stem cells Flashcards
what three criteria does a stem cell need to satisfy
- Undifferentiated or unspecified.
- Have the ability to self-renew.
- Mature and differentiate.
what are the three modes of stem cell division
asymmetric self renewing division - producing one differentiate cell and one stem cell
symmetric differentiating division
symmetric self renewing division
what are the three types of potency that stem cells can possess
totipotency
pluripotency
multipotency
what is totipotency
the ability of a single cell to divide and produce all the differentiated cells in an organism, including extraembryonic tissues.
what cells have totipotency and when does it remain until
the single cell zygotes and (remains until) the 4-8 cells embryo generates the embryo and the extraembryonic tissue (protective membrane that surrounds amnion.
what is pluripotency
the capacity of individual cells to initiate all lineages of the mature organism in response to signals from the embryo or cell culture environment
what is multipotency
cells that have the capacity to self-renew by dividing and to develop into multiple specialised cell types present in a specific tissue or organ.
what cells are multipotent
Most adult stem cells are multipotent stem cells. adult or somatic (resident) stem cells. seen in developing brain.
already acquired specific abilities.
what are the cell stages of progressive differentiation of neurons
zygote embryonic stem cell multipotent stem cells neuronal progenitor differentiating neuronal precursor differentiated cells
what molecular influences are in the stem cell niche
- Paracrine Signalling
- ECM adhesion (eg integrins)
- Juxtacrine signalling
- Endocrine signalling
- Neurotransmitter release
- Asymmetric localisation of cytoplasmic determinant
different combinations of these signals lead to epigenetic and transcriptional regulation
what are features of embryonic stem cells
- Undifferentiated/non-committed
- Self-renewal (immortal)
- Pluripotency: derive from ICM (at blastocyst stage)
- Very tiny, small number, 12 cells in human, give rise to all cell/tissue that make adult human
who won the Nobel prize for physiology and medicines 2007 and for what?
M. evans, M. Capecchi, O. Smithies -
• Reliably incorporate ES cells into embryos, resulting in chimeric animals, carrying genetic mutations
what is the key initiating events of ICM establishment
asymmetric cell divisions
what division leads to expansion of trophectoderm
symmetrical division parallel to apicobasal axis - equal segregation of fate determinants
what division leads to the creation of the ICM
asymmetric division perpendicular to the apicobasal axis - unequal segregation of fate determinants
what are the two things that maintain pluripotency in ICM cells
Pluripotency factors: Nanog, Sox2, Oct4 Hippo signalling (cell density and cell-cell adhesion mediated)
what is the molecular background causing trophectoderm differentiation
(few cell to cell contacts = hippo signaling inactive)
apical polarity proteins in the outer cells recruit AMOT causing suppression of Lat kinase proteins
so Yap is not phosphorylated and is able to enter the nucleus and form a Yap-Tead-Taz transcriptional complex mediating gene expression of CDX2
what is the molecular background of inner cell mass establishment
(apolarity/increased cell to cell contacts = hippo signalling active)
So Lats1/2 phosphorylates AMOT localising it to adherence junctions
AMOT binding of Lats promotes its kinase activity causing phosphorylation of Yap so that it is unable to enter the nucleus and form the transcriptional complex
meaning that CDX2 remains repressed so that Oct4 is continually expressed - promoting pluripotency
when were human embryonic stem cells first isolated
1998
where do hES come from
embryos that develop from eggs that have been fertilized in vitro. (never those fertilised inside a woman’s body)
what are the differences between mES and hES
- mES cells are the most immature, undifferentiated with greatest potential for pluripotency. mES cells are naïve.
- hES cells display some maturation towards the epiblast lineage. hES cells are primed or ready for differentiation. pluripotent
what is matrigel and why is it used in stem eclls
prepared from an extract of Engelbreth-Holm-Swarm mouse tumors. It has been used as a model of basement membrane, which contacts with the basal layer of epithelial cells, endothelial cells, and fat and smooth muscle cells.
commonly used as a basement membrane matrix for stem cells because it retains the stem cells in an undifferentiated state.
hES can provide matched cells for customised tissue repair of which degenerative diseases
- Alzheimer’ – Forebrain neurons
- Parkinson’s – Midbrain neurons
- ALS – Motor neurons
- Cardiovascular diseases – Cardiac muscle cells
- Type I diabetes – Pancreatic β cells
what are the therapeutic limitations of hES cells
- Difficult to differentiate uniformly and homogeneously into a target tissue.
- Immunogenic – embryonic stem cells from a random embryo donor are likely to be rejected after transplantation.
- Tumorigenic – capable of forming tumors or promoting tumor formation.
- Degenerative diseases are complex genetic disorders involving interactions of many genes with environmental factors.
what are the steps to somatic nuclear transfer
enucleation, injection/fusion, and activation.
After removing the oocyte nucleus, the donor cell nucleus is injected or fused with the enucleated oocytes before the reconstructed embryos are activated
what is the practical application of somatic nuclear transfer
reproductive cloning of farm animals that have exceptional qualities
what are induced pluripotent stem cells (iPS)
cells derived from skin or blood cells that have been reprogrammed back into an embryonic-like pluripotent state that enables the development of an unlimited source of any type of human cell needed for therapeutic purposes.
what are the features of iPS cells
iPS cells can be propagated indefinitely.
can form cell types representative of all three germ layers.
can generate entire embryos.
are pluripotent
(like ES cells)
what is microcephaly
a congenital disease characterised by a significant reduction in brain size
what are features/causes of microcephaly
- Caused by a mutation in the gene for CDK5RAP2, a protein regulating the mitotic spindle function.
- Neural stem cells exhibit abnormally low levels of symmetric divisions.
- Leads to premature neuronal differentiation.
- Depletion of the stem cell pool
(Patient-derived cerebral organoids are smaller.)
how were iPS cells used to cure sickle cell anemia in the mouse (Rudolf Jaenisch)
- Generation of autologous iPS cells. (infect tail tip fibroblasts with Oct4, Sox2, Klf4 and c-myc retroviruses)
- Correction of the hemoglobin mutation.
- Differentiation of the iPS cells into hematopoietic stem cells (HSCs).
- Transplantation of HSCs in the (irradiated) mouse cured its sickle-cell phenotype.
what problem prevents therapeutic use of iPS to cure disease in humans
tumour formation, associated with using retroviruses and oncogenes for reprogramming needs to be resolved before iPS cells can be considered for human therapy
what are four major medical uses of hiPS cells
- Making patient-specific iPS cells for modelling diseases (e.g. autism, Down syndrome, diabetes…).
- Combining gene therapy with patient-specific iPS cells to treat diseases.
- Using patient-specific iPS cell-derived progenitor cells in transplantation medicine without the complication of immune rejection.
- Using differentiated cells derived from patient-derived iPS cells for screening drugs and toxicity testing.
what are adult stem cells (aka somatic stem cells) (give 5 features)
- Undifferentiated cells
- Found in small number in most adult tissues
- Finite, may not live as long as ES or iPS cells in culture
- Multipotent in nature – give rise to unipotent progenitor cells
- Give rise to closely related family of cells within the tissue
what are adult hematopoetic stem cells (HSCs)
Multipotent stem cells that give rise to various blood cells
found in the bone marrow of adults, especially in the pelvis, femur, and sternum
what is ontogenesis
the development of an individual organism or anatomical or behavioural feature from the earliest stage to maturity.
what signals HSCs migration through the circulatory system to their niche
HSCs express CXCL4 receptor sensing the chemokine CXCL12 expressed by osteoblasts and stromal cells.
as well as adhesion proteins (eg E selectins and VCAM1)
what shifts in site of hematopoesis occur during development
- Primitive hematopoiesis in the embryonic yolk sac.
- Definitive hematopoiesis in the aortic portion of the aorta-gonad-mesonephros (AGM).
- HSCs migrate through the developed vasculature to the fetal liver.
- Homing where HSCs migrate through the circulatory system and find their tissue-specific niche in the developing bones.
where does primitive hematopoiesis occur
in the embryonic yolk sac
where does definitive hematopoiesis occur
aortic portion of the aorta-gonad-mesonephros (AGM)
what are the two hematopoietic niches
the endosteal and the perivascular
what two things are secreted by osteoblasts to maintain quiescence in long term HSCs
Angiopoietin-1 and Thrombopoietin
where are long term HSCs found
in the endosteal niche adhered to osteoblasts
where are short term active HSCs found
in the perivascular niche associated with blood vessels at oxygen rich pores
what cells do short term HSCs directly interact with
stromal cells including CAR cells (CXCL12-abundant reticular cells) and mesenchymal stem cells
what can stimulate short term HSCs (+derive progenitors) to migrate into the blood
sympathetic connections
what is autologous HSCs transplantation
a type of bone marrow transplantation that attempts to reset the immune system using HSCs from patient themself
(can be used for MS)
what are the steps of autologous HSC transplantation
- Collection - stem cells collected from patients bond marrow or blood
- Processing – blood or bone marrow is processed in the lab to purify and concentrate stem cells
- Cryopreservation – blood or bone marrow is frozen to preserve it
- Chemotharapy – high dose chemotherapy and/or radiation therapy is given to the patient
- Reinfusion – thewed stem cells are reinfused into the patient
why is use of adult stem cells in therapy better than use of ES or iPS cells
- They are somewhat specialized – their inducement may be simpler.
- They belong in the microenvironment “niche” of an adult body, so they tend to cause less tumours than ES or iPS cells
- They are not immunogenic – recipients who receive the products of their own stem cells will not experience immune rejection.
- Relative ease of procurement – some adult stem cells are easy to harvest
where are ES cells derived
the ICM
