CSM News Electronic Edition Volume 5, number 15 November 18, 1995 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmsbio.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web at the URL "http://worms.cmsbio.nwu.edu/dicty.html" ===================== Positions Available ===================== Two APA(I) scholarship s ($19,000 p/a tax free) are available for the following PhD projects:- 1. Role of cell walls in osmotolerance in industrial yeasts: This project will involve the cultivation of yeast, isolation and characterisation of yeast cell walls, separation of cell wall proteins by 2-D gel electrophoresis and gene cloning (Dr. Helena Nevalainen in association with Burns Philp). 2. Characterisation of low abundance proteins in Proteome studies: This project involves use of the Gradiflow preparative separation system to concentrate for 2-D gel analysis proteins of specific isoelectric point (Prof. Keith Williams and Dr. Andrew Gooley in association with Gradipore Ltd.). The projects are available from early 1996 for 3 years and will be located at Macquarie University , School of Biological Sciences. Interested students with a relevant honours or masters degree are invited to contact Susan Graves on Ph 850 8212, Fax 850 8174 or email: sgraves@rna.bio.mq.edu.au. Applications for these positions, including a C.V. and academic record will close on Wednesday December 13 1995. Professor Keith Williams School of Biological Sciences Macquarie University email keith.williams@mq.edu.au =========== Abstracts =========== MECHANICAL PERTURBATION ELICITS A PHENOTYPIC DIFFERENCE BETWEEN DICTYOSTELIUM WILD-TYPE CELLS AND CYTOSKELETAL MUTANTS Ludwig Eichinger*, Bernd Koeppel$, Angelika A. Noegel$, Michael Schleicher*", Manfred Schliwa*, Kees Weijer^, Walter Witke& and Paul A. Janmey& *Inst. Zellbiol., LM-Univ. 80336 Muenchen, FRG; $MPI f. Biochem., 82152 Martinsried, FRG; ^Zoolog. Inst., LM-Univ. 80333 Muenchen, FRG; &Exp. Med. Div., Brigham and Women's Hosp., Harvard Med. School, Boston, MA 02115, USA "corresponding author Biophysical Journal, in press Abstract To determine the specific contribution of cytoskeletal proteins to cellular viscoelasticity we performed rheological experiments with Dictyostelium discoideum wild-type cells (AX2) and mutant cells altered by homologous recombination to lack a-actinin (AHR), the ABP120 gelation factor (GHR), or both of these F-actin crosslinking proteins (AGHR). Oscillatory and steady flow measurements of Dictyostelium wild-type cells in a torsion pendulum showed that there is a large elastic component to the viscoelasticity of the cell pellet. Quantitative rheological measurements were performed with an electronic plate- and-cone rheometer which allowed determination of G', the storage shear modulus, and G", the viscous loss modulus, as a function of time, frequency, and strain respectively. Whole cell viscoelasticity depends strongly on all three parameters, and comparison of wild-type and mutant strains under identical conditions generally produced significant differences. Especially stress relaxation experiments consistently revealed a clear difference between cells that lacked a-actinin as compared to wild-type cells or transformants without ABP120 gelation factor, indicating that a-actinin plays an important role in cell elasticity. Direct observation of cells undergoing shear deformation was done by incorporating a small number of AX2 cells expressing the green fluorescent protein of Aequorea victoria and visualizing the strained cell pellet by fluorescence and phase contrast microscopy. These observations confirmed that the shear strain imposed by the rheometer does not injure the cells, and that the viscoelastic response of the cell pellet is due to deformation of individual cells. -------------------------------------------------------------------- Protection Against Osmotic Stress by cGMP-Mediated Myosin Phosphorylation Hidekazu Kuwayama1, Maria Ecke2, Guenther Gerisch2, Peter J.M. Van Haastert1* 1. Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands 2. Max-Planck-Institut fuer Biochemie, D-82143 Martinsried, Germany * To whom correspondence should be addressed. Science, in press Abstract Conventional myosin is universally utilized as a generator of motive force in eukaryotic cells. Analysis of mutants of the microorganism Dictyostelium discoideum revealed that myosin also provides resistance against high external osmolarities. An osmo-induced increase of intracellular cGMP was shown to mediate phosphorylation of three threonine residues on the myosin tail which caused a relocalization of myosin required to resist osmotic stress. This reorganization of myosin allowed cells to adopt a spherical shape and may provide physical strength to withstand extensive cell- shrinkage in high osmolarities. -------------------------------------------------------------------- [End CSM News, volume 5, number 15]