Abstract
Purpose::
To analyze the growth and patterning of nerves during the development of the mouse cornea.
Methods::
Mouse embryos at embryonic days (E) 11.5, 13.5, 15.5, and 17.5 were obtained from time pregnant Thy1-YFP mice. The localization of nerves was determined by immunofluorescence using anti-neurofilament M and anti-ß III tubulin. Myelination of the developing nerves was probed using a myelin specific fluorescent stain.
Results::
At E 11.5 no innervation of the developing cornea was detected in either whole mount or embryo sections, although nerves were clearly identified in other ocular tissues such as the optic nerve and retina. At E 13.5 large diameter nerve trunks with few branches extending only into the peripheral 1/3 of the developing cornea were observed on whole mount preparations. In cross sections of E 13.5 embryos, these large diameter nerves were located in the middle layers of the cornea. Anti-neurofilament M, but not anti-ß III tubulin antibodies recognized a subset of hexagonal cells on the posterior corneal surface. By E 15.5, corneal nerves had extended to cover the peripheral two-thirds of the cornea and had assumed a finer, more branched appearance. These nerves appeared to be in middle and anterior portions of the developing cornea by analysis of cross sections. At E 17.5, finely branched nerves were seen throughout the developing cornea stroma, with a few fibers at the developing corneal surface. No myelinated nerves were observed in the corneal nerves at the time points evaluated.
Conclusions::
Innervation of the developing cornea begins after E 11.5. A coordinated entry of large diameter, sparsely branched, unmyelinated nerves enter the cornea at E 13.5 and through day E 15.5 to E 17.5 migrate to the central cornea and develop more highly branched, finer neuronal processes (although the dense sub-basal nerve plexus seen in the adult cornea is not yet present). Investigations of the development of corneal nerves provide valuable insights into the cues which target regenerating neurons after corneal injury.
Keywords: cornea: basic science • development • innervation: sensation