The role of NLRP7 in maternal imprinting and early embryonic development

Abstract

NLRP7 is a maternal effect gene in humans whose mutations are responsible for a rare abnormal pregnancy with familial predisposition, biparental complete hydatidiform mole (BiCHM). Given BiCHM exhibits a similar pathology to androgenetic CHM, including overgrowth of trophoblast tissues and dysregulated maternal imprinting, NLRP7 is thought to play an important role in meditating maternal imprinting and early embryonic development in humans. However, due to the lack of rodent models and limited human materials, it has not been possible to reveal the mechanistic function of NLRP7 in maternal imprinting. In this project, hESCs are used as a model system, to investigate the role of NLRP7 in maternal imprinting and its potential relationship with other imprinting modulators, particularly DNMT3L. Firstly, SNPs were identified in selected imprinted genes in hESCs, so that it was feasible to distinguish their two alleles in imprinting studies. In addition, naïve conversion of hESC was achieved to mimic, at least partly, the process of global DNA demethylation, which would enable them to be used to investigate the possible role of NLRP7 in maintaining maternal imprinting during this process. When NLRP7 was overexpressed in hESCs, it showed partial protection of maternal imprinting from global demethylation after naïve conversion, indicating that NLRP7 may be involved in protecting maternally imprinted genes from global demethylation. Furthermore, by analysing gene expression profiles of imprinting related genes, the expression of NLRP7 and DNMT3L were found to be correlated during early embryonic development and the naïve conversion process; and overexpression of NLRP7 can upregulate DNMT3L mRNA expression, which implies a potential link between them. Consequently, my findings demonstrate the possibility of employing hESCs as an alternative and unlimited resource to study NLRP7 in future. More importantly, this is the first time NLRP7 has been shown to directly protect maternally imprinted genes from global demethylation.