Live dynamics of Dictyostelium cofilin suggests a role in remodeling actin latticework into bundles.
Cofilin, an indispensable, actin-regulating protein represents the 'cofilin family' of actin-binding proteins existing in a wide variety of organisms. Our previous and other in vitro studies have implied that cofilin can accelerate transformation of filamentous (F)-actin and (alpha)-actinin latticework into bundles, and overexpression of cofilin induces formation of F-actin bundles in Dictyostelium. Here we expressed an Aequorea green fluorescent protein (GFP)-Dictyostelium cofilin fusion protein in Dictyostelium, and observed the live dynamics to examine the physiological function of cofilin. We show that purified GFP-cofilin binds to actin filaments and decreases the apparent viscosity of actin solution in a similar manner to authentic Dictyostelium cofilin. Expressed GFP-cofilin exhibits normal actin-binding activities in the cytoplasm as represented by incorporation into the actin rods induced with dimethyl sulfoxide. Free moving cells form a crown-like cortical structure on the dorsal surface, and GFP-cofilin exhibits dynamic assembly into actin bundles being formed beneath the cortex. During phagocytosis, GFP-cofilin accumulates into actin bundles formed in the region underlying the phagocytic cups. In cells chemotactically activated with cyclic AMP, GFP-cofilin exhibits a high level of accumulation in projecting leading edges. When the chemo-attraction is experimentally changed, the redistribution of GFP-cofilin towards the new pseudopod occurs in a matter of 30-60 seconds. These results demonstrate that cofilin plays a crucial role in vivo in rapid remodeling of the cortical actin meshwork into bundles.
Aizawa
H
H
Department of Cell Biology, The Tokyo Metropolitan Institute of Medical Science, Japan.
Fukui
Y
Y
Yahara
I
I
D051339:Actin Depolymerizing Factors; D000199:Actins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D016764:Cell Polarity; D004023:Dictyostelium / Q000737:chemistry / Q000166:cytology / Q000235:genetics; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects / Q000235:genetics; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D010587:Phagocytosis; D011554:Pseudopodia / Q000502:physiology / Q000648:ultrastructure; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects / Q000235:genetics
D051339:Actin Depolymerizing Factors; D000199:Actins; D008164:Luminescent Proteins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004121:Dimethyl Sulfoxide