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Lisa Kelly, Heithem El-Hodiri; The homeobox genes Nkx5.3 and sensory organ homeobox (SOHo) are expressed in progenitor cells in the mature Xenopus retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3747.
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© ARVO (1962-2015); The Authors (2016-present)
The retinal homeobox (Rx/RAX) gene is essential for the development and maintenance of retinal progenitor cells and photoreceptors in the vertebrate retina. We are beginning to understand the molecular mechanisms regulating Rx transcription in these cells. We have previously identified three ultra-conserved genomic elements (UCEs) in the Rx genomic locus. One of these, UCE1, is likely to be involved in Rx autoregulation. In an attempt to identify additional trans-acting regulators that operate through UCE1, we analyzed predicted cis-acting elements within UCE1. In addition to the predicted Rx response element we found a predicted cis-acting element for the Nkx family of transcriptional regulators. The purpose of this study is to identify members of the Nkx family that may regulate Rx transcription through UCE1.
Tadpole head cDNA was prepared using the SMARTer Kit (Clontech). Specific cDNAs were amplified by PCR using primers designed according to the Xenopus laevis genome sequence. Gene expression was visualized by non-radioactive in situ hybridization using wholemount or sectioned embryos and antisense riboprobes
Nkx5.3 (aka Hmx1) and sensory organ homeobox (SOHo, aka Nkx5.4, Hmx4) are Nkx family members that are expressed in the neural retina in chicken and fish and, therefore, are potential candidate regulators of Rx UCE1. We isolated cDNAs encoding Xenopus laevis Nkx5.3 and SOHo. We found that both Nkx5.3 and SOHo are expressed in retinal progenitor cells in the developing and mature Xenopus retina. Thus expression of both Nkx5.3 and SOHo overlaps Rx expression in the retinal progenitor cells of the developing and mature Xenopus laevis retina.
To our knowledge, these studies represent the first characterization of Nkx5.3 and SOHo expression in the Xenopus retina. These results indicate that expression patterns of Nkx5.3 and SOHo overlap with the Rx expression domain in the progenitor cells in the mature Xenopus retina. Therefore, Nkx5.3 and SOHo are potential candidate regulators of Rx UCE1.
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