Temporal and spatial expression patterns of FoxN genes in Xenopus laevis embryos.

Using RT-PCR and in situ hybridisation, we have analysed the temporal and spatial expression patterns of Xenopus Fox genes of subclass N. By screening cDNA libraries and by RT-PCR using embryonic RNA and primers derived from EST analyses, we could isolate FoxN2, FoxN4, FoxN5 and different isoforms of FoxN3. FoxN2 and FoxN3 transcripts were found during all developmental stages including early cleavage and tailbud stages. FoxN5 transcripts were only present at early cleavage stages, while FoxN4 expression began after midblastula transition. Spatial expression of FoxN2 was first detected in the early eye field and later, in the branchial arches, the vagal ganglion and in the developing retina. FoxN3 transcripts were found within the animal cap. In post-gastrula embryos, neural crest cells and the early eye field showed strong expression of FoxN3. At late tadpole stages, the branchial arches were stained. FoxN4 was expressed in the early eye field and later in the developing retina cells, the nephrostomes of the pronephric kidney and in the midbrain. A ubiquitous expression of FoxN5 was found in early cleavage stage embryos.