2017/03/29

Goodbye junk-dna!

'Jumping genes' and transposons are cut or silenced by clever mechanisms

Eukaryotic cells are able to produce even thousands of different proteins from one gene. This is why there are even two millions of different proteins in a human body, although there are only about 19,600 protein coding genes used for human cells to produce the huge number of different proteins. This clever mechanism is called alternative splicing. RNA-mediated mechanism uses a gene like a library; it makes a template and modifies it by several ways. Cutting, pasting, recombining, moving, removing etc.

Sometimes some strands (rna-like tetrotransposos) needed for the alternative splicing mechanism are inserted into the genome by mistake. These genomic parasites can be harmful for genomic stability and integrity. Especially in germline cells they can cause serious troubles, even cell death. That's why there are mechanisms designed in the cell, that silence or remove those erroneous genetic sequences. The mechanism is described here:

https://www.labroots.com/trending/cell-and-molecular-biology/5601/transcription-mechanism-sheds-light-junk-dna

Excerpt: "The researchers have found that small pieces of RNA get stitched together into a loop. The investigators were interested in the unicellular ciliate, Paramecium tetraurelia, because they identified small RNA molecules that excise pieces of Paramecium DNA. Looking deeper, there was a kind of feedback loop operating in the excision of DNA segments. Junk DNA was being cut out of the genome, and it is then transcribed into RNA before getting degraded by cellular machinery. The transcribed RNAs act to help cut out even more DNA, building up the RNA production from these excised pieces. However, the resulting RNA pieces are quite small; they are too tiny to be read by normal cellular machinery.

The scientists had to keep digging to learn more about what as happening. "It was an interesting detective work," Nowacki remembers. They had a suspect -- all they needed was to pin it down. "We were not actually looking for the unknown, because we soon had an idea, and then it was all about testing that idea." What they found was that the RNAs were strung together, into strands or concatemers that are about 200 base pairs long and then closed into a loop.

The evidence continues to mount that so-called junk DNA has important functions, likely in the regulation of gene expression and who knows what else. Nowacki suggested that this is the first time, a precise mechanism has been identified whereby deleted, junk DNA is transcribed. That could mean it will finally shed its junky nickname.

Nowacki's lab is working on the NCCR "RNA & Disease -- The Role of RNA Biology in Disease Mechanisms" project, which aims to reveal more about the role of RNA in disease. RNA is a crucial part of gene expression, and disruptions in that system have been linked to cancer, diseases of the heart and brain, and metabolic disorders. Swiss researchers that study different aspects of the function and characteristics of RNA work together at the NCCR, coordinating research using a variety of models like plants, yeast, roundworms, mice and human cells."
 
My comment: The cell uses mistakes for finding more mistakes! An incredible mechanism! There are no selfish genes or jumping genes. Unchecked, unremoved or unsilenced transposons typically cause diseases. Modern science has just found out the link between the ALS disease and unsilenced dna-transposons:

https://medicalxpress.com/news/2017-03-role-storm-genes-als.html

There are no mechanisms for assumed evolution. Life is not driven by gene sequences. Genes are driven by lifestyle. Don't get lost.