Notch is a single-pass membrane receptor that is cleaved to release an intracellular domain (NICD) after interacting with specific ligands (Delta, Jagged) presented by the neighboring cells. Once released, NICD translocates to the nucleus and activates transcription of target genes. The role of Notch is context-dependent. As
an inhibitory signal during lateral inhibition, Notch prevents equipotent cells to adopt the same fate. As an inductive signal, Notch induces the expression of positively acting regulatory molecules in order to promote the developing of a different cellular type in the boundaries of non-equipotent cell populations by cell-cell interaction,
thus regulating the boundary between populations within morphogenetic fields. One known example is boundary generation between dorsal and ventral compartments in the wing imaginal disc in Drosophila, where Delta and Serrate (Jagged) are involved. Our lab demonstrated the major role of some members of the Notch pathway during the development of the Xenopus blastula and gastrula dorsal centers and their descendants, and during the segregation of germ layers [López et al. Development 130, 2225–2238 (2003); López et al. (2005) Development 132, 1035–1046; Revinski et al. (2010) Dev. Biol. 339, 477–492; Acosta et al. (2011) Development 138, 2567–79; Aguirre et al. (2013) PLoS One 8, e54777)]. Anomalies during the establishment and segregation of germ layers cause developmental failures Their severity varies from congenital malformations to embryonic lethality. In Revinski et al (2010), it was possible to demonstrate by gain and loss-of-function that Delta1 (Dll1) and Notch1 are involved in endomesoderm and neural ectoderm delimitation. Notch1 also participates in endoderm and mesoderm delimitation, possibly involving another ligand. One of the developmental anomalies related with the Notch pathway in humans is the Alagille Syndrome, which is caused by  mutations in the gene encoding Jagged 1 (Jag1). However, Jag1 knock-out mice do not reproduce the syndrome. We have found that Jag1 and Dll1 have complementary expression patterns in Xenopus during germ layer segregation. In situ hybridizations at gastrula stage revealed Jag1 expression in the presumptive neuroectoderm and also in the marginal zone, with a “salt and pepper” cellular pattern, corresponding to the sub-blastoporal endoderm, adjacent to the mesoderm ring, where Dll1 is expressed. This pattern suggests that Jag1 might participate in unknown aspects of germ layer development. We are employing the CRISPR/Cas9 gene editing tool for generating loss of function mutations in Jag1 in Xenopus laevis. Preliminary results indicate that mutant embryos show a gastrulation defect, compatible with a role of Jag1 in germ layer segregation. Our aim is to study the role of Jag1 during germ layer development and to establish a model of Alagille syndrome by employing genomic edition with CRISPR/Cas9.