Telencephalic eversion in zebrafish and comparison to mammals. The schematic illustrates how both the outward-growing (eversion) process of the developing telencephalon and its adult morphology of zebrafish (lower row) compares to the telencephalon development (evagination) of mammals (upper row). (A) The telencephalon develops from the anteriormost part of the neural tube. (B–E) In mammals, two bilateral hemispheres develop around a centrally located ventricle. Predominantly glutamatergic pallial zones (warm colors) develop in the dorsal telencephalon, whereas mostly GABAergic subpallial territories (cold colors) are found in the ventral telencephalon. (B’–E’) Likewise, in teleosts like zebrafish, the dorsal and ventral telencephalon, respectively, hold pallial and subpallial territories, however, the ventricle due to the eversion comes to lie on top of the brain. (C’,D’) Proliferation patterns, BrdU-long term labeling, and gene expression studies in zebrafish indicated a complex eversion process that includes a radial migration toward the dorsoposterior pallial (“Dp”) zone (Mueller et al., 2011). The zebrafish dorsal pallium (yellow) subsequently gets overgrown by the pallial amygdala and the medial pallium (MP in orange). (F’) The teleostean eversion process is not comprehensively understood. A major obstacle in the comprehensively understanding both the eversion and comparative anatomy remains the unsolved delineation of the integrative olfactory pallium (IOP – the putative homolog to the mammalian piriform cortex) and of telencephalic entities in the posteriormost extent. Ambiguous structures and focus of this study are colored in gray.
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