Majia here: Cesium is shown in this study to adversely affect embryonic cell fusion in chickens. I imagine similar effects must impact all mammals. The researchers also speculate that cesium causes adverse affects for mitochondrial functioning.
Effects of Cesium on in vitro Myoblast Differentiation: An Electron Microscopic Study Walter Malorni, Pietro L. Indovina, Giuseppe Arancia, Stefania Meschini and Maria T. Santini In Vitro Cellular & Developmental Biology Vol. 26, No. 4 (Apr., 1990) (pp. 399-410)
[Excerpted from ABSTRACT] This paper describes the microscopic evidence supporting a cesium-induced delay in the fusion of chick embryo myoblast membranes during in vitro myogenic differentiation. We have recently demonstrated that the sharp decrease in the conductivity and permittivity of the membranes of these myogenic cells at the time of fusion is delayed 30 h by the addition of cesium to the culture medium (Santini et al., Biochim. Biophys. Acta 945:56-64; 1988).
We report here that this delay in fusion is substantiated by direct microscopic observation and that cesium also induces ultrastructural changes in the myoblast cells themselves. Possible mechanisms by which cesium may cause both the delay in fusion as well as the ultrastructural changes observed are discussed.
[excerpted MANUSCRIPT TEXT pp 408-409] Mitochondria may also be affected by cesium-induced perturbation of the ionic equilibrium in myoblast cells. The mechanisms by which cesium is affecting membrane fusion and ultrastructural morphology are not yet clearly understood. The fact remains, however, that this ion is without a doubt delaying membrane fusion and inducing changes in subcellular organelles.
Although we have suggested that the main mode of action of cesium is to disrupt the ionic equilibrium of the myoblasts, we cannot rule out other possible effects of this ion. For instance, agents that inhibit cytoskeletal integrity and function such as cytochalasin B (Croop and Holtzer, 1975) or colchicine (Bischoff and Holtzer, 1968) can inhibit myoblast fusion as well. (pp. 408-409). [END]