Practice question

Ventral mesoderm and lateral ectoderm secrete BMP4 and BMP2 functioning as morphogens promoting ventral blood, mesothelium and epidermal keratin differentiation via Smad1/5/8 transcription. Organizer dorsal lip secretes extracellular binding proteins Noggin, Chordin and Follistatin that physically sequester BMPs in extracellular space, preventing receptor binding and Smad phosphorylation. Consequently dorsal side experiences low BMP, allowing dorsal mesoderm to differentiate into notochord, somites and ectoderm into neural tissue. BMP blockade creates dorsal-ventral gradient explaining organizer transplantation dorsalizing effects. Their primary action is BMP inhibition not activation.