Developmental biology 5 Flashcards
(27 cards)
At 60 days, what characterises the human fetus?
It is recognisable, with fully differentiated cells, but still requires further development and growth via stem cells.
Why do we need stem cells after cell differentiation is complete?
For repair (e.g., epithelium), renewal (e.g., blood), and growth.
What happens to a cell’s developmental potential as it differentiates?
It decreases.
What is a totipotent cell?
A zygote; can give rise to all body and extraembryonic tissues (placenta)
What is a pluripotent cell?
Inner cell mass cells that can give rise to mesoderm, endoderm, and ectoderm—but not extraembryonic tissues.
What is a multipotent stem cell?
Can give rise to tissue types within a specific organ (e.g., hematopoietic stem cells).
What is a unipotent stem cell?
Can only give rise to one specific cell type (e.g., keratinocyte stem cells)
Where are keratinocyte stem cells located and what do they do?
In the basal layer of the epidermis; they proliferate, differentiate, and migrate upwards, dying after 2–4 weeks.
Why is stem cell retention important in skin grafts?
Long-term success depends on at least 5% epidermal stem cell retention.
How can the hematopoietic system be used clinically?
To replace blood cells in diseases like leukemia, using matched stem cells.q
What kind of division maintains stem cell populations?
Asymmetric cell division
What orientation is needed for proper asymmetric division?
Horizontal plane of division
What happens if stem cells divide vertically?
Two stem cells are produced, instead of one stem cell and one differentiated daughter.
What happens in Drosophila CNS neuroblast delamination?
A neuroblast delaminates, localises determinant proteins, then divides asymmetrically to produce one neuroblast and one differentiating ganglion mother cell
What is the only truly pluripotent stem cell?
Embryonic stem (ES) cells from the inner cell mass.
What is the potency of fertilised eggs up to the 4-cell stage?
Totipotent.
What potency do adult stem cells have?
Multipotent
How can ES cells be used in vitro?
They can be cultured and induced to form mesoderm, ectoderm, or endoderm.
How are chimeric mice made using ES cells?
Clone black mouse ES cells, transfect with a transgene, inject into white mouse blastocyst, and implant into a surrogate mother
What does black/white chimeric mouse fur indicate?
That injected ES cells were truly pluripotent and contributed to all tissues including germ cells
How can we obtain homozygous transgenic offspring in mice?
Breed grey (heterozygous) mice from chimeras until a homozygous generation is produced.
What does Oct4 gene expression indicate?
Maintenance of pluripotency—it is present in zygote, morula, and inner cell mass but absent in trophoblasts and differentiated cells
What are the three genes maintaining ES pluripotency?
Oct4, Sox2, and Nanog.
What is an induced pluripotent stem cell (iPS)?
A differentiated cell (e.g., fibroblast) reprogrammed to pluripotency using Oct4, Sox2, KLF4, and MYC.
