Molecular evolution of the HBII-52 snoRNA cluster.

HBII-52 is a human brain-specific C/D box snoRNA that potentially regulates the editing and/or alternative splicing of the serotonin receptor. Forty-two nearly identical copies of the HBII-52 gene are located immediately downstream of the SNRPN protein-coding gene in an imprinted locus associated with Prader-Willi syndrome. Other eutherian mammals, with genomic assemblies covering the corresponding locus, also have multiple orthologous copies of HBII-52. The SNRPB gene, which is known to have given rise to SNRPN through gene duplication, expresses a C/D box snoRNA, SNORD119, from its fifth intron. Here we show that, despite the fact that they lie in different positions relative to the orthologous SNRPB/SNRPN coding sequences, there are significant sequence similarities between SNORD119 and HBII-52, including the antisense element and the stem-forming regions. By analysing these snoRNAs in marsupial and eutherian mammal genomes, we reconstruct the likely evolutionary history of the HBII-52 cluster and SNORD119 and suggest that they have evolved from a common ancestor.