title: Shared, unique and redundant functions of three members of the class I myosins (MyoA, MyoB and MyoF) in motility and chemotaxis in Dictyostelium.
abstract: Most cell types express two distinct forms of myosin I, amoeboid and short, distinguished by differences in their tail domains. Both types of myosin I have been implicated in the regulation of pseudopod formation in Dictyostelium discoideum. We examined three members of the myosin I family, one amoeboid, MyoB, and two short, MyoA and MyoB, for shared, unique and redundant functions in motility and chemotaxis. We used computer-assisted methods for reconstructing and motion analyzing cells, and experimental protocols for assessing the basic motile behavior of mutant cells in buffer and the responses of these cells to the individual spatial, temporal and concentration components of the natural wave of the chemoattractant cAMP. Analysis of both single and double mutants revealed that all three myosins play independent roles in suppressing lateral pseudopod formation in buffer and during chemotaxis. One, MyoB, also plays a unique role in priming cells to respond to the increasing temporal cAMP gradient in the front of a wave, while MyoF plays a unique role in maintaining the elongate, polarized shape of a cell in buffer, during chemotaxis in a spatial gradient of cAMP and in the front of a cAMP wave. Finally, MyoA and MyoF play redundant roles in the velocity response to the increasing temporal cAMP gradient in the front of a wave. These results, therefore, reveal an unexpected variety of shared, unique and redundant functions of the three class I myosins in motility and chemotaxis. Interestingly, the combined defects of the myosin I mutants are similar to those of a single mutant with constitutive PKA activity, suggesting that PKA plays a role in the regulation of all three class I myosins.
authors.affiliation: W. M. Keck Dynamic Image Analysis Facility, Department of Biological Sciences, The University of Iowa, Iowa City, IA 52242, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Falk
authors.forename: Deborah
authors.initials: D
authors.lastname: Wessels
authors.forename: Leslie
authors.initials: L
authors.lastname: Jenkins
authors.forename: Tien
authors.initials: T
authors.lastname: Pham
authors.forename: Spencer
authors.initials: S
authors.lastname: Kuhl
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Titus
authors.forename: David R
authors.initials: DR
authors.lastname: Soll
mesh_terms: D000818:Animals; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases; D004023:Dictyostelium / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D009154:Mutation; D024461:Myosin Type I / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015800:Protozoan Proteins / Q000378:metabolism*; D011554:Pseudopodia / Q000378:metabolism
chemical_list: C435214:MyoA protein, Plasmodium berghei; C441368:MyoB protein, Toxoplasma gondii; D015800:Protozoan Proteins; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D024461:Myosin Type I; D009218:Myosins