*EASTBIO* How males lose their father’s genes: genomic imprinting in insects

For most organisms, the two copies of a gene - one from their mother, the other from their father - are interchangeable. But sometimes this rule is violated. In a process called genomic imprinting the expression of one of the two copies of a gene is privileged, depending on its parental origin. Genomic imprinting is studied extensively in mammals and plants and most biologists consider it exclusive to these groups. In fact imprinting was first discovered in a different group, the insects, in the 1950s, decades before its discovery elsewhere [1]. Since then however, the instances of genomic imprinting in insects have hardly been addressed and are unknown to most biologists.

The occurrence of genomic imprinting in insects is striking, as it involves a whole genome rather than just a couple of hundred genes as in mammals and plants. In males all genes inherited from his father are first silenced and subsequently eliminated from his sperm. So males only express and pass on their mothers genes to their offspring. This process seems regulated by some of the same epigenetic machinery (methylation, histone modification) [2] as imprinting in mammals but many questions remain: How is the parental origin of chromosomes recognized? How are the chromosomes marked, by which parent and at which stage in development? Why does imprinting only happen in males? Is the genomic imprinting also involved in sex determination?

Understanding the mechanisms of imprinting in these insects will allow for a better understanding of the evolution of this phenomenon, which is found in 10.000s of insects and has evolved repeatedly in different insect orders. Furthermore this study will provide insight in which aspects of the imprinting machinery are evolutionarily conserved across all animals.

This project will use an interdisciplinary approach and a promising new study system: the citrus mealybug (Planococcus citri), a small plant-feeding insect. The project will use next generation sequencing approaches [3] and cytogenetic techniques to study how the distribution of epigenetic modifications across the genome differs between maternal and paternal chromosomes in males and females. And manipulate these modifications (by knocking out the responsible genes) to study the phenotypic effects on genomic imprinting and sex determination.

The project will be supervised by Dr. Laura Ross (Edinburgh, http://lauraross.bio.ed.ac.uk) and Prof. Mike Ritchie. Ross is an evolutionary biologist who uses a combination of genomic and empirical approaches to study insect reproduction. Ritchie (St Andrews) is a leading expert on molecular and evolutionary genetics.

For informal enquiries contact Dr Laura Ross at [Email Address Removed].