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Kristen Kwan, Hannah Gordon, Sydney Stringham, Emily Wirick; Hedgehog signaling mechanisms and the cell movements underlying choroid fissure morphogenesis. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
The choroid fissure is a transient vital structure through which retinal axons exit and vasculature enters the eye. Disruption of choroid fissure development results in uveal coloboma. Loss-of-function mutations in the Hedgehog (Hh) receptor patched2 (ptch2), which result in overactive Hh signaling, result in colobomata in zebrafish and humans. Using 4-dimensional live imaging and cell tracking, we previously identified the morphogenetic basis for normal and ptch2 mutant colobomatous choroid fissure formation. Despite establishing a cellular model, the mechanisms by which overactive Hh signaling disrupts choroid fissure development remain poorly understood. When, where, and how does Hh signaling act to control cell migration and choroid fissure formation?
4D live imaging datasets of eye morphogenesis are acquired via confocal microscopy. To visualize Hh signaling dynamics, we generated double transgenic zebrafish in which both Hh-producing (shh:H2A-EGFP) and Hh-responding (ptch2:H2A-mCherry) cells are labeled. Single cell migration behaviors are visualized using the photoconvertible fluorophore Kaede. To determine whether overactive Hh signaling acts in a choroid fissure cell autonomous or non-autonomous manner to disrupt movements, we utilize blastula cell transplants.
During eye formation, Hh ligand is produced by cells at the ventral midline. Somewhat surprisingly, Hh-responding cells contribute to multiple regions of the optic cup, choroid fissure, and optic stalk, exhibiting increased reporter expression in the ptch2 mutant. Cells migrating to the nasal choroid fissure margin normally exhibit a bipolar morphology and move processively through the optic stalk to the optic cup. In the zebrafish ptch2 mutant, these cells take on an aberrant multipolar morphology and halt migration within the optic stalk. Finally, preliminary experiments suggest that ptch2 mutant cells may migrate normally when transplanted into a wildtype host.
Our results indicate that Hh signaling acts in a complex manner during early eye formation, controlling choroid fissure cell migration, but also affecting other cell populations in the optic cup to disrupt choroid fissure formation in a non-autonomous manner. We are currently determining the mechanisms by which overactive Hh signaling disrupts cell migration, and identifying other cell populations critical for choroid fissure formation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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