What Is the Role of Stem Cells in Gene Expression?

Stem cells do not have a separate set of genes that tells them what to become. Different genes are expressed in different cells, allowing stem cells to produce specialised cells with different structures and functions. Gene expression means using the information in a gene to make a functional product, such as a protein. Changes in which proteins a cell makes change what it can do, even though its DNA sequence generally stays the same.

How does a stem cell specialise?

A stem cell can divide and develop into other cell types. As it specialises, some genes are switched on and others are switched off. Genes that are switched on are transcribed into RNA; for protein-coding genes, the RNA is then translated into a polypeptide. The proteins produced help give the cell its particular characteristics.

Transcription factors are proteins that can stimulate or inhibit the transcription of target genes. By changing which genes are expressed, they help direct cell specialisation. For example, a stem cell developing into a muscle cell expresses genes needed to make proteins involved in contraction. A cell developing along a different pathway expresses a different selection of genes.

Stem cells also show that patterns of gene expression can be changed. Scientists can use transcription factors to reprogram an adult body cell into an induced pluripotent stem cell (iPS cell). Pluripotent means it can develop into many types of body cell. This illustrates the link: changing transcription-factor activity changes gene expression, which changes the cell's potential to specialise. Reprogramming does not require giving the cell an entirely new genome.

Exam mistake to avoid: do not say that a stem cell loses all the genes it does not need when it specialises. Most specialised cells retain the same DNA; what changes is which genes are expressed.