Midbrains of atoh7 mutants are characterized by structural changes in the area of the optic tectum. (A) Dorsal views of representative wildtype and mutant brains. (B) Comparison of the relative area of specific brain parts compared to the area of the whole brain reveals that mutants possess a significantly larger telencephalon (Tel) but a significantly smaller optic tectum (TeO). In contrast, the cerebellum (Cb) displays no difference. (C) Representative cross sections of the optic tectum of wildtype and mutant stained with H&E. The TeO appears reduced in size and the PGZ appears to be thicker. The tectal ventricle (TeV) was also smaller in the mutant brain. (D) Cross section of a zebrafish optic tectum with tectum opticum (TeO, purple), periventricular grey zone (PGZ, red), lateral division of valvula cerebelli (Val), torus longitudinalis (TL), and brain stem (yellow). The red arrow represents the brain stem diameter used as reference. (E) Quantifications confirmed that the area of the TeO (relative to the area of the brain stem was significantly reduced in mutants. (F) The relative area of the PGZ (normalized to brain stem area) was not altered in mutants compared to wildtypes. (G) Quantification of the relative area of the TeV (normalized to the brain stem area) indicated a very strong reduction in mutants. (H) Representative cross sections of the optic tectum stained with H&E. In wildtype, six layers can be distinguished: pia mater (PM), stratum fibrosum marginale (SFM), stratum opticum (SO), stratum fibrosum et griseum superficiale (SFGS), stratum album centrale (SAC), and stratum periventriculare (SPV). In the mutant, no stratum opticum (SO) could be detected and stratum fibrosum et griseum superficiale (SFGS) appeared to be thinner. (I) Quantification of the relative thickness of the SFGS (normalized to brain stem diameter) confirmed a significant reduction in mutants. Scale bars represent 250 µm in overviews and 25 µm in close-ups. Statistics: all data are represented as mean ± SD, unpaired t-test, *P < 0.05; **P < 0.01; ***P < 0.001, or ****P < 0.0001.
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