Cortical wound healing in the amphibian egg: an electron microscopical study

Changes following injury of the animal pole cortex of fertilized uncleaved eggs of Xenopus laevis were studied with the electron microscope. In the course of the healing process the egg surface bordering the exovate protruding from a tear wound is thrown into folds. Pigment granules aggregate in the region below the edges of the damaged area. Concomitantly filament arrays come into being there. Fuzzy material is present in a diffuse and in a condensed form. It coats the membrane in the region of the surface folds as well as membrane surfaces inside the exovate. Parts of the exovate surface are in the form of so-called “crenelated layer.” Probably this layer has a transitory sealing function and is homologous to the “new membrane” formed in wounded amoebae (18). The morphological alterations are interpreted as manifestations of membrane growth, active or passive contraction of filament arrays, and cytoplasmic coagulation. In this context Holtfreter's concept of a “surface coat” and his interpretation of cortical wound healing is reexamined

Cortical wound healing in the amphibian egg: an electron microscopical study

Changes following injury of the animal pole cortex of fertilized uncleaved eggs of Xenopus laevis were studied with the electron microscope. In the course of the healing process the egg surface bordering the exovate protruding from a tear wound is thrown into folds. Pigment granules aggregate in the region below the edges of the damaged area. Concomitantly filament arrays come into being there. Fuzzy material is present in a diffuse and in a condensed form. It coats the membrane in the region of the surface folds as well as membrane surfaces inside the exovate. Parts of the exovate surface are in the form of so-called “crenelated layer.” Probably this layer has a transitory sealing function and is homologous to the “new membrane” formed in wounded amoebae (18). The morphological alterations are interpreted as manifestations of membrane growth, active or passive contraction of filament arrays, and cytoplasmic coagulation. In this context Holtfreter's concept of a “surface coat” and his interpretation of cortical wound healing is reexamined

Lateral mobility of plasma membrane lipids in dividing Xenopus eggs

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

Lateral mobility of plasma membrane lipids in a molluscan egg: Evidence for an animal/vegetal polarity

The lateral diffusion of the lipid analog C₁₄-diI (3', 3'-dihexadecylindocarbocyanine iodide) was measured in the plasma membrane of early embryos of the mollusc Nassarius reticulatus using the FPR-(Fluorescence Photobleaching Recovery) method. At almost all stages measured (from fertilized egg up to 8-cell stage) the diffusion coefficient (D) of the mobile fraction (MF) of C₁₄-diI is significantly higher in the plasma membrane of the polar lobe as compared to the plasma membrane of the animal half of the embryo. These results demonstrate the presence of an animal/vegetal polarity in the plasma membrane of the embryo of Nassarius, possibly related with the polar localization of morphogenetic factors

Lateral mobility of plasma membrane lipids in Xenopus eggs: Regional differences related to animal/vegetal polarity become extreme upon fertilization

Regional differences in the lateral mobility properties of plasma membrane lipids have been studied in unfertilized and fertilizedxaqpus eggs by fluorescence photobleaching recovery (FPR) measurements. Out of a variety of commonly used lipid probes only the aminofluorescein-labeled fatty acids HEDAF (5-(N-hexadecanoyl)-aminofluorescein) and TEDAF (5-(N-tetradecanoyl)-aminofluorescein) appear to partition into the plasma membrane. Under all experimental conditions used these molecules show partial recovery upon photobleaching indicating the existence of lipidic microdomains. In the unfertilized egg the mobile fraction of plasma membrane lipids (∼50%) has a fivefold smaller lateral diffusion coefficient (D = 1.5 X 10⁻⁸cm²/sec) in the animal than in the vegetal plasma membrane (D = 7.6 X lO⁻⁸ cm²/sec). This demonstrates the presence of an animal/vegetal polarity within the Xenopus egg plasma membrane. Upon fertilization this polarity is strongly (>lOOX) enhanced leading to the formation of two distinct macrodomains within the plasma membrane. At the animal side of the egg lipids are completely immobilized on the time scale of FPR measurements (D < 10⁻¹⁰ cm²/sec), whereas at the vegetal side D is only slightly reduced (D = 4.4 X 10⁻⁸ cm²/sec). The immobilization of animal plasma membrane lipids, which could play a role in the polyspermy block, probably arises by the fusion of cortical granules which are more numerous here. The transition between the animal and the vegetal domain is sharp and coincides with the boundary between the presumptive ecto- and endoderm. The role of regional differences in the plasma membrane is discussed in relation to cell diversification in early development

Lateral mobility of plasma membrane lipids in Xenopus eggs: Regional differences related to animal/vegetal polarity

Regional differences in the lateral mobility properties of plasma membrane lipids were studied in unfertilized and fertilized Xenopus eggs by fluorescence photobleaching recovery (FPR) measurements. Out of a variety of commonly used lipid probes only the aminofluorescein- -1abelled fatty acids HEDAF (5-(N-hexadecanoyl)- aminofluorescein) and TEDAF (5-(N-tetradecanoyl)-aminofluorescein) appear to distribute itself in the plasma membrane. Under all experimental conditions used these molecules show partial recovery upon photobleaching, indicating the existence of lipidic microdomains