Thursday, July 24, 2008

Revisiting Lamarck

Now epigenetic inheritance pertaining to DNA methylation influence phenotypic expression. That implies that traits can be inherited without changing the gene sequence at all.

Lamarck might be right in some sense.

After so many years of dismissing Lamarck's theory, AND telling students that no, a giraffe's neck does not grow long because of all the stretching its parents did, I never thought the day will come where one has to look at his theory closely again.

For more read this fascinating article by New Scientist

Some interesting excerpts:
but over the past decade it has become increasingly clear that environmental factors, such as diet or stress, can have biological consequences that are transmitted to offspring without a single change to gene sequences taking place.

Epigenetics deals with how gene activity is regulated within a cell - which genes are switched on or off, which are dimmed and how, and when all this happens. For instance, while the cells in the liver and skin of an individual contain exactly the same DNA, their specific epigenetic settings mean the tissues look very different and do a totally different job. Likewise, different genes may be expressed in the same tissue at different stages of development and throughout life. Researchers are a long way from knowing exactly what mechanisms control all this, but they have made some headway.

Inside the nucleus, DNA is packaged around bundles of proteins called histones, which have tails that stick out from the core. One factor that affects gene expression is the pattern of chemical modifications to these tails, such as the presence or absence of acetyl and methyl groups. Genes can also be silenced directly via enzymes that bind methyl groups onto the DNA. The so-called RNA interference (RNAi) system can direct this activity, via small RNA strands. As well as controlling DNA methylation and modifying histones, these RNAi molecules target messenger RNA - much longer strands that act as intermediaries between DNA sequences and the proteins they code for. By breaking mRNA down into small segments, the RNAi molecules ensure that a certain gene cannot be translated into its protein. In short, RNAi creates the epigenetic "marks" that control the activity of genes.

We know that genes - and possibly also non-coding DNA - control RNAi and so are involved in determining an individual's epigenetic settings. It is becoming increasingly apparent, though, that environmental factors can have a direct impact too, with potentially life-changing implications.

No comments: