226
JOHN RUNNSTRÖM
solution (20 ml of sea water + 5 ml of 2.5 M NaCl solution), the birefringence becomes more evident, and it can be demonstrated that the
birefringence is positive with respect to the radial direction. It was evident that the birefringence was bound to the living cytoplasm, particularly to the villi (Runnström, unpublished data, 1963). After immersion in the hypertonic solution, the oocytes show a smooth
surface, and the same is observed even in eggs that are in meiosis
or have completed meiosis, but still retain the polar bodies (Runnström
and Monné, 1945). The fully mature egg exhibits a birefringence positive in the radial direction that seems stronger than that in the oocyte.
The birefringence is not affected by trypsin treatment of the egg. This
shows that the birefringence is not bound to the vitelline membrane
(Minganti, 1954). Rather, it indicates that the ordered structures of the
cytoplasmic surface are not disturbed by the exposure to trypsin. The
numerous dense protrusions that are spread over the egg surface may
contribute to the birefringence.
When the mature eggs are immersed in hypertonic medium they become wrinkled, as reported above. After a variable time the egg surface
becomes smooth (for photos, see Kriszat and Runnström, 1952, p. 603).
Different females show characteristic differences with respect to the rate
of disappearance of the wrinkling (Wicklund, 1954b). Within one population, all the eggs may remain wrinkled for a certain interval of time, 5,
10, 20, or more minutes; then the number of smooth eggs increases rather
steeply (see Wicklund, loc. cit., Fig. 1).
The wrinkles may be due to local differences in the degree of attachment of the vitelline membrane to the cytoplasmic surface. The
smoothening may mean a loosening of this attachment.
Kaltenbach (1957) found that the smoothening of the wrinkles is
enhanced when the concentration of Ca
2+ increases in relation to that
of Mg
2 +
. An antagonism between these divalent ions exists. The Mg
2+
seems to act by reinforcing certain bonds. In this way the egg surface
becomes more resistant to hypertonic treatment, with the result that the
wrinkling remains for a longer period. On the other hand, Ca
2+ brings
about a gradual loosening of the bonding within the egg surface, which
is manifested in a more rapid smoothening in the hypertonic medium.
This may be an indirect action of Ca
2+ by way of enzyme activation.
Sakai (1960a) has described a method of isolating the cortex of sea
urchin eggs by crushing them in hypertonic MgCl 2 solution. In this
method, advantage is probably taken of the strengthening effect of Mg
on the bonding within the egg surface. The isolated cortex had a thickness which agreed well with the results obtained by Hiramoto (1957).
Parallel to the changes shown to occur in the "hypertonicity test"
JOHN RUNNSTRÖM
solution (20 ml of sea water + 5 ml of 2.5 M NaCl solution), the birefringence becomes more evident, and it can be demonstrated that the
birefringence is positive with respect to the radial direction. It was evident that the birefringence was bound to the living cytoplasm, particularly to the villi (Runnström, unpublished data, 1963). After immersion in the hypertonic solution, the oocytes show a smooth
surface, and the same is observed even in eggs that are in meiosis
or have completed meiosis, but still retain the polar bodies (Runnström
and Monné, 1945). The fully mature egg exhibits a birefringence positive in the radial direction that seems stronger than that in the oocyte.
The birefringence is not affected by trypsin treatment of the egg. This
shows that the birefringence is not bound to the vitelline membrane
(Minganti, 1954). Rather, it indicates that the ordered structures of the
cytoplasmic surface are not disturbed by the exposure to trypsin. The
numerous dense protrusions that are spread over the egg surface may
contribute to the birefringence.
When the mature eggs are immersed in hypertonic medium they become wrinkled, as reported above. After a variable time the egg surface
becomes smooth (for photos, see Kriszat and Runnström, 1952, p. 603).
Different females show characteristic differences with respect to the rate
of disappearance of the wrinkling (Wicklund, 1954b). Within one population, all the eggs may remain wrinkled for a certain interval of time, 5,
10, 20, or more minutes; then the number of smooth eggs increases rather
steeply (see Wicklund, loc. cit., Fig. 1).
The wrinkles may be due to local differences in the degree of attachment of the vitelline membrane to the cytoplasmic surface. The
smoothening may mean a loosening of this attachment.
Kaltenbach (1957) found that the smoothening of the wrinkles is
enhanced when the concentration of Ca
2+ increases in relation to that
of Mg
2 +
. An antagonism between these divalent ions exists. The Mg
2+
seems to act by reinforcing certain bonds. In this way the egg surface
becomes more resistant to hypertonic treatment, with the result that the
wrinkling remains for a longer period. On the other hand, Ca
2+ brings
about a gradual loosening of the bonding within the egg surface, which
is manifested in a more rapid smoothening in the hypertonic medium.
This may be an indirect action of Ca
2+ by way of enzyme activation.
Sakai (1960a) has described a method of isolating the cortex of sea
urchin eggs by crushing them in hypertonic MgCl 2 solution. In this
method, advantage is probably taken of the strengthening effect of Mg
on the bonding within the egg surface. The isolated cortex had a thickness which agreed well with the results obtained by Hiramoto (1957).
Parallel to the changes shown to occur in the "hypertonicity test"