  Thyroid hormone (TH) signalling, an evolutionary conserved pathway, is
crucial for brain function and cognition throughout life, from early
development to ageing. In humans, TH deficiency during pregnancy alters
offspring brain development, increasing the risk of cognitive disorders. How TH
regulates neurogenesis and subsequent behaviour and cognitive functions remains
a major research challenge. Cellular and molecular mechanisms underlying TH
signalling on proliferation, survival, determination, migration,
differentiation and maturation have been studied in mammalian animal models for
over a century. However, recent data show that THs also influence embryonic and
adult neurogenesis throughout vertebrates (from mammals to teleosts). These
latest observations raise the question of how TH availability is controlled
during neurogenesis and particularly in specific neural stem cell populations.
This review deals with the role of TH in regulating neurogenesis in the
developing and the adult brain across different vertebrate species. Such
evo-devo approaches can shed new light on (i) the evolution of the nervous
system and (ii) the evolutionary control of neurogenesis by TH across animal
phyla. We also discuss the role of thyroid disruptors on brain development in
an evolutionary context.
