All in a name: schwannomin versus merlin

Multiple transcription initiation sites, alternative splicing, and differential polyadenylation contribute to the complexity of human neurofibromatosis 2 transcripts

Northern blot analysis has shown that the human neurofibromatosis type 2 (NF2) cDNA hybridizes to multiple RNA species. To examine whether these hybridizing RNA species represent NF2 transcripts, we cloned the complete NF2 cDNA by a combination of techniques: 5' and 3' rapid amplification of cDNA ends, RT-PCR, and searching and sequencing the NF2-related cDNA clones from the IMAGE consortium. We showed that human NF2 transcripts initiate at multiple positions. Analogous to those reported previously, NF2 transcripts undergo alternative splicing in the coding exons. We isolated eight alternatively spliced NF2 cDNA isoforms, including one that contains a new exon termed exon 2', which potentially could encode proteins of different sizes. We assembled the overlapping cDNA fragments, and the longest NF2 cDNA, containing all 17 exons, consists of 6067 nucleotides, which is consistent with the size of the major RNA species hybridized to the NF2 probe. The cDNA has a 425-nucleotide 5' untranslated region upstream from the ATG start codon, and a long 3' untranslated region of 3869 nucleotides. We also isolated two shorter NF2 cDNAs that were terminated by different polyadenylation signal sequences, which indicates that differential usage of multiple polyadenylation sites also contributes to the complexity of human NF2 transcripts. By reference to the transcription initiation site mapped, we analyzed the 5' flanking sequence of the human NF2 gene. Transient transfection analysis in human 293 kidney, SK-N-AS neuroblastoma, and NT2/D1 teratocarcinoma cells with NF2 promoter-luciferase chimeric constructs revealed a core promoter region extending 400 base pairs from the major transcription initiation site. Although multiple regions are required for full promoter activity, a site-directed mutagenesis experiment identified a GC-rich sequence (position -58 to -46), which could be bound by transcription factor Sp1, as a positive cis-acting regulatory element. Cotransfection studies in Drosophila melanogaster SL2 cells showed that Sp1 could activate the NF2 promoter through the GC-rich sequence.

Analysis of the human neurofibromatosis type 2 gene promoter and its expression

OBJECTIVE

It is hypothesized that transcriptional regulation plays an important role for neurofibromatosis type 2 (NF2) expression in Schwann cells and other cell types. The objective of this study is the isolation and characterization of the transcriptional regulatory elements of the NF2 gene.

STUDY DESIGN AND SETTING

A bacterial artificial chromosome library and a partial genomic DNA library were used to isolate the human NF2 gene; NF2 promoter-luciferase constructs were generated, and promoter activities were assayed. This study was carried out in a molecular biology laboratory.

RESULTS

A bacterial artificial chromosome clone with an approximately 100-kilobase insert containing nearly the entire human NF2 gene has been isolated. An additional 5' NF2 sequence has also been cloned. Transient transfection experiments demonstrate strong promoter activity from the NF2 5' flanking DNA.

CONCLUSIONS

The NF2 gene is approximately 100 kilobases long. Both positive and negative regulatory elements are present in NF2 5' flanking regions.

SIGNIFICANCE

Better understanding of the NF2 gene and its regulation will improve molecular diagnostics and ultimately treatment of patients with NF2.