Changes in the organization of the mouse egg plasma membrane upon fertilization and first cleavage: Indications from the lateral diffusion rates of fluorescent lipid analogs

Using the technique of fluorescence photobleaching recovery, we have measured the lateral diffusion of the lipid analogs 3,3′-diacylindocarbocyanine iodides of acyl chain lengths, n = 14 to 22 in the plasma membranes of unfertilized and fertilized CD-1 mouse eggs and two-cell embryos. Mean diffusion coefficients ranged from (3.4 to 7.9) × 10^-9 cm²/sec and mean percentage diffusing ranged from 65 to 82%. Within 10% diffusing fractions are independent of chain length and unaffected by fertilization or first cleavage. In unfertilized and fertilized eggs the diffusion coefficients show relative maxima at n = 16 and 20. In two-cell embryos the relative maximum at n = 16 is suppressed. As was observed by D. E. Wolf, W. Kinsey, W. Lennarz, and M. Edidin (1981, Develop. Biol.81, 133) on sea urchin eggs, the effect of fertilization on diffusion coefficients is chain length dependent. Little change is observed for n = 14 and 18; a slight increase is observed for n = 16; and small decreases are observed for n = 20 and 22. This is interpreted in terms of a reordering of the lipid domains in the plasma membrane upon fertilization and first cleavage.