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
