Logic and evolution: a complete species with lost genes (Introduction)

by David Turell @, Wednesday, July 13, 2016, 02:10 (615 days ago) @ David Turell

Just as we are discussing lost info here is an organism which is without the organizing genes usually running the show:


The planktonic organism Oikopleura dioica, an animal model in the study of evolution and embryonic development in vertebrates (the taxonomic phylum known as chordates), has lost most of the genes related to retinoic acid metabolism—-a molecule thought to be vital to vertebrate physiology and embryonic development.


"Retinoic acid (RA) is a molecule derived from vitamin A (retinol), which is fundamental in the physiology and embryonic development of chordates, including humans. Retinoic acid (RA) is an essential factor in chordates to regulate the expression of genes involved in processes of cell proliferation and differentiation, like those occurring during the embryonic development of organs and systems, or during body patterning.

"The chordate O. dioica is an organism evolutionary close to vertebrates. They both share a similar body plan and some organs or homologue structures like heart, brain or skeleton musculature, which have a RA-dependent development. A big challenge of this study has been to prove that these organs develop in O. dioica without RA due to the massive loss of genes involved in its synthesis and to demonstrate the absence of alternative pathways.


"Gene loss would have enabled O. dioica to develop without vitamin A, which would be a new example of how gene loss can be an evolutionary strategy that allows the adaption of species to biological situations in a beneficial way.

"'Our results are compatible with the loss of genes related to RA in Oikopleura dioica happened in an scenario of regressive evolution, in which the lost functions were not essential for the organism," said professor Ricard Albalat.


"In humans, as in the rest of the chordate species, there are multiple enzymes that regulate the synthesis and degradation of RA. Understanding how these enzymes are regulated is important for our health. Everything points to the RA metabolic machinery as a genetically robust system, forming a pathway which is hard to modify in which several enzymes encoded by multiple genes can do the same function in a redundant way. Moreover, to discover that RA was also important for non-vertebrate animals means that RA metabolic machinery could be ancient, early originated during animal evolution."


"Biological innovation is not necessarily linked to an increase of functional complexity or number of genes, according to the authors. Genomic rearrangements, changes in epigenetics mechanisms, loss of light-receptor organs, decrease of body complexity and size, or increase of the speed of embryonic development and life cycle of O. dioica are some situations that might have allowed the evolution of new ways to create a heart without the requirement of RA.

"According to co-author Cristian Cañestro, "these results show an example of what has been called the 'reverse paradox' of evolutionary and developmental biology (evo-devo), in which morphologically similar structures differ in the genes responsible for their development."

"'The heart is another paradigmatic example we try to understand: how is it possible that O. dioica generates a heart without RA, whereas RA is essential to create this organ in all other chordates?"

Comment: this is a more complex organism than an amoeba, so we can say that evolution generally produces complexity, but at times information can be reduced and an intact complex organism can still be produced. We are still facing the confusion around speciation, and we can see loss of information can still be very productive. it is a confusing area of research.

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