MDR-1 is a transmembrane ATP-dependent effluxer present in organs that transport a variety of xenobiotics and byproducts. Previous findings by our group demonstrated that this transporter is also present in the oocyte mitochondrial membrane and that its mutation led to abnormal mitochondrial homeostasis. Considering the importance of these organelles in the female gamete, we assessed the impact of MDR-1 dysfunction on mouse oocyte quality, with a particular focus on the meiotic spindle organization, aneuploidies, Ca2+ homeostasis, ATP production and mtDNA mutations. Our results demonstrate that young Mdr1 mutant mice produce oocytes characterized by lower quality, with a significant delay in the germinal vesicle (GV) to germinal vesicle breakdown (GVBD) transition, an increased percentage of symmetric divisions, chromosome mis-alignments and a severely altered meiotic spindle shape compared to the wild types. Mutant oocytes exhibit 7000 more single nucleotide polymorphisms (SNPs) in the exomic DNA and twice the amount of mitochondrial DNA SNPs compared to the wild-type ones. Ca2+ analysis revealed the inability of MDR-1 mutant oocytes to manage Ca2+ storage content and oscillations in response to several stimuli and ATP quantification shows that mutant oocytes trend towards lower ATP levels compared to wild types. Finally, 1-year-old mutant ovaries express a lower amount of Sirt1, Sirt3, Sirt5, Sirt6 and Sirt7 compared to wild type levels. These results, together emphasize the importance of MDR-1 in mitochondrial physiology and highlight the influence of MDR-1 on oocyte quality and ovarian aging.

The discovery of PLCζ1 nearly twenty years ago as the primary Ca2+ oscillation inducing factor in the sperm of mammals represented a significant breakthrough in our quest to elucidate the molecules and pathways that promote egg activation during fertilization. The advent of the Intracytoplasmic Sperm Injection technique, which made fertilization possible without sperm capacitation, acrosome reaction, and gamete fusion, strengthened the research that led to the discovery of PLCζ1 and became an essential clinical tool for humans. The use of ICSI combined with the detection of PLCζ1 expression and mutations in infertile patients established the fundamental role of PLCζ1 in human fertility while leading to the discovery of novel components of the perinuclear theca, the site of the residence of PLCζ1 in sperm before fertilization. Remarkably, the more extensive use of ICSI in species other than humans and mice revealed poor success and exposed gaps in our understanding of PLCζ1 release and/or activation. Similarly, fertilization using sperm from mouse models lacking PLCζ1 has produced striking results whose true implications are yet to be determined. Nevertheless, answers to these unresolved questions will produce a complete picture of the adaptations and molecular players that mammalian species employ to ensure the success of the triggering event of embryo development that has linked generations since the beginning of times.

Early development and differentiation require precise control of cellular functions. Lysosomal degradation is a critical component of normal cellular homeostasis, allowing for degradation of signaling molecules, proteins, and other macromolecules for cellular remodeling and signaling. Little is known about the role of lysosomal function in mammalian embryos before gastrulation. Borcs6 is a protein involved in lysosomal trafficking as well as endo‐lysosomal and autophagosome fusion. Here, we show that Borcs6 is necessary for efficient endo‐lysosomal degradation in the early embryo. Although embryos lacking Borcs6 are developmentally comparable to control littermates at E5.5, they are characterized by large cells containing increased levels of late endosomes and abnormal nuclei. Furthermore, these embryos display a skewed ratio of extraembryonic and embryonic cell lineages, are delayed by E6.5, and do not undergo normal gastrulation. These results demonstrate the essential functions of lysosomal positioning and fusion with endosomes during early embryonic development and indicate that the early lethality of BORCS6 mutant embryos is primarily due to defects in the HOPS‐related function of BORC rather than lysosomal positioning.

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