Department of Biology
Polydactyly is a medical term for the presence of extra fingers or toes, a condition similar to ancient, extinct animal species. Our earliest terrestrial ancestors, known as tetrapods (meaning “with four limbs”), had polydactylous limbs that had evolved from fish fins in the transition from aquatic to terrestrial life.
PhD candidate Yacine Kherdjemil and Dr. Marie Kmita, Montreal-based collaborators, discovered a small DNA sequence in the mouse genome known as an enhancer, which modulates the activity of a gene named Hoxa11 involved in limb development in mice. When normal Hoxa11 activity is disrupted, the mice developed polydactylous limbs, suggesting a role of this enhancer in the evolution of limbs with five fingers and toes. Here at the University of Ottawa, PhD candidate Robert Lalonde and Prof. Marie-Andrée Akimenko went looking for this enhancer sequence in the zebrafish genome but found no evidence of its existence in fish, suggesting that it emerged during the fin-to-limb transition. They also showed that Hoxa11 activity in zebrafish significantly differs from what is seen in mice, providing further evidence the enhancer element is indeed a tetrapod innovation. Dissecting the mechanisms of limb development is crucial for understanding the causes of congenital limb malformations.
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