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Germ Cells and Fertilization

Germ Cells and Fertilization. Lecture 30 BSCI 420, 421 Nov 11, 2002 “The final aim of all love intrigues, be they comic or tragic, is the composition of the next generation” - A. Schopenhauer Sexual reproduction Meiosis Oogenesis Spermatogenesis Fertilization. Sexual reproduction

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Germ Cells and Fertilization

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  1. Germ Cells and Fertilization • Lecture 30 BSCI 420, 421 Nov 11, 2002 • “The final aim of all love intrigues, be they comic or tragic, • is the composition of the next generation” • - A. Schopenhauer • Sexual reproduction • Meiosis • Oogenesis • Spermatogenesis • Fertilization

  2. Sexual reproduction • Has an advantage over asexual reproduction: • Increases diversity by producing offspring that are a mixture • of the traits of the parents. • Is diversity an advantage? • If so, • Why is diversity an advantage?

  3. Meiosis • A pair of nuclear divisions that produce four • different haploid cells, usually but not always gametes. • Gametes are haploid cells capable of fusing to produce • A diploid cell called a Zygote. • Gametes can be of identical size and shape (isogamy). • Or they can be different in size and or shape (anisogamy).

  4. Meiosis vs mitosis

  5. 3. Oogenesis Is gamatogenesis of the larger gamete called the egg or ovum.

  6. Oogenesis

  7. Mammalian (rabbit) oocytes (fig 24)

  8. 4. Spermatogenesis Spermatozoon is a small, highly streamlined cell, specialized to deliver a nucleus to an egg far away, and to activate development of the egg.

  9. Spermatogenesis

  10. 5. Fertilization • Involves: • Activation of the sperm and the acrosomal reaction • Activation of the egg • 1. The fast block to polyspermy • 2. The slow block to polyspermy • 3. Initiation of protein, RNA, & DNA synthesis • 4. Fusion of the egg and sperm and male and female • pronuclei

  11. a. Activation of the sperm and the acrosome reaction

  12. Activation of the sperm: Contact w Zona Pellucida Aggregates Receptors Opens Na+ Channels Release of V change opens Exocytosis lytic enzymes VS Ca2+ Ca2+ of Acrosomal Channels influx vesicle Exposure of fertilins

  13. b. Egg Activation: 1. Fast block to polyspermy Sperm binding to Egg cell membrane By fertilin and its receptor on egg Receptor linked Na+ channels open Na+ influx Membrane potential change 0 Fast block to polyspermy -70 1 2 (Discovered by mV time, min E.E. Just contact Afro-Amer Dev.Biologist)

  14. Starfish egg injected with the dye aequorin that fluoresces When the Ca2+ conc increases. At time 0, the egg was fertilized, and a wave of Ca2+ sweeps Over the egg in about 1 min. initiating cortical granule Exocytosis and the slow block to polyspermy.

  15. Slow Block to polyspermy

  16. 2. Slow block to polyspermy Binding of fertilin to receptor on egg Tyrosine kinase activation (both IP3 gated & Ca-Induced) Phospholipase C-g activation IP3 Ca2+ release DAG production PKC activation Cortical granule exocytosis Stimulation of Slow block to 3. protein syn polyspermy RNA syn DNA synthesis

  17. 4. Fusion of pronuclei (MTs green Fl-aT; DNA blue) Fig 35

  18. The merging of mammalian pronuclei after fertilization

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