Project Funding Details

Genomic imprinting is an epigenetically regulated phenomenon for which a small subset of mammalian genes is expressed from only their maternal or their paternal alleles. The majority of the imprinted genes controls the growth of the fetus and the placenta, and abnormal imprinting is associated with growth disorders and cancer. Imprinted genes are organized in clusters and each cluster harbours an Imprinting Control Region (ICR). ICRs are characterized by parent-of-origin-specific methylation that is acquired during gametogenesis and reproduced in somatic cells through cell divisions, and is critical for genomic imprinting maintenance. The ICRs are specifically recognised by the zinc-finger protein ZFP57 and the inactivation of this gene leads to loss of ICR methylation. The product of several imprinted genes affects cell growth and imprinting alterations leading to either bi-allelic acivation or bi-allelic silencing of the imprinted genes are frequently found in human cancer, and imprinting disruption in transgenic mice promotes tumourigenesis and cell immortalization. Although rare mutations acting in cis or in trans in the cancer-associated Beckwith-Wiedemann syndrome (BWS) have been associated with imprinting alterations, the molecular mechanisms underlying most of the imprinting defects in cancer are unknown. Based on preliminary results, we hypothesize that signaling pathways that are altered in cancer and BWS affect the maintenance of mono-allelic ICR methylation in somatic cells. The overall aim of this study is to define the pathways and mechanisms underlying imprinting maintenance and loss in somatic cells. The experimental plan is based on two different approaches. The first one uses mouse and human embryonic stem cells (ESCs) that reproduce the early embryo. We have identified novel factors that are part of the complex recognizing the ICRs and likely involved in the maintenance of its differential methylation. These factors are SMAD1 and SMAD5 that are intracellular mediators of the BMP pathway that is critical for early embryo differentiation and plays important roles in tumorigenesis and cancer progression. We will explore the functional interaction between ZFP57 and SMAD1/SMAD5 and if BMP signalling and other cross-talking pathways interfere with the maintenance of genomic imprinting. The second approach is based on the analysis of BWS patients with specific ICR methylation abnormalities. In this case, we have identified rare and possibly damaging protein variants in BWS cases with IC1 Gain of Methylation or IC2 Loss of methylation with Multi-Locus-Imprinting-Disturbances (MLID). To determine the possible role of these and other trans-acting factors in the maintenance of IC1 and IC2 methylation, we will analyse by locus-specific and exome-targeted re-sequencing a relatively large cohort of patients with these two types of methylation abnormalities. These two approaches have the potential to identify cis-acting elements, trans-acting factors and signalling pathways involved in the maintenance of genomic imprinting in somatic cells and dysregulated in human cancer and cancer-associated syndromes. This work will provide fundamental insights into our understanding of the epigenetic regulation of imprinted genes. As such, it is of high medical relevance for imprinting disorders and epigenetic contributions to cancer development. This knowledge opens new avenues towards prospective therapies in this area.