Parent-of-origin effects are 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. 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, the project aimed to explore a unique genomic system found in the mealybug Pseudococcus viburni: a “selfish” B chromosome that has acquired a way to escape from this genomic exclusion, therefore given itself the capability to be transmitted to the next generation regardless of parental origin.
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. Additionally, it has the potential to add new knowledge of applied value as gene inactivation under genetic conflict has been implicated in a wide range of human diseases and disorders.
The main objectives of the project were to dissect molecularly B chromosome escape from genomic exclusion, by 1) Obtain next generation sequencing data of populations of mealybugs carrying or not the B chromosome; 2) Identify candidate sequences specific to the B chromosome and potentially involved in B chromosome elimination; 3) Assess the epigenetic marks during B chromosome escape.
In conclusion, our project enabled to obtain the complete genome of B chromosome and its host mealybug, and identify potential candidates involved in its transmission to the next generation by circumventing Paternal Genome Elimination. Additionally, protocols were developed on an understudied insect system, yet of economic importance.
