LINE elements as mediators of genomic variability and neuronal plasticity in the brain: development of a zebrafish model
Zusammenfassung der Projektergebnisse
We have developed a zebrafish (Danio rerio) model to get insight into a major recent discovery in human biology: due to the activity of Transposable Elements (TE), the genome of our brain is a mosaic. TEs are considered a type of ‘selfish’ DNA elements, whose only function in our genome is to accumulate new copies of themselves to further be distributed in the population. Among them, LINEs (Long INterspersed Element) and SINEs (Short INterspersed Element) continue to be mobilized in the genome in a significant number of species. The activity of TEs can impact the genome in a myriad of ways, by accumulating heritable new insertions in the germ line. Surprisingly, recent reports have demonstrated the existence of a significant load of somatic LINE/SINE mobilization in selected somatic tissues of human, rodent and more recently fly species. The activity of TEs in the human brain (as shown by the Garcia Perez lab and others, or other somatic tissues represents a paradigm shift for a type of selfish DNA, as its somatic activity is inconsistent with the idea of a piece of selfish DNA. As a consequence, the genome of our brain is a mosaic, although any derived regulatory function, if any, remains to be determined. To further explore the impact of the somatic activity of TEs, we have developed a zebrafish (Danio rerio) model to study the somatic mobilization of zebrafish engineered LINEs in vivo. Thus, we are currently using this model to answer the following questions: 1) Are LINE elements active in somatic tissues of organisms other than humans? I.e. is zebrafish LINE-2 actively retrotransposing in the zebrafish somatic tissues? 2) Does the retrotransposition rate change during development? What is the retrotransposition rate in the different tissues? What is the retrotransposition rate in the central nerval system (CNS)? 3) What’s the impact of LINE activity in the CNS of zebrafish? 4) Does LINE activity in the CNS of zebrafish have any phenotypic consequence?. Briefly, our preliminary results show that endogenous zebrafish LINE-2s are expressed during early embryogenesis in all cells, and later get restricted to skin, neural tissues and inner organs. In larval stages, the expression becomes restricted to brain and inner organs. Engineered LINE-2 retrotransposition during early embryonic stages is taking place in several neural tissues (hindbrain and neural tube, as well as in eye tissue), but also in other somatic tissues like skin, gut, and muscles. The ongoing experiments will shed light on when the observed somatic activity is occurring during development, and which tissues (ecto-, meso-, or endoderm) are showing LINE activity at a certain developmental stage. We will investigate especially the possible somatic activity in later stages. We are further mapping new insertions in the different tissues in order to be able to draw functional conclusions on the real impact these insertions may have.
