Mitochondrial heteroplasmy is the presence of more than one type of mitochondrial genome (mtDNA) within an individual, and in most of the reported cases it seems to be an unfavourable condition. For example, heteroplasmy in humans increases the risk of common age-related disorders as neurodegenerative diseases. The only evolutionarily stable and natural heteroplasmic system in Metazoa is the Doubly Uniparental inheritance (DUI), typical of some bivalves, in which two mitochondrial lineages are present: one transmitted through eggs (F-type) and the other through sperm (M-type). While females are homoplasmic for the F-type, males have M-type-homoplasmic gametes, but heteroplasmic soma. So far, no study has investigated mitochondrial heteroplasmy at the protein level, and no analysis has been performed to clarify if it is present at tissue, cell, or organelle level. We characterized the expression of three mitochondrially-encoded proteins (ND5, CYTB, COX3) in the DUI species Ruditapes philippinarum. Specific antibodies were produced to discriminate, with immunolocalization, between the F and M form of the same protein (variants highly divergent in DUI species) in germ line and somatic tissues of females and males in different developmental stages. Unexpectedly, M-type antibodies labelled mitochondria in female primordial stem cells (PriSCs), undifferentiated germ cells, and early oocytes, while mature eggs and female somatic cells expressed only the F-type. M- and F-type expression in male somatic tissues showed mitochondrial heteroplasmy at the cell level. Interestingly, F-labelled mitochondria were detected in male PriSCs and early germ cells. We hypothesize that PriSCs and undifferentiated germ cells carry both types of mtDNA, but during gamete maturation one of the two genomes disappears, and only the sexspecific mtDNA remains, maintaining the homoplasmy of the germ line. This would imply a selective degradation of mitochondria in adulthood.
Level of mitochondrial heteroplasmy in a natural and stable heteroplasmic system
CIFALDI, CARMINE;PECCI, ANDREA;GHISELLI, FABRIZIO;PASSAMONTI, MARCO;FRANCESCHINI, VALERIA;MAURIZII, MARIA GABRIELLA;MILANI, LILIANA
2017
Abstract
Mitochondrial heteroplasmy is the presence of more than one type of mitochondrial genome (mtDNA) within an individual, and in most of the reported cases it seems to be an unfavourable condition. For example, heteroplasmy in humans increases the risk of common age-related disorders as neurodegenerative diseases. The only evolutionarily stable and natural heteroplasmic system in Metazoa is the Doubly Uniparental inheritance (DUI), typical of some bivalves, in which two mitochondrial lineages are present: one transmitted through eggs (F-type) and the other through sperm (M-type). While females are homoplasmic for the F-type, males have M-type-homoplasmic gametes, but heteroplasmic soma. So far, no study has investigated mitochondrial heteroplasmy at the protein level, and no analysis has been performed to clarify if it is present at tissue, cell, or organelle level. We characterized the expression of three mitochondrially-encoded proteins (ND5, CYTB, COX3) in the DUI species Ruditapes philippinarum. Specific antibodies were produced to discriminate, with immunolocalization, between the F and M form of the same protein (variants highly divergent in DUI species) in germ line and somatic tissues of females and males in different developmental stages. Unexpectedly, M-type antibodies labelled mitochondria in female primordial stem cells (PriSCs), undifferentiated germ cells, and early oocytes, while mature eggs and female somatic cells expressed only the F-type. M- and F-type expression in male somatic tissues showed mitochondrial heteroplasmy at the cell level. Interestingly, F-labelled mitochondria were detected in male PriSCs and early germ cells. We hypothesize that PriSCs and undifferentiated germ cells carry both types of mtDNA, but during gamete maturation one of the two genomes disappears, and only the sexspecific mtDNA remains, maintaining the homoplasmy of the germ line. This would imply a selective degradation of mitochondria in adulthood.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
