Which of the following statements about morphogens is false?
Authentic morphogen definition includes ability to form extracellular gradient and to elicit concentration-dependent transcriptional responses leading to multiple discrete cell states in same tissue. They can be secreted paracrine proteins like Shh, Wnt, BMP acting on nearby cells via membrane receptors or transcription factors like Bicoid that diffuse between cells after translation via syncytium. They influence determination, pattern body axes and operate early embryogenesis establishing positional values. Claiming all morphogens are exclusively transcription factors is inaccurate because majority are secreted ligands signaling via membrane receptors, although some transcription factors also exhibit morphogen properties through intercellular transfer and direct gene activation.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: Morphogen Types and Transcriptional Responses.