The lateral mobility of plasma membrane lipids was analyzed during first cleavage of Xaopus Levis eggs by\ud fluorescence photobleaching recovery (FPR) measurements, using the lipid analogs 5-(N-hexadecanoyl)aminofluorescein\ud (“HEDAF”) and 5-(N-tetradecanoyl)aminofluorescein (“TEDAF”) as probes. The preexisting plasma membrane of the\ud animal side showed an inhomogeneous, dotted fluorescence pattern after labeling and the lateral mobility of both\ud probes used was below the detection limits of the FPR method (D < 10⁻¹⁰ cm²/sec). In contrast, the preexisting plasma\ud membrane of the vegetal side exhibited homogeneous fluorescence and the lateral diffusion coefficient of both probes\ud used was relatively high (HEDAF, D = 2.8 X 10⁻⁸ cm²/sec; TEDAF, D = 2.4 X 10⁻⁸ cm²/sec). In the cleaving egg visible\ud transfer of HEDAF or TEDAF from prelabeled plasma membrane to the new membrane in the furrow did not occur,\ud even on the vegetal side. Upon labeling during cleavage, however, the new membrane was uniformly labeled and both\ud probes were mobile, as in the vegetal preexisting plasma membrane. These data show that the membrane of the\ud dividing Xenopus egg comprises three macrodomains: (i) the animal preexisting plasma membrane; (ii) the vegetal\ud preexisting plasma membrane; (iii) the new furrow membrane
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