Epigenetic silencing of transposable elements in Lake Malawi cichlids

Proper regulation of transposable elements (TEs) by Piwi-interacting RNAs (piRNAs) is critical for fertility and embryogenesis in animals.

Because TEs need to evade silencing to replicate, they are engaged in an evolutionary arms race-type of genetic conflict with their host.

These arms races between TEs and the piRNA pathway result in rapid evolution of piRNAs and piRNA regulatory factors, which in turn leads to genetic incompatibilities observable in interspecific hybrids that are relevant to speciation.

New evidence supports the fast evolution of piRNA pathway factors in the cichlid radiation of Lake Malawi, where 800-1000 different species have evolved in only 800,000-years.

The main objective of TSILENCICH is to understand how TEs and piRNAs co-evolved in these animals, throughout their explosive diversification.I have recently identified an expansion of piRNA pathway factors in Lake Malawi cichlids.

While these factors are enriched in the germline in most metazoan species, in cichlids these genes exhibit remarkably higher expression in the brain, suggesting novel functions.

I will construct new tools to test if piRNAs regulate the expression of TEs in the cichlid brain, and what role this regulation might play in brain development.In addition, I will test the hypothesis that TE epigenetic silencing is compromised in cichlid interspecific hybrids, utilizing A. calliptera and Tropheops sp. mauve, two cichlids with distinct eco-morphological and behavioural characteristics, and their hybrids.

I will profile the epigenetic landscape in the parental species, as well as in fertile F1 and F2 hybrids, to investigate if TE expression becomes progressively more imbalanced across generations.

The proposed work will shed light on the origin of piRNA pathway/TE conflicts and on novel somatic piRNA-driven TE epigenetic silencing in vertebrates.