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BIOL/ BMB 430 DEVELOPMENTAL BIOLOGY CLASS NOTES Class 3 Review of Cell signaling: ligands, receptors, and signaling pathways Reading: 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 Essential Cell Biology or Chapter 15 of Molecular Biology of the Cell . Learning goals: Be able to: 1. 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. 2. Compare and contrast the major developmental signaling pathways (Wnt, TGF - β , Hedgehog, Notch, RTK). 3. 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 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 development. Intercellular signaling 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
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Class 3 Notes 3-­૒2 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.
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