From Embryology

Lab Attendance

Lab 1: --Z3289738 11:49, 25 July 2012 (EST)

Lab 2: --Z3289738 10:12, 1 August 2012 (EST)

Lab 3: --Z3289738 10:08, 8 August 2012 (EST)

Individual Assessments

Lab 1

Q1. Identify the origin of In Vitro Fertilization and the 2010 nobel prize winner associated with this technique and add a correctly formatted link to the Nobel page.

The idea of In Vitro Fertilization began to formulate in the 1890s, when Walter Heape reported the first known case of embryo transplantation in rabbits. In 1953 John Rock extracted the first intact human fertilized egg. The first successful attempt at IVF was in 1978 by Steptoe and Edward.

Robert G. Edwards, the physiologist who developed the In Vitro Fertilization treatment, was awarded the Nobel Prize in Physiology or Medicine in 2010. Nobel Prize Page

Q2. Identify and add a PubMed reference link to a recent paper on fertilization and describe its key findings (1-2 paragraphs).

This article looks into the process of embryo implantation. It demonstrates how the activation of the epithelial Na(+) channel triggers prostoglandin E(2) release,phosphorylation of teh transcription factor CREB and upregulation of cyclooxygenase 2, the enzyme required for prostaglandin production and implantation. They detected maximum Epithelial Na(+) channel activation at the time of implantation in mice, and that blocking or knocking down this channel in mice resulted in failure to implant. These results indicate the importance of the Epithelial Na(+) Channel in the process of implantation, and the consequences of defects such as miscarriage and low success rates in IVF.

<pubmed> 22729284</pubmed>

Lab 2

Q1. Upload an image from a journal source relating to fertilization or the first 2 weeks of development as demonstrated in the practical class. Including in the image “Summary” window: An image name as a section heading, Any further description of what the image shows, A subsection labeled “Reference” and under this the original image source, appropriate reference and all copyright information and finally a template indicating that this is a student image.

Zygotes showing different distribution of NPB in the 2PN and different PB aligment

Q2. Identify a protein associated with the implantation process, including a brief description of the protein's role (1-2 paragraphs)


Trophinin is an membrane adhesive protein expressed on human trophoblastic cells and on uterine endometrium epithelial cells. The protein mediates apical cell adhesion and activate trophectoderm cells for implantation via proliferation and invasion. [1]

Lab Notes

Lab 2

Key Features of Fertilization

  • Fertilization in 1st 1/3 of oviduct
  • Cumulus mass / granulosa cells (?)
    • sperm penetrates through this by wriggling.
    • Cumulus mass holds sperm in place when binding to the zona pellucida.
  • Binds to ZP3 receptor
  • Acrosome reaction (between sperm head and ZP); digests zona pellucida & matures the sperm
  • Sperm head (inner acrosomal membrane) fuses to oocyte membrane. Protein receptors on both membranes are important for fusion as well as the calcium.. exocytosis.. alters ZP to prevent polyspermy.
  • Parthenogenesis- an embryo without sperm contribution, is called parthenogenesis

Key features of Week 1 Development

  • Look at summary diagram
  • Identify names/changes over time
  • Zygote --> blastomere --> blastocyst --> uterine body; via cilia & floating in fluid (secreted by uterine body)
  • Zona Pellucida
    • Pale purple around early conceptors
    • "pale zone" synthesised by oocyte;
    • extracellular matrix;
    • made out of glycoproteins 'ZP proteins 1, 2 and 3'.
    • Each species has its own type of ZP proteins = species specificity.
    • Zp function:
      • 1) Protection of oocyte and blastocyst (like shell around egg).
      • 2) Provides a structure for the blastocyst. Patterns the development of the blastocyst. As the cells proliferate they squish against the ZP and become squamous.
      • 3) Sperm receptor (allows sperm to bind for it).
      • 4) Prevents implantation.
      • 5) Modified by granulosa molecules to prevent polyspermy.
  • Adplantation: egg roles and slowly increases adhesion to surface epithelium (has not yet implanted).
  • Implantation: takes 1 week

Key Features of Week 2 Development

  • Implantation
  • By the end of the week the blastocyst is fully within the uterine wall.
  • Blastocyst:
    • Trophoblast layer;
    • ICM (forms the embryo);
    • Placenta comes from the trophoblasts as well as contributions from the ICM;
  • Carnegie Stages
    • 23 stages of embryonic development
    • Stages 1-5 are 1st week of development
    • Refer to features on the embryos, rather than the size
    • Look at Time line
  • Implantation
    • Trophoblast cells form 2 populations of cells:
      • cytotrophoblasts (single nuclues near ICM)
      • Dividing rapidly mitotically and fused together; multinucleated - synsidiotrophoblasts
  • Stromal area of the uterus:
    • Spiral arteries are held open by trophoblast cells; maintains leaking of maternal blood into the conseptus
    • Uterine glands in epithelium; secrete into surrounding spaces
  • 2 layers of ICM = bilamina embryo
    • ICM mass = epiblast & hypoblast (carnegie stage 4)??
    • stage 5 (invaded the uterine wall)

Week 3

  • Gastrolation = trilamina embryo

Lab 3

  • First 2 weeks: Abnormalities = genetic, spontaneously aborted.
  • After 2nd week, abnormalities = developmental abnormalities, less genetic.

Week 3

Folding events and development of coelums
  • 3 intraembryonic coelums = PPP - pericardial, peritoneal and _
  • 3 extraembryonic coelums = Amnionic, yolk and coleolic
  • Endoderm lines the yolk sac; ectoderm lnies the emnionic sac. these two cavities are completely independent of each other.
  • The third cavity is the large space outside the embryo
  • Amnionic cavity has an overcoat of mesoderm (outer surface)= "extraembryonic mesoderm" --> includes the embryonic stalk as well as the lining of the coleolic sac.

  • Buccopharyngeal membrane. Where oral cavity will form. Ectoderm and endoderm in close proximity, no mesoderm in between.
  • Cloecal membrane = lower end of gastrointestinal tract. Ectoderm and endoderm in close proximity, no mesoderm in between.
  • Site of placental blood vessels? - stalk brought around to ventral surface?
  • Transverse septum lies beneath the heart (beneath the buckapharyngeal membrane) and represents the site of where the emnionic cavity meets the yolk sac. Later contributes to development of the liver.
  • End of 4th week: neural tube (NT) folds - now two layers of ectoderm.
  • Key events of folding is that it brings the amnionic sac from the ventral to the dorsal side (?); therefore the anionic sac is wrapped around the head and caudal end of the embryo, and the yolk sac is squashed in the middle in the midgut region. Therefore the embryo is developing within the amnionic sac.

  • Amnionic cavity increases in volume, filling the amnionic space. The yolk sac gets compressed at the midgut region; lies next to the emnyionic stalk.
  • The amnionic membrane then fuses with the chorionic membrane. From that stage on we have a single cavity in which the embryo develops. The yolk sac is essentially lost.
  • Amnionic fluid space allows the embryo to develop with equal pressure on all surfaces. Structures are not restricted with growth. Fetal stage of development the fetus swallows the fluid allowing development of...
  • Fluid is tightly regulated.
Carnegie stages

5 = implantation 6 = bilamina embryo 7 = flat embryonic disk -

  • Don't need to memorise, just have an idea of the events that are going on


  1. <pubmed>17487845</pubmed>