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MicroRNAs–“Once Dismissed as Junk”–Confirmed To Have Important Gene Regulatory Function

A new paper in Nature magazine again shows that what was “once dismissed as junk” turns out to be another astounding example of complex and specified information in the genome and a crucial part of gene regulation.

In 2008 Scientific American noted that microRNAs were “once dismissed as junk” and said the following:

Tiny snippets of the genome known as microRNA were long thought to be genomic refuse because they were transcribed from so-called “junk DNA,” sections of the genome that do not carry information for making proteins responsible for various cellular functions. Evidence has been building since 1993, however, that microRNA is anything but genetic bric-a-brac. Quite the contrary, scientists say that it actually plays a crucial role in switching protein-coding genes on or off and regulating the amount of protein those genes produce.

A recent study published in Nature, “Mammalian microRNAs predominantly act to decrease target mRNA levels,” has confirmed how microRNAs (miRNAs) have such an important effect upon gene regulation.

A news story in ScienceDaily explains the discovery:

A cell uses each microRNA to dampen the protein production of hundreds of target mRNAs, thereby fine-tuning the cell’s protein output. To create a protein, a cell uses an RNA template that is copied from a gene. A cellular machine called a ribosome then translates this mRNA template into a chain of amino acids to form the protein. Until now, researchers were unsure where in this process microRNAs act — through elimination of mRNA targets or through interference with mRNA-to-amino acid translation without much change in the mRNA.

The paper found that microRNAs regulate gene expression by eliminating mRNA targets by pairing to them so they can “direct destruction of the targeted mRNA.” According to the paper, “For both ectopic and endogenous miRNA regulatory interactions, lowered mRNA levels account for most (?84%) of the decreased protein production.” As the abstract states, “changes in mRNA levels closely reflect the impact of miRNAs on gene expression and indicate that destabilization of target mRNAs is the predominant reason for reduced protein output.”

This evidence now implicates deep levels of design not just in the sequences of protein, but also in the regulation of the entire transcription and translation process. MicroRNAs must be specially tailored to bind to the proper mRNA transcripts in order to foster their degradation and repress translation, when appropriate. Other mechanisms must inhibit repression and allow for translation.

What was “once dismissed as junk” turns out to be another astounding example of complex and specified information in the genome and a crucial part of gene regulation. Which paradigm would have predicted this finding: unguided neo-Darwinian evolution, or intelligent design?


Casey Luskin

Associate Director and Senior Fellow, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



Junk DNA