Isolation and characterization of xnov, a Xenopus laevis ortholog of the chicken nov gene

We have isolated an ortholog (xnov) of the chicken nov gene (for nephroblastoma overexpressed; encoding a putative avian proto-oncogene) from Xenopus laevis (Xl) by screening an Xl ovary cDNA library and genomic library using the entire coding region of human CTGF (encoding connective tissue growth factor) as a probe and by 5'RACE (rapid amplification of cDNA ends). xnov has the same genomic organization as chicken nov, mouse fisp12 and cyr61, but has a unique promoter sequence. The Xl open reading frame (ORF) encodes a 343-amino-acid (aa) polypeptide of 37.9 kDa. Xnov shows 62.9, 60.5, 52.2, 52.1, 47.6 and 45.8% identity with the chicken Nov, human NovH, human CTGF, mouse Fisp12 chicken Cef10 and mouse Cyr61 proteins, respectively. Xnov contains four aa domains which characterize the CTGF family. RT-PCR (reverse transcription-polymerase chain reaction) analysis shows that the xnov mRNA is very low in abundance and appears to be present throughout early Xl development. Our results also indicate that xnov and nov are not orthologs of human CTGF.