We describe two subpopulations of actin antibodies isolated by affinity chromatography from a polyclonal antibody to chicken gizzard actin. One subpopulation recognizes γ actins from smooth muscle and nonmuscle cells, but does not recognize α actin from skeletal muscle. The other subpopulation recognizes determinants that are common to a actin from skeletal muscle and the two γ actin isotypes. Neither antibody recognizes cytoplasmic β actin. Both antibodies recognize only actins or molecules with determinants that are also present in actins. By immunofluorescence we found that the anti-γ actin colocalizes with mitochondria in fibers of mouse diaphragm, and that it does not bind detectably to the I bands of sarcomeres. The antibody that recognizes both α and γ actins stains I bands intensely, as expected. We interpret these observations as preliminary evidence for selective association of γ actin with skeletal muscle mitochondria and, more broadly, as evidence for subcellular sorting of isoactins.
Bibliographical noteFunding Information:
This work was supported by a grant from the Muscular Dystrophy Association and by USPHS grant Al-13700. J. V. P. is a recipient of a Medical Scientist Traineeship (GM-07309); M. F. P. is funded by an NIH predoctoral training grant (GM-07445). We thank Dr. Sol Snyder for use of the cryostat, Dr. Mary Nunnally for help in preparing the antibody to gizzard actin and Sheila Sanders and Janet Siliciano for helpful discussions. The excellent technical assistance of Mrs. Chiew Ko is gratefully acknowledged.
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