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.

             Marie Kmita, professor at the Faculty of Medicine at Université de Montréal
        
        
            Photo : IRCM
        
    
    






                
        
    




        
            
        


        
            


        
            'Finely tuned and precise'
        
    



        
    



        



        



    




            
        

        
        

“This discovery illustrates how development relies on finely tuned and precise orchestration of gene expression," said IRCM president and scientific director Jean-François Côté. 

"Understanding these mechanisms is essential to better grasp the origin of certain malformations."  Beyond limb formation, these findings reveal a fundamental principle of development: cells must not only activate the right genes, but also remember which ones must remain switched off. This regulatory system helps prevent errors that could lead to congenital abnormalities.   The next step in Kmita's research will be to identify the signals that guide the recruitment of these Polycomb complexes to the right genes at the right time—a key question for deepening scientists' understanding of embryonic development and its dysregulation.

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