Novel craniofacial structural birth defect genes

About This Grant

Congenital malformations are the leading cause of death for children under the age of one and 1/33 babies is born with such a birth difference. A significant proportion of these affect the developing face and cleft lip/palate occur in ~1/700 births making it one of the most common structural birth defects. Most craniofacial deficits have a genetic component, but our understanding of the genes and mechanisms involved is woefully incomplete. The overall objective of this application is to use forward genetics (i.e., moving from phenotype to causal gene) in the mouse to identify novel alleles important for multiple aspects of craniofacial development. We will also use sophisticated genetics to both predispose some of the embryos to a perinatal phenotype and to immediately assess if the crucially important hedgehog pathway is disrupted during development. Our rationale is that by taking an unbiased, forward genetic approach we will uncover new and fundamental discoveries in the genetics of craniofacial and brain development. We will utilize N-ethyl-N-nitrosourea (ENU), a chemical mutagen causing random, single base-pair substitutions in the genome. Treatment with ENU is an effective tool for generating heritable changes in the genome with low morbidity and/or mortality. We have previously used this technique to identify many new genes to be important for craniofacial development. One of these discoveries we have made from a previous screen is that P4hb is crucial for proper palate and skeletal development. We have not studied this allele in depth and here we further explore the underlying pathogenic mechanisms of this genetic variant. The major outcome of this proposed research is that new genetic determinants which control craniofacial development will be revealed through the use of ENU mutagenesis in mice. By completing these studies, we will be positioned to use this information together with the newly developed animal models to develop novel hypotheses guiding mammalian craniofacial development. We will accomplish the goals of this application by pursuing the following two specific aims. In Aim 1, we will perform ENU mutagenesis in the mouse and conduct a forward screen for novel genes important for craniofacial development. To further enrich a portion of our screen and quickly assess a potential molecular mechanism, we will incorporate the Patched1-lacZ null/reporter allele into our breeding scheme. This will allow us to both predispose some of the mutants to craniofacial anomalies and quickly assess if the malformation(s) are due to altered hedgehog signaling. We aim to clone and experimentally validate 15 novel mutations over the course of this grant period. Aim 2 will follow up on the P4hb variant previously discovered through ENU mutagenesis and determine the molecular basis for the malformations seen in these mutants. In addition to learning more about the role of this particular gene, the details of the experimental approaches in this aim serves as a benchmark for how we might pursue studies in other alleles identified in Aim1. Together, these studies will identify several genes essential for mammalian craniofacial structure.