The Association of a Class of Saltatory Movements With Microtubules in Cultured Cells

Abstract

Particulate structures in the cytoplasm of HeLa and other cultured cells in interphase undergo rapid individual linear displacements (long saltatory movements, LSM) . By the use of time-lapse microscopy to locate saltating particles prior to fixation and histochemical examination of the cells, structures of several kinds have been shown to move in this manner . Elements that show LSM include lysosomes, pinosomes, ingested carbon particles, lipoidal granules, and unidentified particles that appear as bright objects in positive phase contrast . The pattern of movement of the particles suggests the presence of linear guiding elements radially disposed from the cytocenter (centriole region) . The participation of microtubules in these movements is inferred from the observation that LSM cease after treatment with drugs which depolymerize microtubules, i .e ., colchicine, Vinblastine, and podophyllin . The directions of the microtubules in the cytoplasm of HeLa cells found by electron microscopy are consistent with the aster-like configuration predicted from study of LSM . Further support for this arrangement of cytoplasmic microtubules is provided by light microscope observations of colchicine-sensitive radial arrays of acid phosphatase granules in the cytoplasm of some cell lines .

Microtubular Organization in Elongating Myogenic Cells

“…A common microtubular pattern in cells is a radial dispersion of microtubules from the cell center, a region near the nucleus which usually contains a centriolar pair. Such radially arranged microtubules may be associated with movements of cytoplasmic particles towards or away from the cell center (2,10,22,28,44) or with secretion (21, 45). A good deal of study has been focused on the roles that microtubules 550…”

Demonstration of a Colcemid-Sensitive Attractive Force Acting Between the Nucleus and a Center

“…It is presumed that this system is present in other animal cells, and possibly in plant cells, where it acts dynamically to maintain an association between nuclei and centers . A variety of cell inclusions are moved by Colcemid-sensitive motility (6,9), and the demonstrated nuclear movement may be one more example . More specifically, the motile system described here may be identical with the motile system which moves the female pronucleus following fertilization (7), in which case its properties can be studied without centrifugation and with and without Colcemid .…”

“…Astral ray-and microtubule-associated motility is often Colcemid sensitive (6,7) . If the interaction between the nucleus and the center is also Colce-mid sensitive, then it may be possible to establish conditions such that the aster and the nucleus can be separated .…”

The structure of cytoplasm in directly frozen cultured cells. II. Cytoplasmic domains associated with organelle movements.

“…However, it became apparent to us in viewing whole mounts of cultured cells in the electron microscope that their cytoplasm is not homogeneous, but appeared to have two or more different domains. This was not a unique observation because heterogeneity in cytoplasmic or filament organization in conventionally fixed and thin-sectioned or whole mount cultured cells was well known (5,6,9,22). Freeze-substituted whole mounts may, however, offer new insight into this aspect of cytoplasmic organization because of potentially superior preservation of structure (4).…”

“…The directed movements oforganelles in cultured cells have been related to microtubules through mapping microtubule distribution and disrupting movement using microtubule depolymerizing agents (9). The mechanisms of microtubuleassociated organelle movement in cultured cells, or its regulation and relationship to cellular processes such as secretion and endocytosis has, however, remained elusive, although the involvement of cytoplasmic structures called "microtrabeculae" in movement has been proposed in certain highly differentiated cell types (7,8,27).…”