The embryological and molecular basis of Zic2 involvement in holoprosencephaly

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The brain is the most complex organ in the human body and diseases or disorders of the brain can become evident at any stage of life. Generally such problems have profound consequnces for the affected individuals and their families. One of the most common problems of brain development that is evident either at birth or within the first years of life is called holoprosencephaly (HPE). This condition affects the midline of the brain and the face and can lead to delay in mental, motor and language development, seizures, and obvious facial abnormalities. In its most severe form only one eye develops in the middle of the face, a condition known as cyclopia and a large majority of the severely affected children will die late in gestation or at birth. This condition can be inherited, but because the genetic lesions that cause this problem affect different people differently, people can carry the causative genetic change(s) without knowing it. We need to identify and study the genetic lesions that contribute to this condition in order to begin to understand how we can stop these mutations affecting the developing foetus. Because it is difficult to study embryonic development in humans we have generated a mouse model of this condition. In the mouse model just one gene (called Zic2) is altered and embryos that have two copies of this alteration develop the most severe form of cyclopia and die in the second half of gestation. This means that the normal role of this gene is to stop us developing HPE. We will use this mouse model to see just when and how the Zic2 gene prevents HPE. In addition, we will look to see what other genes Zic2 interacts with by breeding mice that carry the mutation in Zic2 with mice that carry a mutation in a second gene that can also cause HPE. These experiments are very important because if we understand how Zic2 and other genes protect us from HPE we can begin to design strategies to decrease the risk of a child developing this condition.