Mitochondrial RNA defense pathways in the oocyte

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Abstract Maternal aging has dramatic effects on the oocyte quality and competence, and it is well known that mitochondrial function plays important roles in oocyte health. Post-transcriptional gene regulation within the oocyte is also essential for its normal development and function. In somatic cells, mitochondria are key effectors of post-transcriptional gene regulation, where RNA sensors located on the mitochondria react in response to double stranded RNA (dsRNA) to invoke the mitochondrial RNA defense pathway. The role of the mitochondrial defense pathway, which includes RNA-editing and RNA sensing is unknown in the oocyte, even though the oocyte has an abundance of dsRNA within it. Here we provide preliminary data demonstrating an abundance of RNA edits in mouse and human oocytes, the expression of `adenosine deaminase acting on RNA' (ADAR), as well as downstream components of the RNA sensing pathway in mouse and human oocytes. Most importantly, we show that inhibition of ADAR RNA editing in oocytes results in increased accumulation of reactive oxygen species (ROS), thus implicating RNA editing as a regulator of mitochondrial function and possibly oocyte quality. Lastly, data from reproductively old mice indicate that the genes involved in RNA editing (ADAR1) and RNA sensing (p32) are decreased in oocytes, thus potentially leading to aberrant activation of mitochondrial RNA-dependent defense pathway. We propose that oocyte mitochondria are key effectors of the RNA editing and RNA sensing mechanisms within oocytes, under conditions such as aging, hyper-activity of mitochondrial RNA defense may increase ROS accumulation and ultimately impact oocyte quality. The central hypothesis we intend to test in this proposal is that the mitochondrial RNA defense pathway is a critical regulator of oocyte competence/quality. To test the central hypothesis, Specific Aim 1 will identify the specific oocyte RNA edits occurring in three species of mammalian oocytes. Specific Aim 2 will determine the role of ADAR1 and RIG-I/MAVS in the regulation of mitochondrial function in oocytes using state-of-the-art mitochondrial functional assays and assess the impact on oocyte quality/developmental potential. Specific Aim 3 will examine how advanced reproductive age impacts mitochondrial RNA sensing pathways in both mouse and human oocytes. Ultimately, this work may provide a mechanistic link (dsRNA defense pathway) that can explain the known mitochondrial dysfunction associated with oocytes from reproductively old mice and older IVF patients.