Effects of cryoprotectants on actin filaments during the cryopreservation of one-cell rabbit embryos.

A dynamic equilibrium between globular and filamentous actin plays a crucial role in cell structure and motility. Many factors such as pH, ionic strength, temperature, and divalent cations, are known to influence this equilibrium. Some organic solvents, such as those used for the cryopreservation of cells, may also alter the dynamic equilibrium of this system. Fluorescence staining with NBD-phallacidin permits polymerized actin to be visualized in embryos and provides evidence that propanediol depolymerizes actin, whereas dimethyl sulfoxide does not. This depolymerizing effect is reversible after propanediol removal. Biochemical techniques were used to study the influence of these solvents on rabbit skeletal actin. Results obtained by sedimentation, fluorescence, DNase inhibition, electron microscopy, and viscometry analysis demonstrate that propanediol has a dual effect on actin polymers in vitro: it decreases the proportion of filamentous actin and the remaining filaments appear shorter and aggregate to form bundles. In contrast, dimethyl sulfoxide does not alter dramatically the actin polymer integrity. Propanediol is shown to exert a good cryoprotective action on rabbit embryos, while dimethyl sulfoxide does not. We suggest that the depolymerization of actin filaments by propanediol prior to cooling may facilitate the cryopreservation of one-cell rabbit embryos.