Figure 1

Alternative splicing of HMGCR. (A) Genomic organisation of human HMGCR at chromosome 5q13.3. Exons are separated by introns (IVS) and represented by white and black boxes illustrating predicted untranslated regions (UTR) and coding sequences (CDS), respectively. The canonical exon 1a is part of the HMGCR reference sequence (NM_000859) and exons 1b, 1c and 1d are predicted from published ESTs. The red box indicates the cassette exon 13, which is skipped in an alternative HMGCR transcript (NM_001130996). (B) Validation of exon 1a-, 1b-, 1c- and 1d-transcription by RT-PCR using exon-specific primers and a cDNA pool of 44 tissues visualised on a 3% (w/v) agarose gel. RT-PCR identified HMGCR transcripts with different first exons. Transcription of exon 1d could not be confirmed. (C) Exon 13 (159 bp) skipping (Δexon13) of both HMGCR-1a and HMGCR-1b identified by PCR and visualised on a 2% (w/v) agarose gel. cDNA synthesised from skin was used to amplify the HMGCR transcripts from exons 1a and 1b, respectively, through exon 16 followed by nested PCR from exon 10 through exon 14. The existence of HMGCR-1b Δexon13 was confirmed by cloning and sequencing. (D) Multiple sequence alignments of HMGCR exon 1b in different mammalian species showing conservation of exon 1b only in higher primates. The alignment was created using the UCSC Genome Browser “Vertebrate Multiz Alignment & Conservation (46 Species)” track. An in-frame start codon (ATG) is preserved in higher primates and presented as the methionine single letter code (M). Single dashes indicate alignment gaps, and double dashes represent one or more unalignable bases in the gap region.