Disruptions in the development of the eye field result in defects such as microphthalmia (small eye) or anophthalmia (single eye or no eyes) ( Loosli et al., 2003 Voronina, 2003). Cells within this eye field express known eye field transcription factors (EFTFs) including Pa圆, Rax, Otx2, Six3, and Lhx2, among others the eye field contains all necessary progenitor cells to form the neural portions of the eye ( Zuber et al., 2003). 2 Vertebrate ocular developmentĭevelopment of the vertebrate eye and ocular structures is a result of the organized interactions of neuroectoderm (forms the retina and retinal pigment epithelium), surface ectoderm (forms the lens), and periocular mesenchyme made up of mesoderm and cranial neural crest cells (form the ocular blood vessels and anterior ocular structures).īriefly, early in vertebrate development, a single eye field is specified at the border of the anterior neural plate ( Figure 1A) ( Li et al., 1997). Finally, we will highlight outstanding gaps in our knowledge of CHD7 function, and avenues of investigation to further our understanding of how CHD7 activity regulates ocular and retinal development. We will discuss CHD7 function and its contributions to the development of ocular structures, and the potential roles of two of its downstream targets (Sox4 and Sox11) in visual system development. Next, we will describe some of the congenital disorders that result when these processes are disrupted, with a particular focus on CHARGE syndrome. In this review, we will provide an overview of the processes of vertebrate ocular morphogenesis, retinal development, and photoreceptor differentiation, and will compare these processes in zebrafish and mouse, two widely used animal models for development biology research, as well as humans to highlight similarities and differences across vertebrates. A significant amount of work has been completed to better understand pathways involved in ocular morphogenesis and retinal development, however many questions remain about the role and mechanism of individual genes in these processes. Disruptions in eye development and congenital eye defects are often found as part of larger syndromic disorders, including CHARGE syndrome, a genetic disorder characterized by coloboma, heart defects, choanal atresia, growth retardation, genital abnormalities, and ear abnormalities.ĭevelopment of the visual system is highly conserved among vertebrates ( Stenkamp, 2015). Pediatric visual impairment can be life altering, affecting motor, language, emotional, social, and cognitive development ( Wilkinson and Trantham, 2004 West, 2002 Berit Augestad, 2007 Sabra et al., 2009 Rainey et al., 2016). When development of the visual system or eye structures are disrupted, congenital eye defects and pediatric visual impairment may result. The visual system requires signals to be received by the eye, processed through the retina, and interpreted by the brain. Vision, one of our major senses, is considered the largest contributor to perception of the world around us ( Pike, 2012). Finally, we discuss outstanding gaps in our knowledge of the role of CHD7 in eye formation, and propose avenues of investigation to further our understanding of how CHD7 activity regulates ocular and retinal development. In addition, we discuss the current knowledge of CHD7 function and focus on its contributions to the development of ocular structures. This is followed by a comprehensive description of CHARGE syndrome, including discussion of the spectrum of ocular defects that have been described in this disorder. In this review, we provide a general overview of ocular development and congenital disorders affecting the eye. However, the pathogenetic mechanisms that connect loss of CHD7 to the ocular complications observed in CHARGE syndrome have not been identified. Mutations in the gene encoding Chromodomain helicase DNA binding protein 7 (CHD7) cause the majority of CHARGE syndrome cases. One important example is CHARGE syndrome, a genetic disorder characterized by coloboma, heart defects, choanal atresia, growth retardation, genital abnormalities, and ear abnormalities. MAC and retinal degeneration are also observed in systemic congenital malformation syndromes. Disruptions in this process are associated with structural birth defects such as microphthalmia, anophthalmia, and coloboma (collectively referred to as MAC), and inherited retinal degenerative diseases such as retinitis pigmentosa and allied dystrophies. The development of the vertebrate visual system involves complex morphogenetic interactions of cells derived from multiple embryonic lineages. Department of Biology, University of Kentucky, Lexington, KY, United States.
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