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In mice and humans, the locus encoding the gene for small nuclear ribonucleoprotein N (SNRPN/Snrpn), as well as other loci in the region are subject to genomic imprinting. The SNRPN promoter is embedded in a maternally methylated CpG island, is expressed only from the paternal chromosome and lies within an imprinting center that is required for switching to and/or maintenance of the paternal epigenotype. We show here that a 0.9-kb deletion of exon 1 of mouse Snrpn did not disrupt imprinting or elicit any obvious phenotype, although it did allow the detection of previously unknown upstream exons. In contrast, a larger, overlapping 4.8-kb deletion caused a partial or mosaic imprinting defect and perinatal lethality when paternally inherited.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are caused by deficiency of imprinted gene expression from paternal or maternal chromosome 15q11-q13, respectively. Genomic imprinting of the PWS/AS domain is regulated through a bipartite cis-acting imprinting center (PWS-IC/AS-IC) within and upstream of the SNRPN promoter. Here, we show that two Rb-binding protein-related genes, Rbbp1/Arid4a and Rbbp1l1/Arid4b, are involved in the regulation of imprinting of the IC. We recovered these two genes from gene trap mutagenesis selecting for altered expression of an Snrpn-EGFP fusion gene strategy. RBBP1/ARID4A is an Rb-binding protein. RBBP1/ARID4A interacts with RBBP1L1/ARID4B and with the Snrpn promoter, implying that both are part of a protein complex. To further elucidate their roles on regulation of imprinting, we deleted the Rbbp1/Arid4a and Rbbp1l1/Arid4b genes in mice. Combined homozygous deficiency for Rbbp1/Arid4a and heterozygous deficiency for Rbbp1l1/Arid4b altered epigenetic modifications at the PWS-IC with reduced trimethylation of histone H4K20 and H3K9 and reduced DNA methylation, changing the maternal allele toward a more paternal epigenotype. Importantly, mutations of Rbbp1/Arid4a, Rbbp1l1/Arid4b, or Rb suppressed an AS imprinting defect caused by a mutation at the AS-IC. These data identify Rbbp1/Arid4a and Rbbp1l1/Arid4b as new members of epigenetic complexes regulating genomic imprinting at the PWS/AS domain.

BackgroundGiven the uncertainties regarding thyroid nodule assessment and management, physicians require systematically and transparently developed recommendations. This systematic review assesses the quality and consistency of the recommendations of international clinical practice guidelines (CPGs) for the diagnosis and management of thyroid nodules and cancer to assist physicians in making appropriate recommendations.MethodsThe CPGs on the management of thyroid nodules and cancer published before June 2013 were retrieved. All the reviewed guidelines were in English. Four reviewers independently assessed the rigor of guideline development by using the Appraisal of Guidelines Research and Evaluation II (AGREE-II) instrument, and their reported evidence was evaluated.ResultsTen eligible guidelines were included: nine had been developed by professional organizations, and the remaining guideline was endorsed by an independent regional body. Three guidelines achieved a score of greater than 50% in all six AGREE-II domains. Guidelines scored highest on the measurement of ‘scope and purpose’ (≥61.1% for eight CPGs) and lowest on the measurement of ‘applicability’ (≤38.5% for five CPGs). The overall quality ranged from 3.0 to 6.25 on a seven-point scale on the AGREE-II tool. Most CPG recommendations on the management of thyroid cancer were relatively consistent. Guidelines varied regarding the indication of fine-needle aspiration for thyroid nodules, as well as in their suggestions for postoperative radioiodine ablation.ConclusionsOur analysis showed that the current CPGs varied in methodological quality. More effort is needed to improve the quality of recommendations on the diagnosis and management of thyroid nodules and cancer.