DEVELOPMENTAL BIOLOGY CLASS NOTES
3 - 1
Review of Cell signaling: ligands, receptors, and signaling pathways
Chp 6: 139-142, 145-158, 160-161, 164-171
For anyone desiring additional review on cell signaling, the following Alberts pages are also
ed): 15: 831-852, 853-866, 871-890, 893-900; 17: 1014-1017, 1019-1021, 1023;
19: 1084-1090, 1090-1096, 1103-1106, 1110-1111, 1113-1118; 23: 1333-1340.
Be able to:
Describe in general the process by which developmental signals are sent from one cell and received
by other cells, and what happens in the receiving cells as a result.
Compare and contrast the major developmental signaling pathways (Wnt, TGF
, Hedgehog, RTK,
Explain how a mutant component of a signaling pathway can cause a cell to become cancerous.
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
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 development.
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 5 that are 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 extracellular matrix, or non-
diffusible surface components of neighboring cells.
All interact with specific cellular receptors on
For diffusible ligands: Signaling can be classified as autocrine
(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,
Non-diffusible ligands are involved in juxtacrine
signaling, so-called because the signaling and
receiving cells must be in contact for the signal to be transmitted. Ligand molecules imbedded in the
membrane of the transmitting cell interact with specific receptors on an adjacent receiving cell.
Still other signals can come directly from slowly diffusible components of the extracellular matrix