Identification, cloning, and functional analysis of the TATA-less mouse FNDC5 promoter during neural differentiation

FNDC5 (also termed PEP) gene encodes a type I membrane protein which is cleaved and secreted as Irisin hormone. We have identified mouse putative core promoter of FNDC5 and characterized its activity. FNDC5 is located within mouse chromosome 4, spans about 7,534 bp, and consists of 6 exons. The mouse FNDC5 promoter is TATA-less and lacks a consensus initiator sequence. In silico analyses revealed that the core promoter (-561/+101 with respect to translation start site) is located in a GC-rich domain (approximately 70.01 %) with one CpG island as a promoter index and several GC box factors including GC/SP1 which is necessary for transcription of TATA-less promoters. The core promoter showed a lower activity than CMV promoter in CHO and P19 cell lines when located upstream of EGFP CDS in an appropriate expression vector. Data implicated that both exon 1 and intron 1 of the gene are included in the core promoter. Upon treating with retinoic acid, FNDC5 expression was upregulated during embryoid body formation and decreased slowly at final stage of neural differentiation when neurospheres emerged. However, Noggin induction induced up regulation of FNDC5 expression at final stage of neural differentiation. In conclusion, stage dependent expression of FNDC5 is affected by neural induction method used for neural differentiation.