Health,Stem Cells, and Technology

Friday, December 7, 2012

Transposable RNA Elements Control Gene Expression And May Lead To Speciation

Numerous studies over the past decade have elucidated a large set of long intergenic noncoding RNAs (lincRNAs) in the human genome. Research since has shown that lincRNAs constitute an important layer of genome regulation across a wide spectrum of species. However, the factors governing their evolution and origins remain relatively unexplored. One possible factor driving lincRNA evolution and biological function is
transposable element (TE) insertions. In a study at Harvard and MIT, led by Drs. David Kelley, Ph.D. and John Rinn, Ph.D., they comprehensively characterize the TE content of lincRNAs relative to genomic averages and protein coding transcripts.

Dr Kelley and Dr Rinn realized that the movement within the genome of transposable elements can be considered a mutation, and wondered if this mutation has evolutionary consequences. They think it does because when they looked at the relation between such elements and lincRNA genes, they found a number of patterns. First, lincRNAs are much more likely to contain transposable elements than protein-coding genes. More than 83% do so, in contrast to only 6% of protein-coding genes. Second, those transposable elements are particularly likely to be endogenous retroviruses, rather than any of the other sorts of transposons. Third, the TEs are usually found in the bit of the gene where the process of copying RNA from the DNA template begins, suggesting the TEs are involved in switching genes on or off. And fourth, lincRNAs containing one particular type of endogenous retrovirus are especially active in pluripotent stem cells, the embryonic cells that are the precursors of all other cell types. That datum suggests these lincRNAs have a role in the early development of the embryo.

Previous work suggests lincRNAs are also involved in creating the differences between various sorts of tissue, since many lincRNA genes are active in only one or a few cell types. Given that their principal job is regulating the activities of other genes, this makes sense. Even more pointing, studies of lincRNA genes from species as diverse as people, fruit flies and nematode worms, have found they differ far more from one species to another than do protein-coding genes. The lincRNA are, in other words, more species specific. And that suggests they may be more important than protein-coding genes in determining the differences between those species.

What seems to be happening is that endogenous retroviruses are jumping around in an arbitrary way within the genome. Mostly, that will, in evolutionary terms, be either harmless or bad. Occasionally, though, a retrovirus lands in a place where it can change the regulation of a lincRNA gene in a way beneficial to the organism. Such variations are then spread by natural selection in the way that any beneficial mutation would be. But because the variation affects developmental pathways and tissue types, and thus a creature’s form, rather than just a simple biochemical pathway, that could encourage the formation of a new species.

1 comment:

  1. Singleplex Pcr Thanks Dr.Greg Maguire ! You have sharing the awesome information about Transposable RNA.Its awesome. Your article is very helpful for me.