Studying the phenomenon of nucleolar dominance, in which one parental set of ribosomal genes in a hybrid is silenced, Craig Pikaard, Ph.D., Washington University professor of biology in Arts & Sciences and colleagues have identified the protein HDA6 as an important player in the silencing. Using the experimental plant genus Arabidopsis, they have shown that HDA6 is located in the nucleus of Arabidopsis cells, and they have imaged it, characterized it biochemically and defined its role in two cellular activities that help bring about gene silencing.
According to Pikaard, genes can be turned off when acetyl groups ?little two-carbon entities ?are removed from histones, the proteins that wrap the DNA, and when methylation -- a chemical modification of cytosine, one of the four chemical subunits of DNA -- occurs. The removal of acetyl groups is called deacetylation. He and his collaborators found that one of many predicted histone deacetylases in Arabidopsis, HDA6 is a key player in both histone deacetylation and DNA methylation of ribosomal RNA genes. Both types of modification are studied as part of a biological field known as epigenetics, the goal of which is to understand how the packaging of DNA and its associated proteins can affect gene expression. In plants, as well as animals, some epigenetic traits are stable and can be inherited when a cell divides or even into the next generation.
Pikaard explains that understanding how some genes are selectively silenced and how silenced alleles can be turned on again may someday have practical benefits. For instance, tumor suppressor genes that normally help keep cells from dividing uncontrollably are often silenced by DNA methylation and histone
Source:Washington University in St. Louis