Who’s in control?
Your cells contain the same genome but different genes are in use
The store of genes in the nucleus of the cell, the genome, makes your cells human and is identical in every cell. However, there are around 200 different cell types – the differences between these cells lie in which genes are actually in use. Specific sets of genes are switched on and off as cells start to adopt specialised functions during development, a process called differentiation.
The genes, in turn, will generate unique messenger RNA (mRNA) molecules from reading the DNA that is in use (through transcription), and a signature population of proteins and smaller regulatory molecules. The mRNA, and therefore proteins, produced will change as the DNA being transcribed changes in response to the contents of the cytoplasm and messages from outside the cell.
The result is a complex developmental conversation. At one level, the nucleus is controlling the cell. But at another level, the cell and its surroundings can control the information stored in the nucleus, and how it gets used.
Scientists have decoded the entire human genome (through the Human Genome Project), but that does not give a picture of which information is active in any cell. This is registered in the transcriptome (the complete catalogue of mRNA molecules in a cell) and the proteome (the list of all the different proteins present). Unlike the genome, these are constantly shifting, so each is a snapshot in the life of the cell. How the transcriptome and proteome are tweaked by small changes in the cell’s circumstances is one of the biggest topics in current biological research.
A new area of research has been established since the publication of the human genome studies: epigenetics, which encompasses reversible chemical changes made to DNA and proteins associated with DNA storage within the nucleus. These changes affect how the DNA is read, therefore affecting which mRNAs and proteins are present in the cell. Importantly, some of these changes at the epigenome level have been linked with disease (including cancers), so this area of research is crucial in terms of understanding, diagnosing and treating these conditions.Lead image:
Wessex Reg. Genetics Centre/Wellcome Images