Filamin concentration in cleavage furrow and midbody region: frequency of occurrence compared with that of alpha-actinin and myosin.

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Abstract
Affinity-purified rabbit antibody to purified chicken gizzard filamin was used in indirect immunofluorescence to localize filamin in dividing chick embryo cells. The antibody was shown to bind only chick embryo cell filamin when whole cell extracts were analyzed by the sensitive sodium dodecyl sulfate-polyacrylamide gel electrophoresis overlay technique described by Adair et al. (1978, J. Cell Biol. 790:281-285). The results show that filamin is located in stress fibers and membrane ruffles during interphase. As cells prophase, the condensing chromosomes are surrounded by diffuse antifilamin staining. No stress fibers are apparent. During metaphase and anaphase, the staining is bright but diffuse. There is often peripheral membrane staining. Filamin is not concentrated in the spindle region but neither is it excluded from the spindle. During cytokinesis, filamin is found highly concentrated in the cleavage furrow in 16 out of 100 cells examined. This frequency of concentration in the furrow is comparable to that observed for alpha-actinin (14%). Myosin concentration in the furrow is more frequent; it is observed in 37% of the cells examined. Neither myosin, alpha-actinin, nor filamin is observed concentrated in the furrow 100% of the time. We conclude that the results are consistent with, but not sufficient to prove, the hypothesis that alpha-actinin and filamin are essential components of the mechanism of cytokinesis.