Notch signaling promotes proliferative signaling during neurogenesis, and plays a major role in the regulation of embryonic development. Notch and most of its ligands are transmembrane proteins, so the cells expressing the ligands typically must be adjacent to the notch-expressing cell for signaling to occur. The notch ligands are also single-pass transmembrane proteins and are members of the DSL (Delta/Serrate/LAG-2) family of proteins. In Drosophila melanogaster (fruitfly), there are two ligands named _______ and Serrate for notch. In mammals, the corresponding names are Delta-like and Jagged. In mammals there are multiple Delta-like and Jagged ligands, as well as possibly a variety of other ligands, such as F3/contactin.