Cell Differentiation
Determining cell fate
Determining cell fate
Cellular differentiation: The process by
which a less specialised cell becomes a
more specialised cell type.
Differentiation occurs numerous times
development as an animal changes from a
single zygote to a complex system of
tissues and cell types.
Cell differentiation produces dramatic
changes to a cell’s size, shape, metabolic
activity, and responsiveness to signals – this
is despite the fact that all cells in an animal
have the same genome.
Determining cell fate
How do cells with the exact same genome develop
into extremely different cell types?
Determining cell fate
How do cells with the exact same genome develop
into extremely different cell types?
Gene expression.
Differentiation is underpinned by highly
regulated changes in gene expression.
As we’ve already seen, many physiological
processes are controlled by gene products
and thus gene expression (e.g. metabolism,
absorption, membrane potential, etc.).
Development
Development begins with a single cell.
This cell, the zygote, has the ability to give
rise to any cell type in an animal (in a human,
there are 210 cell types), and are thus called
totipotent.
This totipotent parent cell goes through
several divisions before the embryo becomes
a blastula.
At the blastula stage, the animal begins to
display cellular differentiation. Many of these
cells have maintained the ability to develop
into many (but not all) cell types and are
called pluripotent.
Determining cell fate
There are cells in a body that remain more
or less undifferentiated throughout the
animals life.
Stem cells.
Although adult cells can be used to create
new tissues, a much easier route involves
undifferentiated cells – or stem cells.
Embryonic stem cells are cultured by
many labs in hopes of finding a way to
treat dysfunctional tissues by replacing
them with new tissues.
Adult stem cells
Adult stem cells have been found in several
human tissues, including brain, blood, liver,
skin, bone marrow, etc.
However, the stem cells at these locations
can usually only differentiate into the cell
types near their tissues, (e.g. blood stem
cells can only become blood cells).
This is why embryonic stem cell research is
more promising than those from adult
tissues.
They are pluripotent cells.
Location of adult stem cells
The promise of stem cells
Embryonic stem cells are pluripotent,
allowing them the ability to differentiate into
many cell types.
Pluripotent cells are extracted from an
embryo and then cultured in very specific
artificial conditions.
This cell culture can then be induced to
differentiate into any of a number of cell
types. Ideally, stem cells could be injected
into people and repair damaged tissues.
The promise of stem cells
There are many challenges to
stem cell treatment, however.
Injection of undifferentiated
pluripotent cells could differentiate
into multiple cell types and likely
create in teratoma tumors.
Injection of differentiated cells will
likely result in rejection by the
immune system.
Additionally, there are ethical concerns to the use of embryonic stem cells.
The promise of stem cells
Regardless of the specifics of stem cell
treatments, the fact that stem cells have the
potential to become any number of cells
shows how animal cells are basically just a
mixture of blueprints (DNA) and directive
signals (environments and chemical signals).
Cells and animals are just machines that do
what they are told.
Plant cell totipotency
Specialisation of plant cells is not determined
as early as animal cell differentiation. Many
mature plant cells retain their totipotency and
some, with suitable nutrients and the right
chemical stimulation, can develop into
different tissues than what they were initially.
As a result, some plants can be grown
through the process of tissue culture.
This produces clones of the parent plant
and must be done in vitro.
(c/f: role of IAA in plant growth)