Novel mtDNA-encoded proteins and mitochondrial sex determination in the Bivalvia (Mollusca)

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Mitochondria (mt) are known as the "powerhouses of the cell" because they are responsible for most of the energy production in animal cells. They contain their own DNA (mtDNA), which codes for 13 proteins that are involved in energy production. Mutations in mtDNA are responsible for several human diseases including diabetes and cancer. The inheritance of mtDNA in animals has long been believed to be strictly maternal until the discovery of a radically different Doubly Uniparental Inheritance (DUI) system in bivalved mollusks. In DUI, maternal F mtDNA is transmitted to daughters and sons and paternal M mtDNA is transmitted to sons (F vs. M DNA divergence >40%). Breton et al. recently discovered novel (in addition to the typical set of 13) sex-specific mt-encoded proteins in bivalves with DUI, and demonstrated that these proteins are exported from the mitochondria and likely play a role in sex determination. These results are of great value because they show that animal mtDNAs have a larger functional repertoire than previously thought and represent the first case of mtDNA-based sex determination in animals. This challenges textbook biology which state that mt-encoded proteins are uniquely found inside mitochondria to assist in energy production. However, the mechanisms underlying DUI and sex determination are still unknown and the cause of deviation from the strict maternal inheritance rule in bivalves remains an open question. The proposed research aims to better understand (i) the origin and evolution of DUI and the new mt-encoded genes and (ii) the genetic mechanisms that govern DUI and sex determinations in bivalves. This project investigates innovative and potentially transformative ideas in mitochondrial research that will interest a wide range of scientists exploring the fields of organellar inheritance, intergenomic conflict, and evolution of sex determination. It will provide the basis for the development of genetic markers for the manipulation of sex determination for selective breeding programs of economically important bivalves. This work will also shed light on the origin and functions of novel mt-encoded genes and could eventually have medical implications for therapy of mitochondrial diseases.