The zebrafish mutant vps18 as a model for vesicle‐traffic related hypopigmentation diseases

Abstract

Hypopigmentation is a characteristic of several diseases associated with vesicle traffic defects, like the Hermansky-Pudlak, Chediak-Higashi, and Griscelli syndromes. Hypopigmentation is also a characteristic of the zebrafish mutant vps18(hi2499A), which is affected in the gene vps18, a component of the homotypic fusion and protein sorting complex that is involved in tethering during vesicular traffic. Vps18, as part of this complex, participates in the formation of early endosomes, late endosomes, and lysosomes. Here, we show that Vps18 is also involved in the formation of melanosomes. In the zebrafish mutant vps18(hi2499A) the retroviral insertion located at exon 4 of vps18, leads to the formation of two abnormal splicing variants lacking the coding sequence for the clathrin repeat and the RING finger conserved domains. A deficiency of Vps18 in zebrafish larvae results in hepatomegaly and skin hypopigmentation. We also observed a drastic reduction in the number of melanosomes in the eye's retinal pigmented epithelium along with the accumulation of immature melanosomes. A significant reduction in the vps18(hi2499A) larvae visual system capacity was found using the optokinetic response assay. We propose that the insertional mutant vps18(hi2499A) can be used as a model for studying hypopigmentation diseases in which vesicle traffic problems exist.

Zebrafish mutations ingartandpaicsidentify crucial roles for de novo purine synthesis in vertebrate pigmentation and ocular development

“…This lighter appearance could result from decreases in overall melanin levels, or from defects in melanosome distribution within mutant pigment cells. To differentiate between these possibilities we utilized a biochemical purification method to quantify melanin levels at 3.5 dpf and 5 dpf (Maldonado et al, 2006). At both times, gart and paics mutants possessed significantly less melanin (see Fig.…”

“…Melanin quantification was performed as described in Maldonado et al (Maldonado et al, 2006). At least 20 embryos were analyzed per trial, and 2-6 trials were performed using different clutches of embryos.…”

snow white, a Zebrafish Model of Hermansky-Pudlak Syndrome Type 5

“…Pigment is first observed in the embryo at $24 hpf, and hypopigmentation mutants are easily identified soon thereafter. To this end, several zebrafish mutants, including fading vision (fdv; pmel17), fade out (fad; unknown locus), platinum (plt; vps11), vps18, and leberknodel (lbk; vps39), have already been characterized for LRO dysfunction; Pmel17 is critical for melanosome formation, as described above, and vps11, vps18, and vps39 are part of the HOPS complex required for vesicle fusion and tethering (Schonthaler et al 2005(Schonthaler et al , 2008Bahadori et al 2006;Maldonado et al 2006;Thomas et al 2011;see Navarro et al 2008 for review). Given the ability to perform forward genetic screens in zebrafish, the relative ease of cloning mutations from these screens (Bibliowicz et al 2011;Gestri et al 2012;Obholzer et al 2012), and the ability to generate targeted mutations (Cade et al 2012; Dahlem et al 2012;Moore et al 2012;Blackburn et al 2013;Hwang et al 2013), the identification and generation of additional zebrafish models of human albinism disorders should provide a promising complement through which the molecular and cellular underpinnings of these disorders can be elucidated.…”

“…The average amount of melanin in total fish was determined as described (Maldonado et al 2006). Briefly, embryos were dechorionated, pooled (n = 30 embryos/stage, three biological replicates) in 350 ml homogenization buffer (20 mM TrisÁHCl, 2 mM EGTA, 1 mM PMSF), and homogenized with a 25-gauge syringe.…”

Identification and Characterization of Gene Expression Involved in the Coloration of Cichlid Fish Using Microarray and qRT-PCR Approaches

“…In addition, in zebrafish, Copz mutants show a reduction in the retinal pigmented epithelium (Gross et al 2005). In addition, the mutation of three other vesicle trafficking genes in zebrafish is known to result in pronounced hypopigmentation as well as retinal defects (Maldonado et al 2006). As it is thought that pigment granules are synthesized through transport between the endosome and the Golgi, Copz might be involved in the yellow coloration of female PS.…”