Final Activity Report Summary - RETINAL STEM CELLS (Differentiation and morphology of retinal precursor cells in the vertebrate retina) The objective of the proposal, in broad terms, was to further our understanding of the process of eye development in vertebrates, with an emphasis on the morphological changes necessary to form the retinal structure. I have been working on the very earliest events in eye development: when the eyes begin to emerge from the forebrain, forming bilateral structures known as optic vesicles. These will then further grow, change shape and give rise to the eye. Using zebrafish as a model system, I have been investigating how the molecule Rx3 affects this process. Rx3 is a transcription factor, meaning that it controls which genes are expressed in a particular group of cells. Rx3 is present in all future eye cells at early stages; in fish lacking Rx3 function, the eyes fail to form. This is because the eye cells, although present, do not migrate properly to form the optic vesicles. Instead, they behave like other cells of the forebrain, and eventually die. We set out to investigate which genes are regulated by Rx3, and how this regulation affects eye formation. We were particularly interested to find molecules that are directly involved in controlling cell adhesion and migration, since these processes are central to tissue morphogenesis. To investigate this process, we have been imaging cell movements over time: labelling cells with fluorescent proteins and following their migration in the living embryo. My results demonstrate that one of the functions of Rx3 is to exclude the adhesion molecule Nlcam from the eye cells. If I artificially express Nlcam in these cells, their patterns of migration are severely altered, and this results in aberrant eye formation. These results provide a first link between the transcription factor Rx3 and the cellular machinery responsible for coordinating the morphological changes necessary for eye formation. This demonstrates that regulation of the adhesive properties of cells in time and space is essential to allow tissues to form the correct three-dimensional architecture, thus shaping the body.