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J. K. Kubilus, T. F. Linsenmayer; Temporal Regulation of Corneal Innervation by Neuropilin-1 During Chicken Embryonic Development. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4813.
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Corneal innervation is necessary for the perception of pain as well as in the overall maintenance of the cornea through the release of trophic factors. Recently, Semaphorin3A has been suggested to be involved in the initial guidance of axons into the anterior eye during development (Lwigale et al., 2007). Here, we have tested the role of Semaphorin3A and its receptor, Neuropilin-1, on the patterning of corneal innervation at later stages of development when nerves are branching into the epithelium.
The spatial and temporal growth of axons into the cornea was determined using immunohistochemistry in chickens between embryonic day 6 (E6) and E12. Expression of Semaphorin3A and Neuropilin-1was determined using qRT-PCR and in situ hybridization. To study the mechanisms involved in regulating corneal innervation corneal and trigeminal ganglion explants were co-cultured in 3-dimensional collagen gels.
Our observations suggest that nerves initially enter the chicken corneal stroma between E7 and E8. Between E11 and E12 the nerves penetrate Bowman’s membrane, branch and terminate in the apical corneal epithelium. Semaphorin3A is expressed in the corneal epithelium at both E6 and E12 as shown by in situ hybridization, but this expression decreases over time as shown by qRT-PCR. The expression of Neuropilin-1 in the ophthalmic trigeminal ganglion decreases during this time course. In explant co-cultures of E12 ophthalmic trigeminal ganglia with E7 corneas, nerves were able to enter the cornea, whereas E7 ophthalmic trigeminal nerves failed to enter either E7 or E12 corneas.
The decreased expression of Neuropilin-1 in the ophthalmic branch of trigeminal ganglion suggests that this is one mechanism responsible for the pattern of corneal innervation.
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