Confocal micrograph of the head region of a transgenic zebrafish embryo. The large circular structure is the eye, showing the structure of the retina. Some neurons in the brain are highlighted in green by GFP expressed under the control of a specific promoter Dlx4/6. The DLX proteins are postulated to play a role in forebrain and facial development. Therefore, the GFP is only 'switched on' in developing neurons that require this gene. The microtubules in neuronal processes have been labelled using an antibody for tubulin (red).