Practice question

Morphogen patterning predominantly employs Hedgehog, Wnt and BMP pathways that support long-range diffusion, graded distribution and multiple fate thresholds via Gli, beta-catenin and Smad effectors. Sonic hedgehog patterns ventral neural tube and limb posterior bud, Wnt beta-catenin patterns anterior-posterior axis and limb dorsal-ventral, BMPs dorsalize neural tube and pattern digits via Smad-dependent enhancer activation and antagonism with Shh. JAK-STAT mediates cytokine and interferon responses, controlling proliferation, hematopoiesis and Drosophila germline stem cell self-renewal via short-range Unpaired ligand, not generating sustained extracellular gradient specifying several distinct cell types in classical sense, therefore distinguished from bona fide morphogen pathways.