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Heike Kroeger, Wei-Chieh Jerry Chiang, Amanda Nguyen, Jonathan H Lin; Cone Photoreceptors Fail to Form in ATF6-Related Achromatopsia Retinal Organoids. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4762.
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© ARVO (1962-2015); The Authors (2016-present)
ATF6 encodes a transcription factor that is activated during the Unfolded Protein Response to protect cells from ER stress. Loss of function ATF6a mutations have been identified in patients with heritable photoreceptor diseases including achromatopsia (ACHM) and cone-rod dystrophy (CORD). Patients carrying mutant ATF6a alleles have foveal hypoplasia, abrogated cone photoreceptor function, and severely impaired vision from infancy. These phenotypes implicate an essential role for ATF6 during foveal and cone photoreceptor development. Here, we investigated the functional role of ATF6 during rod and cone photoreceptor development using ATF6 deficient patient iPSC cells.
3D retinal organoids generated from ATF6 knock-out human embryonic stem cells (hESCs) and ATF6 mutant patient derived induced pluripotent stem cells (iPSCs) were created to investigate the functional role of ATF6 during early rod and cone differentiation. Electron microscopy combined with OCT embedded; cryosectioned and immunohistological analysis of retinal organoids was used to visualize rod and cones at different developmental stages. RNAseq analysis was performed to determine changes in the transcriptional network in the retinal organoids in presence and absence of functional ATF6.
We discovered that loss of ATF6 function affects early differentiation events by suppressing loss of pluripotency and increasing the expression of early eye development markers, such as PAX6, SIX3 and RX. Microscopic analysis confirmed the presence of rod and cone photoreceptors in ATF6 wild-type retinal organoids. Interestingly, retinal organoids derived from ATF6 knockout hESCs and ATF6 mutant patient iPSCs both showed no development of cone photoreceptors cells in all retinal organoids (up to 290 days of age). By contrast, rod photoreceptor cells, inner limiting membrane, as well as the rod outer and inner segments developed equally well in all retinal organoids. RNAseq analysis revealed the lack of functional ATF6 by significant disruption of the ATF6 transcriptional program.
Our findings show that the cellular mechanism for ACHM and CORD in patients carrying ATF6 mutant alleles is a selective failure to form cone photoreceptors during retinal development while rods appear to be spared. We propose that foveal hypoplasia may emerge as a consequence of a developmental change from cone to rod-dominant retina.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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