Abstract
Uveal coloboma represents one of the most common congenital ocular malformations accounting for up to 10% of childhood blindness (1~ in 5,000 live birth). Coloboma originates from defective fusion of the optic fissure (OF), a transient gap that forms during eye morphogenesis by asymmetric, ventral invagination. Genetic heterogeneity combined with the activity of developmentally regulated genes suggest multiple mechanisms regulating OF closure. The tumor suppressor and FERM domain protein neurofibromin 2 (NF2) controls diverse processes in cancer, development and regeneration, via Hippo pathway and cytoskeleton regulation. In humans, NF2 mutations can cause ocular abnormalities, including coloboma, however, its actual role in OF closure is unknown. Using conditional inactivation in the embryonic mouse eye, our data indicates that loss of Nf2 function results in a novel underlying cause for coloboma. In particular, mutant eyes show substantially increased RPE proliferation in the fissure region with concomitant acquisition of RPE cell fate. Cells lining the OF margin can maintain RPE fate ectopically and fail to transition from neuroepithelial to cuboidal shape. In the dorsal RPE of the optic cup, Nf2 inactivation leads to a robust increase in cell number, with local disorganization of the cytoskeleton components F-actin and pMLC2. We propose that RPE hyperproliferation is the primary cause for the observed defects causing insufficient alignment of the OF margins in Nf2 mutants and failure to fuse properly, resulting in persistent coloboma. Our findings indicate that limiting proliferation particularly in the RPE layer is a critical mechanism during optic fissure closure.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Footnote: The authors wish to be known that, in their opinion, the first 2 authors Wesley R. Sun and Sara Ramirez should be regarded as joint First Authors.
- Abbreviations
- AJ
- Adherens junctions
- Axin2
- Axis inhibition protein 2
- BHLH
- Basic helix-loop-helix
- BrdU
- Bromodeoxyuridine
- CCND1
- Cyclin D1
- Crb1
- Crumbs family member 1
- DAPI
- 4’,6-diamidino-2-phenylindole
- DAPL1
- Death associated protein-like 1
- DCAF1
- DDB1 and CUL4 associated factor 1
- ECM
- Extracellular matrix
- ERM
- Ezrin, radixin, and moesin
- FAT1
- FAT atypical cadherin 1
- FERM
- Ezrin, radixin, and moesin
- FGF
- Fibroblast growth factor
- LATS1/2
- Large tumor suppressor 1/2
- LEF1
- Lymphoid enhancer binding factor 1
- LRP6
- Low density lipoprotein receptor-related protein 6
- MAC
- Microphthalmia, anophthalmia and coloboma
- MITF
- Microphthalmia associated transcription factor
- MST1/2
- Macrophage stimulating 1/2
- NF2 (disorder)
- Neurofibromatosis Type 2
- NF2 (gene)
- Neurofibromin 2
- OF
- Optic fissure
- Otx2
- Orthodenticle homeobox 2
- PAX2
- Paired box 2
- PAX6
- Paired box 6
- PFA
- Paraformaldehyde
- PHH3
- Phospho-histone H3
- pMLC2
- Phospho-myosin light chain II
- PORCN
- Porcupine
- Rd8
- Retinal degeneration 8
- RPE
- Retinal pigmented epithelium
- SCRA
- Sveinsson’s chorioretinal atrophy
- TAZ
- Tafazzin
- TBX5
- T-box 5
- TEAD
- TEA domain family member
- TFAP2A
- Transcription factor AP-2 Alpha
- TRITC
- Tetramethylrhodamine
- TUNEL
- Terminal deoxynucleotidyl transferase dUTP nick end labeling
- VSX2
- Visual system homeobox 2
- WGA
- Wheat Germ Agglutinin
- Wnt
- Wingless-type
- YAP
- Yes-associated protein
- ZO-1
- Zonula occludens-1