Role of NLRP7 and Related Genes in Hydatidiform Moles and Reproductive Failure
Hydatidiform moles (HM) are abnormally developing pregnancies with hyperproliferative trophoblast and absence of a fetus. The more common sporadic complete hydatidiform moles are 46,XX or 46,XY androgenetic conceptions, in which all the genetic material is paternally derived (AnCHM). Rare recurrent hydatidiform moles are clinically and pathologically identical to AnCHM, but have normal biparental inheritance (BiHM) and their molar trophoblast tissues show abnormal expression of imprinted genes and abnormal methylation of CpG islands at imprinting control regions (ICRs). Recently, autosomal recessive mutations in NLRP7, encoding a protein (NLRP7) with a putative role in innate immunity and apoptosis, were identified in women with recurrent BiHM pregnancies.
Prior to this surprising finding, we and others hypothesized that the gene mutated in women with BiHM should be a major regulator of imprinting. However, it is currently not known whether and how NLRP7 might carry out this additional function. Furthermore, it has not yet been studied whether NLRP7 interacts directly with DNA or proteins in chromatin complexes that regulate establishment or maintenance of imprinting marks. Therefore, the overarching hypothesis for this project is that NLRP7 regulates reprogramming and/or maintenance of imprinting marks that are set during human oogenesis by direct interaction with DNA and/or chromatin modifying factors at ICRs.
Because NLRP7 has no rodent orthologue, inactivating mutations in mice cannot be generated. Hence, we propose to use in vitro assays and cell culture systems to explore this hypothesis in three specific aims. In specific aim 1 we will investigate by two complementary methods, electromobility shift assays and chromatin immunoprecipitation, whether NLRP7 associates with methylated and unmethylated CpG sequences at ICRs. For specific aim 2 we will perform yeast-two-hybrid interaction studies and co-affinity purification experiments of NLRP7 with candidate proteins that participate in reprogramming and maintenance of imprinting. For Specific aim 3 we will search for novel NLRP7 interactors by a saturated yeast-two-hybrid screen with the full-length NLRP7 protein and the NLRP7-leucine-rich repeat region.
For all three specific aims, we will first focus our analysis on known or novel interactors that play a role in imprinting. However, if the data do not support a direct role in imprinting, the experiments, will be able to address an alternate hypothesis, which is that the imprinting defects seen in BiHM are secondary to disruption of a more general role of NLRP7 in immune response within reproductive organs and/or the developing oocyte by focusing on candidate proteins for these pathways.
Overall, our goal is to explore new pathways, centered on NLRP7 that are important for imprinting and for reproductive health. Because some women with recurrent BiHM have rare non-molar pregnancies affected by miscarriage, intra-uterine growth retardation or preterm delivery, we predict that this project will uncover candidate genes for these common reproductive disorders, and potentially novel therapeutic targets.
Relevance of the project to IDDRC mission:
Better understanding of how genomic imprinting marks are established in the human germline or maintained will be relevant to numerous human developmental disorders that are associated with imprinting defects of selected specific genes.