NLRP7 and KHDC3L, the Two Maternal-effect Proteins Responsible for Recurrent Hydatidiform Moles, Co-localize to the Oocyte Cytoskeleton
1. Departments of Human Genetics and 2. Obstetrics and Gynecology, McGill University Health Center, Montreal, Quebec, Canada
Hydatidiform mole (HM) is an aberrant human pregnancy with abnormal embryonic development and excessive trophoblastic proliferation. Recessive mutations in the maternal-effect genes, NLRP7 or KHDC3L, are responsible for recurrent HMs (RHMs). However, the exact roles of NLRP7 and KHDC3L in this condition are not fully understood. To gain insights into their functions, we characterize their subcellular localizations in human oocytes and early embryos using regular and confocal immunofluorescence and electron microscopies. We found that in oocytes, from the germinal vesicle until the formation of the zygote, NLRP7 co-localized with KHDC3L mainly to the cortical region. Within this region, electron and high resolution confocal microscopies confirmed the co-localization of NLRP7 and KHDC3L between cortical granules, mitochondria, and other organelles on some cytoskeletal structures that did not overlap exactly with the α-tubulin microtubule network or display similar pattern by immunofluorescence. As the embryo completed its first division, NLRP7 and KHDC3L became excluded from the cell-to-cell contact region, restricted to the outer cortical regions, and were part of some structural complexes that are not E-cadherin dependent. During early cleavage stages, the two proteins displayed different localization patterns. While NLRP7 maintained its polarity until the blastocyst stage where it became homogeneously distributed in the cytoplasm of cells from the inner cell mass and trophectoderm, KHDC3L translocated to the nuclei of cells from both the inner cell mass and trophectoderm at the morula stage.
To better understand how the two oocyte cytoskeletal proteins, NLRP7 and KHDC3L, play a role in cellular proliferation, one of the fundamental aspects of hydatidiform moles, we characterized their subcellular localizations during the cell cycle of somatic cells and will present these recent data at the conference. Our study is the first comprehensive high resolution localization of the only two known maternal-effect proteins, NLRP7 and KHDC3L, in human oocytes, preimplantation embryos, and somatic cells and will contribute to a better understanding of their roles in all aspects of the pathology of hydatidiform moles.