Kiss of life?
The molecular components that mediate the egg activation are discussed. Jacques Loeb, a physiologist, showed that sea-urchin eggs are activated to develop merely by changing the chemical composition of the sea water that bathed them, and without the need of a sperm. Sperm was shown to induce egg activation by triggering the release of calcium, which acts as a cellular messenger in processes like muscle contraction, hormone secretion and the transmission of messages in the brain. A new DNA technology called Expressed sequence tags (EST), used to identify signaling proteins in particular tissues, is also discussed.