Zebrafish as a Model Organism to Study the <em>In Vivo</em> Role of G-Protein Coupled Receptor 17 in Myelination

Abstract

The sheathing of axons with myelin by oligodendrocytes constitutes a necessity for sufficient and rapid nerve conduction within the vertebrate central nervous system (CNS). However to date, the complex molecular mechanisms controlling distinct signalling cascades of myelination are still not decrypted. Recent studies have proposed G-protein coupled receptors (GPCRs), such as Gpr17, as crucial regulators of oligodendrocyte development and myelination. Herein, this study investigates the implication of Gpr17 in myelination in its native signalling environment by using zebrafish (Danio rerio), an ideal suited vertebrate model system for studying myelination in vivo. Additionally, further functionality studies evaluate responsiveness of zebrafish and chimeric human/zebrafish Gpr17 receptors in extrinsic mammalian cellular backgrounds.<br /> While zebrafish Gpr17 transiently transfected in HEK293 cells remained unresponsive towards the small molecule agonist MDL29,951, stimulation of chimeric human/zebrafish receptors containing the human binding domain led to concentration-dependent response curves in Dynamic mass redistribution assays. These results, further confirmed by in vivo assays revealing unaffected oligodendrocyte development and myelination after bath treatment with MDL29,951, imply an impaired zebrafish receptor-ligand interaction both in vivo and in vitro. Investigations with zebrafish demonstrated sustained Gpr17 expression in oligodendrocyte lineage cells during CNS development from 1 to 5 dpf. Moreover, morpholino-induced receptor knockdown provoked a significant reduction of pre-mature and mature oligodendrocyte numbers and disturbed myelination. The reduced cell numbers are assumed to result from impaired migration of pre- mature pre-oligodendrocytes (pre-OLs) accumulating in the ventral spinal cord region. On the contrary, overexpression of Gpr17 in early stages did not influence oligodendrocyte development. Together, the data confirm a crucial role of zebrafish Gpr17 in vivo. Clearly, future studies with knockout animals are strictly necessary to corroborate these findings and conclusively delineate the impact of Gpr17 on oligodendrocyte development and myelination.