A new deletion refines the boundaries of the murine Prader-Willi syndrome imprinting center

Abstract

The human chromosomal 15q11-15q13 region is subject to both maternal and paternal genomic imprinting. Absence of paternal gene expression from this region results in Prader-Willi syndrome (PWS), while absence of maternal gene expression leads to Angelman syndrome. Transcription of paternally expressed genes in the region depends upon an imprinting center termed the PWS-IC. Imprinting defects in PWS can be caused by microdeletions and the smallest commonly deleted region indicates that the PWS-IC lies within a region of 4.3 kb. The function and location of the PWS-IC is evolutionarily conserved, but delineation of the PWS-IC in mouse has proven difficult. The first targeted mutation of the PWS-IC, a deletion of 35 kb spanning Snrpn exon 1, exhibited a complete PWS-IC deletion phenotype. Pups inheriting this mutation paternally showed a complete loss of paternal gene expression and died neonatally. A reported deletion of 4.8 kb showed only a reduction in paternal gene expression and incomplete penetrance of neonatal lethality, suggesting that some PWS-IC function had been retained. Here, we report that a 6 kb deletion spanning Snrpn exon 1 exhibits a complete PWS-IC deletion phenotype. Pups inheriting this mutation paternally lack detectable expression of all PWS genes and paternal silencing of Ube3a, exhibit maternal DNA methylation imprints at Ndn and Mkrn3 and suffer failure to thrive leading to a fully penetrant neonatal lethality.

Temporal and developmental requirements for the Prader–Willi imprinting center

“…The Cmv-cre transgene expresses Cre ubiquitously before implantation (12). Similar to paternal inheritance of a PWS-IC deletion (4,5), PWS-IC +/flox6kb Tg Cmv-cre pups were visibly smaller and had significantly lower birth weights than littermates ( Fig. 1 A and B).…”

“…Using a targeted deletion of a 35-kb region spanning Snrpn exons 1 to 6, we previously reported that the location and function of the PWS-IC is conserved in mice (4). More recently, we found that a 6-kb deletion surrounding Snrpn exon 1 yields an identical phenotype to the 35-kb deletion, demonstrating that all the functional elements of the PWS-IC are within this 6-kb region (5).…”

“…DNA was isolated from newborn brain, digested with the indicated restriction endonucleases, and analyzed by Southern blot as previously described (5). Probe details are available on request.…”

Prader–Willi syndrome: genotype, cause, phenotype and management

“…Deletions in the paternally inherited chromosome 15q11.2-13 region account for 70-75% of cases; 25-30% from maternal uniparental disomy (mUPD) and the remaining from mutations or defects of the IC (Cassidy and Driscoll, 2009;Butler, 2011;DuBose et al, 2011;McAllister et al, 2011; McCandless and The Committee on Genetics, 2011).…”

Mechanisms of activation of the paternally expressed genes by the Prader-Willi imprinting center in the Prader-Willi/Angelman syndromes domains

“…Deletion or loss of function of PWS-IC on the paternal allele leads to abnormal methylation of the entire 2-Mb domain and inactivation of all PEGs, causing PWS (6). Deletion of a 6.0-kb sequence spanning SNRPN exon 1 in the mouse was recently shown to exhibit a complete PWS-IC deletion phenotype, as well (10). Deletion or inactivation of AS-IC on the maternal allele leads to an abnormal methylation pattern of PWS-IC, leading to activation of the paternally repressed genes, including the UBE3A antisense gene, thus inactivation of UBE3A and causing AS (4).…”