The capacity to move specific intracellular granules or vesicles or chromosomes is one of the most important functions of cells. It requires structural features of the cytoplasm such as microtubules or intermediate filaments to give the motion direction and a mechanism that is capable of contraction to provide the motive force. These components are found in chromatophores, which have the added advantage that the motion of the pigment granules is easily followed in living cells by light microscopy. In studies using an erythrophore (red chromatophore) and a 1 MeV electron microscope, we have found that the pigment is supported in a 3-dimensional lattice of fine filaments which contracts when the pigment is aggregated and extends again when the pigment is dispersed. Each granule has a fixed position or address within the lattice. Only a portion of the total lattice within the erythrophore is differentiated to move the pigment; the part which does not move with the pigment contains microtubules, smooth endoplasmic reticulum and mitochondria. One of the major purposes of this proposal is to determine whether other cells show this division of labor with some parts of the lattice set aside specifically to move lysosomes or secretory vesicles and other parts, as in mitosis, to move chromosomes in the mitotic spindle. We propose to use, at the outset, another chromatophore that possesses four different pigments which the cell can move independently of one another.
Our aim i s obvious; it is to see if each pigment has a recognizably individual structural mechanism for pigment motion and whether it resembles that in the erythrophore.
|McNiven, M A; Ward, J B (1988) Calcium regulation of pigment transport in vitro. J Cell Biol 106:111-25|
|McNiven, M A; Porter, K R (1986) Microtubule polarity confers direction to pigment transport in chromatophores. J Cell Biol 103:1547-55|