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Representative immunostaining images of Wnt-responsive Tg(top:GFP)+ (B), 5-HT+ and HuC/D+ (C), and mitotic phospho-histone H3-positive (pH3+) cells (E) in control and lef1 mutants are shown on the left and quantified on the right (B 1, C 1, C 2 and E 1 ). (B-F) Immunostaining and quantification in 3 days postfertilization (dpf) Hc. (A) Estimation of Hc size in control and lef1 mutants. Lef1 promotes neurogenesis in the zebrafish caudal hypothalamus (Hc). This work reveals the surprising finding that conserved signaling pathways can regulate common behavioral outputs through diverse brain circuits during evolution. Furthermore, CRHBP and PMCH show extraordinarily coordinated expression in the primate hypothalamus, indicating that they may act together downstream of Wnt and Lef1 to regulate human behavior. By comparison, the fruit fly Drosophila activates crhbp, similar to zebrafish. In the fish, the pathway triggers genes including corticotropin-releasing hormone binding protein (crhbp), but in mice the same pathway calls into action a different gene, Pro-melanin concentrating hormone (Pmch). From there, however, the process diverges. The pathway is required for formation of anxiolytic neurons in a highly conserved brain region, the hypothalamus.

Gene knockout experiments in mouse and zebrafish show that the molecular signal Wnt acts through the transcription factor Lef1 to inhibit anxiety in both species. This study reveals another common thread that runs through these diverse animals: the molecular origins of their shared behavior. Humans, mice, fish, and even flies exhibit anxiety-like behavior despite the fact that their brain anatomy varies widely.