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Decoration of actin filaments is similar in muscle (left) and epithelial (right) cells.6 E! Y# ~: B+ y/ W. f; p' c
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# O, b( A8 @' b, L8 @Holtzer's work followed a classic study by Huxley (1963). Huxley had reported that in a cell-free system heavy meromyosin (HMM), a proteolytic fragment of myosin, could be incubated with polymerized, filamentous actin and form polarized arrowhead complexes that could be readily visualized in the EM. The orientation of the arrowhead complexes gave a readout of actin organization.0 h+ Y$ O7 F+ F7 }/ Q
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Holtzer and colleagues observed HMM-decorated filaments in every cell type examined, from skeletal and cardiac muscle cells to fibroblasts, chondroblasts, keratocytes, glia, and blood cells. Most decorated filaments in these different cell types localized to stress fibers. HMM-decorated filaments were also seen at the cleavage furrow of metaphase cells and at the core of the microvilli of intestinal and tracheal cells. In an early review of this work, Holtzer et al. (1972) suggested that there might be more than one type of actin and that each might be associated with a variety of actin-binding proteins in different cell types.+ D5 u9 \& d5 i; J8 ?8 g7 V
* j/ K7 g/ `) Q/ X0 Z+ X- D4 BBy the mid- to late-1970s, numerous studies using fluorescent antibodies to nonsarcomeric actin (Lazarides and Weber, 1974) and nonsarcomeric myosin (Adelstein et al., 1971), as well as fluorescent phalloidin for visualizing filamentous actin, confirmed the presence of both actin and myosin in most cells. Different cell types were later shown to contain distinct isoforms of both contractile proteins. In plant cells, actin filaments capable of binding HMM were shown to be involved in cytoplasmic streaming and moving organelles (Palevitz et al., 1974); Allen (1974) made similar observations for animal cells.7 Z1 Q. C F G3 r) S) L2 W, k. W
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Adelstein, R.S., et al. 1971. Proc. Natl. Acad. Sci. USA. 68:2703–2707.! B5 ~6 A6 ^, c# b5 d! H
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Allen, N.S. 1974. J. Cell Biol. 63:270–287.
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6 I( a' E7 K- J6 KHoltzer, H., et al. 1972. Curr. Top. Dev. Biol. 7:229–256.
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# g# R8 e( }3 v: Q6 f- ~Huxley, H.E. 1963. J. Mol. Biol. 77:281–308., g/ ?$ ]8 Y5 p1 t) A& Q6 j
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Ishikawa, H., et al. 1968. J. Cell Biol. 38:538–555.5 p* F; o& w; I h
% r! W! i& k+ s m% G RIshikawa, H., et al. 1969. J. Cell Biol. 43:312–328.
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$ J0 _5 I1 ~" O% f5 ]0 HLazarides, E., and K. Weber. 1974. Proc. Natl. Acad. Sci. USA. 71:2268–2272.1 ~! E" d% N. i, T- H/ d5 x
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Palevitz, B.A., et al. 1974. Proc. Natl. Acad. Sci. USA. 71:363–366.(In the late 1960s, Howard Holtzer's grou) |
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