and Department of Geosciences, motor protein kinesin • This colocalizes hoped that the new opportunities for the University of Arizona, Tucson, Arizona 85721, with the KARI product at the outer sur­ study of their deposits both on other USA. face of the pole body during conjugation CELL BIOLOGY-------------------- but resides at the inner face during mitosis (M. Rose, personal communication). In the filamentous fungus Aspergillus Many routes lead to the pole nidulans and the fission yeast Schizo.mc­ charomyces pombe, genes required for the Caroline E. Alfa and Jeremy S. Hyams proper duplication of the pole body at mitosis also encode homologues of kine­ MICROTUBULES in cells do not arise at morphology and microtubule-nucleating sin" 11. Unlike the pole bodies in S. cerevi­ random. Rather, their organization into characteristics, were used to raise a siae, those in A. nidulans and S. pombe arrays such as the mitotic spindle is battery of monoclonal antibodies which probably act as microtubule organizing choreographed by structures known as recognized three components of relative centres only in mitosis - the timing of microtubule organizing centres, which molecular mass 110,000, 90,000 and their activation coincides with the phos­ were first recognized over 20 years ago', 80,000 (M, 110K, 90K and 80K). The asso­ phorylation of a subset of pole body and which influence the dynamic proper­ ci:Hion of these proteins with the pole proteins" and the appearance at the pole ties and structural integrity body of the two elements of the mitotic of the polymers assembled kinase, cdc2 and its regulatory cyclin sub­ onto them. The purification unit". How (or even if) these modifica­ of organizing centres in bio­ tions relate to the ability of the pole body ~:~:.-\i ~ i' to assemble microtuhules is not known. chemically useful amounts +---- 90K component has proved to be incredibly >-{ Outer plaque --+ _. - But it is tempting to speculate that the link ~ Intermediate li ne ~ difficult because they are 3 is provided by y-tubulin'", which was first small and generally there is found at the pole bodies of A. nidulans hut only one in each cell. But i Nuc~ee:1:~;:~:~;;Jfh·-,,-, , , i : ,-~~~} 1!g~ ~~~~~~:~: which is now thought to be a unique ·a Inner plaque ,- : : • ', , , but ubiquitous component of microtubule now, writing in the latest Cl) .- , , , •, ', issue of Journal of Cell , ,' , : ; , , , , 80K component organizing centres"". The availability of Biology', Rout and Kilmar­ methods to purify spindle pole bodies tin report the isolation and / and of specific probes to a number of characterization of a par- Chromosomal microtubules their component proteins will doubtless ticularly well-studied micro- Pole to pole microtubules - help investigations into these aspects of tubule organizing centre, Diagram of the localizations of the spindle pole body and the pole-body function. Equally clearly, the spindle pole body of the spindle components (from ref. 2). routes to the function of microtuhule budding yeast Saccharomyces cerevisiae. body, initially confirmed by immuno- organizing centres from several directions The spindle pole body of S. cerevisiae is fluorescence light microscopy, was more will continue to converge at the poles. D a three-layered disk embedded in the accurately defined by immunogold elec­ nuclear envelope. During interphase, tron microscopy. The 11 OK species resides Caroline E. Alfa and Jeremy S. Hyams are in microtubules extend from its outer, cyto- between the pole body's central and inncr­ the Department of Biology, University College plasmic face into the growing bud. As most layers: because of its distance from London, Gower Street. London WC1E 68T, UK. cells enter mitosis, the pole body replicates the microtubule ends, it is likely to be a 1. Pickett-Heaps, J.D. Cytob1os3. 257-280 (1969). and about 20 microtubules polymerize structural component rather than being 2. Rout. M.P. & Kilmartin. J.V. J. Cell 810/. 111, 1913- onto the inner, intranuclear surface of involved in microtubule nucleation. On 1927 (1990). 3. Byers, B. & Goetsch, L. J. Bact.124, 511-523 (1975). each daughter, the two sets interdigitating the other hand, the 90K species localizes 4. Peterson. J.B. & Ris, H.J. Cell Sci. 22, 219-242 to form the mitotic spindle''. The yeast at the pole body's two faces (from which (1976) 5 Baum, P., Furlong, C. & Byers, B. Proc. natn. Acad. Sci. spindle pole body is an attractive model microtubules grow) and is therefore a U.S.A 83, 5512-5518 (1986). for the function of microtubule organizing potential regulator of microtubule assem­ 6 Baum, P , Yip, C., Goetsch. L. & Byers. B. Malec. cell. centrcs because mutants affecting its bly (see figure). The 80K protein has a Biol. 8. 5386-5397 (1988) 7. Uzawa, S. eta/. Ce/162. 913-925 (1990) structure, replication and copy number somewhat different distribution, and 8. Hyams, J.S. & Borisy, G.G. J. Cell Biol. 78, 401-414 have been isolated'-'. Moreover, crudely appears to be associated with the regions (1978). 9 Byers, B .. Shriver. K. & Goetsch. L. J. Cell Sci. 30. isolated pole bodies retain their capacity of spindle microtubules close to the poles 331-352 (1978). to nucleate microtubule assemblv in rather than with the pole body itself. 10. Rose. M.D. & Fink. G.R. Cel/48, 1047-1060 (1987). 11 Melun. P.B. & Rose, M.D. Ce//60.1029-1041 (1990). vitro·'". But nothing is known about "their Although these findings do not directly 12 Enos, A.-P. & Morris. N.R. Ce//60. 1019-1027 (1990). biochemistry, nor of the cell-cycle regu- define a role for the proteins concerned, 13. Hagan, I. & Yanagida. M. Nature 347. 563-566 lation of their microtubule-nucleating antibodies against them provide a route to (1990). 14 Engle. D.B .. Doonan. J.H & Morris. N.R. Cell Motil functions. the cloning and manipulation of the cor- Cytoskel.10. 432-437 (1988). Rout and Kilmartin released spindle responding genes and a description of 15 Alfa. CE., Ducommun. B .. Beach. D. & Hyams. J.S Nature 347, 680-682 (1990). pole bodies from highly purified nuclei their function in vivo is doubtless not too 16 Oakley, C.E. & Oakley. B.R. Nature 338. 662-664 using a combination of detergent and far away. This is particularly timely given (1989) 17. Oakley. B.R. , Oakley, C.E .. Yoon. Y &Jung, M. Ce//61, DNase I in low salt conditions. The result- a number of other recent insights into the 1289-1301 (1990). ing preparations, which retain their in vivo spindle pole body from less direct routes. 18 Tanaka. H. etal.J. Cel/Biol.111. 412a (1990). 484 NATURE · VOL 348 · 6 DECEMBER 1990 .
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