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Have you ever wondered why our hands have exactly five fingers? Dr. Marie Kmita’s team certainly has. The researchers at the Institut de recherches cliniques de Montréal (IRCM) have uncovered a part of this mystery, and their remarkable discovery has just been published in the prestigious journal Nature.
A matter of evolution
We have known for several years that the limbs of vertebrates, including our arms and legs, stem from fish fins. The evolution that led to the appearance of limbs, and in particular the emergence of fingers in vertebrates, reflects a change in the body plan associated with a change of habitat, the transition from an aquatic environment to a terrestrial environment. How this evolution occurred is a fascinating question that goes all the way back to the work of Charles Darwin.
This August, researchers in Chicago, Dr. Neil Shubin and his team, demonstrated that two genes—hoxa13 and hoxd13—are responsible for the formation of fin rays and our fingers. “This result is very exciting, because it clearly establishes a molecular link between fin rays and fingers,” said Yacine Kherdjemil, a doctoral student in Marie Kmita’s laboratory and first author of the article published in Nature.
However, the transition from fin to limb was not accomplished overnight. The fossil record indicates that our ancestors were polydactyl, meaning that they had more than five fingers, which raises another key question. Through what mechanism did evolution favor pentadactyly (five fingers) among current species?
One observation in particular caught the attention of Dr. Kmita’s team: “During development, in mice and humans, the hoxa11 and hoxa13 genes are activated in separate domains of the limb bud, while in fish, these genes are activated in overlapping domains of the developing fin,” said Marie Kmita, Director of the IRCM's Genetics and Development research unit, Associate Research Professor in the Department of Medicine at the Université de Montréal and Adjunct Professor in the Department of Medicine at McGill University.
In trying to understand the significance of this difference, Yacine Kherdjemil demonstrated that by reproducing the fish-type regulation for the hoxa11 gene, mice develop up to seven digits per paw, i.e., a return to ancestral status. Dr. Marie Kmita’s team also discovered the sequence of DNA responsible for the transition between fish- and mouse-type regulation for the hoxa11 gene. “It suggests that this major morphological change did not occur through the acquisition of new genes but by simply modifying their activities,” added Dr. Marie Kmita.
From a clinical point of view, this discovery reinforces the notion that malformations during fetal development are not only due to mutations in the genes and may come from mutations in sequences of DNA known as regulatory sequences. “At present, technical constraints do not allow for identifying this type of mutation directly in patients, hence the importance of basic research using animal models”, said Marie Kmita.
About the study
The research project was conducted at the IRCM’s Genetics and Development research unit by Yacine Kherdjemil, Rushikesh Sheth, Annie Dumouchel, Gemma de Martino and Marie Kmita. Robert L. Lalonde and Marie-Andrée Akimenko, from the University of Ottawa, Kyriel M. Pineault and Deneen M. Wellik, from the University of Michigan, as well as H. Scott Stadler, from Shriners Hospital for Children, also collaborated on the study.
The research was funded by the Canadian Institutes of Health Research, the Canada Research Chairs Program, the Natural Sciences and Engineering Research Council and a grant from Shriners Hospital Research. Yacine Kherdjemil also received the IRCM – Michel-Bélanger Scholarship from the IRCM Foundation and a scholarship from the molecular biology program at the Université de Montréal.
About Marie Kmita
Marie Kmita obtained a PhD in cell and molecular biology from the Université de Reims in France. She is Associate IRCM Research Professor and Director of the Genetics and Development research unit. Dr. Kmita is also Associate Research Professor in the Department of Medicine (accreditation in molecular biology) at the Université de Montréal, as well as an Adjunct Professor in the Department of Medicine (Division of Experimental Medicine) at McGill University. Dr. Kmita holds the Canada Research Chair in Molecular Embryology and Genetics. For more information, visit www.ircm.qc.ca/kmita.
About the IRCM
Founded in 1967, the Institut de recherches cliniques de Montréal (IRCM) is a non-profit organization that conducts fundamental and clinical biomedical research in addition to training high-level young scientists. With its cutting-edge technology facilities, the institute brings together 33 research teams, which work in cancer, immunology, neuroscience, cardiovascular and metabolic diseases, systems biology and medicinal chemistry. The IRCM also operates a research clinic specialized in hypertension, cholesterol, diabetes and cystic fibrosis, as well as a research centre on rare and genetic diseases in adults. The IRCM is affiliated with the Université de Montréal and associated with McGill University. Its clinic is affiliated with the Centre hospitalier de l’Université de Montréal (CHUM). The IRCM is supported by the Ministère de l’Économie, de la Science et de l’Innovation (Quebec ministry of Economy, Science and Innovation).
Source:
Anne-Marie Beauregard, Communications Officer
Institut de recherches cliniques de Montréal (IRCM)
514 987-5555 | anne-marie.beauregard@ircm.qc.ca
