EXAM NOTES –LECTURE 1 TO MIDTERM 1
Embryonic human development
• specification before week 9
• later fetal stages contain growth
Till and McCulloch -- hematopoietic niche
• injected bone marrow cells into lethally irradiated mice*
• Hematopoietic stem cells will colonize the spleen and form RBC, granulocytes (WBC), platelet precursors,
• For this "colony-forming cell" to be a true stem cell it had to produce differentiated blood cells & more colony-
• generates a second stem cell capable of becoming a lymphocyte cell (immune system) or myeloid stem cell
(blood cell pre)
• found in the hollow cavities of trabecular bones where the bone marrow resides
• the stem cells are in close proximity to the bone cells (osteocytcs) and the endothelial cells that line the blood
• paracrine factors (Wnts, angiopoietin) combine with signals from Notch and integrin to regulate cell
• Hormonal signals and pressure from the blood vessels help regulate hematopoiesis
• Bone marrow is the niche (endosteum)
Adult stem cells -- in tissues of mature organs & replace tissues of that particular organ
STEM CELL POTENCY -- ability of a stem cell to generate different types of differentiated cells
Pluripotent stem cells
• ability to become all the cell types except trophoblast
• from the ICM of a blastocyst
• germ cells and germ cell tumors can form pluripotent stem cells.
• Embryonic stem cells (ESCs) and Embryonic Germ Cells (EGCs)
• When ES cells are injected into the ICM of a blastocyst, they can behave like ICM cells and give rise to all cell
Committed stem cells -- become relatively few cell types
• difficult to isolate, fewer than 1 out of 1000 cells, low rate of cell division
• Multipotent stem cells
o commitment is limited to a small amount of cells
o adult stem cells
o ex/hematopoietic stem cell
• unipotent stem cells
o found in particular tissues and are involved in regenerating a particular type of cell
o ex/ Spermatogonia
• related to stem cells, but are not capable of unlimited self-renewal
• have the capacity to divide only a few times before differentiating
• called transit-amplifying cells -- usually divide while migrating away from the stem cell niche
Adult Stem Cell Niches
• interactions b/w parts of the embryo create stem cell niches
• niches provide a location of extracellular matrices and paracrine factors allowing them to remain undifferentiated
• niches regulate stem cell proliferation and differentiation by paracrine factors = an uncommitted state
• Too much stem cell differentiation = aging or decay.
• Too much stem cell division = cancers • paracrine factors, cell adhesion molecules, and architecture allow asymmetric cell divisions
Mesenchymal Stem Cells: Multipotent Adult Stem Cells
• epidermis, intestinal epithelium, blood cells are continually replaced by dividing adult stem cells
• Some have a large degree of plasticity = multipotent mesenchymal stem cells (MSC) (AKA bone marrow-derived
• MSC are able to give rise to bone, cartilage, muscle, and fat lineage
• MSC differentiation is influenced by the elasticity of the matrices upon which the cells sit.
o SOFT matrix – (collagen-coated) -- into neural markers (3 tubulin)
o Stiffer matrix – muscle cell (MyoD)
o Hard matrix -- bone cell (CBF)
Totipotent cells -- form every cell in the embryo and the trophoblast cells of the placenta (zygote, first 4-8 blastomeres to
• At 8 cell stage, early blastomeres are totipotent. Later, the ICM cells are pluripotent.
• Early all cells of the 8 cell embryo express Cdx2 and Oct4 transcription factors
• Trophoblast cells express eomesodermin and Cdx2 (which down regulates ICM specific genes Oct4 and nanog)
• ICM express Oct4, nanog, and Sox2 -- they maintain the pluripotent cells
• Oct4 is expressed early and blocks cells from assuming trophoblast cell fates.
• Later nanog, prevents the formation of hypoblast cells and stimulates blastomere self renewal in the
Methods for inducing pluripotency from differentiated cell types
• Somatic cell nuclear transfer (SCNT) into oocytes
• Cell fusion of pluripotent cells with differentiated cells
• Induced pluripotent stem cells (iPSCs) from differentiated cells with a combination of transcription factors
Somatic cell nuclear transfer – cloning a sheep
• Dolly died from a virally induced lung disease in 2003.
• Yamanaka induced formation of pluripotent mouse stem cells from adult fibroblasts by retroviral insertion genes
encoding 4 factors = (Oct3/4, Sox2, c-myc and Klf4)
• nanog was dispensable!!!
• induced pluripotent stem cells (IPSCs) could be injected into ICM cells of the blastocyst and differentiate into
many cell types
Pluripotent ES cells derived from the early embryo can generate all the types of somatic cells
• the original iPS cells differed from mouse ES cells in their gene expression and DNA methylatIon patterns
• when injected into mouse blastocysts, no live animals carrying cells from the original blastocyst & iPS cells were
• IPS didn’t behave like ES cells.
• 2007, 3 groups reported successful in vitro reprogramming of adult mouse skin fibroblasts into pluripotent ES like
o these iPS cells behaved more like ES cells, Gene expression patterns, methylation patterns were almost
o live chimeras could be produced, thus these iPS cells could function like ES cells.
Reprogramming by defined factors
• recently Yamanaka’s group reported success in producing IPSCs from human fibroblasts.
• retroviral insertion increases risk of tumor formation in blastocysts.
• Can adult human cells be reprogrammed? Yes with defined factors
Patient derived olfactory stem cells and spinal cord repair
• “Autologous olfactory mucosal cell transplants in clinical spinal cord injury
• SCNT produces ES cells which can differentiate into functional neurons that can “cure” a Parkinson-‐like disease
Reprogramming adult cell types to produce a de-differentiated embryonic stem (ES) cell state • Indirect routes –
o somatic cell nuclear transfer (SCNT) or cell fusion
o induced pluripotent stem (iPS) cells by the introduction of genes such as Oct4.
• direct route
o Intra-lineage conversion
o fibroblast to macrophage and fibroblast to muscle cell by PU.1 and MyoD
What give rise to the