biomolecules Article Cortisol Directly Stimulates Spermatogonial Differentiation, Meiosis, and Spermiogenesis in Zebrafish (Danio rerio) Testicular Explants Aldo Tovo-Neto 1,2,3 , Emanuel R. M. Martinez 3, Aline G. Melo 3 , Lucas B. Doretto 3 , Arno J. Butzge 3 , Maira S. Rodrigues 1,3 , Rafael T. Nakajima 3 , Hamid R. Habibi 2,4 and Rafael H. Nóbrega 3,* 1 Aquaculture Program (CAUNESP), São Paulo State University, Jaboticabal, 14884-900 SP, Brazil;
[email protected] (A.T.-N.);
[email protected] (M.S.R.) 2 Department of Biological Sciences, University of Calgary, Calgary, T2N 1N4 AB, Canada;
[email protected] 3 Reproductive and Molecular Biology Group, Department of Morphology, Institute of Biosciences, São Paulo State University, Botucatu, 18618-970 SP, Brazil;
[email protected] (E.R.M.M.);
[email protected] (A.G.M.);
[email protected] (L.B.D.);
[email protected] (A.J.B.);
[email protected] (R.T.N.) 4 Department of Physiology and Pharmacology, University of Calgary, Calgary, T2N 1N4 AB, Canada * Correspondence:
[email protected]; Tel.: +55-14-3880-0482 Received: 6 December 2019; Accepted: 14 February 2020; Published: 10 March 2020 Abstract: Cortisol is the major endocrine factor mediating the inhibitory effects of stress on vertebrate reproduction. It is well known that cortisol affects reproduction by interacting with the hypothalamic–pituitary–gonads axis, leading to downstream inhibitory and stimulatory effects on gonads. However, the mechanisms are not fully understood. In this study, we provide novel data demonstrating the stimulatory effects of cortisol on spermatogenesis using an ex vivo organ culture system.