An imprinted antisense transcript at the human GNAS1 locus

Abstract

Recent studies of the GNAS1 gene have shown a highly complex imprinted expression pattern, with paternally, maternally and biallelically derived protein products, raising questions regarding how such transcriptional complexity is established and maintained. GNAS1 was originally identified as the gene encoding an important and widely expressed signal transduction protein, the alpha subunit of the stimulatory G protein G(s). Partial G(s)alpha deficiency results in the hormone resistance syndrome, pseudohypoparathyroidism type 1a. G(s)alpha is encoded by exons 1-13 of GNAS1 and, in most tissues at least, expression of this transcript is biallelic. Two large upstream exons, however, have monoallelic expression patterns, and in each case their transcripts splice onto GNAS1 exon 2. The most 5' of these is maternally expressed, and encodes neuroendocrine secretory protein 55 (NESP55), whose coding region does not overlap with that of G(s)alpha. The other exon, 14 kb further 3', is paternally expressed, and encodes XL(alpha)s (extra large alphas-like protein), translated in-frame with G(s)alpha exons 2-13. This close proximity of two oppositely imprinted promoters suggested the likelihood of important regulatory interactions between them, and to investigate this possibility we have performed a search for other transcripts in the region. Here we show that the maternally methylated region upstream of the XL(alpha)s exon gives rise to a spliced polyadenylated antisense transcript, which spans the upstream NESP55 region. This antisense transcript is imprinted, and expressed only from the paternal allele, suggesting that it may have a specific role in suppressing in cis the activity of the paternal NESP55 allele.

Genetic and epigenetic states of the GNAS complex in pseudohypoparathyroidism type Ib using methylation-specific multiplex ligation-dependent probe amplification assay

“…In contrast to most cases of PHP-Ia, which are caused by a mutation in the coding sequence of the GNAS gene, the majority of PHP-Ib cases are reportedly caused by a methylation alteration of the GNAS locus (5,6). The GNAS complex contains at least four distinct differentially methylated regions (DMRs) (7,8,9). By a parent-specific methylation pattern of most of its different promoters, the GNAS locus gives rise to several transcripts, including the a-subunit of the heterotrimeric stimulatory G protein a (Gsa), the Gsa extra-large variant (XLas), a second alternative gene product encoded by the XL-exon 1 (ALEX), neuroendocrine protein 55 (NESP55), untranslated exon A/B (also known as exon 1A), and an additional antisense transcript (AS) (10).…”

“…By a parent-specific methylation pattern of most of its different promoters, the GNAS locus gives rise to several transcripts, including the a-subunit of the heterotrimeric stimulatory G protein a (Gsa), the Gsa extra-large variant (XLas), a second alternative gene product encoded by the XL-exon 1 (ALEX), neuroendocrine protein 55 (NESP55), untranslated exon A/B (also known as exon 1A), and an additional antisense transcript (AS) (10). The XLas, A/B, and AS transcripts derive exclusively from the paternal allele, whereas NESP55 is maternally derived (7,9). Consistent with this imprinted expression pattern, the promoters of these genes are methylated on the silenced allele.…”

Loss of XLαs (extra-large αs) imprinting results in early postnatal hypoglycemia and lethality in a mouse model of pseudohypoparathyroidism Ib

“…XLαs is imprinted oppositely to NESP55; i.e., its promoter is methylated on the maternal allele and transcriptionally active only on the paternal allele (12,15,16). Within the same differentially methylated region (DMR) and just upstream of the XLαs promoter is a promoter driving expression of a paternally expressed antisense transcript, which is noncoding and traverses the NESP55 exon from the opposite direction (AS; mouse Nespas) (18,19). Like XLαs, this AS transcript is expressed from the paternal allele.…”

A global disorder of imprinting in the human female germ line

“…The NESP55 DMR becomes methylated on the paternal allele in the blastocyst stage, possibly secondary to antisense transcription 21,22 . BiCHM and AgCHM are both completely methylated at this DMR (paternal epigenotype on both alleles).…”