twin epigenetics

Here is a link to the twin study.

Methylation is reversible.

Methylation is reversible.

Until the end of last year it was unclear whether methylation of histone H3 Lysine 4 (H3-K4) was reversible, unlike the acetylation/deacetylation process, which was known to be dynamic.

H3-K4 methylation is linked to accessibility of regions of DNA and active transcription of target genes. The paper suggests that LSD1 acts as a histone demethylase through an oxidation reaction, and that LSD1 is therefore a transcriptional corepressor. The argument of the break through paper that supports the hypothesis is that inhibition of LSD1 increases H3-K4 methylation and causes derepression of transcription target genes.

The paper is Histone Demethylation Mediated by the Nuclear Amine Oxidase Homolog LSD1, Shi, Y., Lan, F., Matson, C., Mulligan, P., Whetstine, J.R., Cole, P.A., Casero, R.A. and Shi, Y., Cell, Volume 119, Issue 7, Pages 941-953 (29 December 2004). There is an accompanying review article in the same issue of the journal.

Here's a link giving some background to the research that was done and describing the moment Yujiang Shi realised what he had found: http://focus.hms.harvard.edu/2004/Dec17_2004/genetics.html

Ingrid Baade

Chimpanzee genome

"The DNA sequence that can be directly compared between the two genomes is almost 99 percent identical. When DNA insertions and deletions are taken into account, humans and chimps still share 96 percent of their sequence. At the protein level, 29 percent of genes code for the same amino sequences in chimps and humans. In fact, the typical human protein has accumulated just one unique change since chimps and humans diverged from a common ancestor about 6 million years ago."

As a reference point, sequence differences between humans are about one tenth this amount.

"The researchers discovered that a few classes of genes are changing unusually quickly in both humans and chimpanzees compared with other mammals. These classes include genes involved in perception of sound, transmission of nerve signals, production of sperm and cellular transport of electrically charged molecules called ions. Researchers suspect the rapid evolution of these genes may have contributed to the special characteristics of primates, but further studies are needed to explore the possibilities."

But there may be a downside. Read on . . .

"The genomic analyses also showed that humans and chimps appear to have accumulated more potentially deleterious mutations in their genomes over the course of evolution than have mice, rats and other rodents. While such mutations can cause diseases that may erode a species’ overall fitness, they may have also made primates more adaptable to rapid environmental changes and enabled them to achieve unique evolutionary adaptations, researchers said."

Of direct relevance to our discussion of transcription factors last week is the comment that thee most rapidly evolving genes are those that "code for transcription factors, which are molecules that regulate the activity of other genes and that play key roles in embryonic development."