Practice question

Left-right asymmetry in C. elegans morphogenesis involves Nodal-related signaling despite absence of classical Nodal in worms. Recent work identifies UNC-6/Netrin and TGFbeta family member TIG-3 related to Activin/Nodal acting through SMA-6 and DAF-4 receptors regulating asymmetric positioning of gut, gonad and AB lineage divisions such as ABar spindle skewing. While early cleavage asymmetry uses Notch and Wnt, later organ laterality requires this Activin-like cascade. Although vertebrates use Nodal-Lefty-Pitx2, conserved type I and II TGFbeta pathway components were shown to influence nematode left-right handedness of blastomere divisions and gut rotation, classified as Nodal/Activin related signaling module.