ScienceDaily (Apr. 6, 2010) — Biologists long have known that both the appearance of organisms and their inner workings are shaped by evolution. But do the same genetic mechanisms underlie changes in form and function? A new study by scientists at the University of Michigan and Taiwan's National Health Research Institutes suggests not.
Do the same genetic mechanisms underlie changes in form and function? Researchers recently turned to a database of knockout mice -- lab mice that have been engineered to lack particular genes -- to answer that question. (Credit: iStockphoto)
In the study, U-M evolutionary biologist Jianzhi "George" Zhang and colleagues Ben-Yang Liao and Meng-Pin Weng set out to systematically test a hypothesis proposed by molecular biologist Sean Carroll in 2005. Carroll posited that changes in morphology (such things as shape, color and structure of external and internal parts) occur through different genetic mechanisms than changes in physiology (inner workings). Carroll backed up his assertion with examples, but the idea, which challenged previous dogma, was controversial, Zhang said.
To test the hypothesis, Zhang's team turned to a database of knockout mice -- lab mice that have been engineered to lack particular genes.
"We found about 5,200 genes that have been knocked out in the mouse and the resulting effects studied," said Zhang, a professor of ecology and evolutionary biology. "From those genes, we looked for genes that, when knocked out, affect only morphological traits, not physiological traits. We got about 900 of those genes, which we call morphogenes."
The researchers also found about 900 "physiogenes" -- genes that affect only physiological traits, not morphology.
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Ben-Yang Liao a,1, Meng-Pin Weng a, and Jianzhi Zhang b,1
-Author Affiliations
aDivision of Biostatistics and Bioinformatics, Institute of Population Health Sciences, National Health Research Institutes, Miaoli County 350, Taiwan, Republic of China; and
bDepartment of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109
Edited by Sean B. Carroll, University of Wisconsin, Madison, WI, and approved January 6, 2010 (received for review September 9, 2009)
Abstract
The relative importance of protein function change and gene expression change in phenotypic evolution is a contentious, yet central topic in evolutionary biology. Analyzing 5,199 mouse genes with recorded mutant phenotypes, we find that genes exclusively affecting morphological traits when mutated (dubbed “morphogenes”) are grossly enriched with transcriptional regulators, whereas those exclusively affecting physiological traits (dubbed “physiogenes”) are enriched with channels, transporters, receptors, and enzymes. Compared to physiogenes, morphogenes are more likely to be essential and pleiotropic and less likely to be tissue specific. Morphogenes evolve faster in expression profile, but slower in protein sequence and gene gain/loss than physiogenes. Thus, morphological and physiological changes have a differential molecular basis; separating them helps discern the genetic mechanisms of phenotypic evolution.
evolutionary rate gene expression molecular evolution phenotypic evolution
Footnotes
1To whom correspondence may be addressed. E-mail: jianzhi@umich.edu orliaoby@nhri.org.tw.
Author contributions: B.-Y.L. and J.Z. designed research; B.-Y.L. and M.-P.W. performed research; B.-Y.L., M.-P.W., and J.Z. analyzed data; and B.-Y.L. and J.Z. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0910339107/DCSupplemental.
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