Maternally contributed Nlrp9b expressed in human and mouse ovarian follicles contributes to early murine...

The aim of the study is to investigate presence and role of the gene encoding the maternally contributed nucleotide-binding oligomerization domain (NOD)-like receptors with a pyrin domain (PYD)-containing protein 9 (NLRP9) in human and mouse ovaries, respectively, and in preimplantation mouse embryo development by knocking down Nlrp9b.

Expression levels of NLRP9 mRNA in human follicles were extracted from RNA sequencing data from previous studies. In this study, we performed a qPCR analysis of Nlpr9b mRNA in mouse oocytes and found it present. Intracellular ovarian distribution of NLRP9B protein was accomplished using immunohistochemistry. The distribution of NLRP9B was explored using a reporter gene approach, fusing NLRP9B to green fluorescent protein and microinjection of in vitro-generated mRNA. Nlrp9b mRNA function was knocked down by microinjection of short interference (si) RNA targeting Nlrp9b, into mouse pronuclear zygotes. Knockdown of the Nlrp9b mRNA transcript was confirmed by qPCR.

We found that the human NLRP9 gene and its corresponding protein are highly expressed in human primordial and primary follicles. The NLRP9B protein is localized to the cytoplasm in the blastomeres of a 2-cell embryo in mice. SiRNA-mediated knockdown of Nlrp9b caused rapid elimination of endogenous Nlrp9b mRNA and premature embryo arrest at the 2- to 4-cell stages compared with that of the siRNA-scrambled control group.

These results suggest that mouse Nlrp9b, as a maternal effect gene, could contribute to mouse preimplantation embryo development. It remains to investigate whether NLRP9 have a crucial role in human preimplantation embryo and infertility.