Unit 5 Egg Activation Cell Signaling Ca2 IP3 Calcium indicators allow us to visualize calcium concentration Adapted from Campbell et al 5e Fig 11 14 A calcium wave is triggered by fertilization in Medaka micropyle where sperm enters Gilbert 10e Fig 4 20 Phospholipase C gamma leads to calcium release Phospholipase C Modified from Campbell et al 5e Fig 11 14 Calcium induced calcium release produces a calcium wave IP3 Ca2 IP3 can serve as an initial trigger but calcium causes adjacent ER calcium channels to open in a chain reaction adapted from Dawson 2003 Curr Biol 13 R424 Egg activation Src non receptor tyrosine kinase activation leads to PLC activation Gilbert 7e Fig 7 29a see 10e Fig 4 22 Egg activation putting it together Gilbert 10e Fig 4 23 Ca2 DAG stimulate a Na H exchanger leading to a pH increase Ca2 pH increase lead to macromolecular synthesis Egg activation RNA synthesis is not immediate incorporation of radioactive amino acids is a measure of protein synthesis rate Gilbert 10e Fig 4 26 Transcription is eventually required but translation is required immediately for normal development Adapted from Gilbert 3e Fig 14 11 Conclusion There must be maternal mRNAs that are stored in the egg and translated after fertilization these allow early but not later development Egg activation protein synthesis is immediate incorporation of radioactive amino acids is a measure of protein synthesis rate Gilbert 3e Fig 2 33 Egg activation protein synthesis is stimulated by pH increase and calcium Gilbert 3e Fig 2 34b Review MPF Regulation in Frog Oocytes Fertilization causes elevated calcium Simplified from Gilbert 10e Fig 17 22 Pronuclear migration unites the male and female pronuclei haploid egg pronucleus diploid nucleus haploid sperm pronucleus The sperm brings in a centrosome associate with the centriole of the flagellum Alberts et al 3e Fig 20 28 Pronuclear migration is guided by the sperm aster sperm aster female pronucleus male pronucleus sea urchin Gilbert 10e Fig 4 27 Pronuclear migration dynein moves the female pronucleus along MTs Pronuclear apposition Payne et al 2003 J Cell Sci 116 4727 4738 Humans fertilization issues Obstructions blocked Fallopian tubes obstructive azoospermia Inefficient cumulus zona penetration laser scoring zona drilling Poor sperm motility lack of functional flagellum intracyosplasmic sperm injection ICSI Humans zona drilling aids sperm penetration Courtesy M Berns UC Irvine Humans Intracytoplasmic Sperm Injection ICSI bypasses normal sperm egg union Parthenogenetic activation can produce a diploid without fertilization Chemicals ionomycin Ca2 ionophore DMAP suppresses first cleavage Washington Post Dec 7 2001