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D.M. Wallace, M. Donovan, T.G. Cotter; Histone Deacetylase Activity Regulates Apaf–1 and Caspase 3 Expression in the Developing Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3131.
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The purpose of this study is to investigate the transcriptional mechanism involved in the maintenance of the post–mitotic retina. We have previously observed the down–regulation in expression of Apoptosis protease activating factor–1 (Apaf–1) and caspase 3 in the retina during postnatal development. Apoptosis is a form of programmed cell death essential for both tissue development and maintenance of tissue homeostasis. Apaf–1 and the cysteine proteases known as caspases are genes central to the intrinsic apoptotic pathway
SDS–polyacrylamide gel electrophoresis and semi–quantitative PCR were used to examine Apaf–1 and caspase 3 expression levels during development, TdT–mediated dUTP Nick End Labelling (TUNEL) and DNA laddering were used to identify cells undergoing apoptosis under various conditions in retinal explant systems. Histone extractions and nuclear fractions were prepared from various age retinas to investigate histone acetylation and histone deacetylase (HDAC) activity
We report that a decrease in expression of Apaf–1 and caspase 3 during retinal development correlates with a decreased susceptibility to an apoptotic stimulus. Furthermore, we show that treatment with a histone deacetylase inhibitor, trichostatin A (TSA) results in widespread hyperacetylation in the retina. This observed hyperacetylation coincides with a transcriptional activation of Apaf–1 and caspase 3 and subsequent induction of apoptosis in P5 and P15 retinas. However, in agreement with the absence of transcriptional activation at P60, inhibition of HDAC activity is not sufficient to induce apoptosis in the mature retina.
Overall we can conclude from these results that down–regulation of key apoptotic genes such as Apaf–1 and caspase 3 in the developing retina correlates with a decreased susceptibility to apoptotic stimuli to ensure survival of the retina. Furthermore, we propose that in the early post–natal retina HDAC activity governs the transcriptional regulation of these genes as treatment with a HDAC inhibitor alleviates this transcriptional repression by switching the balance in favour of acetylation. This up–regulation of Apaf–1 and caspase 3 coincides with an induction of apoptosis. Interestingly, in the mature retina we do not observe a transcriptional activation of these genes or induction of apoptosis suggesting the presence of a further regulatory mechanism.
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