Developmental biologists have long been fascinated by the first steps of life. Yet one point remained unexplained.
A research team including Antonio Giraldez, from the Department of Genetics at Yale University, has been working on discovering how our genome is awakened, and thus, how we start to develop hours from fertilization.
Let us start at the beginning.
Mere hours after fertilization, a unique genome is created by chromosomes from the egg and the sperm. However, to begin with, this genome is inactive.
In order for embryonic development to begin, this genome has to be activated. This is, then, the beginning of the development of an embryo.
"This is the beginning of life from an embryonic standpoint"
Giraldez said: "What hasn't been clear is how and what kick-starts the transcriptional activity of the embryonic genome, so that the embryo starts taking control of its own development with its own genetic blueprint."
Giraldez and his team discovered that two factors were required in order to activate the DNA in the genome.
Their research was published on Monday in the journal Developmental Cell.
The team focused their research on the pattern of transciption within the nucleus of zebrafish embryos. They, then, created tools to visualize the first activated gene in the zebrafish genome.
"Now we can visually look inside the nucleus and analyze how the first gene within the silent genome is awakened," said Shun Hang Chan, lead author of the study.
What are the two factors needed?
What the team discovered by observing the embryos of zebrafish was that two proteins are needed in order to activate the genome: P300 and Brd4. Both are produced by the female.
If either or both of these proteins are blocked, or their activity is disrupted, the development of the embryo is in turn blocked.
What the team discovered was that even if these two proteins are blocked, they could get around this by activating the embryonic genome by artificially inducing P300 and Brd4.
"These molecular factors act as a sort of molecular timer, which sets the timing of genome's awakening," Giraldez said.
"Finding these key factors involved in genome activation serve as the critical first step towards our understanding of how life begins."