The occurrence and intracellular distribution of myosin and actin in melanophore-like cells derived from a goldfish erythrophoroma cell line have been studied by means of sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblot and immunofluorescence using antisera against chick gizzard myosin heavy chain and carp skeletal muscle actin. SDS-PAGE of the cell extracts separates out one band at 200 kDalton; this is conjugated with the anti-myosin antiserum. Immunofluorescence using the anti-myosin antiserum discloses that myosin in these cells occurs in two forms: discrete, minute clusters and thin filaments bearing a resemblance to "stress fibers". The former is distributed evenly over the entire cytoplasm in the cells with dispersed pigments and, upon pigment aggregation, accumulates densely around collapsed melanosomes. The latter runs as thin bundles either radially along the cell center-to-periphery axis or connecting the corners of cell margins; it gives a similar profile in all states of the motile response. Immunofluorescence using the antiactin antiserum or rhodamine-conjugated phalloidin discloses that actin is similarly distributed to myosin, suggesting its possible existence as actomyosin. Simultaneous translocation of the amorphous forms of myosin and actin with melanosomes indicates that they may be involved in pigment migration.
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