The heterodimeric c-Jun/c-Fos, an activator protein-1 (AP-1) has been implicated in mesoderm induction (Dong et al., 1996; Kim et al., 1998) whereas the homodimer of c-Jun was reported to be involved in neural inhibition during the early development of Xenopus embryos. During the early vertebrate development AP-1 involvement in the neural induction is still not clearly understood. We report here that AP-1 has a role in Zic3 expression, a critical proneural gene and a primary regulator of neural and neural crest development (Nakata et al., 1997; Nakata et al., 1998). AP-1 was able to induce the Zic3 gene in a dose dependent manner but other homo- or hetero-dimeric proteins, such as c-Jun/c-Jun, JunD/FosB or JunD/Fra-1 were not. The inhibition of AP-1 activity using morpholino antisenses of c-jun mRNAs blocked the Zic3 expression induced by activin. In addition, co-injection of c-jun mRNA rescued the down-regulated Zic3 expression. The promoter region of isolated Zic3 genomic DNA was found to possess several consensus-binding site of AP-1. Thus, in the functional assays, AP-1 could increase promoter activity of Zic3 gene. These findings suggest that proneural gene, Zic3 may be regulated by heterodimeric AP-1(c-Jun/c-Fos) and it may have a role in activin signaling for the regulation of neural specific gene, Zic3.
Activins/pharmacology/physiology ; Animals ; Base Sequence ; Binding Sites/genetics ; Consensus Sequence/genetics ; Dimerization ; Embryo, Nonmammalian/metabolism ; *Gene Expression Regulation, Developmental ; Homeodomain Proteins/*genetics ; Molecular Sequence Data ; Promoter Regions (Genetics)/genetics ; Proto-Oncogene Proteins c-fos/genetics/physiology ; Proto-Oncogene Proteins c-jun/genetics/physiology ; RNA, Antisense/genetics ; Research Support, Non-U.S. Gov't ; Transcription Factor AP-1/genetics/*physiology ; Transcription Factors/*genetics ; *Transcription, Genetic ; Up-Regulation ; Xenopus Proteins/*genetics ; Xenopus laevis/*embryology/*genetics