Embryos shape their limbs: a key discovery of "genetic brakes"

Canadian scientists have made a significant advance in understanding the mechanisms that enable embryos to properly form their limbs, thanks to new research led by Université de Montréal medical professor Marie Kmita at the Montreal Clinical Research Institute (IRCM).

In findings published in the journal PNAS, Kmita and her team highlight the crucial role of certain molecular systems that act as true “genetic brakes,” ensuring that development proceeds correctly.

At the very beginning of limb formation, certain genes must be activated to initiate the process. But once this first step is completed, those same genes must be rapidly switched off to allow subsequent genetic programs to take over and complete development.

The new research at the IRCM shows that two groups of proteins, known as Polycomb complexes (PRC1 and PRC2), cooperate to silence these genes at the right time.

In mice, the researchers demonstrated that altering one of these systems already leads to abnormalities in gene expression. When both systems are disrupted simultaneously, the consequences are major: early genes remain active and normal limb development is severely compromised.