Lecture 7 fast block and polyspermy.pptx

Fast Block and Polyspermy Lecture 7 How Is Polyspermy Prevented? The problem: there are millions of sperm. How is it that only one enters the egg??? Statistical analysis indicated that cortical reaction (5- 10 minutes duration) too slow to prevent multiple sperm from entering Is there anoth...

Fast Block and Polyspermy Lecture 7 How Is Polyspermy Prevented? The problem: there are millions of sperm. How is it that only one enters the egg??? Statistical analysis indicated that cortical reaction (5- 10 minutes duration) too slow to prevent multiple sperm from entering Is there another mechanism also at work? How is polyspermy prevented??? Fast Block to Polyspermy Laurinda Jaffe (daughter of Lionel Jaffe) Sea Urchin Fertilization Used electrophysiology to test membrane potential You can measure current or voltage change relative to an external electrode You can insert a second electrode and pump/measure current to maintain a stead state You can artificially clamp a membrane at specific potential difference (voltage) Fast Block to Polyspermy Laurinda Jaffe Membrane potential alters immediately at fertilization Voltage clamping can either prevent or facilitate fertilization, depending on where voltage is clamped High voltage prevents, low voltage facilitates polyspermy Nicotine inhibits fast block Laurinda Jaffe – took work of the Hertwigs (1887) that nicotine induced polyspermy Found that nicotine inhibits amplitude of electrical block – polyspermy ensues. Normal Nicotine  Generalized Response: frogs, echinoderms, marine worms, mammals +15 mV -70 mV few seconds 30 minutes time Final Proof Test Voltage clamp high: Fertilization occurs = depolarization: No fertilization Fast Block to Polyspermy commences +15 mV -70 mV Release Voltage clamp: Fertilization possible time Nicotine inhibits fast block Artificial Depression of potential difference (Sodium Iodide) permits visualization of multiple inseminations (polyspermy) fertilizations -70 mV Other mechanisms to prevent polyspermy Micropyle – Fish Insects D-G are goldfish, H is loach, I is Zebrafish Yanagimachi ety al (2017). Chemical and Physical Guidance of Fish Spermatozoa into the Egg through the Micropyle1. Biology of Reproduction. 96. 10.1093/biolre/iox015.  Polyspermy as the norm: urodeles, birds, reptiles Reproduction and Development, Volume: 87, Issue: 3, Pages: 358-369, First published: 16 July 2019, DOI: (10.1002/mrd.23235) Basal Body from sperm and egg each nucleate microtubule growth Mitotic spindles grow Maternal and paternal chromosomes align, diploidy is restored Peripheral or late spindles and associated chromosomes bulldozed out of the game and degenerate