Yes - I know we don't have any zebrafish members. Probably no fish at all.
There will be few, if any, who are in the least surprised by the fact that thyroid hormone is important in development. The story here will be similarly unsurprising. But so good to read that it is being investigated. And that results seem quite clear.
I suggest that if we consider life-time maintenance as being, more or less, continuing development processes, we end up expecting poor conversion and low T3 will impact everyone. And maintenance processes will fail just as described.
Therefore, it is essential for those who need it to have low T3 issues addressed promptly - before myelination issues occur and accumulate.
This follows posts about human development in the context of either hypothyroidism or hyperthyroidism and, indeed, about breech birth.
Thyroid hormone deficiency during zebrafish development impairs central nervous system myelination
• Brenda Minerva Farías-Serratos,
• Iván Lazcano,
• Patricia Villalobos,
• Veerle M. Darras,
• Aurea Orozco
• Published: August 17, 2021
• doi.org/10.1371/journal.pon...
Abstract
Thyroid hormones are messengers that bind to specific nuclear receptors and regulate a wide range of physiological processes in the early stages of vertebrate embryonic development, including neurodevelopment and myelogenesis. We here tested the effects of reduced T3 availability upon the myelination process by treating zebrafish embryos with low concentrations of iopanoic acid (IOP) to block T4 to T3 conversion. Black Gold II staining showed that T3 deficiency reduced the myelin density in the forebrain, midbrain, hindbrain and the spinal cord at 3 and 7 dpf. These observations were confirmed in 3 dpf mbp:egfp transgenic zebrafish, showing that the administration of IOP reduced the fluorescent signal in the brain. T3 rescue treatment restored brain myelination and reversed the changes in myelin-related gene expression induced by IOP exposure. NG2 immunostaining revealed that T3 deficiency reduced the amount of oligodendrocyte precursor cells in 3 dpf IOP-treated larvae. Altogether, the present results show that inhibition of T4 to T3 conversion results in hypomyelination, suggesting that THs are part of the key signaling molecules that control the timing of oligodendrocyte differentiation and myelin synthesis from very early stages of brain
Full paper freely accessible here:
I am new here and need your opinion!
Iron deficiency and inflammation affect T4 to T3 conversion
nervous system role in thyroid stimulation 
