Humans with mutations in Sox2 are frequently blind due to anophthalmia (absence of eyes) and display defects of the pituitary and hypothalamus, two brain regions critical for normal post-natal development. Our laboratory has developed two strains of mice that express lower than normal (or hypomorphic) levels of SOX2 protein in order to better understand how these phenotypes develop in humans, as well as to increase our general knowledge of central nervous system (CNS) morphogenesis. Importantly, Sox2 hypomorphic mice display similar phenotypes as humans with Sox2 mutations, including anophthalmia. My project specifically focuses on how eye defects develop in Sox2 hypomorphic embryos.

                                     

Figure 1 shows control and Sox2 hypomorphic mouse embryos at approximately E14.5. At this point the eyes of the Sox2 hypomorphic embryo have completely degenerated. In order to determine why this happens, I examine Sox2 hypomorphic embryos at several stages of eye development using a variety of techniques. One of the most useful properties of Sox2 hypomorphic embryos is that they express an EGFP reporter allele that faithfully recapitulates Sox2 expression at all stages of development. Figure 2 shows two images of a control E10.5 embryo. Although the retina lies below the surface of the embryo, it can still be seen as a green ring under UV fluorescence. The circle in the middle of the ring is the lens, which also expresses SOX2. By examining embryos whole mount, it is possible to learn something of how eye development proceeds in Sox2 hypomorphic embryos.

                                   

Although very useful, whole mount analysis does not allow us to observe what is occurring within the embryo. One of the techniques I use to examine the embryo’s interior is scanning electron microscopy (SEM), a microscopy technique that uses electrons rather than light to create an image, and so can reveal much smaller details. Figure 3 shows an E9.5 control embryo and an SEM image of the developing brain and eyes of a similarly aged embryo. During this gestational period the eyes are simple vesicles that have budded off of the neural tube. Figure 4 shows a similar view of the eyes and brain only a day later, after a significant degree of morphological development.