Isolation of the Xenopus nrp-1 gene and analysis of its expression following the midblastula transition in injected Xenopus embryos.

During embryogenesis the differentiation of distinct tissues is marked by the expression of tissue-specific genes. In Xenopus, the neural-specific gene nrp-1 is activated following the midblastula transition (MBT), and is then expressed exclusively in developing neural tissue. To pursue an investigation of the transcriptional regulation of nrp-1, the genomic DNA encoding nrp-1 was isolated and its structure analyzed. Nrp-1 lacks a canonical TATA box proximal to the start site of transcription, but the 5' flanking sequence is highly GC-rich. Injection studies with nrp-1/chloramphenicol acetyltransferase and luciferase constructs demonstrate that in Xenopus embryos, 200 nt of the 5' flanking sequence of nrp-1 are sufficient to drive the expression of reporter genes soon after the MBT, albeit not in a tissue-specific manner. This expression is enhanced by the inclusion of larger regions of the nrp-1 gene.