2 FORMS OF XENOPUS NUCLEAR FACTOR-7 HAVE OVERLAPPING SPATIAL BUT DIFFERENT TEMPORAL PATTERNS OF EXPRESSION DURING DEVELOPMENT

Xenopus nuclear factor 7 (xnf7) is a maternal gene product that functi ons in the determination of the dorsal-ventral body axis. We have clon ed two xnf7 cDNAs, xnf7-O and xnf7-B, that have a different temporal p attern of expression. The cDNAs differ by 39 amino acid residues scatt ered throughout the molecule. Most of the changes were conservative in nature. Using gene specific probes we found that xnf7-O transcripts w ere abundant in oocytes and decreased until the neurula stage, after w hich they increased in abundance. Xnf7-B transcripts were in low abund ance in oocytes and were expressed at high levels at the neurula stage and in adult brain. Both xnf7-O and xnf7-B transcripts at the neurula stage were localized in the dorsal region of the embryo, including th e neural folds and somites. Xnf7 was not expressed in ventralized embr yos that lacked dorsal structures, thereby substantiating its dorsal l ocalization in the embryo. The promoter region of the xnf7-O gene does not possess a TATA box but does contain E2F, USF, Spl-like and AP1 bi nding sites within the first 421 bp from the transcription initiation site. A 62 bp fragment of the xnf7-O promoter containing the Sp1-like and E2F sites can direct proper spatial expression of a transgene in e mbryos.