Analysis of cellular & genetic interactions between retina & periocular mesenchyme that underlie choroid fissure closure
Lead Research Organisation:
University College London
Department Name: Cell and Developmental Biology
Abstract
Eye colobomas encompass a group of common eye defects affecting people of all ages, but especially young children. These pathologies are a common cause of visual problems, can cause retinal detachment and cataracts, and often lead to blindness in affected patients. Colobomas are usually congenital conditions diagnosed by detection of a notch, gap, hole or fissure in any of the structures of the eye, including the cornea, retina and optic nerve. The defects in the ocular structures associated with the colobomas result from a failure in the embryonic formation of the eye. During embryogenesis, the forming eye and optic nerve undergo dramatic shape changes that lead to the closure of a fissure present on one side of the eye (the choroid fissure), and eventually to the formation of the intact globe of the eye. If choroid fissure closure is disrupted, an ocular coloboma develops. Recent studies by us and others indicate that cells outside the retina play a critical role in choroid fissure closure. Although the importance of these periocular mesenchyme cells (POM) is now established, we do not know how they function, and how they are affected in coloboma conditions. Resolving these issues is fundamental if we are to understand coloboma pathologies and find ways of preventing or treating them.
In this project, we will use zebrafish embryos which are small and transparent facilitating the study of normal development and disease in the intact animal. Together with its amenability to genetic analysis, these features make the fish embryo an excellent model system to study eye formation in normal and pathological conditions. Indeed, highly sophisticated imaging techniques will allow us to visualise all of the cells in the developing eye in the living zebrafish embryo. We will use a variety of approaches to label subpopulations of POM cells and assess their behaviour during eye formation. We will then generate fish devoid of POM cells at different time points during eye development and compare the process of choroid fissure closure in these and in healthy conditions. In addition, we will use genetic techniques to identify the molecules responsible for the communication between POM and retinal cells during choroid fissure closure. These analyses will enable us to establish new models for human eye diseases and will allow us to gain further insight into normal eye development and into the causes of hereditary ocular malformations.
In this project, we will use zebrafish embryos which are small and transparent facilitating the study of normal development and disease in the intact animal. Together with its amenability to genetic analysis, these features make the fish embryo an excellent model system to study eye formation in normal and pathological conditions. Indeed, highly sophisticated imaging techniques will allow us to visualise all of the cells in the developing eye in the living zebrafish embryo. We will use a variety of approaches to label subpopulations of POM cells and assess their behaviour during eye formation. We will then generate fish devoid of POM cells at different time points during eye development and compare the process of choroid fissure closure in these and in healthy conditions. In addition, we will use genetic techniques to identify the molecules responsible for the communication between POM and retinal cells during choroid fissure closure. These analyses will enable us to establish new models for human eye diseases and will allow us to gain further insight into normal eye development and into the causes of hereditary ocular malformations.
Technical Summary
The choroid fissure is a transient opening on the ventral side of the optic cup through which blood vessels enter, and retinal axons leave, the developing eye. Failure of the choroid fissure to close results in ocular colobomas, a family of common ocular pathogeneses that can cause severe visual impairement. Despite this fact, virtually nothing is known about the genetic mechanisms and cell movements that underlie choroid fissure closure. Recent studies indicate that periocular mesenchyme (POM) cells outside the retina play a critical role in choroid fissure closure but as yet, we do not know what they do, where they go or how they function.
In this project, we will exploit the outstanding optical properties of the zebrafish embryo for high resolution in vivo imaging to explore the identity of the POM cells required for choroid fissure fusion, determine when and how they function and elucidate the molecular pathways that mediate fusion. We will utilise two primary approaches to study choroid fissure closure: the first will be to resolve the cellular and tissue interactions that occur during ventral eye formation and to determine which cells and which interactions regulate choroid fissure closure; the second will be to use genetic and transgenic approaches to identify the genes and signalling mechanisms that participate in fusion of the ventral lips of the nasal and temporal retina. For our studies, we will use transgenic and other approaches to label subpopulations of POM cells and use high resolution 4D imaging to assess their behaviour during morphogenesis. We will then use transgenic, genetic and laser ablation approaches to remove POM cells at different time points during morphogenesis to determine their roles. Finally, we will use a combination of forward and reverse genetic techniques to resolve the genetic basis of the interaction between POM and ventral retinal cells during choroid fissure closure. Our work and that of others has already implicated a variety of upstream transcriptional regulators and signalling pathways in the cross talk between ventral eye cells and POM and our focus in this proposal will be upon those factors that regulate cell and tissue behaviours before and during the closure process.
In this project, we will exploit the outstanding optical properties of the zebrafish embryo for high resolution in vivo imaging to explore the identity of the POM cells required for choroid fissure fusion, determine when and how they function and elucidate the molecular pathways that mediate fusion. We will utilise two primary approaches to study choroid fissure closure: the first will be to resolve the cellular and tissue interactions that occur during ventral eye formation and to determine which cells and which interactions regulate choroid fissure closure; the second will be to use genetic and transgenic approaches to identify the genes and signalling mechanisms that participate in fusion of the ventral lips of the nasal and temporal retina. For our studies, we will use transgenic and other approaches to label subpopulations of POM cells and use high resolution 4D imaging to assess their behaviour during morphogenesis. We will then use transgenic, genetic and laser ablation approaches to remove POM cells at different time points during morphogenesis to determine their roles. Finally, we will use a combination of forward and reverse genetic techniques to resolve the genetic basis of the interaction between POM and ventral retinal cells during choroid fissure closure. Our work and that of others has already implicated a variety of upstream transcriptional regulators and signalling pathways in the cross talk between ventral eye cells and POM and our focus in this proposal will be upon those factors that regulate cell and tissue behaviours before and during the closure process.
