Tcf7l2 function is required for ventral habenula (vHb) development. (a-c) Dorsal views, anterior to the top. kisspeptin-1 expression in the vHb (circle) is not affected by the upregulation of Wnt/beta-catenin signaling in (b) axin1 mutant embryos, but absent in (c) tcf7l2exl/exl mutants. (a’- c”’ ) MIPs, anterior to the left, dorsal views of axons innervating the MR in Et(1.0otpa:mmGFP)hd1 transgenic embryos. H2A-CFP labels the cell nuclei. (b’- b”’ ) Upregulation of Wnt signaling in axin1 mutants does not affect MR innervation by vHb efferent axons. (c’- c”’ ) In tcf7l2exl/exl mutants, the MR are not innervated. White arrowheads and white boxes highlight the location of MR innervating axons, absent in (c’- c”’ ). The gamma was adjusted to values between 0.70 and 0.80. vHb, ventral habenula; MR, median raphe.