Telencephalic eversion in embryos and early larvae of four teleost species

1. The telencephalon of ray-finned fishes undergoes eversion, which is very different to the evagination that occurs in most other vertebrates. Ventricle morphogenesis is key in order to build an everted telencephalon. Thus, here we use the apical marker zona occludens 1 (ZO1) to understand ventricle morphology, extension of the tela choroidea and the eversion process during early telencephalon development of four teleost species: giant danio ( Devario aequipinnatus), blind cavefish (Astyanax mexicanus), medaka (Oryzias latipes) and paradise fish ( Macroposus opercularis). In addition, by using immunohistochemistry against tubulin and calcium binding proteins, we analyse the general morphology of the telencephalon, showing changes in the location and extension of the olfactory bulb and other telencephalic regions from 2 to 5 days of development. We also analyse the impact of abnormal eye and telencephalon morphogenesis on eversion, showing that cyclops mutants do undergo eversion despite very dramatic abnormal eye morphology. We discuss how the formation of the telencephalic ventricle in teleost fish, with its characteristic shape, is crucial event during eversion.