1. Test – Monday, April 14
Q&A – next lecture
Friday, 3 PM, Higgins 300??
Group presentations
Groups D and G – we need to meet
April 16th - who will be here?

2. Stem cells
Cell fates become increasingly restricted during development
Stem cells are capable of giving rise to several different kinds of cells

3. What happens during early development?
What kinds of stem cells are found in adults?
How are embryonic stem cell lines derived and maintained in the lab?

4. DNA is the same in all cells
Development is based on differential gene activation (and inactivation)
Ability of cells to acquire different fates decreases during development
Fertilized egg
6 days
Blastocyst cells are able to give rise to all cell types
6 months
Characteristic sets of genes are active in different tissues

5. Totipotent – all fates are possible
During development, the pathways that a cell can take are thought to become progressively more limited at each node
Totipotent – all fates are possible
Pluripotent – multiple fates are possible
Waddington’s epigenetic landscape (1953)
Fates are more restricted

6. Embryonic stem cells are derived from blastocysts
Blastocysts form at ~day 5 and implant at ~day 7
Human embryos do not survive in culture past ~day7
Implantation is required for development past the blastocyst

7. Embryonic stem cells are derived from the inner cell mass of blastocysts
Totipotent cells that can give rise to all the cells found in adult animals (unknown in humans)
Blastocyst
6 day
Outer cell mass forms the placenta together with maternal cells

8. Three major germ layers form at ~14-16 days of development
Different germ layers give rise to different tissue types
Adult tissues retain small stem cell populations with restricted ranges of developmental potentials

9. Early human development
Tracks 4-9
9 min

10. What happens during early development?
What kinds of stem cells are found in adults?
How are embryonic stem cell lines derived and maintained in the lab?

11. Adults maintain stem cell populations throughout life
Adult stem cells have a more restricted range of developmental fates
Stem cell divisions can be asymmetric: one cells remains a stem cell and the other daughter cell differentiates

12. Red cells represent ~98% cells
Hematopoietic stem cells in bone marrow give rise to all blood cells
Red cells represent ~98% cells

13. Stem cells in adult tissues
Tracks 25-30
7 minutes

14. Clinical procedures already take advantage of adult stem cells
Hematopoietic stem cell (HSC) transplants are often done after chemotherapy, to treat leukemia and other conditions
Donors and recipients need to be carefully matched for bone marrow transplants
Foreign tissues are normally rejected by the body’s immune system

15. Other sources of HSCs include:
Peripheral blood
Small numbers of HSCs can be cultured from peripheral blood
Umbilical cords
HSC are more proliferative and less frequently rejected than bone marrow HSC
Cord blood can be frozen and stored

16. Skin grafts are a routine part of medicine
Problems include graft rejection and sterility

17. Stem cells in the skin basal layer divide every week
Cells move vertically as they differentiate
Dead cells are sloughed off as dust……..

18. A patient’s own skin cells may also be grown in tissue culture and then transplanted to the injured area of the patient

19. What happens during early development?
What kinds of stem cells are found in adults?
How are embryonic stem cell lines derived and maintained in the lab?

20. Preimplantation genetic diagnosis
Most embryonic cell lines have been developed from unused embryos produced for in vitro fertilization (IVF)
Procedure involves:
series of hormone injections to stimulate oocyte production in woman
surgical removal of oocytes from the ovary
fertilization with sperm in a culture dish
embryo selection after several cell divisions in culture
implantation of embryos into uterus
Preimplantation genetic diagnosis
(PGD)
One of the 8 cells in the 3 day embryo can be removed for DNA analysis

21. Embryonic stem cell lines in the labs
Tracks 35-40
8 minutes

22. Embryonic stem cells are derived from inner cell mass of blastocysts
What’s in the pipette??
Investigators try to direct the course of differentiation by controlling the growth factors in the culture medium

23. Investigators are trying to identify the factors that guide cells along different developmental pathways
~ day 6-7 embryo

24. Profound philosophical debate about embryonic stem cells (ESC) has entered the political arena in several states. During the Bush administration, investigators were no longer allowed to develop new ESC lines from unused embryos from IVF clinics.
Several states have had ballot initiatives to allow ESC research.
In your opinion, should scientists be allowed to construct ESC lines from unused human embryos?
Yes No
Not sure

25. Some of the debate is centered around when life begins.
When do you think life begins?
Conception
Blastocyst
Gastrula
End of first trimester
Birth

26. Twinning can occur at various times in the early embryo
Early blastocyst
Days 5-9
Late blastocyst
Day 9+
Pre-blastocyst
Two placentae
Common placenta
Embryonic cells begin to specialize
Small %
Danger conjoined
~1/3
~2/3

27. Evolutionary remnants are still detectable (gill slits, tail)
Embryo at 5 weeks
Just a few inches long
Evolutionary remnants are still detectable (gill slits, tail)

28. Fetus at 8 weeks
Bathed in amniotic fluid
Organ systems have been established