Study Questions – Lecture 12 Stem Cell and Ectoderm Fate
1. What is a stem cell?
Relatively undifferentiated cell from the embryo, fetus, or adult that, when it divides,
produces one cell that retains its undifferentiated character and remains in the stem cell
niche; and a second cell that leaves the niche and can undergo one or more paths of
2. What is a stem cell niche?
An environment (regulatory microenvironment) that provides an environment of
extracellular matrices and paracrine factors that allows cells residing within it to remain
relatively undifferentiated. Regulates stem cell proliferation and differentiation.
3. What is the difference between an embryonic stem cell and an adult stem cell?
Embryonic stem cells are derived from the inner cell mass of mammalian blastocysts and
can make all cells of the embryo.
On the other hand, adult stem cells are those found in the tissues of a mature organ. These
stem cells are usually involved in replacing and repairing tissues of that particular organ,
and can only form only a subset of cell types.
4. What is the difference between totipotency, pluripotency, and multipotency? Is
there such a thing as unipotency?
Totipotency describes the cells that can make every cell type (including the trophoblast in
mammals). This state in mammals only lasts until the 8 cell stage and compaction.
Pluripotency describes the cells that can become all cell types except the trophoblast in
mammals. These cells are those in the inner cell mass of the blastocyst, but germ cells
and germ cell tumours are also considered to be pluripotent.
Multipotency describes cells that are more limited and can only differentiate into a
relatively smaller amount of cell types. These cells are most adult stem cells (e.g.
hematopoietic stem cell).
Unipotency does exist, it describes cells that can only differentiate into one cell type (e.g.
spermatogonia leading to sperm cells).
5. How is a progenitor cell different from a stem cell?
A progenitor cell is related to a stem cell, but differs as it is not capable of unlimited self-
renewal. They can divide a few times before differentiating. 6. There is much excitement about the possibility of “stem cell therapy” or tissue
engineering”. How, in principle, would these concepts be practiced?
In theory, stem cells would be harvested from the patient, allowed to multiply and
differentiate, injected back into the body, and allow for healing to occur.
7. Why does hair go grey with age?
Hair goes grey with age as stem cell populations are not maintained as well as we get
older. This could be due to fatigue of stem cell niches, which is found at the bulge along
the hair follicle. As we age, the bulge disappears and the melanocyte stem cells that
provide pigment is as well leading to gray hair.
8. What three populations of cells are derived from the ectoderm during the process of
Primary neurulation results in three cell popularities:
-neural tube (brain and spinal cord)
-external epidermis (skin)
-neural crest cells (from where the above two populations meet)
9. What is the difference between the notochord and the neural tube?
The notochord is a transient rodlike mesodermal structure that forms the supporting axis
of the chordate embryo. It has an important role in inducing and patterning the nervous
The neural tube results from the folding of neural plates (dorsal ectoderm), forming both
the brain and spinal cord.
10. What is a neuroblast?
A neuroblast is a neural precursor cell.
11. Describe the general process of neurulation – including the difference between
primary and secondary neurulation? What general processes are involved in
The general process of neurulation consists of both primary and secondary neurulation.
Primary neurulation involves invagination and rolling up of a sheet of cells.
Secondary neurulation involves new neural epithelium forming from mesenchymal cell
condensation and subsequent cavitation. 12. How is cadherin expression related to neural tube closure?
Cadherin expression is necessary for the fusion of neural folds along the dorsal midline.
This requires changes in cadherin expression from E-cadherin to N-cadherin, causing
changes in cell adhesion and neural cells separate from epidermal cells.
13. What is spina bifida? How can