PROJECT SUMMARY To devise new innovative treatments for craniofacial malformations, disease, and injuries, more research is needed to understand developmental mechanisms that control proper jaw formation. Normal facial morphogenesis involves precisely timed interactions between the embryonic brain and face. Independent facial primordia grow until they appose and fuse to form functional jaws. Due to the complexity of this process, it is unsurprising that the jaw anomalies, including size-related jaw irregularities such as micrognathia, retrognathia, and maxillary hypoplasia, cleft palate, and cleft lip are among the most common birth defects. This study will provide critical data to address this unmet need by focusing on how altering growth of the brain and/or face during early development influence the time and success of facial primordia fusion. We employ a unique chimeric system to manipulate either neural crest mesenchyme, which is the cell population that gives rise to most of the craniofacial bones, or basal forebrain. Chick and duck have very different jaws as well as rates of maturation thus, transplanting neural folds or basal forebrain between duck and chick embryos generates chimeras that carries two distinguished cell populations that have species-specific cellular and molecular mechanisms through which differences in shape and size are achieved. Previous research of the etiology of cleft lip has determined that dysregulation of facial prominence growth plays a major role, because key developmental events such as the facial prominence contact and fusion are dependent on successful growth. Additionally, our data from a developmental morphospace of embryonic facial morphogenesis predicts that brain growth impacts the shape and spaciotemporal character of the phenotypic landscape in which these critical events occur. These results indicate that there are not only molecular interactions between the face and brain that play a key role, but also that there are architectural components of the brain that are critical to successful facial prominence fusion. This application aims to experimentally test the hypothesis that modulation of the size and/or timing of the growth of the brain and/or face during early development increases the incidence of cleft lip. Further, this study will determine the smallest regions/tissues in early embryo that contribute to increasing the liability of clefting. Aim 1 will test how variation in size and spaciotemporal growth affect face shape and cellular processes (proliferation and apoptosis) in embryos pre- to post fusion. Aim 2 will determine the extent to which alterations to WNT- signaling affects the success of fusion and changes the liability of clefting. This aim will provide specific insight into molecular mechanisms of WNT-signaling that propagate craniofacial shape variation across species. Together, the two Aims will add significantly to our understanding of the contributions of brain and face to cleft...