Nature is genetically modified

A small rainforest frog from Madagascar has a quirk in its genome. The same peculiarity that is found in another frog, the one with the forked tongue, or in the reed frog, or in a large number of other frogs that inhabit the forests and humid environments of Madagascar. The fact is that, in fact, that genetic trait is shared not only by Madagascar frogs, but also by many of the snakes that eat them. In fact, researchers recently discovered something unusual: the majority of Madagascar’s frog species inherited a gene, called BovB, which originated in snakes, and is widespread in these reptiles – even in Malagasy species.

Even more shockingly, after examining the genomes of frog and snake species around the world, scientists have found that this gene has somehow been passed from snakes to frogs at least 50 times across the planet; but in Madagascar this happened with an enormously greater frequency.

It’s not the only case: herring and smelt, unrelated fish that swim in the freezing coastal waters of the Arctic, North Pacific and North Atlantic Oceans, have exactly the same gene for a protein that prevents their blood from freezing ; he probably switched from herring to smelting. Laurie Graham, a molecular biologist at Queen’s University in Canada, and her colleagues reported this result last year, and it was so bizarre, they had to work hard to get their work published.

Now, it is well known, and we have also talked about it on these pages, that parasites, and in particular retroviruses, by infecting eggs and sperm of vertebrates can change their genome, inserting their own pieces of genetic information into the DNA of the host, which can thus suddenly evolving new phenotypes; but how is it possible for a vertebrate to be able to insert pieces of its own genome into that of another vertebrate?

There is a very clear possibility: it could be that certain viruses, and especially retroviruses, can function not only by integrating their genetic information into the host, but from time to time acquiring pieces of its genome from the host, which then could then be passed on to a subsequent host. It is therefore necessary to prove whether the transfer of DNA can occur not only from viruses to vertebrates – a fact that has been established and which has produced useful evolutionary innovations in the latter, including humans – but also in the other direction, i.e. from vertebrates or other animals to viruses.

In an article published last December, the genomes of 201 eukaryotes and 108,842 viruses were analysed. Thus, evidence of more than 6,700 gene transfers was found, with host-to-virus transfers approximately double the number of virus-to-host transfers.

Why do viruses “steal” genetic information from their hosts? One of the most striking examples of utility for viruses lies in a particular “theft”, well documented in several viruses. Histones are proteins that in animals and plants serve to pack DNA correctly inside the cell; considering that, for example in humans, the total DNA contained in each cell has an overall length of about 3 meters, it is clear that keeping it organized in a compact structure that enters a cell nucleus, with a diameter of about ten billionths metre, requires very special proteins – precisely the histones – able to control which part is “unrolled” when it is necessary to read the genetic information. Naturally, compacting one’s genetic material in an orderly manner is also a very useful function for viruses, which are much smaller than a cell nucleus; thus, the instructions for making these proteins, accidentally incorporated into the genome of some viruses, have become integral parts of the genome of several groups of these parasites. This also happened recently, given that the sequences are identical to those of the hosts from which they come – that is, there was not enough time to accumulate mutations.

Now, for a virus to randomly acquire advantageous genetic information from a host, there must exist a mechanism which frequently has the result of integrating the host’s DNA into the virus’s genome, because the latter cannot a priori “choose” what is useful; and this material, when the virus integrates into a host of a different species, will be transmitted to that one, becoming its stable heritage if the infection involves oocytes or spermatozoa and if the thing is not lethal.

Since the reproductive tract of all living beings is subject to viral infection, and indeed there are specialized viruses, the illustrated mechanism is probably very widespread, as gradually appears from the new horizontal gene transfer data not only between different animals, but even between different living kingdoms – from plants to insects, for example.

The truth is that, despite the narrow barriers of supposed “naturalness” into which certain misunderstood ecological ideas would like to force us, genetic information circulates between individuals, species and living kingdoms with a promiscuity sufficient to increase the possibilities of generating advantageous varieties from the point of view of natural selection; and a large part of the wonderful variety we observe is the daughter of this continuous mixing, much more efficient in producing new phenotypes than gradual and slow mutation.

Nature is genetically modified and nobody checks the safety of the organisms that arise from the innumerable processes of gene transfer.