How genes shift from mother to baby

Researchers from the New Jersey-based Princeton University have decoded the shift from maternal genes to the embryo's genes during development.

Learning how organisms manage this transition could help scientists understand larger questions about how embryos regulate cell division and differentiation.

"At the beginning, everything the embryo needs to survive is provided by mother but eventually, that stuff runs out and the embryo needs to start making its own proteins and cellular machinery," said postdoctoral researcher and first author Shelby Blythe.

The study, published in the journal Cell, provides new insight into the mechanism for this genetic hand-off which happens within hours of fertilisation when the newly fertilised egg is called a zygote.

To find out what controls this maternal to zygotic transition, Blythe conducted experiments in the fruit fly which has long served as a model for development in higher organisms including humans.

The experiments revealed that the slower cell division is a consequence of an upswing in DNA errors after the embryo's genes take over.

Cell division slows down because the cell's DNA-copying machinery has to stop and wait until the damage is repaired.

Blythe found that it was not the overall amount of embryonic DNA that caused this increase in errors.

Instead, his experiments indicated that the high error rate was due to molecules that bind to DNA to activate the reading, or transcription, of the genes.

These molecules stick to the DNA strands at thousands of sites and prevent the DNA copying machinery from working properly.

To discover this link between DNA errors and slower cell replication, Blythe used genetic techniques to create fruit fly embryos that were unable to repair DNA damage and typically died shortly after beginning to use their own genes.

"This provided evidence that the process of awakening the embryo's genome is deleterious for DNA replication," the authors wrote.

The work enables researchers to explore larger questions of how embryos regulate DNA replication and transcription.

Additionally, these early embryos allow them to study how the cell builds and installs features that are so essential to the fundamental processes of cell biology.