A nonimprinted Prader-Willi Syndrome (PWS)-region gene regulates a different chromosomal domain in trans but the imprinted PWS loci do not alter genome-wide mRNA levels

Prader-Willi syndrome (PWS) is a complex neurobehavioral disorder that results from loss of function of 10 clustered, paternally expressed genes in a 1.5-Mb region of chromosome 15q11-q13. Many of the primary PWS region genes appear to have nuclear RNA regulatory functions, suggesting that multiple genetic pathways could be secondarily affected in PWS. Using a transgenic mouse model of PWS (TgPWS) with an ∼4-Mb chromosome 7C deletion of paternal origin that models the neonatal phenotype of the human syndrome we compared by oligonucleotide microarrays expression levels of ∼12,000 genes and ESTs in TgPWS and wild-type brain. Hybridization data were processed with two distinct statistical algorithms and revealed a dramatically reduced expression of 4 imprinted genes within the deletion region in TgPWS mice, with 2 nonimprinted, codeleted genes reduced twofold. However, only 3 genes outside the deletion were significantly altered in TgPWS mouse brain, with ∼1.5-fold up-regulation of mRNA levels. Remarkably, these genes map to a single chromosome domain (18B3), and by quantitative RT-PCR we show that 8 genes in this domain are up-regulated in TgPWS brain. These 18B3 genes were up-regulated in an equivalent manner in Angelman syndrome mouse (TgAS) brain, which has the same deletion but of maternal origin. Therefore, the trans-regulation of the chromosome 18B3 domain is due to decreased expression of a nonimprinted gene within the TgPWS/AS mouse deletion in mouse chromosome 7C. Most surprisingly, since 48-60% of the genome was screened, it appears that the imprinted mouse PWS loci do not widely regulate mRNA levels of other genes and may regulate RNA structure.