Journal of Cell Science, Vol 13, 727-739, Copyright © 1973 by Company of Biologists

Submitted on May 21, 1973

The Patterned Organization Of Thick And Thin Microfilaments In The Contracting Pseudopod Of Difflugia

¹ Department of Biological Sciences, State University of New York at Albany, 1400 Washington Avenue, Albany, New York 12222, U.S.A.; Department of Biological Structure, University of Miami School of Medicine, Box 875, Biscayne Annex, Miami, Florida 33152, U.S.A.
² Department of Biological Sciences, State University of New York at Albany, 1400 Washington Avenue, Albany, New York 12222, U.S.A.

The lobopodial pseudopods of the shelled amoeba Difflugia undergo a rapid active contraction and length shortening which results in movement of the organism, or rapid pseudopod retraction. In polarized light, the pseudopod shows high birefringence before and during this normal contraction, suggesting a high degree of linear organization, and a complex pattern of changes. Immediately conventional fixation begins, pseudopods retract rapidly, and show changes in birefringence. When longitudinal sections are viewed in the electron microscope, such fixed, contracting pseudopods are seen to contain thick (14-16 nm) and thin (5-8 nm) microfilaments. Montages demonstrate that these microfilaments are found in close parallel association with each other, and lie parallel and peripheral to the longitudinal axis of the pseudopod, which is the axis of contraction. This distribution suggests that the patterned microfilaments could be involved in the shortening process and that they could account for the birefringence seen in the contracting pseudopod. Rapid alignment, or assembly, is also suggested.