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Bbrhuft t1_j91bx8b wrote

It's a bit of a mystery. However, the evolutionarily roots of iodine cell signalling is very acient, almost all all multicellular life uses iodine containing molecules, including plants.

A recent interesting hypothesis proposed that... Given that almost all multicellular life uses iodine containing cell signalling molecules, they must have evolved very early billions of years ago in early single celled organisms, and the development of multicellularity and iodine containing cell signalling molecules went hand in hand.

The reason why iodine was used, is that molecules that contain iodine are highly reactive and often powerful antioxidants, they are very useful.

Crockford, S.J., 2009. Evolutionary roots of iodine and thyroid hormones in cell–cell signaling. Integrative and comparative biology, 49(2), pp.155-166.

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agate_ t1_j921et4 wrote

This is a neat answer, but I hope someone will tackle what I think is the most interesting part of OP’s question: why is iodine biochemistry apparently localized in the thyroid? It’s not like we have specific organs for zinc or manganese chemistry. (Or do we?)

What animals have a thyroid? Is iodine chemistry localized in a different organ in the ones that don’t?

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isaacwoods_ t1_j925jbo wrote

It’s precisely because elemental iodine is very reactive. The thyroid has follicles, where iodine is pumped into a gel in ion form, and then enzymatically converted into elemental iodine, where it then attacks thyroglobulin to create thyroid hormones. The final hormones are the only molecules allowed out of the follicular lumen back into the blood.

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geistererscheinung OP t1_j94ootq wrote

Elemental iodine? In my thyroid?? Wow, that's really cool. Wikipedia said that the iodation of tyrosine by elemental iodine is a really streamlined process, indicating how T3 and T4 evolved.... Thank you for your answer!

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CrateDane t1_j9267og wrote

> > > > > What animals have a thyroid?

Vertebrates. Invertebrate chordates have an organ called the endostyle, which has some functional similarity and is very likely the evolutionary predecessor to the thyroid gland.

> Is iodine chemistry localized in a different organ in the ones that don’t?

Well... many aquatic invertebrates may rely mainly on exogenous thyroid hormones, so they don't need an organ for it. Other invertebrates may have their own endogenous production of thyroid hormones, but without a dedicated organ. Yet other invertebrates, particularly outside the bilaterians, may be less reliant on thyroid hormones in the first place, since they seem to lack an ortholog of the thyroid hormone receptor.

Here is an interesting review article about thyroid hormone signaling in invertebrates.

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geistererscheinung OP t1_j94owd9 wrote

Thank you for your answer. I'll try to read that article soon. Thyroids are turning out to be really interesting biochemically!

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thewizardofosmium t1_j92sn0v wrote

It's really no different from other hormones: they are only synthesized in one organ and then released into the body. Sex hormones are mainly (not exclusively) synthesized in the gonads, etc.

It is fascinating that the body regulates thyroid hormones the same way a chemical plant would regulate a key chemical today. The pituitary gland monitors the level of thyroxine in the blood and emits thyroid stimulating hormone in greater or lesser amounts if the thyroxine level is too low or too high. The thyroid, physically located separate from the pituitary, then produces thyroxine depending on the TSH level it senses. If the sensing function and the synthesis function were physically located at the same place, the body couldn't control what was happening.

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geistererscheinung OP t1_j94p4o2 wrote

Thank you for your answer. Kinda cool how isolated the thyroid is...yet how tightly controlled the process must be.

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geistererscheinung OP t1_j933iyi wrote

Thank you for emphasizing that. Localization was my original question, and I added the others for support.

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DrRob t1_j93ac79 wrote

Just about all hormones are made and stored in their own glands and released carefully in response to circulating chemical signals. One really unpleasant symptom cluster from cancers of hormone producing glands is indiscriminate outpouring of hormones by the now unregulated cancerous cells which are still well organized enough to produce hormones unchecked. This can happen with the thyroid, adrenals, pituitary, etc.

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Saxamaphooone t1_j93927e wrote

The majority is stored in the thyroid, but it’s also stored in the breasts, prostate, rectum, and many other places as well.

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thewizardofosmium t1_j92svub wrote

I can't read the citation now, but the thyroid hormones affect mitochondrion function, so iodine was key to the metabolism of mitochondria.

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sparky_1966 t1_j93e9q0 wrote

Thyroid hormones affect regulation of mitochondria and their metabolism, but through signaling. Iodine isn't directly part of metabolism. That may have been what you meant, just wanted to be clear.

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_AlreadyTaken_ t1_j92q3dh wrote

Plus it is commonly found in seawater. So if life evolved in seawater it would use elements available to it.

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cherrypez123 t1_j92ydji wrote

How did people far from the ocean survive back in the day? If they couldn’t access iodized salt or anything else from the ocean?

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xiaorobear t1_j93dex7 wrote

Other animals are a good source!

Meat, eggs, and dairy all are good sources of iodine- and some organs especially liver. Apparently 1300 years ago someone in China had already figured out you could treat goiter by giving the patient ground up animal thyroid gland. Pretty cool.

https://en.wikipedia.org/wiki/Goitre#History

Also apparently in more iodine-rich soil, plants uptake enough to also be a good source, probably where the animals at lower trophic levels are getting it.

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obliviousofobvious t1_j926m4p wrote

Does this indicate that the thyroid itself (or what will become the thyroid) goes back to the earliest days of our biological ancestors?

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comparmentaliser t1_j93ejgh wrote

Does all life get iodine through other iodine containing organisms? Or do some get it through natural sources, like iodised salt (assuming that it occurs naturally).

It would he interesting it f it’s something that just got perpetually recycled since the dawn of life.

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nicuramar t1_j93jshy wrote

> It’s a bit of a mystery.

But

> The reason why iodine was used, is that molecules that contain iodine are highly reactive and often powerful antioxidants,

So, it’s not a mystery? Or just not a mystery why it was originally used, but rather how it was retained?

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Psychological_Lion38 t1_j94m1x1 wrote

I don’t have anything to add to this. But wow. I hope to be as knowledgeable in a topic as you are one day. Very well put (granted I don’t really understand a lot of the technical terms). But yea man, keep it up!

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geistererscheinung OP t1_j94ogzz wrote

Thank you for your response. I'll try to look over that article. The reactivity/antioxidant part is especially interesting.

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