The expression of a novel cxcr4 gene in Xenopus embryo

The aim of the present work was to identify a homologue of zebrafish cxcr4b in Xenopus, which could be involved in primordial germ cell (PGC) guidance migration. Following a BLAST analysis, the clone gi 27519681, homologous to the zebrafish gene z-cxcr4b, was identified, inserted into pCMV-SPORT6 plasmid and cloned in Escherichia coli. Embryonic expression of x-cxcr4b was analyzed by RT-PCR. X-cxcr4b was weakly expressed maternally but sharply increased after the mid-blastula transition (MBT), declining significantly at stage 45 when PGCs migration is complete. In contrast, RT-PCR of isolated presumptive PGCs showed strong maternal expression at stage 8, which decreased by stage 10 post-MBT and was not detected at stage 14. Whole mount in situ hybridization of x-cxcr4b mRNA showed that this gene is expressed in neural and haematopoietic tissues, and should be linked to important processes during embryonic development of these organs. Although weak staining could be seen in some samples within the anterior endoderm, expression of x-cxcr4b was never coincident with that of Xpat mRNA, which labels PGCs restricted to the posterior endoderm. Therefore, maternal x-cxcr4b is specifically downregulated within PGCs at pre-migratory stages while it is expressed in other tissues.