1 December 2011
Marked proteins provide instructions for gene expression after fertilization
When a sperm fertilizes an egg, their individual genes combine to form a new genome in what is known as a zygote. Basically, activation of the zygotic genome represents the transfer of developmental control from the parents to the offspring. The factors that regulate expression of the zygotic genome have not been explored and are not well understood. Now, a new study published by Cell Press on December 1st in the journal Developmental Cell identifies "decorations" that mark the zygotic genes before they are activated and may serve to regulate expression of critical developmental genes.
It is well established that one major mechanism for regulating gene expression is histone modification. Histones are proteins that are like spools around which the long strands of DNA are wound. Histones can be altered to repress or promote gene transcription. "Previous work has demonstrated that developmental genes are marked by modified histones in sperm, and this suggests a potential predictive role for histone modification in the regulation of zygotic genome activation," suggests senior study author, Dr. Philippe Collas from the University of Oslo and the Norwegian Center for Stem Cell Research.
In collaboration with colleagues at the Norwegian School of Veterinary Science, the University of Birmingham and the Genome Institute of Singapore, Dr. Collas examined histone modifications on zebrafish genes before and after activation of the zygotic genome. They were able to accomplish this because after fertilization, there is a brief period during which the zebrafish zygote undergoes several rounds of cell division before any of the zygotic genes are activated. They found that histone modifications of inactive zygotic genes guided the developmental gene expression program.
Taken together, the results suggest that there is a "pre-patterning" of the developmental program that is in place prior to gene activation."Intriguingly, these findings suggest that early developmental instructions may be provided by specific marking of the sperm and egg genomes by modified histones, which may be transmitted to the embryo through fertilization," explains Dr. Collas.
Listen to podcast interview with Philippe Collas here