Test 4. Lecture 38 Flashcards
The ____________ of some internal
organs are also able to proliferate
to replace damaged tissue.
___________, normally arrested in the
G0 phase of the cell cycle, are stimulated to proliferate if large
numbers of liver cells are lost (e.g., by surgical removal).
epithelial cells
Liver cells
____________are less differentiated, self-renewing cells present in most adult
tissues.
They retain the capacity to proliferate and replace differentiated cells
throughout the lifetime of an animal.
The key property of stem cells:
They divide to produce (1) one daughter cell that remains a stem cell and (2) one
daughter cell that divides and differentiates.
Stem cells are self-renewing and serve as a source of differentiated cells
throughout life.
Stem cells
- Many types of cells have short life
spans and must be continually
replaced by proliferation of stem
cells:
_________________
of the skin and in the lining of the
digestive tract.
2. Hematopoietic (blood-forming) stem cells were the first to be identified. There are several types of blood cells with specialized functions; all are derived from the same population of stem cells.
Blood cells, sperm, epithelial cells
- Epithelial cells that line the
intestines live only a few days
before they die by apoptosis. - New cells are derived from the
continuous but slow division of
______________________ - New cells proliferate for three to
four cell divisions and then
differentiate
stem cells at the bottom of intestinal crypts.
Skin and hair are also renewed by ___________
The epidermis, hair follicles, and sebaceous glands are all maintained
by their own stem cells.
stem cells.
Stem cells also play a role in repair of damaged tissue.
Skeletal muscle normally has little cell turnover but can regenerate rapidly in
response to injury or exercise.
_____________ (stem cells of adult muscle) are normally arrested in G0, but they
proliferate in response to injury.
Satellite cells
Most adult tissues have stem cells, which reside in distinct micro-environments or
niches (e.g., intestinal crypts).
Niches provide the signals that maintain stem cells throughout life and control the
balance between self-renewal and differentiation.
Adult stem cells have potential utility in clinical medicine.
_______________ is important in the treatment of many cancers to replace cells damaged by toxic
chemotherapy drugs
Hematopoietic stem cell transplantation (bone marrow transplantation)
- Epithelial stem cells are used in the form of skin grafts to treat
burns, wounds, and ulcers.
Epidermal skin cells can be cultured and then transferred to the
patient. Because the patient’s own skin is used, it eliminates
the problem of rejection by the immune system. - _________can be grown indefinitely as pure stem cell populations that have ____________—the capacity to
develop into all of the different types of cells in adult tissues.
Thus there is enormous interest in embryonic stem cells for both
basic research and clinical applications.
Embryonic stem cells
pluripotency
Embryonic stem cells were first cultured from mouse embryos in 1981.
These cells are an important experimental tool:
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– They can introduce altered genes into mice.
– They provide a model system to study the events associated with cell
differentiation
• Human embryonic stem cell lines were first established in 1998.
• This raised the possibility of using embryonic stem cells in clinical
transplantation therapies to diseases such as Parkinson’s, Alzheimer’s,
diabetes, and spinal cord injuries.
• Mouse embryonic stem cells are grown in the presence of_____________, required to maintain the cells in the undifferentiated state.
If LIF is removed, the cells aggregate and differentiate.
• Stem cells will differentiate along specific pathways if appropriate growth
factors are added.
• Methods have been developed to differentiate stem cells into cardiomyocytes and use them to repair heart damage in mice
growth factor LIF
In 1997, Ian Wilmut and
colleagues cloned Dolly the sheep.
Dolly arose by a process called
______________
Other mammals have since been
cloned, but it is a difficult and
inefficient process.
somatic cell nuclear
transfer.
In _____________, a nucleus from an adult human cell would be transferred to
an ___________.
The resulting embryo could produce differentiated cells for transplantation therapy.
This would bypass the problem of tissue rejection
therapeutic cloning
enucleated egg
Problems to be overcome:
Low efficiency of generating embryos by somatic cell nuclear
transfer.
Ethical concerns with respect to the possibility of cloning human beings (_______________) and with respect to the
destruction of embryos.
These difficulties may be overcome by using ________________: reprogramming somatic cells to
resemble embryonic stem cells.
Only four transcription factors introduced by retrovirus vectors are
sufficient to reprogram adult mouse somatic cells.
Adult human fibroblasts can also be reprogrammed to
pluripotency.
reproductive cloning
induced pluripotent stem cells
Several combinations of transcription
factors have recently been shown to
induce pluripotency.
They activate a transcriptional program that is also expressed in embryonic cells.
Transcription factors _________,_______and
___________ play central roles in this program.
These factors form an autoregulatory loop,
positively regulating each other’s
expression.
They also activate other genes that
maintain the pluripotent state, while
repressing genes that enable
differentiation.
Oct4, Sox2, Nanog
______________: reprogramming
somatic cells to other types of
differentiated cells (e.g., fibroblasts to
muscle cells or neurons).
This would bypass the need for pluripotent stem cells.
Mouse fibroblasts have been turned into
heart muscle cells and nerve cells
using only three transcription factors
Transdifferentiation
