Identification and analysis of the promoter region of the human NeuroD-related factor (NDRF)1

NEUROD1 acts in vitro as an upstream regulator of NEUROD2 in trophoblast cells

The basic helix-loop-helix (bHLH) transcription factors NEUROD1, NEUROD2 and ATH2 are expressed during first trimester human placental development. We determined the transactivation potential of each of these factors in trophoblasts by measuring changes in the endogenous gene activity using absolute quantification by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) after transient transfection. In these assays, NEUROD1 was found to transiently transactivate NEUROD2 in trophoblast cells. Promotor truncation assays, using luciferase constructs, showed the presence of two domains in the NEUROD2 promotor, which showed increased activity after NeuroD1 transfection. Each of these NeuroD1-responsive domains contains an E-box sequence. The NEUROD2 transactivation data fit with the spatial expression pattern of NEUROD1 and NEUROD2, since they are expressed in endovascular trophoblasts. This expression pattern, as well as the present transactivation results, might suggest the presence of a NEUROD differentiation cascade during first trimester human placental development.

Genomic structure and promoter analysis of the human alpha1, 6-fucosyltransferase gene (FUT8)

GDP-L-Fuc:N-acetyl-beta-D-glucosaminide alpha1,6-fucosyltransferase (alpha1,6FucT) catalyzes the transfer of a fucosyl moiety from GDP-fucose to the asparagine-linked GlcNAc residue of complex N-glycans via alpha1,6-linkage. We have cloned the genomic DNA which encodes the human alpha1,6FucT gene ( FUT8 ) and analyzed its structure. It was found that the gene consists of at least nine exons spanning more than a 50 kbp genomic region, and the coding sequence is divided into eight exons. The translation initiation codon was located at exon 2, and thus exon 1 encodes only 5'-untranslated sequences. Transcription initiation site of FUT8 was determined by 5'-rapid amplification of the cDNA end and a primer-extension analysis using the total RNA isolated from SK-OV-3 cells, which have a high level of alpha1,6FucT activity. We then characterized the FUT8 promoter region by a reporter gene assay. The luciferase reporter assay indicated that the 5'-flanking region of exon 1, which covered about 1 kbp, conferred the promoter activity in SK-OV-3 cells. This region contains potential binding sites for some transcription factors, such as bHLH, cMyb, GATA-1, as well as a TATA-box, but not a CCAAT motif. 5'-Untranslated sequences found in ESTs and the cDNA for the FUT8 suggest the presence of an additional exon(s) at the upstream of the first exon identified in this study, and therefore, the transcription of the gene would be regulated by multiple promoters.

A fragment of the Neurogenin1 gene confers regulated expression of a reporter gene in vitro and in vivo

The basic helix-loop-helix transcription factor neurogenin1 is required for proper nervous system development in vertebrates. It is expressed in neuronal precursors during embryonic development and is thought to play a role in specifying neuronal fate. To investigate the regulation of neurogenin1 expression, the transcriptional start site of the gene was identified and a 2.7-kb fragment ending in the first exon was shown to possess basal promoter activity. This 2.7-kb fragment was able to promote expression of reporter genes in P19 cells under conditions in which expression of endogenous neurogenin1 was induced. Importantly, the 2.7-kb fragment was able to drive expression of a lacZ reporter gene in transgenic mice in most tissues in which neurogenin1 is normally expressed, including those peripheral ganglia that fail to develop in neurogenin1 "knockout" mice. These findings identify a regulatory region containing elements responsible for appropriate expression of a gene with a crucial role in generating the vertebrate nervous system.

Structure of the mouse NDRF gene and its regulation during neuronal differentiation of P19 cells

We have isolated and characterized the mouse gene for NDRF (neuroD-related factor), a basic helix-loop-helix transcription factor implicated in neural development and function. The gene consists of two exons and the entire protein-coding sequence is encoded by a single downstream exon. RNA blot hybridization analysis revealed that NDRF mRNA was detectable at day 4 and increased to a maximal level at day 6 during neuronal differentiation of P19 cells. To elucidate the regulatory mechanisms of the NDRF gene expression during this process, a construct containing the genomic DNA fragment of about 3 kbp upstream of the NDRF coding region fused to a luciferase reporter gene was transfected into P19 cells, and stable transformants were pooled for assay of luciferase activities. When the stable transformants were treated with RA and aggregated to induce neuronal differentiation, the luciferase activities were induced in a temporal expression pattern similar to that of the endogenous NDRF mRNA. Further experiments using a series of deletion and mutation constructs indicated that the 376-bp sequence in the 5'-flanking region of the NDRF gene is important, and that one of the E boxes in the sequence plays a critical role in the regulated expression. Transient transfection experiments also showed that the same E box is required for the transactivation of the NDRF promoter activity by neurogenin 1. These results suggest that the NDRF gene expression is regulated by an E box-binding factor during neuronal differentiation of P19 cells.

Structure and regulation of the human NeuroD (BETA2/BHF1) gene

In this study, we isolated and characterized the human NeuroD (BETA2/BHF1) gene. This gene was found to consist of two exons and one intron. The promoter regions were well-conserved compared with the mouse NeuroD gene. Two transcription start points (TSPs) were determined by the oligo-capping method. One TATA box was located at -31 bp from the lower TSP. The results of a transient transfection assay using the human neuroblastoma cell line IMR-32 and hamster insulin tumor cell line HIT-T15 suggested that there are at least three positive regulatory regions in the promoter. In these regions, four E boxes (CANNTG), named the E1 to E4 boxes, and two GC boxes were present. Cotransfection of the NeuroD expression vector into IMR-32 cells enhanced the NeuroD promoter activity by about 4-fold. A deletion and mutation analysis revealed that the E1 and E4 boxes, especially the E1 box, are associated with autoactivation and that E2 and E3 boxes are not associated with autoactivation. As mutation analysis of E3 box showed a decrease in the enhancer activity to the basal level, it showed that the E3 box is important to activate the NeuroD transcription. These results raised the possibility that the NeuroD gene expression is positively regulated through the E box sequence, not only by NeuroD itself but also by another E box binding protein.