For his graduate project at the University of Toronto, Manfred Lohka wanted to answer one simple question: what enzyme was controlling the decondensation of a sperm nucleus when it entered the egg? At the time, an egg protease was thought to be involved, so he figured he should start by making egg extracts in which to test sperm. He got much more than he bargained for, including the birth of a potent cell-free biochemical assay.
After harvesting a test tube of eggs from Rana pipiens frogs, Lohka could spin the eggs at low speed and pop the cytoplasmic contents out of their plasma membranes “just like taking the skin off a grape.” If he added Xenopus laevis sperm heads to the activated cytoplasm, he observed that the sperm heads transformed into pronuclei and then mitotic chromosomes (Lohka and Masui, 1983).
But it wasn't until Lohka...
