Have you ever wondered why our legs grow on the bottom of our bodies and not on the top? Well, Researchers at EPFL (Ecole Polytechnique Federale de Lausanne) and the University of Geneva (Unige) have recently solved this mystery and published their findings on October 13, 2011 in the journal Science.
The secret to the way our bodies develop the way do they do lies in the fact that each embryo is developed by segmentation. Denis Duboule, a professor at EPFL and Unige stated that “we’re made up of thirty-odd horizontal slices” and that “these slices correspond more or less to the number of vertebrae we have”. However, another key element in our development is timing. Timing is a huge factor in determining where our limbs and organs end up in the final stages of growth, but what exactly controls our body’s biological clock? We all know that DNA plays a role in this process, but how do genes seem to synchronize themselves so perfectly?
The answer lies in very specific genes, known as “Hox”. Hox genes are placed in a specific and unique arrangement throughout each segment of the embryo, one exactly after the other on the DNA strand. First the neck, then the thorax, then the lumbar, and so on. In the embryo's first moments, the Hox genes are dormant, packaged like a spool of yarn on the DNA. When the time is right, the strand begins to unwind. When the embryo begins to form the upper levels, the genes encoding the formation of cervical vertebrae come off the spool and become activated. Then it is the thoracic vertebrae's turn, and so on down to the tailbone.
Hox genes function the way they do because of Hox proteins, which are considered to be a form of transcription factors because they are capable of binding to specific nucleotide sequences on the DNA called enhancers and either activate or repress genes. The same Hox protein can act as a repressor at one gene and an activator at another.
As you can see, the Hox genes play a crucial role in our bodies development. However, they also play a huge role in understanding how we differ from other species. With a more detailed description of how these genes function, scientists will be able to learn more about the role of evolution in the world.