NLRP9B protein is dispensable for oocyte maturation and early embryonic development in the mouse

Nlrp9a, Nlrp9b and Nlrp9c are preferentially expressed in oocytes and early embryos in the mouse. Simultaneous genetic ablation of Nlrp9a and Nlrp9c does not affect early embryonic development, but the function of Nlrp9b in the process of oocyte maturation and embryonic development has not been elucidated. Here we show that both Nlrp9b mRNA and its protein are expressed in ovaries and the small intestine. Moreover, the NLRP9B protein was restricted to oocytes in the ovary and declined with oocyte aging. After ovulation and fertilization, NLRP9B protein was found in preimplantation embryos. Confocal microscopy demonstrated that it was mainly localized in the cytoplasm in the oocytes and blastomeres. Thus, this protein might play a role in oocyte maturation and early embryonic development. However, knockdown of Nlrp9b expression in GV-stage oocytes using RNA interference did not affect oocyte maturation or subsequent parthenogenetic development after Nlrp9b-deficient oocytes were activated. Furthermore, Nlrp9b knockdown zygotes could reach the blastocyst stage after being cultured for 3.5 days in vitro. These results provide the first evidence that the NLRP9B protein is dispensable for oocyte maturation and early embryonic development in the mouse.