Later the discovery of DNA structure, considerable amount of attention has been paid to only a small part (<2 %, let us round it to 2%) of the entire genome, Genes. The DNA that codes for an RNA, which in turn makes a protein, who performs the biological functions in the body. “What about rest of the 98 % ?”
In the third quarter of 20th century, Dr. Susumu Ohno, a geneticist and evolutionary biologist coined a term ‘Junk DNA’ to represent this 98% of the non coding genome. As a natural human tendency, we generally do not look into something which was labelled ‘useless’. However, Dr. Susumu has contributed very significantly calling it as “Junk”, because of which much of the focus was on the coding part of the genome or very less attention has given to non-coding part. The research on the protein-coding genome has revealed important (rather causal?) mutations, structural variations of many common diseases. Thanks Dr. Susumu.
On the other hand, much of the so called “Junk DNA” also transcribed just like the protein coding part. “How much percentage” is still an open question (more a debate?). It is in the 90’s people started inspecting this large part of the transcribed non-coding genome for its function. In the early 90’s, one of the first non-coding transcripts, XIST (a lncRNA) was discovered, with some variations from the protein coding transcripts. In the late 90’s, John Rinn, now at Harvard, was serendipitously discovered a transcript lacking ORF, while probing for coding genes on chromosome 22 (at Yale University). This lead to the discovery of HOTAIR in the later years.
Fast forward to the early 21st century ...
Now we are in an era which evidenced the superfast development of the technology. The “Next Generation Sequencing (NGS)” technology has revolutionized many areas of the biology research, including understanding of the coding and non-coding part of the genome deeply. Unlike previous methods, NGS allowed to look into the genome of the many individuals simultaneously. DNA-seq provided a way to get a global picture of mutations, structural variations of a particular cancer type or other disease by inspecting the genomes of large number of patients in a very short timespan. RNA-seq, an excellent tool for exploring the whole transcriptome of a cell, assisting the researchers to catch the transcripts transcribed from the non-coding part of the genome. Many studies have already proved that these non-coding transcripts are involving in the regulation of gene expression and the expression of them is cell type, tissue, developmental stage specific, there is an increasing chance of using them as the diagnostic markers for many disease types.
Like proper planning is required to place the bricks in order to build a complete house, transcribed non-coding genome is having plans to control expression of genes and other gene activities in healthy and disease states as well. This clearly indicates “Junk is not really junk, in this case it is important non-coding section” as we no more willing to call it as Junk.
As Aubrey de Grey, co-founder of “Strategies for Engineered Negligible Senescence” (SENS), believes “if the technology develops with the current pace, the human life expectancy increases to 1000 years and the person who lives up to 1000 years is among us now”. I strongly believe that Genomics will have a major role in this context.