Multiple Functions of Notch Signaling during Early Embryogenesis

Abstract

Notch signaling is involved in multiple developmental programs across the animal kingdom. This major pathway typically mediates cell-cell interactions where the sending cell presents a transmembrane ligand belonging to the Delta/Jagged family. The ligand activates the transmembrane receptor Notch in the receiving cell. Consequently, Notch undergoes enzymatic cleavage, releasing the intracellular domain (NICD). This results in NICD translocation to the nucleus and transcriptional activation of Notch target genes, typically of the hes1–7 and hey families. More recently, non-canonical Notch activities diverging from the canonical pathway were discovered and are thought to represent ancestral modes of the pathway. This chapter presents a comprehensive review of the expression patterns and experimental functional evidence collected for Notch receptors, ligands, and hes1–7/hey genes in key processes during early embryogenesis in Xenopus. Their involvement in body axis formation; germ layer and dorsal midline development; neural border, neural crest, and placode formation; primary neurogenesis; and somitogenesis is discussed. The information presented in this chapter identifies important knowledge gaps and provides the molecular foundation for building developmental process-specific gene regulatory networks involving this pathway.