his slides

• Gametogenesis:

  • Occurs in gonads
  • Involves meiosis to produce haploid cells
• Fertilization:

  • Occurs in oviduct; restores diploid state
  • Production of new cell (embryo) with unique genome
• Cleavage:

  • Zygote to morula (ball of cells)
  • Leads to formation of cavity containing blastocyst
  • Outer trophectoderm: extraembryonic tissues (i.e., placenta)
  • Inner cell mass: embryonic proper & extraembryonic yolk sac
• Gastrulation:

  • Formation of 3 primitive germ layers: ecto-, meso-, endo-derm
  • 3 major axes identifiable: dorsal-ventral; cranial-caudal (anterior-posterior); medial-lateral (including right-left)
• Formation of Body Plan or Morphogenesis
• Organogenesis:

  • Growth & differentiation of organ rudiments into organs & organ systems
• Origin of Primordial Germ Cells:

  • Primordial germ cells migrate from yolk sac to genital ridge (future internal reproductive organ)
  • Become invested by testes cords
• Spermatogenesis:

  • Primordial germ cells differentiate into spermatogonia in seminiferous tubules
  • Undergo meiosis & differentiate into spermatozoa
• Oogenesis:

  • Primordial germ cells migrate from yolk sac to genital ridge (future internal reproductive organ)
  • Surrounded by somatic support cells; differentiate into oogonia
  • Meiosis begins; dormant in prophase I
  • Completion of first meiosis & arrested in metaphase II (MII)
  • MII oocyte contains maternal factors required for early totipotent embryo formation (zygote - 8C)
  • Fertilization triggers completion of meiosis; then formation of zygote
• Maternal-to-Zygotic Transition:

  • Early embryogenesis requires maternal RNAs
  • Ovulation, Fertilization, Preimplantation Development
  • Cleavage (cell doubling), Zygote-to-blastocyst formation
  • 1st cell fate decision: extraembryonic (trophectoderm, i.e., placenta) vs embryonic (inner cell mass) tissue
  • Maternal RNA Requirement
  • Minor Zygote Genome Activation
  • Major Zygote Genome Activation
  • Embryo becomes independent of maternal RNAs
• Cleaving Zygote & Formation of Blastocyst:

  • Cleavage
  • Increase in cell number but not in embryo size
  • Cells begin to segregate to form future outer trophoblast & inner cell mass cells
  • Morula-Blastocyst Transition
  • Cell fate change defined spatially & molecularly
• Implantation:

  • Occurs in body of the uterus
  • Trophoblast cells of the outer trophectoderm of the blastocyst divides to generate syncytiotrophoblast
  • Syncytiotrophoblast invades uterine lining
  • Produces human Chorionic Gonadotropin (hCG)
  • hCG stimulates corpus luteum to produce progesterone
  • Essential for maintaining the uterine lining during pregnancy
  • Maternal-Fetal Immune Interaction
• Formation of the Primitive Streak:

  • Begins to form ~15 days, midsagittal plane
  • Marks onset of gastrulation
  • Consists of pit, node, and groove
  • Local epiblast cells ingress & undergo extensive migration to contribute to the 3 germinal layers
  • Rudiments of major axes are discernible
  • Induction & Formation of the Primitive Streak
  • Cell Behavior
  • Repression (anterior visceral endoderm)
  • Induction (extraembryonic epiblast)
  • Local cell
• Gastrulation:

  • Associated with a type of cell division, directed migration, convergent extension, and delamination
  • Repression occurs in the anterior visceral endoderm
  • Induction occurs in the extraembryonic epiblast
  • Local cell-cell interactions are involved
• Onset of Gastrulation:

  • Epiblast cells migrate into and away from the primitive streak
  • Midline-ventral-lateral migration of epiblast cells is called ingression
• Continued Gastrulation:

  • Extensive ingression and subsequent migration to set up various mesodermal domains and induction of the neural plate
  • Formation of the 3 embryonic germinal layers: Ectoderm, Mesoderm, Endoderm
• Formation of Definitive Endoderm:

  • Cells lateral to the primitive streak undergo epithelial-to-mesenchymal transition (EMT)
  • Epiblast cells ingress and displace underlying hypoblast laterally to become the future lining of the gut and gut derivatives
• Formation of Intraembryonic Mesoderm:

  • Epiblast cells migrate between definitive endoderm and overlying epiblast to become intraembryonic mesoderm
• Derivatives of Intraembryonic Mesoderm:

  • Early Epiblast cells ingress and migrate bilaterally between endoderm and overlying epiblast
  • Reorganization of intraembryonic mesoderm gives rise to different mesodermal derivatives such as cardiogenic mesoderm, paraxial mesoderm, somites, intermediate mesoderm, and lateral plate mesoderm
• Neurulation:

  • Involves the formation, shaping, and bending of the neural plate
  • Closure of the neural tube involves ectoderm pinching off and overlies roof plate and neural crest domain of the dorsal neural tube
  • Cranial and caudal neuropores close on specific days
• Neural Crest Migration & Derivatives:

  • Neural crest cells arise from specific levels along the anterior-posterior axis and migrate to populate adjacent segments
  • Neural crest derivatives include melanocytes, dorsal root ganglia, chain ganglia, neurons of the aorta, and neurons of the enteric or digestive system
• Neural Crest Derivatives:

  • Dorsal root ganglia contain cell bodies of sensory neurons
  • Chain ganglia contain post-ganglionic neurons of the sympathetic nervous system
  • Enteric nervous system controls movement of smooth muscles of the gut and digestive functions
• Dorsal-Ventral Patterning of the Neural Tube:

  • Surface ectoderm produces inductive signals that control dorsal fate of the neural tube
  • Notochord produces inductive signals that control ventral fate of the neural tube
  • Paraxial mesoderm produces signals that control intermediate identity of the spinal cord
• Hox Genes:

  • Clustered in a stretch of chromosome and encode for transcription factors
  • Spatial colinearity and temporal colinearity are important in Hox gene activity
  • Posterior prevalence contributes to anterior-posterior segmental identity