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H. Boije, F. Hallböök; Temporal and Spatial Expression of the Transcription Factor FoxN4 in the Developing Chick Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5906.
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© ARVO (1962-2015); The Authors (2016-present)
A function for FoxN4 has been implied in retinal cell fate determination and the purpose of this work was to study its role in the developing chick retina. Previous work in mouse, by Li et al. 2004, suggest that the transient expression of Foxn4 is vital for early born interneurons. By understanding the decisive events during the formation of different types of retinal neurons the ultimate aim of this work is to direct differentiation of retinal progenitor cells in vitro.
-RACE (rapid amplification of cDNA ends) was performed and the full-length FoxN4 cDNA was characterized.-In situ hybridization and qRT-PCR was used to describe the normal expression pattern of FoxN4 in relation to Ptf1a, Prox1, Isl1 and Lim1.-A peptide antibody was raised, affinity purified, and evaluated in comparison to the in situ results.-Overexpression and knock down of FoxN4 by introducing vectors and siRNA into the developing eye.
The FoxN4 expression was transient, commencing already in the stage 12 - 14 optic vesicles. During development a large population of progenitor cells were labeled in the prospective inner nuclear layer. Expression was downregulated as the retinal progenitor cells differentiated but remained in the periphery stage 38 - 41. Ptf1a, Prox1, Isl1 and Lim1 expression appeared by stage 20 - 24, concomitant with the first post-mitotic ganglion-, amacrine-, and horizontal cells. While the Ptf1a expression also appeared transiently, Prox1, Isl1 and Lim1 expression remained in several differentiated cells including the horizontal cells.
The early expression in the optic vesicle, prior to interneuron differentiation, together with the late expression, suggests a broader function of FoxN4 than previously proposed. It is likely to have a role in early retinal progenitor cells and to be a factor involved in late born neurons and glia cells. This information is crucial for upcoming studies trying to further decipher its function in retinal subtype formation. The order of expression supports a scheme where Ptf1a and Prox1 is downstream of FoxN4 and that FoxN4 and Ptf1a have transient roles during fate specification while Prox1, Isl1 and Lim1 have roles that are important for the generation of the neuronal subtypes.
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