Retinomotor movements are morphological changes in the outer retina in response to changing light conditions. They can be separated into two components: Migration of pigment granules within the microvilli of the retinal pigment epithelium (RPE) and positional changes in photoreceptor cells. These positional changes optimize exposure of the cone and rod photoreceptors to light. The aim of this study was to analyze both the time course of retinomotor movements in the adult zebrafish and the maturation of these processes in the developing fish. We show that retinomotor movements are used as a dark/light adaptation mechanism in zebrafish. In adult zebrafish, melanin granules of the RPE migrate with constant speed and reach the fully light adapted (LA) state approximately after 1h. In contrast, about two thirds of double cone outer segment movements are finished in 5min, and are fully completed in 10 to 20min. During development there are three crucial stages leading to mature retinomotor movements in response to light: at 5dpf (days post fertilization) the migration of pigment granules begins, at 20dpf the pigment granules condense in the apical part of the RPE microvilli, and at 28dpf, concomitant with the functional maturation of rods, the double cones contract as in adult retinas. Anat Rec Part A, 288A: 653-662, 2006.

The development of the eye lens is one of the classical paradigms of induction during embryonic development in vertebrates. But while there have been numerous studies aimed at discovering the genetic networks controlling early lens development, comparatively little is known about later stages, including the differentiation of secondary lens fibre cells. The analysis of mutant zebrafish isolated in forward genetic screens is an important way to investigate the roles of genes in embryogenesis. In this study we describe the zebrafish mutant bumper (bum), which shows a transient, tumour-like hyperproliferation of the lens epithelium as well as a progressively stronger defect in secondary fibre cell differentiation, which results in a significantly reduced lens size and ectopic location of the lens within the neural retina. Interestingly, the initial hyperproliferation of the lens epithelium in bum spontaneously regresses, suggesting this mutant as a valuable model to study the molecular control of tumour progression/suppression. Behavioural analyses demonstrate that, despite a morphologically normal retina, larval and adult bum(-/-) zebrafish are functionally blind. We further show that these fish have defects in their craniofacial skeleton with normal but delayed formation of the scleral ossicles within the eye, several reduced craniofacial bones resulting in an abnormal skull shape, and asymmetric ectopic bone formation within the mandible. Genetic mapping located the mutation in bum to a 4cM interval on chromosome 7 with the closest markers located at 0.2 and 0cM, respectively.

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