Abstract
Purpose :
Epigenetic modifications play critical roles in controlling the proliferation and differentiation of retinal cells. We showed previously that histone methyltransferases (HMTases), G9a and Ezh2, are transiently expressed in the perinatal retina and particularly enriched in retinal ganglion cells (RGCs). However, selective inactivation of Ezh2 alone in RGCs does not affect RGC development or function. We thus investigated whether Ezh2 and G9a work in conjunction to regulate fetal gene repression following maturation in RGCs.
Methods :
Mice carrying targeted deletion of Ezh2 with (mEzh2-/-G9a+/-) or without deletion (mEzh2-/-) of one G9a allele in RGC progenitors were generated using Math5-Cre, which drives gene deletion in ~50% of RGCs. G9a and Ezh2 expression in mEzh2-/-G9a+/- mouse retina and controls were investigated by qPCR. H3K27me3 depositions were detected by immumoflurescence staining. RGC counts were carried out in the retina of P0 in mice, and RGC function was assessed by ERG positive scotopic threshold response (pSTR). Retinal cell apoptosis was examined by TUNEL. The proliferation of retinal progenitors was quantified by EdU. To determine the impact of targeted Ezh2 and/or G9a allele deletion on RGCs, we implemented RNA-seq gene profiling and genome-wide ChIP analysis with RGCs isolated from P0 pups.
Results :
The levels of G9a and Ezh2 were both reduced in the mEzh2-/-G9a+/- mouse retina compared to wild type mice. Interestingly, while H3K27me3 deposition was significantly decreased in the ganglion cell layer (GCL) of mEzh2-/-mice compared to wild type mice, there was a much further loss of H3K27me3 deposition in the GCL of mEzh2-/-G9a+/- mice. RGC loss and pSTR reduction were only detected in mEzh2-/-G9a+/-, but not mEzh2-/-mice, as compared to wild type controls. TUNEL and EdU staining showed comparable apoptosis and cell proliferation in the mEzh2-/-G9a+/- mouse retina compared to mEzh2-/- and wild type mice RNA-seq and ChIP analysis supports that loss of H3K27me3 in RGC progenitors of mEzh2-/-G9a+/- mice led to the reduced expression of RGC-lineage genes but increased expression of cell cycle and progenitor-related genes.
Conclusions :
An interplay between Ezh2 and G9a regulates fetal gene repression in RGCs through mediation of H3K27me3 deposition. Gene expression abnormity in RGC development by deletion of Ezh2 and one G9a results in RGC loss and dysfunction.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.