Nlrp2, a Maternal Effect Gene Required for Early Embryonic Development in the Mouse

Maternal effect genes encode proteins that are produced during oogenesis and play an essential role during early embryogenesis. Genetic ablation of such genes in oocytes can result in female subfertility or infertility. Here we report a newly identified maternal effect gene, Nlrp2, which plays a role in early embryogenesis in the mouse. Nlrp2 mRNAs and their proteins (∼118 KDa) are expressed in oocytes and granulosa cells during folliculogenesis. The transcripts show a striking decline in early preimplantation embryos before zygotic genome activation, but the proteins remain present through to the blastocyst stage. Immunogold electron microscopy revealed that the NLRP2 protein is located in the cytoplasm, nucleus and close to nuclear pores in the oocytes, as well as in the surrounding granulosa cells. Using RNA interference, we knocked down Nlrp2 transcription specifically in mouse germinal vesicle oocytes. The knockdown oocytes could progress through the metaphase of meiosis I and emit the first polar body. However, the development of parthenogenetic embryos derived from Nlrp2 knockdown oocytes mainly blocked at the 2-cell stage. The maternal depletion of Nlrp2 in zygotes led to early embryonic arrest. In addition, overexpression of Nlrp2 in zygotes appears to lead to normal development, but increases blastomere apoptosis in blastocysts. These results provide the first evidence that Nlrp2 is a member of the mammalian maternal effect genes and required for early embryonic development in the mouse

Dynamic Replacement of Histone H3 Variants Reprograms Epigenetic Marks in Early Mouse Embryos

Upon fertilization, reprogramming of gene expression is required for embryo development. This step is marked by DNA demethylation and changes in histone variant composition. However, little is known about the molecular mechanisms causing these changes and their impact on histone modifications. We examined the global deposition of the DNA replication-dependent histone H3.1 and H3.2 variants and the DNA replication-independent H3.3 variant after fertilization in mice. We showed that H3.3, a euchromatic marker of gene activity, transiently disappears from the maternal genome, suggesting erasure of the oocyte-specific modifications carried by H3.3. After fertilization, H3.2 is incorporated into the transcriptionally silent heterochromatin, whereas H3.1 and H3.3 occupy unusual heterochromatic and euchromatin locations, respectively. After the two-cell stage, H3.1 and H3.3 variants resume their usual respective locations on heterochromatin and euchromatin. Preventing the incorporation of H3.1 and H3.2 by knockdown of the histone chaperone CAF-1 induces a reciprocal increase in H3.3 deposition and impairs heterochromatin formation. We propose that the deposition of different H3 variants influences the functional organization of chromatin. Taken together, these findings suggest that dynamic changes in the deposition of H3 variants are critical for chromatin reorganization during epigenetic reprogramming

Mitochondrial dysfunction leads to telomere attrition and genomic instability

Mitochondrial dysfunction and oxidative stress have been implicated in cellular senescence, apoptosis, aging and aging-associated pathologies. Telomere shortening and genomic instability have also been associated with replicative senescence, aging and cancer. Here we show that mitochondrial dysfunction leads to telomere attrition, telomere loss, and chromosome fusion and breakage, accompanied by apoptosis. An antioxidant prevented telomere loss and genomic instability in cells with dysfunctional mitochondria, suggesting that reactive oxygen species are mediators linking mitochondrial dysfunction and genomic instability. Further, nuclear transfer protected genomes from telomere dysfunction and promoted cell survival by reconstitution with functional mitochondria. This work links mitochondrial dysfunction and genomic instability and may provide new therapeutic strategies to combat certain mitochondrial and aging-associated pathologies.<br/

ex vivo culture for preimplantation mouse embryo to analyse pluripotency

International audienceA couple of days after fertilization of a mouse oocyte by a sperm, two sequential cell differentiation events segregate pluripotent cells that can be identified by the presence of specific markers. Early mammalian embryos are relatively easy to recover as they are not yet implanted in the uterus matrix. Several decades of experimentation have enabled to find appropriate media to culture them, and therefore provide an excellent way to test different experimental set-up such as the use of signalling inhibitors. We provide here a commonly used protocol to culture preimplantation embryos as well as a method to detect pluripotent cells in blastocysts