Reversible epigenetics and seasonal neuroendocrine plasticity

Epigenetic modification such as DNA methylation and histone acetylation, are important molecular events that act to regulate gene transcription. The general assumption is that epigenetic events are permanent. Seasonal rhythms are associated with extensive genomic plasticity in a diverse range of tissues and cellular phenotypes. Using a seasonally breeding species, this presentation will demonstrate light and hormone dependent regulation of DNA methylation in the adult hypothalamus. In Siberian hamsters, a simple change in day length leads to marked variation in the levels of DNA methyltransferase 1 and 3b expression in the hamster hypothalamus. One genomic region in particular, Type 3 deiodinase (DI03) is one target of the light induced change sin DNMTl/3b expression with greater levels of dio3 promoter methylation in hamsters when housed in long days compared to short days. Studies that assessed the sufficiency of melatonin revealed timed injections were able to reduce DNMTl/3b expression and DI03 promoter methylation. The development of refractoriness in hamsters was associated with a complete reversal in dnmtl/3b enzyme expression and dio3 promoter methylation. Data obtained from male European starlings brains that support light induced, reversible changes in the expression of enzymes involved in demethylation. Altogether, the data will indicate the DNA methylation in the adult brain is dynamic and reversible.