Monday, 3 January 2022

Evolution News - How Evolution Transformed a Common Ancestor's Genes to Make Snake Venom and Human Saliva

Venoms in snakes and salivary protein in mammals share a common origin | Okinawa Institute of Science and Technology Graduate University OIST

Here is an interesting paper for at least two reasons:

Firstly, for people who understand evolutionary biology, there is the evidence of common origins in that the genes for producing venom in snakes are also present and produce related proteins in mammals, albeit non-venomous proteins.

Secondly, for Creationist victims of the Intelligent [sic] Design Hoax, there is the complete reliance by the biologists who wrote it on the Theory of Evolution by Natural Selection for the explanation, with no hint whatsoever that the imminent collapse of the TOE and its abandonment by science in favour of intelligent [sic] design, or whatever the latest product Creationist frauds are trying to sell their target marks as an alternative to genuine science is, as has been predicted (any day now real soon!) by Creationist frauds, since about 1940. In fact, what would be a historic first where an established scientific theory is replaced by a guess with no supporting evidence, looks about as likely (and as nonsensical) as that of the QAnon 'coming storm' or the return from the grave of John F. Kennedy, Jnr. to overthrow the Biden presidency and reinstall Trump in the Oval Office.

The paper, by Agneesh Barua of the Ecology and Evolution Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan, Ivan Koludarov of the Animal Venomics Group, Justus Leibig University, Giessen, Germany and Alexander S. Mikheyev of the Research School of Biology, Australian National University, Canberra, ACT, Australia, is published, open access, in BMC Biology. According to the Okinawa Institute of Science and Technology Graduate University (OIST) news item:
Venoms are cocktails of toxic proteins that have evolved across the whole animal kingdom, typically as a method of killing or immobilizing prey. The oral venom systems found in snakes are particularly complex, and the origin of their venoms is still unclear.

Agneesh Barua, co-first author
PhD student
OIST, Okinawa, Japan.
  • A new study has found that venoms found in snakes and mammals share a common origin
  • Researchers traced the origin of a class of toxins, called kallikrein serine proteases, to a salivary protein found in a common ancestor
  • Results from the evolutionary tree also showed that non-toxic salivary kallikreins in mammals, including those found in mice and human saliva, also evolved from the same ancestral gene
  • The study provides strong evidence for the hypothesis that venom evolved from a common group of genes with toxic potential that existed in the ancestor of snakes and mammals

Press Release
Snakes, some lizards and even a few mammals can have a venomous bite. Although these lineages split more than 300 million years ago, their venoms have evolved from the same ancestral salivary protein, reported scientists today in BMC Biology.

Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) in Japan and the Australian National University focused on a class of toxins found in most snake venoms and all other reptile and mammalian venoms called kallikrein serine proteases and traced their origins to a gene found in a common ancestor.

In that paper, we hypothesized that in the ancestor of snakes and mammals, there was a common group of genes that had a toxic potential. Snakes and mammals then took different evolutionary paths, with snake lineages evolving diverse and increasingly toxic concoctions, while in mammals, venom did evolve, but to a much lesser degree. But what we wanted to know is whether the toxins within mammal and snake venom evolved from a common ancestral gene.

There are so many different serine proteases that have a high degree of similarity, that until now, it was too difficult to isolate the right genes needed to determine the evolutionary history.

This is really strong evidence for our hypothesis that venom evolved from a common group of genes in an ancestor that had a toxic potential but the most surprising thing was that non-toxic salivary kallikreins, like those found in humans and mice, also evolved from the same ancestral gene.

Agneesh Barua
In a previous paper, Barua and his colleagues found that the mammal salivary gland and snake venom gland share a similar pattern of activity in a group of regulatory genes, suggesting that the foundation needed for venom to evolve exists in both snakes and mammals.

Kallikrein serine proteases are a kind of protein-degrading enzyme, which play a key role in regulating blood pressure. Mammal saliva contains small quantities of these proteins, although their function remains unclear to this day. But in venomous snakes and mammals, like shrews and solenodons, these proteins have evolved toxicity. When injected in high amounts, they drastically reduce blood pressure, potentially causing unconsciousness and even death.

Early on, researchers noticed biochemical similarities between kallikrein serine proteases in snake venoms and those in mammal saliva, but scientists did not know until now whether they were, in fact, related.

With recent advances in genomic methods, the research group were able to identify and compare all the kallikrein genes in reptiles, amphibians, fishes and mammals to create an evolutionary tree.

Excitingly, they found that snake venom kallikrein serine proteases and mammal salivary kallikreins did evolve from the same ancestral gene.

Salivary kallikreins, like those found in mice, humans, and venomous mammals like shrews and solenodons, are closely related to toxic serine protease kallikreins found in venomous snakes.
In fact, the researchers found that the non-toxic kallikreins in mammal saliva were more closely related to the venomous toxins found in snakes than to other kallikreins found within mammals.

Overall, this evidence suggests that salivary kallikrein proteins in mammals, including humans, also have the evolutionary potential to become toxic.

But, Barua quickly added, there is a caveat. “Just because we have the building blocks to evolve venom doesn’t mean this will occur. Venom is really energetically expensive to make, so there had to be a strong ecological pressure for it, which humans, and most mammals don’t have.”

But what this does tell us, he said, is that the line between venomous and non-venomous mammals is blurrier than previously thought.
Perhaps most devastating for Creationism is the summary to the paper in BMC Biology:
Origins and diversification of tissue kallikreins (TKL). A TKL genes are located at a single genomic locus. In mammals, TKL genes are found in a single cluster, but in reptiles, they are scattered across two to three nearby clusters located several hundred kilobases apart. Venom evolution is associated with expansions of toxin-containing gene clusters, but there are also lineage-specific expansions that are not linked to venom evolution (e.g. turtles and mice). In existing genomic assemblies, the TKL clusters are often fragmented (represented by dashed line) across different scaffolds, but they share many common genes and are clearly contiguous (Supplementary Figure 1 and 2). B Phylogenetic analysis revealed that tetrapod TKLs originated from a common ancestor with vertebrate anionic trypsins, which are commonly expressed in the pancreas and are found elsewhere in the genome. TKLs diverged into two distinct clades, one comprising the KLK4-KLK15 lineages and the other the KLK1/2/3-SVSP/SVL lineage that contains toxipotent genes. Species silhouettes represent members of entire clades rather than a strict node to species demarcation. For a more conventional format, please refer to phylogeny (Supplementary Figure 2 and supplementary dataset 1) in supplementary. Serine protease-based toxins are homologs deriving from the same ancestral gene, implying that these toxins originated in parallel venoms in reptiles and mammals

Evolution can occur with surprising predictability when organisms face similar ecological challenges. For most traits, it is difficult to ascertain whether this occurs due to constraints imposed by the number of possible phenotypic solutions or because of parallel responses by shared genetic and regulatory architecture. Exceptionally, oral venoms are a tractable model of trait evolution, being largely composed of proteinaceous toxins that have evolved in many tetrapods, ranging from reptiles to mammals. Given the diversity of venomous lineages, they are believed to have evolved convergently, even though biochemically similar toxins occur in all taxa.

Here, we investigate whether ancestral genes harbouring similar biochemical activity may have primed venom evolution, focusing on the origins of kallikrein-like serine proteases that form the core of most vertebrate oral venoms. Using syntenic relationships between genes flanking known toxins, we traced the origin of kallikreins to a single locus containing one or more nearby paralogous kallikrein-like clusters. Additionally, phylogenetic analysis of vertebrate serine proteases revealed that kallikrein-like toxins in mammals and reptiles are genetically distinct from non-toxin ones.

Given the shared regulatory and genetic machinery, these findings suggest that tetrapod venoms evolved by co-option of proteins that were likely already present in saliva. We term such genes ‘toxipotent’—in the case of salivary kallikreins they already had potent vasodilatory activity that was weaponized by venomous lineages. Furthermore, the ubiquitous distribution of kallikreins across vertebrates suggests that the evolution of envenomation may be more common than previously recognized, blurring the line between venomous and non-venomous animals.
And, as though evidence of common ancestry and evidence that the TOE is not only alive and well but has immense explanatory power, wasn't bad enough for Creationists, we also not only have the fact that mutations have changed the genetic information in ways which give the same gene different meaning in different taxa, but the subtle refutation of the latest hoax by Michael J Behe and his Deception Institute masters, that all mutations are devolutionary [sic] and are therefore a degradation of the original perfection of creation, in complete agreement with a fundamentalist interpretation of the Adam & Eve myth about an ancestral couple's [sic] sin causing all life on earth to devolve by 'genetic entropy'.

Don't laugh! Some scientifically illiterate fools actually believe the latter!

I challenge any Creationist to explain how this evidence of divergence from a common ancestor could be described as 'devolution' or 'degradation'. Have mammals or venomous snakes got the inferior genes or genes which are less fit for their purpose than the common ancestor's genes were? How does the increasing effectiveness of snake venom over time represent 'degradation'? How does the failure by mammals to evolve costly venom even though they inherited the potential to do so, because to do so would not be cost-effective in their ecological niche, represent 'devolution'?

And why would an intelligent designer give so many vertebrate taxons the potential for producing venomous salive, then only use them in a small handful of species?

Simple questions, but I'm betting no Creationist can give a coherent, scientific answer which accords with Creationist dogma, without recourse to evidence-free religious superstition presented as established facts!

Thank you for sharing!

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1 comment :

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