Distinct regional and subcellular localization of the actin-binding protein filamin A in the mature rat brain.

Filamin A (FLNa) is an actin-binding protein that regulates cell motility, adhesion and elasticity by cross-linking filamentous actin. Additional roles of FLNa include regulation of protein trafficking and surface expression. Whereas the functions of FLNa during brain development are well studied, little is known on its expression, distribution and function in the adult brain. Here, we characterize in detail the neuroanatomical distribution and subcellular localization of FLNa in the mature rat brain, by using two antisera directed against epitopes at either the N'- or the C'-terminus of the protein, further validated by mRNA expression. FLNa was widely and selectively expressed throughout the brain, and the intensity of immunoreactivity was region dependent. The most intensely FLNa-labeled neurons were found in discrete neuronal systems including basal forebrain structures, anterior nuclear group of thalamus, and hypothalamic parvocellular neurons. Pyramidal neurons in neocortex and hippocampus, as well as magnocellular cells in basolateral amygdaloid nucleus were also intensely FLNa-immunoreactive, and strong FLNa labeling was evident in the pontine and medullary raphe nuclei and in sensory and spinal trigeminal nuclei. The subcellular localization of FLNa was evaluated in situ, as well as in primary hippocampal neurons. Punctate expression was found in somata and along the dendritic shaft, but not detected in dendritic spines. These subcellular distribution patterns were recapitulated in hippocampal and neocortical pyramidal neurons in vivo. The characterization of the expression and subcellular localization of FLNa may provide new clues to the functional roles of this cytoskeletal protein in the adult brain. J. Comp. Neurol., 2012. (c) 2012 Wiley Periodicals, Inc.