By studying the Pitx1 gene, one of the genes involved in the building and construction of the lower limbs, a team from the University of Geneva (UNIGE), in Switzerland, has discovered how a little disturbance in the activation process of this gene is at the origin of clubfoot, a common foot malformation. Even a totally functional gene can not act appropriately without one of its genetic switches. And when just one of these switches is missing out on, the percentage of cells where the gene is active declines, preventing the lower limbs from being developed correctly. “When the switch is turned on, it starts the transcription of a gene into RNA, which in turn is translated into a protein that can then perform a particular task,” explains Guillaume Andrey, teacher in the Department of Genetic and Developmental Medicine at the UNIGE Faculty of Medicine, who led this research. Beyond the Pitx1 gene and clubfoot, the UNIGE researchers have actually discovered a basic principle whose mechanism might be found in a big number of genes.
Throughout embryonic development, hundreds of genes should be specifically triggered or quelched for organs to construct correctly. This control of activity is directed by brief DNA series that, by binding certain proteins in the cell nucleus, function as true ON/OFF switches. “When the switch is turned on, it initiates the transcription of a gene into RNA, which in turn is translated into a protein that can then carry out a specific task,” describes Guillaume Andrey, teacher in the Department of Genetic and Developmental Medicine at the UNIGE Faculty of Medicine, who led this research study. “Without this, genes would be continuously changed on or off, and therefore not able to act selectively, in the best place and at the correct time.”
In basic, each gene has several switches to guarantee that the mechanism is robust. “However, could the loss of among these switches have repercussions? This is what we wanted to evaluate here by taking as a design the Pitx1 gene, whose function in the construction of the lower limbs is well known,” says Raquel Rouco, a post-doctoral researcher in Guillaume Andreys laboratory and co-first author of this study.
A reduction in cellular activation that leads to clubfoot
To do this, the researchers modified mouse stem cells utilizing the genetic modification tool CRISPR-CAS 9, which makes it possible to include or get rid of particular elements of the genome. “Here, we eliminated among Pitx1s switches, called Pen, and added a fluorescence marker that permits us to imagine the gene activation,” discusses Olimpia Bompadre, a doctoral student in the research study group and co-first author. “These customized cells are then aggregated with mouse embryonic cells for us to study their early stages of development.”
Generally, about 90% of cells in future legs trigger the Pitx1 gene, while 10% of cells do not. “However, when we got rid of the Pen switch, we discovered that the percentage of cells that did not trigger Pitx1 rose from 10 to 20%, which was enough to modify the building and construction of the musculoskeletal system and to cause a clubfoot,” describes Guillaume Andrey. The proportion of non-active cells increased especially in the immature cells of the lower limbs and in the irregular connective tissue, a tissue that is important for constructing the musculoskeletal system.
The very same system in numerous genes
Beyond the Pitx1 gene and clubfoot, the UNIGE scientists have found a basic concept whose system might be found in a big number of genes. Flawed genetic switches might thus be at the origin of developmental diseases or numerous malformations. Moreover, a gene does not manage the development of a single organ in the body, but is generally associated with the building and construction of a large variety of organs. “A non-lethal malformation, such as clubfoot for instance, might be an indication of conditions in other places in the body that, while not right away visible, could be far more dangerous. If we can properly analyze the action of each anomaly, we could not only read the info in the genome to find the origin of a malformation, however also anticipate results in other organs, which would silently establish, in order to intervene as early as possible,” the authors conclude.
Reference: “Cell-specific changes in Pitx1 regulative landscape 1 activation triggered 2 by the loss of a single enhancer” 13 December 2021, Nature Communication.DOI: 10.1038/ s41467-021-27492-1.
UNIGE Scientists have actually discovered how the absence of a genetic switch can lead to malformations throughout embryonic advancement.
By studying the Pitx1 gene, one of the genes involved in the construction of the lower limbs, a group from the University of Geneva (UNIGE), in Switzerland, has found how a small disruption in the activation process of this gene is at the origin of clubfoot, a typical foot malformation. Even a fully functional gene can not act correctly without one of its genetic switches. And when simply one of these switches is missing out on, the percentage of cells where the gene is active declines, preventing the lower limbs from being developed effectively.
