Stem cells Flashcards
(29 cards)
Why do developmental biologists study how a single cell can turn into a complex organism?
It reveals key regulatory pathways repeatedly used for embryonic development.
Explains how cellular specialization, tissue patterning, and organogenesis occur.
What is a stem cell, and why is it significant?
A stem cell is a cell that can self-renew (make another stem cell) and produce a differentiated progeny.
Understanding them could lead to repairing ageing organs, diseased tissues, or injuries—like a “fountain of youth.”
What did transplantation of mouse gastrulation-stage embryos into ectopic sites show?
It produced teratocarcinomas containing cells from all three germ layers (mesoderm, endoderm, ectoderm).
Led to culturing embryonal carcinoma (EC) cells in vitro, which are pluripotent and can regenerate tumors.
Who demonstrated that a single EC cell could form a tumor and regenerate itself?
Pierce (1964) showed that one EC cell could cause a tumor and self-renew, producing more EC cells.
When were permanent pluripotent mouse ES cell lines first established?
In 1981 by Martin, and independently by Evans and Kaufman.
These lines derived from blastocysts can produce a whole mouse (pluripotent).
Why are mouse ES cells historically significant?
Their discovery revolutionized mouse genetics by enabling knockout/knock-in techniques.
They can differentiate into any tissue, allowing powerful genetic studies of specific genes.
From which stage of the embryo are mouse ES cells typically harvested?
From the inner cell mass of an early preimplantation blastocyst.
How do researchers generate a chimeric mouse with genetically altered ES cells?
Engineer or modify ES cells in vitro.
Inject them into a host blastocyst.
Implant into a surrogate female mouse.
Offspring may have tissues from both host blastocyst and altered ES cells.
What are the basic steps in creating a “knockout” mouse?
Transfect ES cells with a targeting vector.
Apply chemical selection to find correctly targeted cells.
Inject these cells into a blastocyst and implant.
Breed the resulting chimeric mice to obtain stable gene knockouts.
Why are knockout mouse models essential in the post-genomic era?
With ~20,000–30,000 genes in the human genome, functional studies are crucial.
Knockout mice clarify gene function, disease mechanisms, and potential therapies.
What was the key finding in Thomson et al. (1998)?
They derived human ES cell lines from in vitro fertilized (IVF) blastocysts.
Cultured about 40 inner cell mass (ICM) cells on feeder layers for several months.
The cells maintained self-renewal and could form multiple tissue types.
Why was using feeder layers necessary in Thomson’s work?
ES cells need support cells (e.g., mouse embryonic fibroblasts) to provide:
A surface for attachment.
Conditioned media containing growth factors (like bFGF) that prevent differentiation.
How do human ES cells remain undifferentiated in culture?
High levels of bFGF (basic Fibroblast Growth Factor).
Feeder layers or Matrigel-coated plates (for ECM support).
These conditions mimic signals that keep cells in a pluripotent state.
Why is it challenging to keep ES cells from differentiating?
In the embryo, ES cells spend only a brief time in the pluripotent state.
Culture aims to “trick” cells into continually self-renewing without maturing into specialized cells.
Distinguish between unipotent, multipotent, pluripotent, and totipotent cells.
Unipotent: Can give rise to one cell type.
Multipotent: Can give rise to many cell types within a certain lineage.
Pluripotent: Can form all cell types in the body (e.g., ES cells).
Totipotent: Can form every cell type including extra-embryonic tissues (like the placenta).
How did Thomson’s group confirm the pluripotency (or totipotency) of their ES cells?
They injected the cells into mice, observing teratoma formation.
Teratomas contained tissues from all three germ layers (endoderm, mesoderm, ectoderm).
What two key properties define embryonic stem cells?
Immortality (self-renewal without senescence).
Pluripotency (ability to form all cell types in the adult body).
How do ES cells achieve “immortality” in culture?
igh telomerase activity maintains telomeres, preventing the shortening that typically leads to cell aging.
Normal somatic cells have a finite division limit (Hayflick limit).
What is the Hayflick limit, and how do ES cells circumvent it?
A finite number of population doublings (~30–80) after which normal cells become senescent.
ES cells produce telomerase, which maintains chromosome ends, allowing indefinite divisions.
Why is telomerase also significant in some cancers?
Many cancer cells re-activate telomerase, enabling them to divide indefinitely (similar to ES cells).
What is DNA methylation, and where does it commonly occur in mammals?
The addition of a methyl group (–CH₃) to cytosine nucleotides, typically at CpG dinucleotides.
About 60–90% of CpG sites in the mammalian genome are methylated.
What does the “p” in “CpG” stand for, and why is it significant?
“p” refers to the phosphodiester bond linking cytosine and guanine.
CpG islands (300–3,000 bp) often occur in gene promoters, influencing gene expression.
How does methylation of CpG islands affect gene expression?
Unmethylated promoter CpG islands: Typically active gene transcription.
Methylated promoter CpG islands: Usually leads to gene silencing.
What are the main types of histone modifications that affect DNA packaging?
Methylation
(De)acetylation
Phosphorylation
Ubiquitination
Sumoylation
