Journal of Cell Science, Vol 10, 79-93, Copyright © 1972 by Company of Biologists

Submitted on January 8, 1971
Revised on June 21, 1971

Spindle Shape Changes as an Indicator of Force Production in Crane-Fly Spermatocytes

¹ Department of Biological Sciences, State University of New York at Albany, Albany, New York 12203, U.S.A.; Laboratorium für Elektronenmikroskopie, Institut für Allgemeine Botanik, Eidgenössische Technische Hochschule, Zürich, Switzerland

Changes in spindle shape during the first and second meiotic divisions in living Nephrotomasuturalis spermatocytes have been studied and recorded cinematographically with phase-contrast, Nomarski differential interference, and polarization microscopy. With the Nomarski system 2 classes of discrete spindle filaments (new terminology) have been observed: continuous filaments that extend between the poles and appear to form a cage-like framework within which the chromosomes move, and kinetochore filaments which are attached to the chromosomes at their kinetochores and converge toward the poles. Spindle deformation occurs in a manner consistent with the hypothesis that whatever tensile forces are transmitted by the kinetochore filaments are balanced by compressive forces acting on the cage-like framework of continuous filaments causing them to become splayed. Just when these forces would be expected to reach a maximum, kinetochore filaments undergo a noticeable increase in contrast. It has not been determined whether this change represents a crowding of linear elements or addition of dry mass to a constant number of linear elements.