neural development of fish

According to the review article,fish that have had the DIO3 gene knocked out (a gene that binds to T4 and prevents it from affecting certain cells) have a higher neural crest cell proliferation migration and activation as well as apoptosis. In adult mice, hypothyroidism decreases mitotic neuroblast but not proliferation progenitosin SGZ, decreased number of committed neural progenitors and mature neuroblast and have reduced level of immature hippocampus neurons. Other studies have shown that OPC derived from SVZ-NCS requires a TH free environment, and a decrease in TH leads to a decrease in neurogenesis but not in oligodendrogenesis. The figure in the review article indicates that an increase in TH would cause the NSC commitment, and the lack of TH would cause determination in glial cells.  In studies that were conducted with TTR null mice, which have a lower thyroid hormone level, had reduced the apoptosis of progenitors in SGZ in adults. Other studies using TRa1 and DIO3 also confirm that in general, an increase in thyroid hormone leads to an increase in neurogenesis and neuron cell differentiation. A decrease in thyroid hormone generally indicates that there is a higher amount of oligodendrogenesis, as well as better remyelination of neurons. However, all of these studies are done in adult rodent brains and not developing zebrafish brains.