Large-scale high-throughput mouse gene knockout studies have generated considerable data with respect to adult phenotypes of viable homozygous mouse strains. However, many strains do not survive into the post- natal period. The current KOMP2 initiative provides a tremendous opportunity to determine how the disruption of numerous genes impacts embryonic development and to provide insight into the gene networks responsible for normal embryogenesis and fetal development. These studies are especially relevant to the investigation of the underlying causes of human pregnancy loss and structural birth defects. Importantly, some of the most frequent developmental abnormalities observed in large-scale mouse knockout studies are also common human birth defects. Defects in neural tube closure and neural crest formation account for a high proportion of birth defects in humans and these defects can have severe consequences on viability. This reinforces how knowledge gained from the study of mouse models can impact our understanding of human pathology. This proposal brings together three experts - Williams, Clouthier, and Niswander - who have extensive and collaborative experience in the detailed characterization of embryonic mutations that disrupt neural tube closure, craniofacial formation, and heart development. Our experience in forward genetic screens and high- throughput characterization makes us cognizant of the necessity for rapid analysis of mutant strains in order to minimize the shelf-time of the live colonies. Our goal in Aim 1 is to expand and complement the phenotyping information for the KOMP2 strains by providing a detailed histological assessment of strains that would not otherwise undergo this gold standard of analysis at KOMP2. All data will be uploaded and available through a publicly accessible website, with annotations and ontologies established by IMPC, MGI and KOMP2. Aims 2 and 3 will delve much deeper into the cellular and molecular mechanisms responsible for the defects seen in neural tube (Aim 2) and neural crest (Aim 3) formation in a select number of KOMP2 strains. Aim 2 is relevant for understanding the causes of human neural tube defects such as exencephaly and spina bifida (1 in 1000 births). Molecular assays and genetic interaction studies will provide pathway information to elucidate the genetic networks that orchestrate NT closure. Innovative live-imaging will explore how changes in gene function alter the cell behaviors that underlie neural tube morphogenesis. Aim 3 is relevant to major abnormalities associated with neural crest pathology include craniofacial defects (1.5 in 1000 births), heart defects (1 in 125 births), and enteric nervous system defects (1 in 5000 births). Aim 3 will study formation, migration and differentiation of the neural crest ad its interactions with surrounding tissues. Furthermore, tissue-specific knockout studies will determine if the observed defects are autonomous to the neural crest or if they are caused by defective signaling interactions with other tissues, particular the ectoderm. Overall these proposed studies will provide biological insight into the function of new genes arising from the KOMP2 centers.