BIOL/ BMB 430
DEVELOPMENTAL BIOLOGY CLASS NOTES
Review of Cell signaling: ligands, receptors, and signaling pathways
Box 1E, p 26 wnt
Box 4A, p 131 signaling
Box 5B, p 184 FGF
Box 5C, p 190 Notch
p 75 hedgehog
For anyone desiring additional review on cell signaling refer to Chapter 16 of
or Chapter 15 of
Molecular Biology of the Cell
Learning goals: Be able to:
Describe in general the process by which developmental signals are sent from one cell and
received by other cells, and what can happen in the receiving cells as a result.
Compare and contrast the major developmental signaling pathways (Wnt, TGF
Hedgehog, Notch, RTK).
Explain how a mutant component of a signaling pathway can cause a cell to become
Differential gene expression and other cell functions in development are often controlled by
signals from one cell to another, requiring signaling molecules (ligands), receptors, and
machinery for transducing signals through the cell membrane and communicating with the
nucleus or cytoskeleton, or both. Some of this machinery should be familiar to you from cell
biology. In today’s class, we will discuss mechanisms of cell communication used during
Signaling pathways are ancient and highly conserved during evolution, and most of them are
found in all phyla. Some have been adapted for special functions, but
many of them seem to play
similar developmental roles in all organisms where they have been found
. There are actually
fewer than 20 currently recognized intercellular signaling pathways that take care of all known
signaling events, and only a handful that are known to be involved in development. This means
that each signaling pathway has many different functions during development.
Classes of transmembrane signaling pathway
Ligands can be small diffusible molecules, large molecules in the extracellular matrix, or
non- diffusible surface components of neighboring cells. All interact with specific cellular
receptors on receiving cells.
For diffusible ligands: Signaling can be classified as autocrine (self-signaling), paracrine,
(signaling between nearby cells), and endocrine, (signaling over a long distance, usually via the
bloodstream.) Of these, paracrine signaling is most important for embryonic development.
Ligands for paracrine signaling are all diffusible between cells, they range from small to quite
large, slowly diffusing molecules. Many of the important paracrine ligands are so-called growth
factors, described below.
Non-diffusible ligands are involved in juxtacrine signaling, so-called because the signaling