Genomic imprinting is an epigenetic phenomenon where gene expression is regulated in a parent-of-origin-specific manner. Maternal imprinting, established by de novo DNA methylation during oocyte development, is generally protected from global DNA demethylation post-fertilization. In the context of complete hydatidiform mole (CHM), the loss of maternal imprinting in cells from molar tissue with defective NLRP7 suggests that NLRP7 may play a role in maintaining maternal imprinting. NLRP7, a human maternal effect protein, is highly expressed in developing oocytes and preimplantation human embryos. However, its specific function in regulating maternal imprinting remains unclear. In this project. human embryonic stem cells are utilised as a cell model to investigate the role of NLRP7 in maternal imprinting during this conversion process and to explore the molecular mechanisms involved.
Single nucleotide polymorphisms (SNPs) were identified in hESCs, enabling the analysis of their allelic expression patterns in imprinting studies. NLRP7 expression was found to be very low in primed hESCs but increased at the late stages of naïve conversion. This suggests that the initial low level of NLRP7 might contribute to the loss of maternal imprinting. Subsequently, NLRP7 was overexpressed in hESCs, which were then reprogrammed to a naïve state. Maternal imprinting was partially retained in these naïve NLRP7-overexpressing hESCs, whereas paternally imprinted genes maintained. This indicates that NLRP7 specifically protects maternal imprinting from global demethylation. Moreover, NLRP7 was predominantly localised in cytoplasm, with a small amount of NLRP7 present in the nucleus, and it co-localized with spindle fibres during cell division. Consequently, my findings demonstrate NLRP7 can partially rescue the loss of maternal imprinting during global DNA demethylation process. More importantly, this is the first time showing that NLRP7 can be in closely contact with nuclear DNA during cell division. This localization suggests a possible mechanism by which NLRP7 regulates maternally imprinted genes.