Behavior of the Cell Surface During Cleavage

IV. Polar lobe formation and cleavage of the eggs of Ilyanassa obsoleta Say

抄録

1) Linear stretching and shrinkage of the surface of Ilyanassa eggs as viewed from the side (perpendicular to the egg and spindle axes) was studied by the method of attaching kaolin particles.
2) During the second maturation division with its accompanying form change, the animal pole region (animal furrow region) follows a continuous course of shrinkage, and after the cell regains a spherical form, it remains shrunken. The region of the spindle pole (polar region) sometimes shrinks and sometimes stays unchanged, which is more characteristic of the vegetal area; that is, this region is transitional in nature. In both cases, a temporary stretching can be seen in connection with the lobe formation. Around the constriction between the main cell body and the polar lobe, the temporary stretching is more marked, and in the spherical stage following division, the surface returns to the initial state with no shrinkage. In the surface of the lobe, the temporary stretching is much increased, and the surface remains stretched, even after the cell acquires a spherical shape.
3) During cleavage, the animal pole region (animal furrow region) shows a characteristic initial shrinkage phase which is followed by a stretching of about 250%. After the cleavage, a residual stretching of about 190% is observed. The polar region has no initial shrinkage phase and the maximum stretching is 120 to 150%, with a correspondingly slighter residual stretching. The surface of the constriction starts to stretch with no initial shrinkage phase and attains a maximum of nearly 500%, the greatest expansion in any part of the egg surface. However, the residual stretching is comparatively slight. The surface of the polar lobe exhibits an expansion of a little over 200% with no initial shrinkage. The residual stretching, when compared with the spherical stage before the first cleavage, must be very slight if any exists at all. The cleavage furrow in the vegetal side of the smaller blastomere (vegetal furrow region) behaves much like the animal furrow region, but the initial shrinkage phase is lacking. This is presumably due to the presence of the polar lobe.
4) A shrinkage of the animal pole region during the second maturation division, which is maintained through the subsequent spherical stage, and a permanent stretching of the surface of the polar lobe during the same period indicate that the surface material of Ilyanassa eggs is shifted from the vegetal side to the animal side during the second maturation division.
5) In cleavage, the surface of Ilyanassa eggs behaves fundamentally like the surface of sea urchin eggs.
6) The possibility of the formation of a new surface at the contact area of the blastomeres is discussed.