Genetic systems and B chromosome

 

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DAPI stained Japanese mealybug embryos, with top embryo showing paternal genome condensation (bright spots) indicating a male embryo and where the paternal genome is eliminated during sperm formation. The female embryo (bottom) has heterogeneous staining due to both parental genomes being uncondensed and active.

Parent-of-origin effects are considered an important factor in the evolution and development of mammals and plants. Work on genomic imprinting has primarily focused on these two groups, yet reproduction in thousands of insect species involves an extreme form of imprinting known as “Paternal Genome Elimination” or PGE.

In this case, males recognise, silence and, during sperm formation, discard the chromosomes they inherited from their father. Only the mother’s chromosomes are inherited from the males. The molecular mechanisms responsible for parental origin recognition and process of elimination during sperm formation remain largely unknown.

To redress this, my current research project (BNPGE), funded by a Marie Skłodowska Curie Independent Fellowship, aims at exploring a unique genomic system found in the obscure mealybug Pseudococcus viburni: a “selfish” B chromosome that has acquired a way to escape from paternal genomic exclusion, therefore given itself the capability to be transmitted to the next generation regardless of parental origin.

Using comparative transcriptomic and genomic analyses, as well as epigenetic approaches, BNPGE proposes to dissect molecularly how this B chromosome escapes from genomic exclusion. This system provides a rare chance to acquire novel insights into the epigenetic mechanisms underlying the recognition and exploitation of a chromosome’s parental origin, a widespread and evolutionarily conserved yet under-appreciated phenomenon.