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Paul Robert Fisher and the Microbial Cell Biology Group

|Photo of| Paul Fisher

email: P.Fisher@latrobe.edu.au
phone: +61-3-9479-2229
fax: +61-3-9479-1222

I am Professor of  Microbiology at La Trobe University here in Melbourne, Australia. I lecture to second year and third year science undergraduates and to 4th year (honours) students and I run the Microbial Cell Biology Laboratory . There are presently 3 Honours students, 6 postgraduate students (M.Sc/Ph.D.), a research assistant and myself working in the group. Our main research interest is the molecular genetics of signal transduction in the cellular slime mould Dictyostelium discoideum, one of a handful of non-mammalian model organisms recognized by the NIH for their importance in biomedical research. We study signal transduction during phototaxis and thermotaxis in the multicellular slug stage and discovered that these behaviours are highly sensitive to genetic defects affecting the mitochondria.

Dictyostelium discoideum is a cellular slime mould whose natural habitat is soil and leaf litter where it predates bacteria by phagocytosis, grows and divides by mitosis. You can hear more about it in a radio interview that took place on the 25th June 2000 (as a ca. 4 Mb mp3 file or a ca. 9 Mb wav file ) on "Einstein-A-Go-Go", the weekly Sunday science broadcast from the Melbourne community radio station 3RRR.

The Dictyostelium discoideum life cycle begins with differentiation of starving amoebae to a form where they become capable of synthesizing, secreting and being attracted by extracellular cAMP. The resulting aggregation process forms a multicellular migratory organism, the "slug", which migrates through a cellulose/protein extracellular matrix, the "slime sheath", that collapses behind to form a trail. Slugs are phototactic, thermotactic and weakly chemotactic. After a variable period of migration the slug stops and forms a fruiting body consisting, to a first approximation, of a droplet of spores supported by a tapered stalk and basal disc.

The behaviour and morphogenetic movements are controlled by the tip via what are believed to be extracellular tip activation and inhibition signals. The tip activation signal is probably carried by 3-dimensional scroll waves of cAMP emanating from the tip. The tip inhibition signal has been proposed to be carried by a small non-volatile, diffusible molecule (Slug Turning Factor, STF), and/or ammonia, and/or adenosine. Phototactic and thermotactic behaviour seem to be controlled by modulation of the tip activation/inhibition system. We are investigating the signal transduction pathways in slug behaviour using a combination of pharmacological, genetic, cell physiological and molecular biological approaches. Our recent work has revealed a protein signalling complex for phototaxis in which the participating proteins are assembled on a scaffold provided by the actin-binding protein filamin.

We discovered that signal transduction for phototaxis and thermotaxis in slugs is more sensitive to the presence of mitochondrial defects than other cellular activities such as growth and division. Thus phototaxis and thermotaxis are impaired by mitochondrial mutations created by plasmid insertions in a minority of the mitochondrial genomes in the cell. The same defects are observed when the folding of proteins in the mitochondria is impaired by antisense inhibition of the expression of chaperonin 60. Chaperonin 60 is encoded on a nuclear gene and is required for the proper folding of proteins in the mitochondria. Undersupply of chaperonin 60 therefore causes serious mitochondrial disease. The severity of the undersupply caused by antisense inhibition is determined by the number of copies of the antisense inhibition construct and this is different in every every cell line carrying the construct. This allows the generation of genetic dose-response curves relating phenotype to the severity of the underlying genetic defect. In addition to the phototaxis and thermotaxis defects, mitochondrial disease in Dictyostelium causes slow growth (without affecting the rate of uptake of nutrients by phagocytosis or pinocytosis), a misdirection of cells into the stalk differentiation (programmed cell death) pathway, and less efficient aggregation. All of the defects are a result of chronic activation of the cellular energy-sensing alarm protein AMPK. The Dictyostelium mitochondrial disease model thus suggests that the complex pathology of human mitochondrial disease might be explained partially by chronic AMPK signalling rather than an energy insufficiency  per se. This discovery resulted in my being awarded the Australasian Science Prize for 2007 and provides a completely new understanding of how mitochondrial dysfunction damages cells.You can hear more about this discovery in an interview conducted by Dr. Moira Gunn on May 7th, 2007 in a BioTech Nation radio broadcast of September 28th, 2007 and made available on line by ITConversations. A major research interest of the laboratory is therefore to study mitochondrial biogenesis and function and the roles of mitochondria in modulating cellular signal transduction pathways.

The third major project in the laboratory concerns intracellular Ca2+ signals. Using an assay based on expression in Dictyostelium of recombinant aequorin, a Ca2+-sensitive luminescent protein, we are able to measure cytosolic Ca2+ concentrations in a population of cells every 20 msecs, down to concentrations of about 25 nM to within a few nM. Using this assay we are studying signal transduction pathways involving intracellular Ca2+ signals initiated by various extracellular stimuli including the morphogen DIF and the chemoattractants cAMP and folic acid.

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Selected publications

  1. Fisher, P.R., Smith, E. and Williams, K.L. (1981). An extracellular chemical signal controlling phototactic behaviour by D. discoideum slugs. Cell 23, 799-807.
  2. Fisher, P.R. and Williams, K.L. (1982). Thermotactic behaviour by Dictyostelium discoideum slug phototaxis mutants. J. Gen. Microbiol. 128, 965-971.
  3. Fisher, P.R., Dohrmann, U. and Williams, K.L. (1984). Signal processing in Dictyostelium discoideum slugs. Modern Cell Biol. 3, 197-248.
  4. Darcy, P.K. and Fisher, P.R. (1989). A role for G-proteins and inositol phosphate signalling in Dictyostelium discoideum slug behaviour. J. Gen. Microbiol. 135, 1909-1915.
  5. Darcy, P.K. and Fisher, P.R. (1990). Pharmacological evidence for a role for cAMP signalling in Dictyostelium discoideum slug behaviour. J. Cell Sci. 96, 661-667.
  6. Fisher, P.R., Karampetsos, P.D., Wilczynska, Z. and Rosenberg, L.T. (1991). Oxidative metabolism and heat shock enhanced chemiluminescence in Dictyostelium discoideum. J. Cell Sci. 99, 741-750.
  7. Darcy, P.K., Wilczynska, Z. and Fisher, P.R. (1994). The role of cGMP in photosensory and thermosensory transduction in Dictyostelium discoideum. Microbiol. 140, 1619-1632.
  8. Darcy, P.K., Wilczynska, Z. and Fisher, P.R. (1994). Genetic analysis of Dictyostelium slug phototaxis mutants. Genetics 137, 977-985.
  9. Wilczynska, Z. and Fisher, P.R. (1994). Analysis of a complex plasmid insertion in a phototaxis-deficient transformant of Dictyostelium discoideum selected on a Micrococcus luteus lawn. Plasmid 32, 182-194.
  10. Barth, C., Wilczynska, Z., Pontes, L., Fraser, D.J. and Fisher, P.R. (1996). Efficient circularization in Escherichia coli of linear plasmid multimers from Dictyostelium discoideum genomic DNA. Plasmid 36, 86-94.
  11. McMahon, T.L., Wilczynska, Z., Barth, C., Fraser, D.J., Pontes, L. and Fisher, P.R. (1996). Replicon rescue: a novel strategy to clone the genomic DNA flanking insertions of integrating shuttle vector DNA. Nucleic Acids Research 24, 4096-4097.
  12. Schaap, P., Nebl, T. and Fisher, P.R. (1996). A slow sustained increase in cytosolic Ca2+ levels mediates stalk gene induction by differentiation inducing factor in Dictyostelium. EMBO J. 15, 5177-5183.
  13. Fisher, P.R. (1997). Genetics of phototaxis in a model eukaryote, Dictyostelium discoideum . Bioessays 19, 397-408.
  14. Wilczynska, Z., Barth, C. and Fisher, P.R. (1997). Mitochondrial mutations impair signal transduction in Dictyostelium discoideum slugs. Biochem. Biophys. Res. Comm. 234, 39-43.
  15. Nebl, T. and Fisher, P. R. (1997). Intracellular Ca2+ signals in Dictyostelium chemotaxis are mediated exclusively by Ca2+ influx. Journal of Cell Science 110, 2845-2853. Full text pdf file at J. Cell Science online.
  16. Fisher, P.R., Noegel, A.A., Fechheimer, M., Rivero, F., Prassler, J. and Gerisch, G. (1997). Photosensory and thermosensory responses in Dictyostelium slugs are specifically impaired by absence of the F-actin cross-linking gelation factor (ABP-120). Current Biology 7, 889-892.
  17. Barth, C., Fraser, D.J. and Fisher, P.R. (1998). Co-insertional replication is responsible for tandem multiple formation during plasmid integration into the Dictyostelium genome. Plasmid 39, 141-153.
  18. Barth, C., Fraser, D.J. and Fisher, P.R. (1998). A rapid, small scale method for characterization of plasmid insertions in the Dictyostelium genome. Nucleic Acids Research 26, 3317-3318.
  19. Barth, C., Greferath, U., Kotsifas, M. and Fisher, P.R. (1999). Polycistronic transcription and editing of the mitochondrial small subunit (SSU) ribosomal RNA in Dictyostelium discoideum. Current Genetics 36, 55-61. Full text pdf file at Current Genetics on line.
  20. Schenk, P.W., Nebl, T., Fisher, P.R. and Snaar-Jagalska, B.E. (1999). A serpentine receptor-dependent, Gb- and Ca2+ influx-independent pathway regulates mitogen-activated protein kinase ERK2 in Dictyostelium. Biochem. Biophys. Res. Comm. 260, 504-509.
  21. Wilkins, A., Khosla, M., Fraser, D.J., Spiegelman, G.B., Fisher, P.R., Weeks, G. and Insall, R.H. (2000). Dictyostelium RasD is required for normal phototaxis, but not differentiation or pattern formation. Genes & Development 14, 1407-1413. Full text pdf file at Genes & Development on line.
  22. Fisher, P.R. (2001). Genetic analysis of phototaxis in Dictyostelium. Chapter 19 in Photomovement. ESP Comprehensive Series in Photosciences Vol 1.pp. 519-559. Edited by D-P. Hader & M. Lebert. Elsevier Science Ltd. Amsterdam. Preprint Version (3 Mbyte pdf file) made available with permission from Elsevier Science Ltd.
  23. Barth C., Greferath U., Kotsifas M., Tanaka Y., Alexander S., Alexander H. and Fisher P.R. (2001). Transcript mapping and processing of mitochondrial RNA in Dictyostelium discoideum. Current Genetics 39, 355-364. First published On Line 21, June 2001. DOI 10.1007/s002940100196. Full text at Current Genetics.
  24. Fisher, P.R. (2002). Phototaxis: microbial. In Encyclopedia of Life Sciences. Nature Publishing Group. London.
  25. Kotsifas, M., Barth, C., Lay, S.T., de Lozanne, A. & Fisher, P.R. (2002). Chaperonin 60 and mitochondrial disease in Dictyostelium. J. Muscle Research and Cell Motility. 23, 839-852.
  26. Nebl, T., Kotsifas, M., Schaap, P. & Fisher, P.R. (2002). Multiple pathways connect chemoattractant receptors and Ca2+ channels in Dictyostelium. J. Muscle Research and Cell Motility. 23, 853-865.
  27. Gilson, P.R., Yu, X-C., Hereld, D, Bareth, C., Savage, A., Kiefel, B., Lay, S., Fisher, P.R., Margolin, W., & Beech, P.L. (2003). Two Dictyostelium orthologs of the prokaryotic cell division protein, FtsZ, localize to mitochondria and are required for the maintenance of normal mitochondrial morphology. Eukaryotic Cell 2, 1315-1326. ( Full text)
  28. Wilkins, A., Szafranski, K., Fraser, D.J., Bakthavatsalam, D., Muller, R., Fisher, P.R., Glockner, G., Eichinger, L., Noegel, A. & Insall, R.H. (2005). The Dicytostelium genome encodes numerous RasGEFS with multiple biological roles. BMC Genome Biology 6, R68.
  29. Fisher, P.R. (2005). Microbial development. In Encyclopedia of Molecular Cell Biology and Molecular Medicine Vol. 8. pp 289-342. Ed. R.A. Meyers. Wiley-VCH, Weinheim. Preprint version.
  30. Wilczynska, Z., Happle, K., Muller-Taubenberger, A., Schlatterer, C., Malchow, D. & Fisher, P.R. (2005). Release of Ca2+ from the endoplasmic reticulum contributes to Ca2+ signaling in Dictyostelium. Eukaryotic Cell. 4, 1513-1525.
  31. Fisher, P.R. & Annesley, S.J. (2006). Slug phototaxis, thermotaxis and spontaneous turning behaviour. In "Dictyostelium discoideum Protocols." Methods in Molecular Biology. 346, 137-170. Ed. L Eichinger & F. Rivero. Humana Press.
    Accompanying directional statistics package for use in the R environment for statistical computing - DirStats
  32. Fisher, P.R. & Wilczynska, Z. (2006). The ER contribution to cytosolic Ca2+ signals in Dictyostelium depends upon extracellular Ca2+. FEMS Letters 257, 268-277.
  33. Ahmed A.U., Beech, P.L., Lay, S.T., Gilson, P.R.  & Fisher, P.R. (2006). Import-associated translational inhibition - novel in vivo evidence for cotranslational protein import into Dictyostelium mitochondria. Eukaryotic Cell 5, 1314-1327.
  34. Bandala-Sanchez, E., Annesley, S.J. and Fisher, P.R. (2006). A phototaxis signalling complex in Dictyostelium discoideum. European Journal of Cell Biology. 85, 1099-1106.
  35. Bokko, P.B., Francione, L., Bandala-Sanchez, E., Ahmed, A.U., Annesley, S.J., Huang, X., Khurana, T., Kimmel, A.R. & Fisher, P.R. (2007). Diverse Cytopathologies in Mitochondrial Disease Are Caused by AMPK Signalling.  Molecular Biology of the Cell 18, 1874-1886. Published March 1, 2007 as 10.1091/mbc.E06-09-0881 (Copyright American Society for Cell Biology).  (Supplemental videos. Copyright American Society for Cell Biology).
  36.  Barth, C., Le, P. & Fisher, P.R. (2007). Mitochondrial biology and disease in Dictyostelium. Int. Rev. Cytology 263, 207-252.
  37. Annesley, S.J.,  Bandala-Sanchez, E., Ahmed, A.U. & Fisher, P.R. (2007). Filamin repeat segments required for photosensory signalling in Dictyostelium discoideum. BMC Cell Biology 8,48 .
  38. Ludlow, M.J., Traynor, D., Fisher, P.R. & Ennion, S.J. (2008). Purinergic-mediated Ca2+ influx in Dictyostelium discoideum. Cell Calcium. 44, 567-579.
  39. Francione, L., Smith, P.K., Accari, S.L., Taylor, P.E., Bokko, P.B., Bozzarro, S., Beech, P.L. & Fisher, P.R. (2009). Legionella pneumophila multiplication is enhanced by chronic AMPK signalling in mitochondrially diseased Dictyostelium cells. Disease Models and Mechanisms. In Press.
  40. Ahmed, A.U. & Fisher, P.R. (2009). Import of nuclear-encoded mitochondrial proteins: a cotranslational perspective. International Review of Cell and Molecular Biology 273, 49-68.
  41. Annesley, S.J. & Fisher, P.R. (2009). Dictyostelium discoideum – a model for many reasons. Mol. Cell. Biochem. Published Online 22 April 2009. DOI 10.1007/s11010-009-0111-8.

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You can get more information about Dictyostelium discoideum and the people who work with it from the Dictyostelium World Wide Web Site.

Other sites of interest are:

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Experimental Protocols

Some of our protocols:

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Created on 7-Jul-1995 18:54:25.15

Last modified on 30-May-2009 16:21:00.00

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