Each of our cells contains DNA, the genetic code that instructs the cells in our body and is responsible for aspects of health and disease. Individual instructions from our DNA are called genes, which are turned on or off— or “expressed”—at different levels of abundance depending on environmental conditions and the necessity to perform a process: for example, growth, digestion after meals, fighting an infection, repairing UV damage, etc..When expressed, genes are converted— or “transcribed”—into a chemically modified version of the DNA instruction called RNA. Because they carry instructions from DNA, they are called messenger RNA and provide the code for making proteins—considered the main players in the functions of the cells and body.
Additionally, RNAs may be non-protein coding and play important roles in regulating gene expression by directly controlling transcription-the process of making an RNA copy of a gene sequence—from DNA or by regulating the stability of other RNAs; when functioning in this capacity, they are referred to as regulatory RNAs. Regulatory RNAs are therefore critical for maintaining appropriate gene expression and may ultimately impact the activity of biological pathways. Abnormal RNA expression has been implicated in numerous human diseases, including autoimmune diseases.
Collectively, all the RNAs are referred to as the transcriptome. Given that genes are converted to RNAs when expressed, identification and quantification of RNAs in the transcriptome allows for the direct measurement and profiling of gene expression. Recent advances in genomic sequencing technology led to RNA sequencing, which allows for the affordable, rapid, reproducible, and high-throughput identification and quantification of RNA levels and is currently being used in numerous clinical applications.