Project Abstract
Ocular developmental defects, like Anophthalmia and Microphthalmia, cause 10% of childhood
blindness, yet in many cases the cause is unknown. In cases of bilateral anophthalmia and
microphthalmia, the underlying cause has been primarily linked to mutations in two anterior
neural patterning transcription factors: Sox2 and Otx2. Anterior neural patterning precedes eye
field formation, which gives rises to the neural retina and retinal pigment epithelium progenitors,
yet how anterior neural plate patterning is molecularly linked to eye field formation is unknown.
Our recent work provides insight into this connection. At the start of anterior neural plate
formation in Xenopus laevis, we found expression of T-box transcription factor, Tbx3. Our
preliminary data shows that Otx2 directly activates Tbx3 at this stage in vivo. Among all the eye
field transcription factors that we have investigated, Tbx3 is the only one involved in both early
neural induction and eye field determination. In culture Tbx3 is required to generate
neuroepithelium from human embryonic stem cells, however the in vivo role of Tbx3 during early
mammalian development has not been studied, in part because null mutations are embryonic
lethal. Our preliminary data shows that Tbx3 is required for normal eye formation, since
conditional ablation in the optic cup results in a thinner optic nerve and fewer dorsal retinal
ganglion cells. Our working hypothesis is that mouse Tbx3 is required even earlier, at the onset
of neural induction. In Aim 1, we will determine when Tbx3 is first required for mouse eye
formation by conditionally deleting Tbx3 prior to neural plate formation, and separately, eye field
formation. Using Xenopus laevis we will investigate the regulation of Tbx3 during neural
induction and eye field determination. In Aim 2, we will determine how loss of Tbx3 in the optic
cup affects the formation of dorsal retinal ganglion, and possibly other retinal cells, in both
mouse and frog. Our proposal is in line with NEI’s Programs and Research Priorities on Retinal
Disease that states as one of its goals, to “study the disease pathogenesis and genetic factors
that underlie structure, function, and the biology of retinal diseases.” Completion of this R21 will
provide an integrated view of the genes linking early neural plate and eye field formation and
lead to a better understanding of the signaling pathways that, when altered, result in
Anophthalmia and Microphthalmia.