Practice question

Bone morphogenetic protein signaling must be tightly modulated by extracellular antagonists conserved from flies to mammals. Noggin, Chordin, Sclerostin, Gremlin bind BMP ligands BMP2/4-like DBL-1 and SMA-6 receptor ligands preventing receptor engagement with ALK-SMAD cascade. In C. elegans, homologous antagonists shape dorsal-ventral patterning indirectly via sma-9. Noggin exemplifies inhibition by sequestering BMPs with cysteine-rich domain creating low BMP zones allowing neural induction. This mirrors Spemann organizer secreting Chordin to dorsalize ectoderm during gastrulation, conserving mechanism for tissue specification and extracellular modulation of morphogen activity.