24 research outputs found
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
Pinocytosis in the developing egg of Limnaea stagnalis L.
In 1946 Raven, working with sections of Limnaea eggs, described numerous
vacuoles appearing in the ectoplasm at the 40 cell stage. Their content was strongly
eosinophilic and with all stains used the colour of the vacuole content corresponded
to that of the egg capsule fluid surrounding the egg.
During the development of the egg the albumen vacuoles became larger and larger,
occupying at the 120 cell stage a large part of the ectoplasm.
Also at the 40 cell stage small conical or hemispherical vesicular protrusions could
be observed on the surface of some blastomeres. Others had the appearance of small
thickened rings of variable diameter, protruding slightly above the surface of the cells
and surrounding a crater-like field.
At the 120 cell stage their number had increased considerably and 40-60 of such
ringlets were observed in most eggs. Since the formation of the ringlets corresponds in time to the absorption of albumen
by the cells, Raven put forward the hypothesis that they represent inlets destined for
the ingestion of egg capsule fluid by the developing egg. In order to test this hypothesis
it seemed worthwile to study these structures by electron microscopy
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 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
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