Sparks fly at the moment of fertilisation. 

"Finding these key factors involved in genome activation serve as the critical first step towards our understanding of how life begins."

Human life begins at conception. To quote just one authoritative human embryology textbook:  "Human development begins at fertilisation when a sperm unites with an oocyte [ovum] to form a single cell zygote. This highly specialised, totipotent cell marks the beginning of each of us as a unique individual." (Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). 

This fact is uncontroversial from a scientific point of view (however much it might be debated by some abortion advocates). However, the exact mechanism by which embryonic development begins has long fascinated developmental biologists.

How does human development start?

As a result of fertilization, a unique genome forms from chromosomes contributed by the egg from the mother and sperm from the father. However, this new genome is initially inactive and must be "awakened" to begin the transcription of its DNA and start embryonic development.

A research team including Antonio Giraldez, from the Department of Genetics at Yale University, has been working on discovering how this first step in human life happens.

"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," he said.

"Molecular timer"

Dr Giraldez and his team, who published their research on Monday in the journal Developmental Cell, discovered that two factors were required in order to activate the DNA in the genome. 

The research focused on the pattern of transciption within the nucleus of zebrafish embryos. The team then created tools to visualize the first activated gene in the zebrafish genome. 

They discovered that two proteins are needed in order to activate the genome: P300 and Brd4, which are both produced by the mother. If either or both of these proteins are blocked, or their activity is disrupted, the development of the embryo is in turn blocked. 

"These molecular factors act as a sort of molecular timer, which sets the timing of genome's awakening," Dr Giraldez said.

"Finding these key factors involved in genome activation serve as the critical first step towards our understanding of how life begins."