"We found a specific evolutionary mechanism to account for a portion of the
intricate biological complexity of our species, "said Ariel Fernandez, professor of
of bioengineering at Rice University. "It's a defense mechanism, a process that
allows us to address the fitness consequences of inefficient selection. It
enables some of our proteins to be more specialized in time, and in turn
makes us more complex. "
Fernandez is the author of a paper scheduled to appear in the December issue of the journal Genome Research. The line of research is available.
Fernandez said the study draws from past performance by its own research group and from the seminal work of Michael Lynch, distinguished professor of biology at Indiana University and recently elected to the National Academy of Sciences. Lynch's work has shown that natural selection is less effective in humans, compared with simple creatures such as bacteria. This "inefficiency of selection" is derived from the smaller population size of humans compared with unicellular organisms.
"In all organisms, genes are duplicated from time to time, for reasons not
fully understand, "said Fernandez." When working efficiently, natural selection
eliminates many of these copies, which are called 'paralogs. In our previous
work, we saw an unusual number of gene copies had survived in the human
genome, which makes sense given the inefficiency of selection in humans. "
In previous research on protein structure, the team of Fernandez noted that some proteins are packaged worse than others. Moreover, they found that the least efficient Packed proteins are structurally stable only when coupled with associated proteins to form complexes.
Proteins "These poorly packed are potential troublemakers when gene duplication
happens, "said Fernandez." The more copies of paralogs encodes the protein that
the body needs. This is called an "imbalance of doses, and that can make us sick.
For example, the imbalance in the doses have been implicated in Alzheimer's disease and other
diseases.
Given the inefficiency of selection, Fernandez knew that badly packed paralogs encoding proteins could remain in the human genome for a while. So he and graduate student decided to examine whether Jianpeng Chen had kept duplicates of genes in the genome of time for random genetic mutations affect the difference paralogs. Fernandez and Chen, now a senior researcher in Beijing, China, Cross-examined databases on genomics, protein structure, regulation and protein expression in these paralogs microRNA problematic.
"The longer these duplicated genes become inefficient due to the selection, the
more likely to undergo a random mutation, "said Fernandez." Parties
gene acts to regulate the expression of proteins - by binding with microRNAs, for
example. We found numerous cases where the random mutations had caused paralogs
as opposed to express, so that eliminated the harmful dose
imbalances ".
Lynch said that one aspect of research that is potentially revolutionary Fernandez is the trend of proteins to develop a more open structure in complex organisms.
"This observation is consistent with the general theory that large agencies with
relatively small size of the population - compared with microbes - are subject to
vagaries of random genetic drift and therefore the accumulation of very slightly
deleterious mutations,
Lynch said.
At first, he said, the accumulation of these mutations may promote stability slight breakdown of proteins. This in turn opens the door to interactions with other proteins that can restore a measure of that lost stability.
"These are the roots potential for the emergence of novel protein-protein
interactions, which are the hallmark of evolution in the complex, multicellular
species, "Lynch said." In other words, the origins of some key aspects of the
evolution of complexity can be caused completely adaptive
processes.
Fernandez said the research reveals how increasingly specialized proteins can evolve. He drew an analogy to a company hired two delivery drivers initially covering the same parts of the city, but eventually specialize in offering only specific neighborhoods.
"Over time, even if times become tough, you can not dismiss any of them
because each of them became so specialized that your company needs both, "
He said.
The simplest is a creature, less specialized proteins it has. Humans and other mammals in order many specialized proteins needed to build the specialized tissues of the skin, skeleton and organs. Even more specialized proteins are required to maintain and regulate them. This complexity requires making a duplicate original of all trades of genes retained, but this will not happen unless the selection is inefficient. This is often a point of controversy between supporters of evolution and intelligent design.
Fernandez and Chen looked duplicated genes in the human genome and found that the poorer focused on a protein was most likely that distinguish paralogs through specialization.
"This supports the case of evolution, because it shows that you can drive
complexity, with random mutations in the duplicated genes, "said Fernandez." But this
also means that random drift must prevail over Darwinian selection. In other
words, if Darwinian selection has been ruthlessly efficient in humans - as it is in
bacteria and unicellular eukaryotes - then our level of complexity not
possible ".
The research is supported by the National Institutes of Health.
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