BIO361 Fertilization (2) PDF

Structure of the egg: sea urchin vs mammal Both are about 100 mm in diameter Figure 7.5 Mammalian eggs immediately before fertilization (Part 2) Cumulus cells are derived from Granulosa cells Broadcast spawning, as observed in many aquatic organisms, is the res...

Structure of the egg: sea urchin vs mammal Both are about 100 mm in diameter Figure 7.5 Mammalian eggs immediately before fertilization (Part 2) Cumulus cells are derived from Granulosa cells Broadcast spawning, as observed in many aquatic organisms, is the result of environmental queues. Q1: What types of environmental queues can you think of? Q2: If many different species are all spawning in the same body of water, how do species-specific sperm-egg interactions occur? How does Nature prevent fertilization of egg from species A by sperm from species B? Figure 7.7 Sperm chemotaxis in the sea urchin Arbacia punctulata A2a: Chemoattraction/Chemotaxis t= 0 20 sec 40 sec 90 sec RESACT: A 14 aa peptide Fluorescent calcium indicator is used Figure 7.8 Model for chemotactic peptides in sea urchin sperm (Part 1) Resact is a small peptide: CVTGAPGCVGGGRL Speract is another small peptide: GFDLNGGGVG Arbacia makes Strongylocentrotus Resact makes Speract RGC is a receptor guanylyl cyclase (you might have heard of adenylyl cyclase in the production of cAMP?) Figure 7.10 Acrosome reaction in sea urchin sperm A2b: Species-specific acrosomal reaction Figure 7.9 Species-specific induction of the acrosome reaction by sulfated polysaccharides in the egg jelly coat Figure 7.11 Species-specific binding of the acrosomal process to the egg surface in sea urchins A2c: Species-specific binding of acrosomal process Figure 7.6 Summary of events leading to the fusion of egg and sperm cell membranes in sea urchin fertilization, which is external Does anyone see a problem here? Figure 7.14 Aberrant development in a dispermic sea urchin egg Figure 7.14 Aberrant development in a dispermic sea urchin egg (Part 1) Figure 7.15 Membrane potential of sea urchin eggs before and after fertilization One solution: Fast block to polyspermy We don’t think this happens in internal fertilizers. Why? Figure 7.16 Formation of the fertilization envelope and removal of excess sperm A second solution: Slow block to polyspermy Figure 7.17 Cortical granule exocytosis and formation of the sea urchin fertilization envelope Udx1 is a calcium-dependent dual oxidase Figure 7.19 Endoplasmic reticulum surrounding cortical granules in sea urchin eggs Figure 7.18 Calcium release across a sea urchin egg during fertilization Figure 7.20 Probable mechanisms of egg activation Figure 7.21 Roles of inositol phosphates in releasing calcium from the endoplasmic reticulum and the initiation of development Where have we seen this? Figure 7.24 Nuclear events in the fertilization of the sea urchin Mammalian Fertilization Figure 7.23 Hypothetical model for mammalian sperm capacitation Step 1: Capacitation Mammalian Fertilization Step 2: Sense and follow thermal and chemical gradients Chemical: Progesterone Step 3: Undergo acrosome reaction – a zona pellucida- mediated event Proteolytic enzymes that breakdown barrier to egg Figure 7.25 Recent model for the recognition of sperm by the mouse zona pellucida Mammalian Fertilization Step 4: Fuse with the egg plasma membrane Izumo Juno Figure 7.27 Izumo protein and membrane fusion in mouse fertilization Figure 7.28 Cleaved ZP2 is necessary for the block to polyspermy in mammals Ovastacin: A protease found in cortical granules Figure 7.29 The “zinc spark” at fertilization Zinc Zn2+ Acrosomal enzymes (e.g., matrix metalloproteases) Visualizing the Zn-spark in real time Figure 7.30 Pronuclear movements during human fertilization