xCOUP-TF-B regulates xCyp26 transcription and modulates retinoic acid signaling for anterior neural patterning in Xenopus

Early embryogenesis in Xenopus development depends on correct anterior-posterior (A-P) neural patterning during gastrulation. It is known that high levels of retinoic acid (RA), a major intracellular signaling molecule, determine posterior cell fate, also reflecting an involvement in A-P neural patterning. Here we show that the known RA effector, xCOUP-TF, plays important roles in head development of Xenopus embryo. xCOUP-TF-B injection into the dorsal region of embryos induced formation of an abnormal head with small eyes. Analysis of brain marker gene expression revealed that xCOUP-TF-B injection induced slight anteriorization in embryos and attenuated the effects of RA treatment. This anteriorization effect was enhanced when xCOUP-TF-B was co-injected with xCyp26A or xCyp26C, which are known RA metabolizing factors. Furthermore, xCOUP-TF-B injection enhanced xCyp26A/C transcription. Together, these results suggest that xCOUP-TF and xCyp26 are both regulated by Wnt signaling, and cooperatively function in RA signaling to affect A-P neural patterning.