Habenular nucleus, zebrafish

This figure shows an abnormally symmetric habenular nucleus of a mutant zebrafish embryo 4 days post-fertilization. The habenular nucleus is a part of the epithalamus which connects the limbic system (responsible for instinct and mood) to other regions of the brain. The arrangement of the habenular axons is highlighted in cyan and a subtype of neurons normally enriched in the left epithalamus is highlighted in magenta. In wild-type embryos, different neuronal subtypes, with a typical molecular signature and neural connectivity pattern, are produced in different ratios in the left and right habenular nucleus thus conferring a unique asymmetric nature. Nevertheless, there are naturally occurring mutants where this pattern of asymmetry is disrupted. These mutants are used as invaluable tools to understand the molecular mechanisms governing brain lateralization during embryonic development. Width of image is 200 micrometres.