I'm looking for suggestions for papers to start from (or links to heated blog debates) in researching the evolution of thought over the last few decades regarding the causal role of histone modifications and DNA methylation in the regulation of gene expression. Ie, are these epigenetic marks merely left as traces of the true causal agents (TFs and small RNAs) or do they play a more causal role in regulating and perpetuating levels of gene expression?