Meeting Abstract
Heteroplasmy is the presence of more than one type of mitochondrial genome within an individual, a condition commonly reported as unfavourable and affecting mitonuclear interactions. So far, no study has investigated heteroplasmy at the protein level, and whether it occurs within tissues, cells, or organelles. The only known evolutionarily stable and natural heteroplasmic system in Metazoa is the Doubly Uniparental Inheritance (DUI), reported so far in ~100 bivalve species, in which two mitochondrial lineages are present: one transmitted through eggs (F-type) and the other through sperm (M-type). Because of such segregation, the mitochondrial OXPHOS proteins reach a high sequence divergence (up to 52%) between the two lineages in the same species. Gamete homoplasmy allows to compare the biochemical activity and the evolutionary features of the two sex-linked variants, and the high sequence divergence between F- and M-type proteins provides a unique opportunity to study their expression and assess level and extent of heteroplasmy. Immunolocalization showed heteroplasmy at the organelle level in undifferentiated germ cells of both sexes, and in male soma. Thus, during gametogenesis only the sex-specific mitochondrial variant is maintained, possibly due to meiotic drive and/or selection of a specific phenotype (such as membrane potential or membrane tag). Molecular and phylogenetic evidence suggests that DUI evolved from the common strictly maternal inheritance, so the two systems share the same underlying molecular mechanism, making DUI a useful system for studying mitochondrial biology.
