Stem Cells?

Question

How do you measure pluripotency for a cell size?

Answer 1

The potential for a cell to give rise to multiple lines of differentiated cell types is termed pleuripotency. This is the defining characteristic of stem cells. Not all types of stem cells have totipotency, or the ability to differentiate into ALL lines of cells within the organism, instead, many stem cells are already differentiated along a particular line. For example, there are pluripotential blood cell progenitors that give rise to any of the types of white blood cells (leukocytes), but these cannot become bone or muscle.

Pluripotency is not a function of cell size. Instead, it is a function of the switching on and off of genetic control mechanisms within the chromosome structures. DNA has multiple switching methods, including things like methylation, physical sequestration of genes around histone proteins, and transcription control switches formed of DNA bound protiens that either get in or out of the way, depending on signaling molecules.

Stem cells are not particularly large, and they are relatively nondescript under the microscope. They tend to have prominent nuclei and a moderate amount of cytoplasm. They do not have strongly identifiable characteristics suggestive of the type of tissue that they can become. Once they do develop these types of characteristics, they are becoming more differentiated.

What makes stem cells special, relative to terminally differentiated cell lines, is that the cascade of genetic changes leading to the development of one or another mature cell types has yet to occur. Once it does, it seems that it cannot be undone in a manner that preserves potential. In fact, "dedifferentiation" is a process that seems to actually occur in nature. Unfortunately, that process is called CANCER.