sperm

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Author:
kbroady
ID:
181693
Filename:
sperm
Updated:
2012-11-04 21:33:05
Tags:
development
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Description:
lecture 5
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  1. gametogenesis
    • development of mature gametes = sperm and eggs
    • includes processes of mitosis, meiosis, morphogenesis, differentiation
  2. PGC
    where do they appear?
    what do they express?
    • primordial germ cell
    • germ line is separated from somatic cells during the 2nd week post-fertilization
    • appear in epiblast of pre-embryo
    • appear several weeks before gonad appears
    • express TF Oct4
  3. PGC migration
    • migrate during 3rd and 4th weeks
    • migrate through yolk sac, hindgut, and dorsal mesentery
    • arrive at gonadal ridge at week 5
    • chemotaxis is one likely mechanism (w/c-kit and SCF)
  4. what can happen if PGCs don't migrate correctly to the gonad?
    may become germ cell tumors (teratomas and teratocarcinomas) in ectopic locations
  5. c-kit
    SCF
    • c-kit is a receptor
    • SCF (stem cell factor) is the ligand for c-kit
    • cells expressing c-kit and SCF surround PGCs along their migration pathway
    • humans with loss of function mutations in c-kit are infertile
  6. Oct-4
    a transcription factor expressed by PGCs
  7. BMP-4
    required for activating migration of PGCs
  8. when do male germ line cells enter meiosis?
    after puberty
  9. Piebald Syndrome
    defect in pigmentation due to mutation in c-kit
  10. lines of evidence supporting role for c-kit in migration and proliferation of PGCs
    • correlation: associated in time and location with migration pathways
    • necessary: mutations lead to mice who are sterile, anemic (blood stem cell defects), and have pigmentation defects (neural crest cell defects - migration)
    • sufficient: adding SCF to PGCs in vitro rescues cell locomotion defects
  11. gonadal environment
    testes or ovary - environment exerts profound influence on the subsequent development of the germ cell to enter either oogenesis or spermatogenesis
  12. retinoic acid (RA)
    Stra8
    • RA = signaling molecule, meiosis inducing substance
    • Stra8 = TF
  13. spermatogenesis
    spermatogonia (mitosis) primary spermatocytes (meiosis I) secondary spermatocytes (meiosis II) spermatids (spermiogenesis) spermatazoa
  14. stem cell properties
    • differentiate
    • self-renew
    • spermatogonia are stem cells
  15. Sertoli cells
    • in close association with male germ line cells through all stages of spermatogenesis
    • provide a niche for spermatogenesis
    • function to suuport, nourish, and protect male germ line
    • synthesize and secrete androgen binding protein (ABP)
  16. ABP
    • androgen binding protein
    • allows sufficient testosterone within seminiferous tubules for spermatogenesis
  17. Leydig cells
    • in close proximity to Sertoli cells
    • outside seminiferous tubule
    • somatic cells that produce testosterone
  18. spermatids
    • haploid
    • connected via cytoplasmic bridges and share proteins
  19. spermiogenesis
    process of haploid spermatid undergoing morphogenesis into fully formed spermatozoon
  20. parts of a spermatozoa
    • acrosome
    • protamine-rich nucleus (protamine is a sperm-specific chromatin)
    • mitochondrial midpiece
    • flagellar tail
  21. when do sperm become motile?
    • immotile in the testes
    • following ejaculation, sperm undergo capacitation in the female reproductive tract
  22. paternal age effect on reproduction
    increase in achondroplasia, Marfan, schizophrenia

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