Changes in organization and microtubule assembly activity of the centrosome during lymphocyte stimulation

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Abstract
Changes in the organization of centrosomes in mouse splenic T lymphocytes stimulated by concanavalin A (con A) were examined by EM of serial sections. In both resting and stimulated lymphocytes the single centrosome consists of a pair of centrioles, satellite bodies and pericentriolar material. In resting cell centrosomes the satellite bodies are preferentially associated with, and appear to be attached by short stalks to, one of the centrioles. The satellite bodies are the primary sites of microtubule termination in the resting cell centrosome. During stimulation by con A there is a several-fold increase in microtubule content. This is correlated with an overall increase in centrosome size, an apparent increase in the size and in the number of satellite bodies, and a redistribution of satellite bodies to occupy a position between the 2 centrioles. Increased numbers of microtubules are detected terminating on the satellite bodies and in the pericentriolar material of the stimulated cell centrosome. Microtubule assembly from centrosomes in vitro was assessed by EM using detergent-permeabilized lymphocytes that were prepared to remove endogenous microtubule and supplied with purified bovine brain tubulin. Satellite bodies are evidently major sites of microtubule assembly in both resting and stimulated cell centrosomes and show that the centrosomes of stimulated cells assemble more microtubule in vitro than resting cell centrosomes. This parallels the increase in microtubule content in intact lymphocytes stimulated by con A and suggests that the changes in centrosome organization and microtubule assembly capacity that occur during stimulation are causally related.