The deafness gene dfna5 is crucial for ugdh expression and HA production in the developing ear in zebrafish.
ABSTRACT Over 30 genes responsible for human hereditary hearing loss have been identified during the last 10 years. The proteins encoded by these genes play roles in a diverse set of cellular functions ranging from transcriptional regulation to K(+) recycling. In a few cases, the genes are novel and do not give much insight into the cellular or molecular cause for the hearing loss. Among these poorly understood deafness genes is DFNA5. How the truncation of the encoded protein DFNA5 leads to an autosomal dominant form of hearing loss is not clear. In order to understand the biological role of Dfna5, we took a reversegenetic approach in zebrafish. Here we show that morpholino antisense nucleotide knock-down of dfna5 function in zebrafish leads to disorganization of the developing semicircular canals and reduction of pharyngeal cartilage. This phenotype closely resembles previously isolated zebrafish craniofacial mutants including the mutant jekyll. jekyll encodes Ugdh [uridine 5'-diphosphate (UDP)-glucose dehydrogenase], an enzyme that is crucial for production of the extracellular matrix component hyaluronic acid (HA). In dfna5 morphants, expression of ugdh is absent in the developing ear and pharyngeal arches, and HA levels are strongly reduced in the outgrowing protrusions of the developing semicircular canals. Previous studies suggest that HA is essential for differentiating cartilage and directed outgrowth of the epithelial protrusions in the developing ear. We hypothesize that the reduction of HA production leads to uncoordinated outgrowth of the canal columns and impaired facial cartilage differentiation.
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ABSTRACT: Zebrafish (Danio rerio) remains a versatile model organism for the investigation of early development and organogenesis, and has emerged as a valuable platform for drug discovery and toxicity evaluation [1-6]. Harnessing the genetic power and experimental accessibility of this system, three decades of research have identified key genes and pathways that control the development of multiple organ systems and tissues, including the heart, kidney, and craniofacial cartilage, as well as the hematopoietic, vascular, and central and peripheral nervous systems [7-31]. In addition to their application in large mutagenic screens, zebrafish has been used to model a variety of diseases such as diabetes, polycystic kidney disease, muscular dystrophy and cancer [32-36]. As this work continues to intersect with cellular pathways and processes such as lipid metabolism, glycosylation and vesicle trafficking, investigators are often faced with the challenge of determining the degree to which these pathways are functionally conserved in zebrafish. While they share a high degree of genetic homology with mouse and human, the manner in which cellular pathways are regulated in zebrafish during early development, and the differences in the organ physiology, warrant consideration before functional studies can be effectively interpreted and compared with other vertebrate systems. This point is particularly relevant for glycosylation since an understanding of the glycan diversity and the mechanisms that control glycan biosynthesis during zebrafish embryogenesis (as in many organisms) is still developing.Nonetheless, a growing number of studies in zebrafish have begun to cast light on the functional roles of specific classes of glycans during organ and tissue development. While many of the initial efforts involved characterizing identified mutants in a number of glycosylation pathways, the use of reverse genetic approaches to directly model glycosylation-related disorders is now increasingly popular. In this review, the glycomics of zebrafish and the developmental expression of their glycans will be briefly summarized along with recent chemical biology approaches to visualize certain classes of glycans within developing embryos. Work regarding the role of protein-bound glycans and glycosaminoglycans (GAG) in zebrafish development and organogenesis will also be highlighted. Lastly, future opportunities and challenges in the expanding field of zebrafish glycobiology are discussed.Glycoconjugate Journal 05/2012; · 1.88 Impact Factor
- Journal of Urology - J UROL. 01/2011; 185(4).
Chapter: Chapter 9 Less-Common Techniquespages 445-471;