Introduction to Signaling Flashcards
What is the definition of signaling?
Part of any communication process that governs basic activities of cells and coordinates all cell actions
What are the components of cell signaling?
What is endocrine signaling?
Signal acts at some distance from its site of production
What is paracrine signaling?
When the signal molecule acts on cells locally at its site of production.
Example: when [glucose] in blood is low, alpha cells in pancreas will secrete glucagon. This stimulates the breakdown of glycogen in liver/muscle (endocrine) but also acts locally to “prime” beta cells to let them know that an influx of glucose is coming and they should be prepared to secrete insulin (paracrine).
What is neurocrine signaling?
Signals that act across a synapse
What is juxtracrine signaling?
Signaling that requires cell to cell contact
Ex: intestinal crypts
What is autocrine signaling?
When a signaling molecule acts on the same cell that produced the signal.
Describe the process of neutrophil extravasation
When macrophages in tissue sense foreign material, they express chemokines. This causes the nearby epithelial cells of blood vessesl to express adhesion molecules. When neutrophils in the blood stream comes in contact with the adhesion molecules, they express counter receptors and roll along the surface of the epithelium until the adhesion molecules and receptors make high - affinity contact. Helper proteins create a break in the epithelium allowing the neutrophil to enter the tissue where they recognize chemokines secreted by macrophages. The chemokines help lead the neutrophils to the microbes or material that needs to be degraded.
What role does the extracellular matrix play in signaling?
Resident cells imbeded in the ECM secrete collagens to ground the substance of the ECM. In the process of generating the ECM, they also trap several growth factors in the ECM called latent growth factors. When neutrophils enter a tissue and migrate via chemotaxis, they must secrete proteases to degrade the ECM to migrate. This can release these latent growth factors. However, this also damages the ECM so there must be a counter response to neutrophil recruitment or else the tissue could be permanently damaged.
What is a second messenger?
A small molecule produced within the cell that helps mediate the effector response
What is a signal transducer?
A wide variety of proteins that serve to transmit the signal throughout the cell
Does a second messenger only bind to the same receptor?
No - second messengers can bind to different receptors in different cell types to produce a unique physiology
Explain what is happening in this image and the roles of Wnt, BMP and EGF.
Wnt and EGF - promote proliferation of stem cells
BMP - promotes differentiation
Figure A shows a zoomed out view of the topography of the intestinal tract. Figure B shows the space between villi, called crypts, that contain two types of cells - paneth cells and stem cells. Figure C shows a close up of the junction between paneth and stem cells, showing that they display juxtacrine signaling between one another.
Intestinal Crypts
- In the presence of Wnt and EGF, what does notch signaling promote?
- As the stem cells in the crypts divide, they are pushed out of the crypt and up into a transition zone between the crypt and the villus surface. What happens to these cells?
- What happens to notch signaling under the influence of BMP?
- What effect does this have on neighboring cells in the transition area?
- What effect does this have on the ratio of goblet : absorptive cells?
- Stem cell renewal (proliferation)
- Wnt and EGF are expressed in greatest concentration in the crypt, so as the cells are pushed out of the crypt, the cells are subject to the effects of BMP, which promotes their differentiation into epithelial cells.
- The cells are no longer under the influence of Notch signaling (Wnt and EGF) so they lose their stemness and express the notch ligand instead. These cells are destined to become goblet cells.
- As soon as one cell begins differentiation and secretes notch ligand (Wnt and EGF), that ligand will stimulate neighboring cells in the transition area to express notch receptors so notch signaling remains active for these cells. As such, they are destined to become absorptive cells.
- More absorptive cells than goblet cells
