Analysis of the role of microtubules and actin in erythrophore intracellular motility.

Abstract

The Holocentrus erythrophore, a red pigment cell, represents a model system for the study of organized intracellular transport. We have investigated the possibility that microtubules and actin are integral components of the pigment translocating motility machine. By creating cells that have total or partial loss of the microtubule framework we have demonstrated that the presence of microtubules is essential for organized, radial transport of the pigment granules. However, in the absence of microtubules, some undirected movement of the pigment can be stimulated; this suggests that a nonmicrotubular component of the cytoplast is responsible, at least in part, for the generation of motive force. In order to test the hypothesis that this component consists of actin or actomyosin, we examined the effects of probes for these classical motility proteins. Neither microinjection of phalloidin, DNase I or Nethylmaleimide-modified heavy meromyosin nor exogenous application of cytochalasin B has any effect on pigment motion, although these materials do block the actin-mediated motility of other systems in our hands. Therefore, intracellular particle transport in erythrophores does not appear to be actin or actomyosin-based.

Molecular Characterisation of Colour Formation in the Prawn Fenneropenaeus merguiensis

“…In their study, the authors used colchicines and cytochalasin B to disrupt the microtubules and microfilaments, and observed inhibition of pigment concentration and dispersion in ovarian erythrophores of the fiddler crab. Further studies appeared to have resulted in similar findings, as, for example, Beckerle & Porter [53] analysed granule movement in the erythrophores of the squirrelfish Holocentrus ascensionis , which the authors ascribed mainly to microtubules. However, there also appeared to be microtubule-independent movement that was believed to be due to actin microfilaments.…”

Actin‐dependent carotenoid droplet dispersion in permeabilized cultured goldfish xanthophores

“…These cells disperse their CDs in response to ACTH, MSH, or their second messenger CAMP and aggregate their CDs in the absence of these agents [reviewed by Tchen et al, 1986, 19881. Compared to other fish chromatophores, namely, the melanophores [Rozdzial and Haimo, 1986a,b;Schliwa, 1979; and reviews by Fujii and Oshima, 1986;Obika, 19861 of several fishes and the squirrel fish erythrophores [Beckerle and Porter, 1983;Stearns and Ochs, 1982;Stearns et al, 19861, goldfish xanthophores have several different features: smaller pigment organelles of relatively uniform size (approximately 40 nm in diameter), slower rates of pigment translocations (approximately 0.5 p d m i n in the case of dispersion and much slower in the case of aggregation), and modes of CD translocations that are distinctly different from microtubule-dependent organelle translocations. These properties suggest that the translocations of CDs might be governed by a mechanism(s) different from that in melanophores and in squirrel fish erythrophores [reviewed by Lo and Tchen, to be submitted].…”

Kinesin is responsible for centrifugal movement of pigment granules in melanophores.

“…The main function of these large cells, which have a well-developed radial system of microtubules (13), is a fast and synchronous redistribution of hundreds of pigment granules that is completely dependent on integrity of cytoplasmic microtubules (14,15) and ATP as an energy source (16)(17)(18)(19). As in many other eukaryotic cells, the plus ends of microtubules in melanophores are at the cell periphery, and the minus ends are associated with the centrosome (20).…”