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.

Location of 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)