Serge McGraw - CHU de Ste Justine, Montréal, Canada

Research Scientist, Embryonic and Developmental Epigenetics Lab, Centre de Recherche du CHU Ste-Justine
Assistant Professor, ​ Department of Obstetrics and Gynecology, Faculty of Medicine, Université de Montréal

Abstract

Rare germline heterozygous mutations in functional DNMT3A (DNA methyltransferase 3A) domains cause an overgrowth intellectual disability syndrome called Tatton-Brown-Rahman Syndrome (TBRS). DNMT3A is essential for establishing DNA methylation marks, epigenetic modifications implicated in gene regulation and genome stability, that are crucial to establish and maintain proper cellular identity. We remain unaware of how pathogenic sequence variants in human DNMT3A contribute to alterations in molecular and cellular processes at the origin of the neurodevelopmental disorders observed in TBRS patients.

Using cells from two TBRS patients carrying different single mutations in the methyltransferase domain of DNMT3A (DNMT3A+/mut), as well as control patients (DNMT3A+/+), we generated induced-pluripotent stem cells (iPSC), derived these cells into neuronal progenitor cells (NPC) and terminally differentiated neurons to uncover the impacts of pathogenic DNMT3A haploinsufficiency during brain cell development. We show that DNA methylation and gene expression alterations present in DNMT3A+/mut iPSC are exacerbated during the progression into NPC. A significant number of these alterations are conserved between mutations, pointing towards common pathways targeted by the PRC2 repressive complex (Polycomb 2 repressive complex). When we further differentiate DNMT3A+/mut into cortical neurons, the neurons show significant expression alterations associated with key genes (eg., NEUROD1, FOXJ1, PAX6, PAX7) regulating brain development and cell fate commitment, and related to characteristic phenotypes observed in TBRS patients.

Our data suggest that, as pluripotent cells undergo cellular differentiation and lineage commitment, the negative impact of pathogenic DNMT3A mutations on the distribution of DNA methylation marks and gene expression profiles intensifies, thus potentially altering cell fate and contributing to the developmental outcomes observed in TBRS patients.

Biography

Dr. Serge McGraw is an Associate Professor in the Department of Obstetrics and Gynecology at the Université de Montréal (Montréal, Canada).  His principal research interests are focused on the harmful developmental outcomes caused by epigenetic instabilities arising from alterations in DNA methylation profiles during early embryogenesis. By combining in vitro stem cell (mES, patient iPS) models as well as in vivo mouse models with multi-omics sequencing approaches, his laboratory aims at understanding how perturbations in the early embryonic program may lead to epigenetics errors driving in the occurrence of prenatal or after birth developmental disorders.