Rohon-Beard sensory neurons are induced by BMP4 expressing non-neural ectoderm in Xenopus laevis

Rohon-Beard mechanosensory neurons (RBs), neural crest cells, and neurogenic placodes arise at the border of the neural- and non-neural ectoderm during anamniote vertebrate development. Neural crest cells require BMP expressing non-neural ectoderm for their induction. To determine if epidermal ectoderm-derived BMP signaling is also involved in the induction of RB sensory neurons, the medial region of the neural plate from donor Xenopus laevis embryos was transplanted into the non-neural ventral ectoderm of host embryos at the same developmental stage. The neural plate border and RBs were induced at the transplant sites, as shown by expression of Xblimp1, and XHox11L2 and XN-tubulin, respectively. Transplantation studies between pigmented donors and albino hosts showed that neurons are induced both in donor neural and host epidermal tissue. Because an intermediate level of BMP4 signaling is required to induce neural plate border fates, we directly tested BMP4's ability to induce RBs; beads soaked in either 1 or 10 ng/ml were able to induce RBs in cultured neural plate tissue. Conversely, RBs fail to form when neural plate tissue from embryos with decreased BMP activity, either from injection of noggin or a dominant negative BMP receptor, was transplanted into the non-neural ectoderm of un-manipulated hosts. We conclude that contact between neural and non-neural ectoderm is capable of inducing RBs, that BMP4 can induce RB markers, and that BMP activity is required for induction of ectopic RB sensory neurons.