TSILENCICH · Epigenetic silencing of transposable elements in Lake Malawi cichlids

Epigenetic silencing of transposable elements in Lake Malawi cichlids

Transposable elements (TEs), also known as “jumping genes”, are mobile genetic elements able to mobilise from one piece of DNA into another. The mobilisation of TEs can generate genome instability and DNA damage. To counteract the detrimental effects of their mobilisation, TEs must be silenced. Several molecular pathways have evolved in animal germ cells, cells that differentiate into gametes, to silence TEs, thus protecting future generations from genomic instability derived from TE mobilisation. A specific class of small RNAs that interact with Piwi Argonaute proteins, termed Piwi-interacting RNAs (piRNAs), is a major driver of TE silencing in animal germ cells and is generally required for animal fertility. The antagonistic relationship between TEs and TE silencing factors of the host leads to an evolutionary arms race and fast evolution of both opposing components. These interactions and fast evolution can create reproductive incompatibilities that may act as barriers to hybridisation. Cichlid fishes of the East African Great Lakes and surrounding bodies of water are the most species-rich adaptive radiation in vertebrates. This means this group of animals has diverged explosively, into approximately two thousand species, in East Africa in the last ten million years. These fishes have adapted to all the available niches in the lakes and rivers of East Africa, acquiring along the way tremendous variation in morphology, colour, diet, and behaviour. The genetic and molecular basis of cichlid phenotypic diversity remains a topic of great interest to understand how organisms adapt fast and speciate. Furthermore, tilapias are a non-radiating assemblage of African cichlids related to the radiating cichlid lineages in East Africa. As the second most produced group of fish in aquaculture worldwide, tilapias comprise a fish group with great economic importance. Genomic studies of East African cichlids have uncovered recurrent hybridisation during the evolutionary history of the radiations. In fact, hybridisation has been proposed to fuel the radiations. This project sought to discover how cichlids tolerate hybridisation, particularly regarding TE regulation by the piRNA pathway. First, we have conducted important groundwork to understand the transcriptional activity of TEs in cichlids as well as their epigenetic silencing by the piRNA pathway. We have performed reciprocal crosses between two cichlid species of Lake Malawi and found a degree of embryonic lethality in the F2 hybrid generation, consistent with post-zygotic incompatibilities. We are dissecting the molecular basis of the embryonic lethality, as well as its accompanying developmental defects. In conclusion, the scientific objectives of TSILENCICH successfully illuminate how animals tolerate genetic conflict and genetic incompatibilities. The training objectives of TSILENCICH were also achieved, providing a substantial positive impact in the researcher’s career. Given the current pressure exerted on biodiversity by fast climate change, it is important to understand how animals adapt to their environment and the molecular drivers or barriers to adaptation.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз