1.11 Building New Bones with Skin Cells
For the past thirty years, scientists have been developing new technologies and
products to help replace damaged organs with parts grown in the laboratory.
Biologists have recently been able to change human skin cells into bone and
cartilage, the tissues that ears, noses, knees, and hips are made of. Recently,
biologists have been studying certain types of cells that can be forced to
stem cell an unspecialized cell that change their identities. Most of these biologists are focusing on stem cells—
may transform into a specialized cell immature (unspecialized) cells that can, in theory, be transformed into any of
the specialized cells of the body. Other researchers are working with certain
mature (specialized) cells, such as skin cells, that they have been able to
DID YOU KNOW ? transform into other types of specialized cells, such as bone and cartilage cells.
Organ Donation in Canada
Canada’s organ-donation rate is
among the lowest of all the Stem Cells
developed countries. More than Every human being begins life as a single cell called a zygote—formed from
3000 Canadians are waiting for an the combination of a sperm cell and an egg cell. This cell is not a bone cell, a
organ transplant. One organ donor
can donate numerous organs and brain cell, or a skin cell. It is not specialized. However, in the cell’s nucleus,
tissues, including lungs, heart, liver, there are 46 DNA molecules containing all of the instructions (genetic
kidneys, pancreas, bowel, eye tissue, information) necessary to transform it into any of the specialized cells of the
skin, heart valves, bone, tendons,
veins, and ligaments. You can
mature human body. The information in DNA is organized into sections
indicate your wish to become an called genes, each gene coding for a particular characteristic of the cell. Why
organ donor on your health card or does a cell like a zygote not use all of the information in its genes? Biologists
your driver’s licence. Discuss this don’t yet have a satisfactory answer to this question, but experiments seem
decision with your family so your
wishes are known.
to indicate that some of the chemical reactions controlling the genetic
information are blocked. In other words, some of the genes are “turned off.”
Therefore, in a zygote, the genes for producing the characteristics of a muscle
cell or a bone cell are turned off, and only the genes for producing an
unspecialized cell are turned on. These are stem cells. As the zygote divides by
mitosis, it becomes a collection of unspecialized stem cells called an embryo.
As an embryo continues to develop, various genes turn on in some of its
cells, causing them to transform or differentiate into specialized cells.
Specialized cells form tissues and organs, such as bone, heart, liver, and skin.
However, not all cells specialize. Even in the adult human, stem cells may be
found in bone marrow, skin, the spinal cord, and the brain. Stem-cell research
has shown that under certain experimental conditions, embryonic and adult
stem cells can be encouraged to become almost any kind of specialized cell.
Embryonic Stem Cells and Cloning
The use of tissues from human embryos raises many moral and ethical
concerns, and while stem cells are found in adult tissues, they are difficult to
isolate and collect because they make up only one out of every 10 000 cells.
Using stem cells to produce tissues for transplantation may also cause
medical complications. Just as the body rejects transplanted organs from
donors, it can reject tissues grown from donated stem cells. Scientists have
48 Unit 1 NEL
Case Study 1.11
discovered ways of avoiding this type of tissue and organ rejection through
a process called cloning. Cloning produces cells that are genetically identical
to the cells of the recipient, and thus are not rejected by the recipient’s
immune system. Nevertheless, cloning is a highly controversial process.
Two forms of cloning are therapeutic cloning and reproductive cloning.
In therapeutic cloning, the nucleus of a human egg cell is replaced with the therapeutic cloning the
nucleus of a body cell (such as a skin cell) from the person who needs the production of cloned embryos for
the purpose of obtaining stem cells
organ transplant. The egg cell is stimulated with a short pulse of electricity,
and it then develops into an embryo from which stem cells can be removed. reproductive cloning the
These stem cells are genetically identical to those of the donor of the body- production of fully formed cloned
cell nucleus and can be used to produce tissues that will not be rejected by organisms
the donor’s immune system. Therapeutic cloning raises moral and ethical
dilemmas because human embryos are created and then destroyed in the
Reproductive cloning begins like therapeutic cloning. An egg-cell nucleus is
replaced with a body-cell nucleus and stimulated to develop into an embryo.
The only difference is that in reproductive cloning the embryo is not used as a
source of stem cells; instead, it is implanted in a uterus and allowed to develop
into an adult clone—an exact genetic copy of the donor. Dolly, the first cloned hair shaft
sheep, was produced by this method. Reproductive cloning also raises serious
moral and ethical dilemmas because it creates embryos artificially, and
because it introduces the possibility of creating humans for the sole purpose
of providing tissues and organs for other humans.
Skin Stem Cell Research
In 2001, Dr. Freda Miller and colleagues at the University of Montreal
Neurological Institute (MNI), discovered that skin contains stem cells that
may transform into a number of other cell types, including nerve cells, muscle
cells, and fat cells. Further research has shown that some types of stem cells in
fat tissue hair root
skin may transform into bone and cartilage cells.
Skin is the largest and most accessible organ in the body. Within the hypodermis
dermis, the middle layer of human skin (Figure 1), are specialized cells called Figure 1
fibroblasts. Recently, a number of researchers have been able to transform Human skin
fibroblasts into bone and cartilage cells. From a small piece of skin no more
than a few cubic millimetres in volume, scientists have been able to produce fibroblast an unspecialized skin cell
enough bone or cartilage to fill a cavity 200 to 300 times that size. And
because the original fibroblasts come directly from the patient, there is no
risk of rejection.
In order to change fibroblasts into bone cells, scientists attach skin cells
to sticky netting made of protein, and surround the cells with phosphate
minerals like those normally found in bone. Within weeks, the fibroblasts act
just like bone cells and begin to produce the hard material that makes bones
rigid. When fibroblasts are packed tightly together and deprived of oxygen (a
condition normally found in cartilage tissue), they soon transform into
NEL Cellular Biology 49
Some of the promising applications of this research include the treatment of
gum disease (also called periodontal disease) (Figure 2(a)) and osteoarthritis,
a degenerative disease of the joints (Figure 2(b)). In advanced gum disease, the
bone in the jaws deteriorates and teeth are lost. In osteoarthritis, a breakdown
in the cartilage of hips, knees, and other joints causes thousands of patients
every year to undergo painful hip- and knee-replacement surgery. Cartilage
and bone replacement using skin fibroblasts may some day help cure these
(a) Advanced gum disease
(b) Osteoarthritis (in the knee on
the right) (a) (b)
Case Study 1.11 Questions
Understanding Concepts (b) Injury to the cartilage in knee joints is common
1. (a) What is a stem cell? among athletes. A procedure called autologous
(b) How may stem cells be used to help humans? chondrocyte transplantation (ACT) is sometimes
2. Explain how genes determine whether a cell is a used to replace damaged knee cartilage. Briefly
stem cell or a specialized cell. describe the ACT procedure, and explain how the
research described in this case study could help
3. (a) What are fibroblasts?
improve the process.
(b) Why are fibroblasts of interest to transplantation
biologists? GO www.science.nelson.com
(c) What medical advantages do fibroblasts have
over stem cells in transplantation? 6. Some scientists have been able to change stem cells
obtained from fat tissue into cells that resemble nerve
4. Describe the processes biologists use to change
cells. Conduct research to determine how newly
fibroblasts into bone and cartilage cells.
transformed fat cells can function as nerve cells.
Making Connections GO www.science.nelson.com
5. (a) What are some of the uses of bone and cartilage
cells that have been made from fibroblasts?
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