López-Abad Miriam, Iglesias-Platas Isabel, Monk David
Servicio de Neonatología, Sant Joan de Déu, Centro de Medicina Maternofetal y Neonatal Barcelona, Hospital Sant Joan de Déu y Hospital Clínic, Universitat de Barcelona Barcelona, Spain.
Imprinting and Cancer group, Cancer Epigenetic and Biology Program, Institut d'Investigació Biomedica de Bellvitge Barcelona, Spain.
Front Genet. 2016 Apr 26;7:62. doi: 10.3389/fgene.2016.00062. eCollection 2016.
The cyclin-dependent kinase (CDK)-inhibitor 1C (CDKN1C) gene is expressed from the maternal allele and is located within the centromeric imprinted domain at chromosome 11p15. It is a negative regulator of proliferation, with loss-of-function mutations associated with the overgrowth disorder Beckwith-Wiedemann syndrome. Recently, gain-of-function mutations within the PCNA domain have been described in two disorders characterized by growth failure, namely IMAGe (intra-uterine growth restriction, metaphyseal dysplasia, adrenal hypoplasia congenita and genital abnormalities) syndrome and Silver-Russell syndrome (SRS). Over-expression of CDKN1C by maternally inherited microduplications also results in SRS, suggesting that in addition to activating mutations this gene may regulate growth by changes in dosage. To determine if CDKN1C is involved in non-syndromic IUGR we compared the expression and DNA methylation levels in a large cohort of placental biopsies from IUGR and uneventful pregnancies. We observe higher levels of expression of CDKN1C in IUGR placentas compared to those of controls. All placenta biopsies heterozygous for the PAPA repeat sequence in exon 2 showed appropriate monoallelic expression and no mutations in the PCNA domain were observed. The expression profile was independent of both genetic or methylation variation in the minimal CDKN1C promoter interval and of methylation of the cis-acting maternally methylated region associated with the neighboring KCNQ1OT1 non-coding RNA. Chromatin immunoprecipitation revealed binding sites for CTCF within the unmethylated CDKN1C gene body CpG island and putative enhancer regions, associated with the canonical enhancer histone signature, H3K4me1 and H3K27ac, located ∼58 and 360 kb away. Using 3C-PCR we identify constitutive higher-order chromatin loops that occur between one of these putative enhancer regions and CDKN1C in human placenta tissues, which we propose facilitates expression.
细胞周期蛋白依赖性激酶（CDK）抑制剂1C（CDKN1C）基因由母本等位基因表达，位于染色体11p15的着丝粒印记区域内。它是增殖的负调节因子，功能丧失突变与过度生长疾病贝克威思-维德曼综合征相关。最近，在两种以生长发育迟缓为特征的疾病中发现了PCNA结构域内的功能获得性突变，即IMAGe（宫内生长受限、干骺端发育不良、先天性肾上腺发育不全和生殖器异常）综合征和Silver-Russell综合征（SRS）。母系遗传的微重复导致CDKN1C过表达也会引发SRS，这表明除了激活突变外，该基因可能通过剂量变化来调节生长。为了确定CDKN1C是否参与非综合征性宫内生长受限，我们比较了来自宫内生长受限和正常妊娠的大量胎盘活检样本中的表达水平和DNA甲基化水平。我们观察到，与对照组相比，宫内生长受限胎盘组织中CDKN1C的表达水平更高。所有外显子2中PAPA重复序列杂合的胎盘活检样本均显示出适当的单等位基因表达，且未观察到PCNA结构域的突变。表达谱与最小CDKN1C启动子区间的遗传或甲基化变异以及与相邻KCNQ1OT1非编码RNA相关的顺式作用母本甲基化区域的甲基化无关。染色质免疫沉淀揭示了未甲基化的CDKN1C基因体CpG岛和推定增强子区域内CTCF的结合位点，这些区域与位于约58和360 kb远处的典型增强子组蛋白标记H3K4me1和H3K27ac相关。使用3C-PCR，我们在人胎盘组织中鉴定出这些推定增强子区域之一与CDKN1C之间存在的组成性高阶染色质环，我们认为这促进了表达。
