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Lucy Wong, Zhaoxin Jiang; G9a and Ezh2 are important for RGC cell fate determination during development. Invest. Ophthalmol. Vis. Sci. 2016;57(12):645.
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© ARVO (1962-2015); The Authors (2016-present)
Histone methyltransferases G9a and Ezh2 depositing methyl groups on Histone3 lysine 9 and Histone3 lysine 27, respectively, are two main players in epigenetic modification. In this study, we used conditional knockout mice (cdKO) to examine the phenotypical, functional and genetic changes G9a and Ezh2 deficiency causes in mouse retinal ganglion cells (RGC) and shed light on their function during retinal development.
A Math5-Cre driven Cre-loxP system was used to delete G9a and Ezh2, alone (G9a-/- or Ezh2-/-) or both (cdKO), in RGCs. Retinal functions were examined by electroretinography (ERG) from 6 weeks (wks) to 3 months (m). Mice were sacrificed at postnatal day 0 (P0) and 6wks for RGC and axon counting. Retinal progenitor cell proliferation and death were detected by EdU incorporation and TUNEL, respectively, at embryonic day 14 and P0. For RNA-sequencing analysis, P0 retinas and purified RGCs of wild-type (WT) and mutant mice were used.
cdKO mice showed lower amplitudes of ERG a-wave and b-wave and positive scotopic threshold response (pSTR), compared to WT mice, while mice carrying single G9a or Ezh2 deficiency in Math5-expressing cells (G9a-/- or Ezh2-/-) showed normal phenotype. There was also significant reduction in the number of RGCs and axons in cdKO compared to WT and G9a-/- or Ezh2-/- mice. With RNA-Sequencing, we found that in cdKO P0 RGCs, genes related to apoptosis and cell cycle arrests such as Rag1, Cdkn2a are drastically upregulated. Importantly, RGC related genes, such as Brn3a, Shh are down-regulated, while notably, photoreceptor specific genes are up-regulated in RGCs of cdKO mice, suggesting dysregulation of cell fate specification and gene expression. Vice versa, we noted upregulation of RGC specific genes in non-RGC population of cdKO mice.
G9a and Ezh2 deficiency leads to retinal dysfunction, reduced RGC genesis and dysregulation of gene expression. Our results suggest that G9a and Ezh2 are involved in the regulation of RGC differentiation and cell fate specification.
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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