Abstract
Purpose:
Optic nerve astrocytes play a crucial role in the survival of retinal ganglion cells as well as retinal homeostasis. During development, astrocytes exhibit changes in expression profiles as a result of chromatin reorganization. Chromatin reorganization can be induced through histone modifying enzymes. We examined the expression of histone deacetylases (HDACs), a class of histone modifying enzyme in murine and chick optic nerve (ON) as a first step towards understanding the epigenetic influence on astrocyte lineage development.
Methods:
Expression of Class I, II and IV HDACs were examined by Western blotting and quantitative real-time polymerase chain reaction (QPCR) in murine ON whereas Western blotting was used to confirm the expression patterns in Chick ON. ONs were isolated from chick embryos at E5 (embryonic day 5), E8 and E18 stages whereas from mouse at E16, PN5 (post natal day 5) and PN30 stages to coincide with various phases of astrocyte development. The protein from isolated ONs was quantified and resolved by SDS-PAGE using specific antibodies. Total RNA was isolated from mouse ONs, cDNA synthesized and QPCR was performed using specific primers to assess changes in gene expression.
Results:
The expression of Class I HDACs namely HDAC1, 2, 3 and 8 decreased with development in mouse optic nerve as confirmed by both western blotting and QPCR. Among class II HDACs, mRNA expression of HDAC4, 6, 7 and 10 decreased whereas mRNA expression of other class II HDACs, HDAC5 and 9, and HDAC 11, a class IV HDAC showed a fluctuating pattern in mouse optic nerve with development. Western blot analysis showed increased expression of HDAC4 and 5 and decreased expression of HDAC 9, 10 and 11 in mouse optic nerve. The expression of most of the HDACs in the mouse ON decreased significantly with development. However, the protein expression of acetylated lysine significantly increased with development. In chick ON, protein expression of HDAC1, 2, 3, 4, 5 and 9 decreased with development whereas HDAC8 showed a fluctuating pattern
Conclusions:
Decreasing levels of expression of majority of HDACs in mouse and chick optic nerve and increasing levels of acetylated lysine suggest an increase in transcriptional activity during the course of development. The fluctuating pattern or increased expression observed in some of the HDACs suggests differential regulation of some of the developmental genes.
Keywords: 629 optic nerve •
497 development