Alternative transcription initiation and splicing variants of the DHRS4 gene cluster

The DHRS4 (short-chain dehydrogenase/reductase superfamily member 4) gene cluster, consisting of DHRS4 and its copy gene DHRS4L2, is localized on 14q11.2. The DHRS4 gene product NADP(H)-dependent retinol oxidoreductase participates in the metabolism of retinoids. The expression patterns of the DHRS4 gene cluster were investigated in human neuroblastoma cells. Transcript analysis of the DHRS4 gene cluster using 3'- and 5'-RACE (rapid amplification of cDNA ends), reverse transcription-PCR and bioinformatics approaches showed an alternative transcription start site in the copy gene DHRS4L2 which generates two transcripts, DHRS4A1 (GenBank (R) nucleotide sequence database accession number AY616183) and DHRS4A2 (AY943857), together with at least six alternative splicing variants (DHRS4A_v1-6) (AY920361, AY920362, DN237886, DN237887, DN237890 and DN237892 respectively), resulted from alternative splicing. DHRS4A1 and DHRS4A2 were specifically transcribed in neuroblastoma cells. RNA structural analysis of DHRS4A1 and DHRS4A2 suggested that they are non-coding RNAs. Expression analysis of DHRS4 by quantitative real-time PCR and Western blotting showed a lack of correlation between the levels of transcription and translation in the tissues examined. Bisulfite genomic sequencing PCR experiments indicated that the expression of DHRS4L2 was regulated by methylation of its CpG islands.