The bees do it

This is a very interesting pop science version of a real article (as usual, hidden behind a paywall). By studying bees as a model organism the researchers have exposed interesting insights about epigenetics.

Now with all the hype about DNA and the Human Genome Project you might think finding genes, or even the functional parts of the “junk” DNA (as I previously commented) is all we need to know about how organisms work. But it’s not. There is a whole other major area to understand and that is epigenetics.

Now what does that mean? For a human being we have about 200+ cell types. All those cells have the same genes but in each cell type only certain genes are active. This is known as cell differentiation. In any cell we have another process, gene regulation, which determines which genes are active, but that’s short-term, a cell responding to its current internal state and external environment. Differentiation is long-term, genes permanently silenced. Liver cells have shut off the genes that might be used in neurons and vice-versa.

So what is the mechanism for shutting off genes. The most common is DNA methylation (for a complete explanation I suggest you read the source or other articles). In this case a methyl group is attached to the DNA at various locations and this suppresses transcriptional activity. In more precise terms:

DNA methylation may affect the transcription of genes in two ways. First, the methylation of DNA itself may physically impede the binding of transcriptional proteins to the gene, and second, and likely more important, methylated DNA may be bound by proteins known as methyl-CpG-binding domain proteins (MBDs). MBD proteins then recruit additional proteins to the locus, such as histone deacetylases and other chromatin remodeling proteins that can modify histones, thereby forming compact, inactive chromatin, termed heterochromatin.

Typically these modifications are permanent, but also can be passed on, primarily on the maternal side. Typically the DNA is demethylated when the zygote is formed but in some case it is carried into the zygote, hence the epigenetic term.

Now back to the article. In bee hives all the workers are female but more interestingly they are all genetically identical. In fact some people actually look at the social insects as a single multicelluar organism rather than individuals because having individuals with identical genomes is just like our cells. But “identical” in this case is the genetic component and this research shows the epigenetic component is not identical.

The identical female bees have one of two “professions”: nurse or forager. Now given they are genetically identical the behaviors(s) each bee performs to achieve its “profession” must be due to epigenetic features (we might assume “learning” as another mechanism but for such simple organisms something more fundamental is the likely cause) and in fact that is what this study found. There is significantly different methylation  in the cells in the brains of the two bees. The article goes into some detail about this I won’t repeat here. A skeptic might note that this still isn’t definitive proof because some other reason by lead to separating the bees into professions and the epigenetic changes merely reflect that.

But finally the more fascinating part is that these epigenetic factors can be reversed, when needed. The experimenters did the simple trick of removing the nurses. Somehow the hive collectively senses it has the wrong balance of “professions” and some foragers revert to being nurses (now it would really be interesting to see an explanation of how that happens). And nurses that were formerly foragers have the same methylation as the nurses who had always been nurses.

Having identified the regions of the bees’ genome that differentiates nurses and foragers now another step can be taken to determine exactly which genes and how those genes cause something as complex as the “professional” behavior of the bees, but I suspect it will be a long time before we see that article.


About dmill96

old fat (but now getting trim and fit) guy, who used to create software in Silicon Valley (almost before it was called that), who used to go backpacking and bicycling and cross-country skiing and now geodashes, drives AWD in Wyoming, takes pictures, and writes long blog posts and does xizquvjyk.
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