Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Bio200 Signaling and Fertilization Outline Questions Understanding Fertilization • How do cells signal to each other? – What molecules are released, and what molecules are used to recognize signals? – Why would a cell need to signal to another cell? • What are the three cell-cell signaling events necessary for successful sea urchin fertilization? • How does the acrosomal reaction allow the sperm to fertilize the oocyte? • What protections are used by the oocyte to defend itself? Cell-to-Cell Signaling • We ve already talked about cell-to-cell signaling several contexts, – Growth factors, hormones, secreted proteins, etc • There is a vast array of cell signaling methods, which include – – – – – Lipid-soluble signals Cell-to-cell contact mediated by receptors Signal receptors Second messengers and enzymes Direct cytoplasmic contact – A quick tour is in order… Lipid-soluble signals, (the easy way) Steroid hormone 1. Lipid-soluble (small, hydrophobic) signal diffuses across plasma membrane into cell. Plasma membrane 2. Signal binds to receptor, inducing conformational change or binding to a carrier. Receptor in cytosol No membrane proteins are required Target gene DNA Nuclear membrane Nucleus 3. (example) Complex binds to DNA, inducing a change in gene activity. Intermembrane Signal Receptors Intercellular signal Cell binding receptor 1. Signal is received. Outside of cell Inside of cell Second messengers Intracellular signals Receptor protein in membrane 2. Signal is transduced. 3. Signal is amplified. 4. Cell responds. Direct cell contact/signalling Tubule of ER passing through plasmodesmata Smooth endoplasmic reticulum Direct cell contact/signalling Tubule of ER passing through plasmodesmata Smooth endoplasmic reticulum Gap junctions Membrane proteins from adjacent cells line up to form a channel What does this have to do with fertilization? Fertilization in the open ocean Gametes Adult sea urchin • Advantages of this method, – Cheap – Long distance – Synchronizable Jelly coat layer • Problems, – Low probability of success in massive expanse of water – Many predators – Confusion between species Sperm Nucleus Vitelline envelope Plasma membrane Cortical granules Yolk granules Homing in on the Egg, Resact and resact receptor • To help the sperm find the egg Egg – Egg releases a small 10-aa peptide resact – Resact diffuse from the egg into nearby water – Sperm use this concentration gradient to guide towards egg • Sperm have two swim motions, – Low ligand binding = turn – High ligand binding = straight – Why does this set of rules get the sperm to the egg? – Chemotaxis Acrosome Packaging, Sea Urchin Sperm Anatomy Nucleus Acrosome Centriole Actin monomer pool Actin polymerase enzyme Acrosome Packaging, Sea Urchin Sperm Anatomy Y Nucleus Acrosome Y Centriole Actin monomer pool Actin polymerase enzyme Digestive Enzyme Jelly coat factor receptor Bindin The acrosomal reaction Animations to watch at home http://worms.zoology.wisc.edu/urchins/acrosome2.html An excellent longer video: http://www.youtube.com/watch?v=_5OvgQW6FG4 from 2:14 for the acrosome reaction Bindin and Fertilizin Bindin is exposed along the acrosomal process Y Y Plasma membranes fuse, nucleus/centriole are inserted Binds to the fertilizin receptor on the egg !"##$%&'()*+$,#(-*&&Ͳ.)/,/.(*,$0*12,"(*$3Ͳ2,"(*$3%$31$34 *5*3(6%$31$3 /31+*,($&$0$3 7#*/8,.)$3#9: ;"- -"8&1 <8(/($"3# $3 ()*#* 2,"(*$3# /++*.( #2*.$/($"3= ;"--"8&1<8(/($"3#$3()*#*2,"(*$3#/++*.(#2*.$/($"3= Possibly the first well‐characterized protein‐protein binding event: bindin and fertilizin. How would mutations in these proteins affect speciation? Gene Mutated Normal location of the protein Fertilzation rate of mutant Other phenotype? “Bindin” receptor protein Exterior of sperm membrane 4.4% Sperm pass jelly coat layer well “Resact” receptor protein Exterior of sperm membrane 21.3% Fertilization in test tube is 100% Sperm-specific receptor protein Exterior of sperm membrane 8.5% Sperm on vitelline envelope fertilize well Jelly coat proteins Forming jelly coat layer on oocyte 8.5% No visible difference in oocyte layers Wild-type sperm and oocytes n/a 100% Sperm find oocyte and reach vitelline envelope layer quickly Motivations for Sperm and Egg Sperm Egg No Sperm Entry 1 Sperm Enters 2+ Sperm Enter Polyspermy is a major concern for the egg Blocking polyspermy, The Calcium Wave Calcium Wave Video http://www.youtube.com/watch?v=BH06WgFua_4 Blocking polyspermy: Cortical Granules • Calcium wave causes cortical granules to fuse with egg plasma membrane • Carbohydrates are released into the inter-layer space • This thick fluid absorbs water and swells, pushing away the vitelline envelope. Blocking polyspermy, Fertilization Membrane Pulls Away This clears other sperm away from the plasma membrane by ~6 seconds after sperm entry Slow Block Video http://www.youtube.com/watch?v=MHWkltLbJp0 Blocking polyspermy, the Fast block • The egg is still vulnerable to polyspermy in the first few seconds – Especially problematic with many sperm reaching the jelly coat at nearly the same time • The Fast Block system uses the change in membrane potential in the egg to help protect against a second sperm – Change in membrane potential rapidly and temporarily distorts fertilizin structure – This inactivates all fertilizin molecules for ~6 seconds + + + + + + + - - - - - - + - + - + - + - + + - - - + - Key Concepts • Cell-cell signaling is a widespread and varied molecular interaction that helps cells define their role, position, and communication. • Cells can release small molecule signals (like hormones) and have specific receptors for each signal that they need to receive. • Sea urchin fertilization models cell-cell signaling in three separate interactions between signaling molecules (resact, jelly coat factor, bindin) and their respective receptors. • These reactions are species specific • Communication is 2-way through these process • This ensures that the correct binding is reached to minimize waste • The acrosomal reaction allow the pre-packaged components of sea urchin sperm to facilitate a rapid and accurate fertilization. • Oocytes use both a fast-block and a slow-block mechanism to prevent fatal polyspermy fertilizations.