CHARACTERIZATION OF DNASE-I HYPERSENSITIVE SITES IN THE MOUSE 68-KDA NEUROFILAMENT GENE

Four brain-specific DNase I hypersensitive sites (HSS) have previously been identified flanking the mouse 68-kDa neurofilament gene within a 1.7 kb upstream sequence which confers neuronal specificity of expres sion of this gene in transgenic mice. Previously several DNA-binding f actors were detected at the HSS closest to the transcription start sit e (HSSI). However, no major brain-specific factors were identified, su ggesting a possible role for the three remaining IISS in conferring ti ssue-specificity to the NF-L gene. Sequence analysis of the NF-L promo ter region demonstrated the presence of an extensive CT repeat and sev eral potential binding sites which are also found in other neurofilame nt promoters. Gel mobility shift assays revealed a similar but not ide ntical banding pattern with brain and liver nuclear extracts al HSS2, and HSS3, however the banding pattern for HSS4 was predominantly brain -specific. DNase I footprinting revealed several factors binding to th e upstream HSS regions in brain and liver nuclear extracts. These incl ude a CCAAT box at HSS2, a novel brain-specific footprint near an aden ovirus promoter element E2aE-C beta and a single liver-specific footpr int associated with an POU/octamer binding site at HSS4. The presence of brain-specific gel shift bands and tissue-specific footprints assoc iated with HSS4, suggest that this region may play an important role i n the regulation of the NF-L gene.