Experimental evidence of cytoplasmic localization in an amphibian oocyte.

animal pole pigmented conex yolk-rich cytoplasm vegetal pole sperm penetrating €99 crescent V a gray fertilized egg A Many amphibian eggs have a dark pigment concentrated in cytoplasm near the animal pole. At fertilization, the cytoplasm shifts, and exposes a gray crescent—shaped region just opposite the sperm‘s entry point. The first cleavage normally distributes half of the gray crescent to each descendant cell. gray crescent of salamander zygote First cleavage plane; gray crescent split equally. The blastomeres are separated I experimentally. Two normal larvae develop from the two blastomeres. B In one experiment, the first two cells formed by normal cleavage were phys- ically separated from each other. Each cell developed into a normal larva. gray crescent of salamander zygote First cleavage plane; gray I crescent missed entirely. The blastomeres are separated I experimentally. A ball of Only one undifferentiated normal larva cells forms. develops. C In another experiment. a zygote was manipulated so one descendant cell received all the gray crescent. This cell developed normally. The other gave rise to an undifferentiated ball of cells.