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 nephr oblastoma overexpressed; encoding a putative avian proto-oncogene) fro m Xenopus laevis (Xl) by screening an Xl ovary cDNA library and genomi c library using the entire coding region of human CTGF (encoding conne ctive tissue growth factor) as a probe and by 5'RACE (rapid amplificat ion of cDNA ends). xnov has the same genomic organization as chicken n ov, 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 Cef 10 and mouse Cyr61 proteins, respectively. Xnov contains four aa domai ns which characterize the CTGF family. RT-PCR (reverse transcription-p olymerase chain reaction) analysis shows that the xnov mRNA is very lo w in abundance and appears to be present throughout early Xl developme nt. Our results also indicate that xnov and nov are not orthologs of h uman CTGF.