Teneurin evolution and brain-specific functions

Abstract

Teneurins are a novel family of type II transmembrane proteins. They are highly conserved from invertebrates to vertebrates, in which four paralogs exist, called teneurin-1 to -4. Their main expression site is the developing nervous system, where they are expressed in distinct non�overlapping patterns. Further studies suggest that they have important functions in many different developmental processes, mainly at sites of migration and pattern formation. The exact mechanism of action of the teneurins is still under investigation. However, it does involve homophilic interactions and the release of the intracellular domain from the membrane and its translocation into the nucleus. In the first part of the thesis, I am presenting a study of the possible evolutionary origins of teneurins, identifying a teneurin-like gene in the choanoflagellate Monosiga brevicollis. Furthermore, alternative splicing of the intracellular domain and conservation of nuclear localization sequences and protease cleavage sites were analyzed. In the second part of the thesis, I analyzed the transcriptional regulation of human teneurin�1, contributing to its patterned expression in the brain. I found a novel conserved alternate promoter, upstream of the annotated transcription start. The transcription factor Emx2 directly binds to a single conserved homeobox binding site in this novel promoter, in vitro and in vivo and Emx2 is able to activate teneurin-1 expression in reporter assays, as well as on the endogenous level. In the third part of the thesis, I investigated the homophilic interactions of teneurins, using an atomic force microscope (AFM) as a single cell force spectroscope (SCFS). This showed that the intracellular domain is essential for mediating adhesion forces, established by homophilic interactions by the extracellular domains. The NHL repeats of teneurins located in the large extracellular part between the EGF-like repeats and the YD-repeats are essential in discriminating homophilic versus heterophilic interactions. Finally, I could show that the homophilic interactions mediated by the NHL domains provide a signal for slowing down neurite outgrowth of Nb2a cells.