OVEREXPRESSION OF A NOVEL XENOPUS REL MESSENGER-RNA INDUCES TUMORS INEARLY EMBRYOS

The Rel family of transcriptional activators form a large diverse grou p of proteins that are involved in the activation of genes involved in immunity, development, apoptosis and cancer. So far, none of the rel genes cloned in mammals appear to be required for embryonic developmen t. We have cloned and characterized a cDNA from an embryonic cDNA libr ary that encodes a novel Xenopus Rel protein, called Xrel3. Xrel3 is a member of the cRel subfamily and is most closely related to but disti nct from other Xenopus Rel members. The expression of Xrel3 mRNA was i nvestigated using Northern analysis, RNase protection assay, reverse t ranscriptase-linked polymerase chain reaction and in situ hybridizatio n, Messages are present maternally and are slightly enriched in the eq uatorial region of the blastula stage embryo. At gastrulation, the acc umulation of Xrel3 messages declines to undetectable levels but then i ncreases after neurulation. In situ RNA hybridization was used to dete rmine the spatial location of Xrel3 messenger RNA in embryos. Messages are localized to the developing forebrain, dorsal mid-hindbrain regio n, the inner ear primordium, or otocyst, and in the notochord. Overexp ression by microinjection of Xrel3 RNA induced tumors in the developin g embryo that appeared after gastrulation, The location of the tumors depended on the location of the injection site. These results suggest that Xrel3 might have a generalized role in regulation of cell differe ntiation in the embryo.