Decoration of spindle microtubules with Dynein: evidence for uniform polarity.

Abstract

Studies were conducted to determine whether the microtubules present within native spindles isolated from eggs of the surf clam, Spisula solidissima, could bind dynein obtained from axonemes of Tetrahymena thermophila. Sodium dodecyl sulfate gel electrophoresis revealed that the high MW polypeptides that make up dynein cosedimented with the isolated spindles. The ATPase activity of dynein bound to the spindle microtubules was stimulated approximately 7-fold. The birefringence retardation of spindles incubated without dynein decreased from 1.4 nm to an undetectable level within 45 min; that of spindles incubated for the same period of time with dynein was 1.0 nm, .apprx. 70% of its initial value, indicating that dynein stabilized spindle birefringence. Ultrastructural analysis revealed that each spindle microtubule was decorated with 4-7 dynein arms attached by their B end, that which cross-bridges the B-subfiber within native axonemes. The polarity of the spindle microtubules could be determined by the orientation of the bound dynein arms. The 1/2-spindle probably is composed of microtubules possessing the same polarity.