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The brain of adult zebrafish: steroid synthesis, signalling and potential roles in constitutive and reparative neurogenesis.

Nicolas Diotel 1, Elisabeth Pellegrini2, Colette Vaillant2 and Olivier Kah2

1: Team GEICO, Plateforme CYROI - Université de la Réunion, Saint-Denis, France2: Team NEED, IRSET, IFR 140, Rennes, Francenicolas.diotel@gmail.com

Among vertebrates, teleosts are unique in many respects. They exhibit really peculiar features, such as strong brain aromatase activity, intense neurogenesis and high capability for brain repair. In addition, some of them are also able to change sex during adulthood, implying special gonadal and brain plasticity. In the last few years, zebrafish has gained strong popularity as a model to study adult neurogenesis and brain regeneration. Interestingly, in zebrafish, the estrogen-synthesizing enzyme (aromatase B) is only expressed in radial glia cells that act as neural “stem” cells. Together, these data suggest key roles for aromatase and estrogens in constitutive and reparative neurogenesis. Here, we show that (1) the brain of adult zebrafish is a steroidogenic organ able to synthesize a wide variety of neurosteroids, (2) that radial glial cells are targeted by steroids, and (3) we finally provide evidences that 17β-estradiol inhibits neural progenitor proliferation and newborn cell migration. However, estradiol effects on neuronal differentiation and cell survival are not so clear. Last but not least, we developed a model of mechanical lesion of the telencephalon in order to investigate the potential involvement of estrogens in regenerative neurogenesis. Preliminary results tend to show that 17β-estradiol does not favour brain cell proliferation after stabwound. In contrast to other models, such as birds and mice, aromatase expression does not appear to be up-regulated after brain lesion. Altogether, these data suggest major differences between fish and other vertebrates with respect to estrogen production and function in adult and reparative neurogenesis.

key words: aromatase, neurogenesis, neurosteroid, radial glial cell, zebrafish

Supported by the EU Lifecycle, ANR Need and Proof programs.