Xenopus Polycomblike 2 (XPcl2) controls anterior to posterior patterning of the neural tissue

A novel gene, Xenopus Polycomblike 2 (XPcl2), which encodes a protein similar to Drosophila Polycomblike was cloned and characterized. Polycomblike belongs to the Polycomb group proteins, which maintain stable expression patterns for the clustered homeotic genes in the Drosophila embryo by forming multimeric complexes on chromatin. XPcl2 shows greater amino acid sequence homology to human and mouse M96 (hPcl2, mPcl2) than Xenopus Pcl1 (XPcl1), mouse Tctex3 (mPcl1) and human PHF1 (hPcl1), indicating that at least two types of Polycomblike genes are conserved between amphibians and mammals. XPcl2 mRNA is present both maternally and zygotically, and the temporal expression profile is distinct from XPcl1, another member of the Polycomblike family in Xenopus. XPcl2 is highly expressed in the anterior-dorsal region of Xenopus following the neurula stage in a manner similar to XPcl1. Overexpression of XPcl2 disturbs the development of the anterior central nervous system, eye and cement gland. In the XPcl2-overexpressing embryo, a hindbrain marker, Krox20, and a spinal cord marker, HoxB9, are expressed more posteriorly, suggesting an alteration in the anterior-posterior patterning of the neural tissue. In addition, XPcl2 represses Zic3- and noggin-induced anterior neural markers, but not neural crest markers in animal cap explants. These results indicate that XPcl2 regulates anterior neural tissue development and the anterior-posterior patterning of the neural tissue.