What Do Organisms Mean? > Natural Genome Remodeling > Summary
A project by Stephen L. Talbott

Previous     Next >

Natural Genome Remodeling

Summary

In 1983, Nobelist Barbara McClintock suggested that organisms respond to stress by altering their own genomes “in a ‘thoughtful’ manner” and based on their “knowledge” of themselves. We know today that genomic change of all sorts is rooted in the remarkable expertise of the organism as a whole.

The organism sees to the replication of chromosomes in dividing cells, maintains surveillance for all sorts of damage, and repairs or alters damage when it occurs — all with an intricacy and subtlety of well-gauged action. In certain human immune system cells, portions of DNA are repeatedly cut and then stitched together in new patterns, yielding the huge variety of proteins required for recognizing an equally huge variety of foreign substances that need to be rendered harmless. Clearly, our bodies have gained the skills for elaborate reworking of their DNA

This reworking includes direct chemical modification (such as methylation) of millions of nucleotide bases in the human genome — modification that varies according to context. But the cell’s contextualization of its genome extends far beyond such changes, leading to the stable incorporation of the genome in some 250 major cell types, each of which has the “same” genome, yet a genome that functions in a radically different way, subserving the needs of radically different contexts, from bone to blood to liver to brain.

The organism also directly duplicates and modifies some of its genes, and indirectly duplicates genes or larger DNA segments through reverse transcription of RNA back into DNA. These processes have long been known, but our knowledge of the organism’s genome-modifying skills is now being hugely expanded. For example, two duplicated genes can, via a number of different pathways, fuse into a single chimeric gene. And not only protein-coding RNAs, but also small, regulatory RNAs, can be reverse transcribed into DNA and their functions diversified. Protein-coding genes have even been created from scratch — from