Acquired Traits Can Be Inherited Via Small RNAs
ScienceDaily (Dec. 5, 2011) — Columbia University Medical Center (CUMC) researchers have found the first direct evidence that an acquired trait can be inherited without any DNA involvement. The findings suggest that Lamarck, whose theory of evolution was eclipsed by Darwin's, may not have been entirely wrong.
In an early theory of evolution, Jean Baptiste Larmarck (1744-1829) proposed that species evolve when individuals adapt to their environment and transmit those acquired traits to their offspring. For example, giraffes developed elongated long necks as they stretched to feed on the leaves of high trees, an acquired advantage that was inherited by subsequent generations. (Credit: © bonniemarie / Fotolia)
The study is slated to appear in the Dec. 9 issue of Cell.
"In our study, roundworms that developed resistance to a virus were able to pass along that immunity to their progeny for many consecutive generations," reported lead author Oded Rechavi, PhD, associate research scientist in biochemistry and molecular biophysics at CUMC. "The immunity was transferred in the form of small viral-silencing agents called viRNAs, working independently of the organism's genome."
In an early theory of evolution, Jean Baptiste Larmarck (1744-1829) proposed that species evolve when individuals adapt to their environment and transmit those acquired traits to their offspring. For example, giraffes developed elongated long necks as they stretched to feed on the leaves of high trees, an acquired advantage that was inherited by subsequent generations. In contrast, Charles Darwin (1809-1882) later theorized that random mutations that offer an organism a competitive advantage drive a species' evolution. In the case of the giraffe, individuals that happened to have slightly longer necks had a better chance of securing food and thus were able to have more offspring. The subsequent discovery of hereditary genetics supported Darwin's theory, and Lamarck's ideas faded into obscurity.
However, some evidence suggests that acquired traits can be inherited. "The classic example is the Dutch famine of World War II," said Dr. Rechavi. "Starving mothers who gave birth during the famine had children who were more susceptible to obesity and other metabolic disorders -- and so were their grandchildren." Controlled experiments have shown similar results, including a recent study in rats demonstrating that chronic high-fat diets in fathers result in obesity in their female offspring.
Nevertheless, Lamarckian inheritance has remained controversial, and no one has been able to describe a plausible biological mechanism, according to study leader Oliver Hobert, PhD, professor of biochemistry and molecular biophysics and a Howard Hughes Medical Institute Investigator at CUMC.
Dr. Hobert suspected that RNA interference (RNAi) might be involved in the inheritance of acquired traits. RNAi is a natural process that cells use to turn down, or silence, specific genes. It is commonly employed by organisms to fend off viruses and other genomic parasites. RNAi works by destroying mRNA, the molecular messengers that carry information coded in a gene to the cell's protein-making machinery. Without its mRNA, a gene is essentially inactive.
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Transgenerational Inheritance of an Acquired Small RNA-Based Antiviral Response in C. elegans
Oded Rechavi1, Gregory Minevich1, Oliver Hobert1
1 Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY 10032, USA
Received 2 September 2011; revised 13 October 2011; Accepted 25 October 2011. Published online: November 23, 2011. Available online 23 November 2011.
Induced expression of the Flock House virus in the soma of C. elegans results in the RNAi-dependent production of virus-derived, small-interfering RNAs (viRNAs), which in turn silence the viral genome. We show here that the viRNA-mediated viral silencing effect is transmitted in a non-Mendelian manner to many ensuing generations. We show that the viral silencing agents, viRNAs, are transgenerationally transmitted in a template-independent manner and work in trans to silence viral genomes present in animals that are deficient in producing their own viRNAs. These results provide evidence for the transgenerational inheritance of an acquired trait, induced by the exposure of animals to a specific, biologically relevant physiological challenge. The ability to inherit such extragenic information may provide adaptive benefits to an animal.
► Viral replication triggers an RNAi-dependent viral silencing response in C. elegans ► The acquired silencing response is transgenerationally transmitted ► Transgenerational transmittance is non-Mendelian and involves small antiviral RNAs ► An RdRP is required for long-term maintenance of the silencing response
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