I am not a biology student, but just want to know if GULO gene are present only in mammals or all species possess it ?
And is GULO gene active in human fetus?
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$\begingroup$ On Genecards it is mentioned that the GULO pseudo gene being expressed in humans in many major tissues. In that case the gene might be active although not encoding for a functional enzyme. $\endgroup$ – David Jonsson Jun 10 '19 at 16:01
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GULO encodes L-gulonolactone oxidase which catalyses a step in the biosynthetic pathway to ascorbic acid (vitamin C).
I did a BLAST search at NCBI using the mouse GULO protein as probe, excluding mammals, and I saw highly significant hits in reptiles, birds, sea urchins, fungi and bacteria. I conclude that this enzyme, (or very close relatives) is ubiquitous.
Humans (and other primates; also guinea pigs and the Dalmatian coach hound) have a defective GULO gene and so require dietary ascorbate.
Since the gene is non-functional in humans it isn't expressed in the foetus.
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$\begingroup$ Wrong in regard to "Since the gene is non-functional in humans it isn't expressed in the foetus." See my answer. $\endgroup$ – David Jonsson Jun 10 '19 at 16:01
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De Tullio writes
We know from other studies that pseudogenes are not inert, but can have a significant role in epigenetic control of gene expression (Poliseno et al. 2010). Could this also apply to the human gulonolactone oxidase pseudogene? Time (and much research) will tell.
De Tullio, M. C. (2010) The Mystery of Vitamin C. Nature Education 3(9):48
https://www.nature.com/scitable/topicpage/the-mystery-of-vitamin-c-14167861/
On Genecards it is mentioned that the GULO pseudo gene being expressed in humans in many major tissues. In those cases the gene might have an epigenetic role.
