Distribution of constitutively expressed MEF-2A in adult rat and human nervous systems

Myocyte enhancer factor 2A (MEF-2A) is a calcium-regulated transcription factor that promotes cell survival during nervous system development. To define and further characterize the distribution pattern of MEF-2A in the adult mammalian brain, we used a specific polyclonal antiserum against human MEF-2A to identify nuclear-localized MEF-2A protein in hippocampal and frontal cortical regions. Western blot and immunocytochemical analyses showed that MEF-2A was expressed not only in laminar structures but also in blood vessels of rat and human brains. MEF-2A was colocalized with doublecortin (DCX), a microtubule-associated protein expressed by migrating neuroblasts, in CA1 and CA2 boundaries of the hippocampus. MEF-2A was expressed heterogeneously in additional structures of the rat brain, including the striatum, thalamus, and cerebellum. Furthermore, we found a strong nuclear and diffuse MEF-2A labeling pattern in spinal cord cells of rat and human material. Finally, the neurovasculature of adult rats and humans not only showed a strong expression of MEF-2A but also labeled positive for hyperpolarization-activated, cyclic nucleotide-regulated (HCN) channels. This study further characterizes the distribution pattern of MEF-2A in the mammalian nervous system, demonstrates that MEF-2A colocalizes with DCX in selected neurons, and finds MEF-2A and HCN1 proteins in the neurovasculature network.