Poster Session 1 - R3
1,2Kyunga Kim, 1,2,3Andrea Jurisicova
1 Dept. of Physiology, University of Toronto; 2 Lunenfeld-Tananbeum Research Institute, Sinai Health System, Toronto, Canada, 3 Dept. of Obstetrics and Gynecology, University of Toronto, Toronto, ON, Canada
While it is well known that women experience a decline in fertility as they age, the cellular pathways that underlie this phenomenon are unclear. Our lab has previously shown that down-regulation of biosynthesis of coQ, a lipophilic molecule crucial for mitochondrial function, may contribute to the diminished oocyte and embryo quality observed with age. To further study the role of coQ in female fertility, we created a mouse line with an oocyte-specific deletion of Pdss2, a component of the coQ biosynthetic pathway. We have found that similar to aged embryos, developmental potential of preimplantation embryos from Pdss2-deficient females is poor. A significant proportion is unable to progress past the 2 to 4 cell stage. The objective of the study was to understand why Pdss2 deficiency leads to embryo development arrest. We observed that markers of mitochondrial mass and function were generally decreased in Pdss2-deficient 2-cell embryos. In addition to assessing mitochondria, we also explored whether a lack of maternal-zygotic transition (MZT) may contribute to poor developmental rates. MZT is a crucial event in embryogenesis during which transcription of the embryonic genome is initiated and maternal factors are degraded. As embryos that fail to undergo MZT arrest during cleavage stages of embryogenesis, we reasoned Pdss2-deficient embryos might also have MZT defects. We first tested whether Pdss2-deficient embryos cannot degrade maternal factors by measuring markers of autophagy. LysoTracker staining showed no significant changes in lysosomal function. However, p62 levels were increased in Pdss2-deficient 2-cells, indicating potential lack of autophagy. We also observed significantly decreased levels of H3K27me3, a histone modification that facilitates proper embryonic genome activation, in Pdss2-deficient embryos. We thus have found some evidence that improper MZT may underlie poor developmental potential in Pdss2-deficient embryos in addition to mitochondrial dysfunction. Quantitation of mRNA levels of embryonic genes via qRT-PCR is currently underway to confirm that embryonic genome activation is affected in Pdss2-deficient embryos,