with regards to the CNS and neural crest. Pax3 and Pax7 are promoters of both neural crest cell survival along with promoting environmental stress resistance. In mouse embryos Pax3 blocks the tumor suppressor gene p53, which is necessary for controlled proliferation and genomic stability, is expressed in all cells of the neurula. During early development Pax3 is expressed at the posterior and lateral area of the neural plate, the same region that the neural crest arises from. Neural crest defects were found to occur in mouse and human Pax3 mutants, indicating an importance of functionality. Within chicks, frogs and fish Pax3/Pax7 are activated by Wnt and FGF signaling. Pax3 and Pax7 are also required for neural crest induction after depletion of the two genes resulted in the lack of activation of the specific neural crest genes Snail2 and Foxd3, which didn't allow further development or emigration of neural crest. Using knockouts has been helpful for understanding the role and functions of several genes found in the neurula. For example, Wnt-1 was found to have no role in the closing of the neural plate, despite being present at the tip of the neural folds when it is closing. Though mutants of Wnt-1 does lead to pattern defects within the brain. Notch1 is involved with formation of somites. HNF-3 is needed for development of the notochord and node. The gene Apolipoprotein B, which is involved in transporting and metabolizing fat soluble molecules in the blood, is expressed in the yolk sac and fetal liver. Within the neurula in Xenopus laevis, development genes Xwnt-3 and Xwnt-4 are present. References Embryology of nervous system