Fertilization is the process by which two gametes, be it an egg and a sperm in mammals or an mt+ cell and an mt- cell in green algae, fuse to create a new individual, called a zygote. The zygotic genome represents a dual contribution of genetic information from each of the parents. However, the newly formed zygote does not immediately use its own genes; it is initially dependent upon existing factors derived from the gametes.
Studying the green algae, Chlamydomonas, Dr. William J. Snell and colleagues have identified at least one of the molecular cues that regulates the activation of the zygotic genome.
Dr. Snell and colleagues determined that the abnormal expression of the mt+ gamete-specific gene, gsp1, in mt- gametes induces zygotic development without gamete fusion. Dr. Snell and colleagues generated transgenic mt- gametes that express gsp1 in response to light. When exposed to light, these transgenic gsp1 expressing mt- gametes simulate zygote development both in cell morphology and in gene expression patterns.
Dr. Snell and colleagues have discovered that under gsp1 expressing conditions, most of the events that are associated with fertilization are in fact dispensable for zygote gene induction. As the activation of zygote gene transcription has remained an illusive biological process both in plants and in animals, the discovery that GSP1 regulates zygote gene activation in algae represents a starting point from which others can begin to unravel the process in higher organisms.