Targeted expression of the dominant-negative FGFR4a in the eye usingXrx1Aregulatory sequences interferes with normal retinal development

Abstract

Molecular analysis of vertebrate eye development has been hampered by the availability of sequences that can selectively direct gene expression in the developing eye. We report the characterization of the regulatory sequences of the Xenopus laevis Rx1A gene that can direct gene expression in the retinal progenitor cells. We have used these sequences to investigate the role of Fibroblast Growth Factor (FGF) signaling in the development of retinal cell types. FGFs are signaling molecules that are crucial for correct patterning of the embryo and that play important roles in the development of several embryonic tissues. FGFs and their receptors are expressed in the developing retina, and FGF receptor-mediated signaling has been implicated to have a role in the specification and survival of retinal cell types. We investigated the role of FGF signaling mediated by FGF receptor 4a in the development of retinal cell types in Xenopus laevis. For this purpose, we have made transgenic Xenopus tadpoles in which the dominant-negative FGFR4a(ΔFGFR4a) coding region was linked to the newly characterized regulatory sequences of the Xrx1A gene. We found that the expression ofΔFGFR4a in retinal progenitor cells results in abnormal retinal development. The retinas of transgenic animals expressing ΔFGFR4a show disorganized cell layering and specifically lack photoreceptor cells. These experiments show that FGFR4a-mediated FGF signaling is necessary for the correct specification of retinal cell types. Furthermore, they demonstrate that constructs using Xrx1A regulatory sequences are excellent tools with which to study the developmental processes involved in retinal formation.

Differential role of 14‐3‐3 family members in Xenopus development

“…Previous work demonstrated that the FGF receptor 1 is not required for early Xenopus eye induction or patterning (Kroll and Amaya, 1996), and inactivation of FGF by use of a dominant-negative FGF receptor 1 did not prevent animal blastomeres from contributing to the retina (Moore and Moody, 1999). In contrast, a more recent study in transgenic frogs showed that FGF receptor 4a is required for the correct specification of retinal cell types (Zhang et al, 2003). Also, another group demonstrated that an interaction between FGF and ephrinB1 is required for morphogenetic movements that underlie eye field formation (Moore et al, 2004).…”

Regulation of vertebrate eye development by Rx genes

“…The regulatory elements of the Xenopus tropicalis and laevis Rx gene are located in the 5' upstream region of the gene (Hirsch et al, 2002;Zhang et al, 2003). These sequences are able to direct gene expression into the developing eyes and ventral hypothalamus.…”

“…2 K,L). We used these sequences to investigate the role of FGF signaling mediated by the FGFR-4 in the specification of retinal cell types (Zhang et al, 2003).…”

Molecular links among the causative genes for ocular malformation: Otx2 and Sox2 coregulate Rax expression

“…These genes are involved in the specification of the eye field and the proliferation of retinal progenitor cells. Furthermore, previous studies have shown that the 5Ј-upstream regions of Rax in Xenopus laevis and Xenopus tropicalis contain cis-regulatory elements that direct Rax expression in the developing eye (22,23). However, the trans-acting factors that bind directly to the cis-regulatory elements to regulate Rax expression remain unknown.…”