Expression and regulation of mouse selenoprotein P transcript variants differing in non-coding RNA

Abstract

Selenoprotein P (Sepp1), a glycoprotein rich in selenium, is thought to function in selenium transport throughout the body. The sepp1 gene locus potentially produces three alternative transcripts that differ only in their 5′ untranslated regions (5′UTRs) and not in their protein coding regions, as indicated by transcript information in genomic databases. Here we investigated the distribution, relative expression, and biological significance of these transcript variants. We confirmed the expression of Sepp1 transcript variants using PCR and sequencing. Using 5′-RACE, we identified multiple 5′-termini upstream from three different splice donor sites, and a single splice acceptor site for exon 2. We found regional and temporal changes in variant expression in select adult and neonate murine tissue and brain regions. Distribution of variants in heart and kidney varied with stage of development. Notably, the Sepp1b variant was localized specifically to the hippocampus in brain. Targeted silencing of individual variants using RNAi demonstrated the biological importance for all transcript variants in cell viability. Additionally, we determined that the Sepp1b variant is a specific target for the miR-7 microRNA by means of its unique 5′UTR structure. Our results emphasize the importance of non-coding transcript variations as a regulatory means for Sepp1 expression in different tissues and stages of development. The presence of a variant localized in the hippocampus and regulated by a microRNA may have implications for the known deficits in synaptic function caused by genetic deletion of Sepp1.

Keywords: :

• 5′UTR
• RNAi
• Sepp1
• hippocampus
• microRNA
• selenium
• selenoprotein
• transcript variants

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

The authors thank Suguru Kurokawa for helpful suggestions and discussion, and Arjun Raman and Arlene Parubrub for manuscript review. Research supported by NIH P20 RR016467/GM103466 (FPB), NIH RO1 NS40302 (MJB), Hawaii Community Foundation Ingeborg v.F. McKee Fund 08PR-43031 (FPB) and NIH G12 RR003061/MD007601 which supports the JABSOM histology/imaging core facility. All animal procedures and experimental protocols were approved by the University of Hawaii Institutional Animal Care and Use Committee.