Distinct regional and subcellular localization of the actin‐binding protein filamin a in the mature rat brain

Yoav Noam,Tallie Z Baram,Shawn Mcclelland,Yuncai Chen,Markus U Ehrengruber,Lise Phan,Wytse J Wadman,Erik M Manders

doi:10.1002/cne.23106

Abstract

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. Although 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 and 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 FLNa was 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.

Highlights

The actin network is composed of highly organized structures that determine the morphology of the cell and influence cellular signaling by controlling trafficking and distribution of membrane-bound proteins
We report that 1) in the mature rat brain, filamin A (FLNa) is expressed across wide range of regions; 2) the distribution of FLNa is selective, as demonstrated by varying degrees of immunoreactive density and intensity across distinct neuronal populations; 3) FLNa is present in somata and along the dendrites of select neuronal populations; and 4) both in vivo and in vitro, dendritic FLNa-ir signal is distributed in puncta along the shaft and is minimally detected in spines
MRNA and protein levels of FLNa are downregulated during development (Sheen et al, 2002), moderate levels of FLNa have been consistently observed in adult brain (Fox et al, 1998; Petrecca et al, 2000; Sheen et al, 2002; Wang et al, 2008)

Summary

Introduction

The actin network is composed of highly organized structures that determine the morphology of the cell and influence cellular signaling by controlling trafficking and distribution of membrane-bound proteins. The presence of FLNa in the adult brain has been well documented (see, e.g., Fox et al, 1998; Petrecca et al, 2000; Sheen et al, 2002; Wang et al, 2008), a systematic analysis of its expression patterns and subcellular distribution is lacking. Such characterization can be especially helpful in light of the potential roles that FLNa may play in receptor and ion channel trafficking. We combine immunocytochemical approaches in vivo and in vitro to characterize the selective expression of FLNa in the rat brain and the subcellular localization of this actin-binding protein in mature neurons

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Results

Conclusion