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James Kenneth Kubilus, Christopher Talbot, Thomas Linsenmayer; Developmental expression of SV2 in embryonic chicken corneal epithelium. Invest. Ophthalmol. Vis. Sci. 2017;58(8):962.
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© ARVO (1962-2015); The Authors (2016-present)
Within the cornea, intraepithelial corneal nerves (ICNs) help to protect the cornea by acting as the afferent limb of the blink reflex, as well as by modulating the production of tears. Without ICNs, the cornea is more susceptible to damage. In addition to these functions, ICNs are also thought to play a role in the health and homeostasis of the cornea through the release of trophic factors. These trophic factors have been shown previously to support the cells of the corneal epithelium. Though the ICNs innervating the cornea are thought to terminate predominately as “simple” free nerve endings, the mechanisms involved in their release of trophic factors is unclear. Here, we sought to investigate this mechanism by determining the expression pattern of SV2, a marker of synaptic vesicles within the cornea during development.
Embryonic chicken anterior eyes from embryonic day 4 (E4) through E17 were dissected and either fixed or frozen fresh for immunohistochemistry with antibodies against SV2. Transmission electron microscopy (TEM) was used to observe morphological changes. Western blot was used to further examine the expression of SV2.
The embryonic cornea of the chicken is innervated in a series of precise stages, with nerves first appearing in the corneal epithelium between E10 and E11. Immunohistochemistry showed that SV2 labeling did not appear in the epithelium until after this time point, suggesting that SV2 is specific for vesicles within the nerves. This punctate SV2 labeling was present in all levels of the corneal epithelium, but localized predominately at the basolateral borders between cells in both the subbasal nerve plexus as well as within the apical squamous layer. Western blot of corneal epithelial lysates showed that corneal SV2 migrated at a different molecular weight than SV2 from brain. Also, unlike brain derived SV2, this migration was not affected by the deglycosylating enzyme PNGASE.
Our data show that the appearance of SV2 correlates with the appearance of nerves in the cornea. However, corneal SV2 is different in its size and glycosylation. This suggests that the mechanisms though which ICNs release trophic factors are likely not as “simple” as previously thought and may be unique to the cornea.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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