222
JOHN RUNNSTRÖM
Β. Mechanism and Effect of Ca
2+ Uptake
311
C. Shifts in Enzyme Activity
312
D. Phase Separation and Mixing as Driving Forces
314
E. Concatenations in the Fertilization Process
315
V. Concluding Remarks
317
References
320
I. Vitelline Membrane and Cortical Particles in Oocytes and
Mature Unfertilized Sea Urchin Eggs
A. The Structure of the Vitelline Membrane and the Cortical Layer
It is generally accepted that the cytoplasm of a cell is limited outside
by a "unit membrane" or "plasma membrane.'' This consists of two
layers of lipid molecules enclosed between two layers of proteins (the
model of Danielli, 1936). More elaborate models have been proposed, for
example, by Sjöstrand (1963). The thickness of the unit membrane was
found by measurement on electron micrographs to be 80-100 Â. This
membrane is assumed to maintain the semipermeability and to be the
site of the resting potential of the cell. In the following the term "plasma
membrane" will be used. The term "cytoplasmic surface" will refer to the
outer layer of the plasma membrane.
Outside the unit membrane a further membrane is found in the female germ cells of sea urchins. This is called the "vitelline membrane."
Runnström and Monné (1945) demonstrated that, upon exposure of
oocytes of Psammechinus
miliaris to hypertonic sea water, a smooth-surfaced membrane is elevated when the cells shrink. The hyaline zone
which appeared was called "the vitelline zone" by them. The presence
of a vitelline membrane in oocytes was shown by Runnström et al.
(1945). This membrane is peeled off the oocyte when it elongates upon
prolonged exposure to hypertonic solution (loc. cit., Fig. 7) or to periodate (Runnström and Kriszat, 1950b, Fig. 11). The process involves
a separation of a superficial layer of the oocyte from the bulk of protoplasm, including the nucleus, Lönning (1964) also showed by electron
microscopy that a vitelline membrane is present in the oocyte. It is a
very delicate membrane with thicker (ca. 100 Â) nodes alternating with
thinner regions. It is easily removed during the processing for electron
microscopy; owing to this there are many preparations in which the
vitelline membrane is not perceptible. The vitelline membrane is in contact with the top of the rather numerous villi that emerge from the cell
surface. Under the effect of a hypertonic medium containing a detergentlike substance extracted from sea urchin sperm (A III or sperm lysin)
the vitelline membrane dissolved gradually. Extremely fine granules
exhibiting lively Brownian movement appeared around oocytes that
JOHN RUNNSTRÖM
Β. Mechanism and Effect of Ca
2+ Uptake
311
C. Shifts in Enzyme Activity
312
D. Phase Separation and Mixing as Driving Forces
314
E. Concatenations in the Fertilization Process
315
V. Concluding Remarks
317
References
320
I. Vitelline Membrane and Cortical Particles in Oocytes and
Mature Unfertilized Sea Urchin Eggs
A. The Structure of the Vitelline Membrane and the Cortical Layer
It is generally accepted that the cytoplasm of a cell is limited outside
by a "unit membrane" or "plasma membrane.'' This consists of two
layers of lipid molecules enclosed between two layers of proteins (the
model of Danielli, 1936). More elaborate models have been proposed, for
example, by Sjöstrand (1963). The thickness of the unit membrane was
found by measurement on electron micrographs to be 80-100 Â. This
membrane is assumed to maintain the semipermeability and to be the
site of the resting potential of the cell. In the following the term "plasma
membrane" will be used. The term "cytoplasmic surface" will refer to the
outer layer of the plasma membrane.
Outside the unit membrane a further membrane is found in the female germ cells of sea urchins. This is called the "vitelline membrane."
Runnström and Monné (1945) demonstrated that, upon exposure of
oocytes of Psammechinus
miliaris to hypertonic sea water, a smooth-surfaced membrane is elevated when the cells shrink. The hyaline zone
which appeared was called "the vitelline zone" by them. The presence
of a vitelline membrane in oocytes was shown by Runnström et al.
(1945). This membrane is peeled off the oocyte when it elongates upon
prolonged exposure to hypertonic solution (loc. cit., Fig. 7) or to periodate (Runnström and Kriszat, 1950b, Fig. 11). The process involves
a separation of a superficial layer of the oocyte from the bulk of protoplasm, including the nucleus, Lönning (1964) also showed by electron
microscopy that a vitelline membrane is present in the oocyte. It is a
very delicate membrane with thicker (ca. 100 Â) nodes alternating with
thinner regions. It is easily removed during the processing for electron
microscopy; owing to this there are many preparations in which the
vitelline membrane is not perceptible. The vitelline membrane is in contact with the top of the rather numerous villi that emerge from the cell
surface. Under the effect of a hypertonic medium containing a detergentlike substance extracted from sea urchin sperm (A III or sperm lysin)
the vitelline membrane dissolved gradually. Extremely fine granules
exhibiting lively Brownian movement appeared around oocytes that