The dramatic chromosome instability in certain tumors might reflect a synergy of spindle checkpoint defects with hypoxic conditions. In Caenorhabditis elegans and Drosophila melanogaster, spindle checkpoint activation has been implicated in the response to acute anoxia. The activation mechanism is unknown. Our analyses in D. melanogaster demonstrate that oxygen deprivation affects microtubule o...

Eight cases of uveal malignant melanoma were studied with the electron microscope with the purpose of comparing the ultrastructural features of the three basic cell types (spindle A, spindle B, and epithelioid) originally described by Callender under the light microscope. Five of the eight tumors were of pure cell type, and three were mixed. This was undertaken because of earlier diverse opinio...

The mitotic spindle is structurally and functionally defined by its main component, the microtubules (MTs). The MTs making up the spindle have various functions, organization and dynamics: astral MTs emanate from the centrosome and reach the cell cortex, and thus have a major role in spindle positioning; interpolar MTs are the main constituent of the spindle and are key for the establishment of...

In asymmetric divisions, the mitotic spindle must align according to the cell polarity axis. This is achieved through targeting astral microtubules emanating from each spindle pole to opposite cell cortex compartments. Saccharomyces cerevisiae is a powerful genetic model for dissection of this complex process. Intense research in this yeast has rendered detailed models for a program linking act...

Changes in birefringence retardation (BR) and length of Chaetopterus meiotic metaphase-arrested spindles produced by increased hydrostatic pressure were observed with polarized-light microscopy using a newly developed optical pressure chamber. Increased pressure produced rapid, reversible decreases in spindle BR and length. Pressures of 3,500 psi or higher at 22 degrees C caused complete disapp...

I n higher eukaryotes, the position of cytokinesis is determined by the position of the mitotic spindle (Rappaport, 1990). Generally, the spindle sits in the middle of the cell and cytokinesis produces two equivalent cells. However, many developmental processes require specific positioning of the cleavage plane and, hence, the mitotic spindle. For example, control of spindle position can be use...

In mitosis, a spindle checkpoint plays important roles at the metaphase-anaphase transition to ensure the formation of a bipolar spindle, the completion of connecting chromosomes to microtubules and the alignment of all chromosomes at the spindle equator before initiation of anaphase. Components of the spindle checkpoint were first identified through genetic screens in budding yeast and some ch...

The function of the spindle to accurately segregate chromosomes during cell division is universal among eukaryotes. A common feature of metaphase spindles is their bipolar structure, with microtubule (MT) minus ends pointing toward the poles and MT plus ends toward the center, with a subset of them connecting to chromosomes at the kinetochores. However, wide variation in spindle assembly, size,...

The intranuclear spindle of yeast has an electron-opaque body at each pole. These spindle plaques lie on the nuclear envelope. During mitosis the spindle elongates while the nuclear membranes remain intact. After equatorial constriction there are two daughted nuclei, each with one spindle plaque. The spindle plaque then duplicates so that two side-by-side plaques are produced. These move rapidl...

Mitosis in the amebo-flagellate Naegleria pringsheimi is acentrosomal and closed (the nuclear membrane does not break down). The large central nucleolus, which occupies about 20% of the nuclear volume, persists throughout the cell cycle. At mitosis, the nucleolus divides and moves to the poles in association with the chromosomes. The structure of the mitotic spindle and its relationship to the ...