Juxtanodin in retinal pigment epithelial cells: Expression and biological activities in regulating cell morphology and actin cytoskeleton organization

Abstract

Juxtanodin (JN, also known as ermin) was initially identified as an actin cytoskeleton-related oligodendroglial protein in the rat central nervous system. It was subsequently also found in the rat olfactory neuroepithelium, especially at the apical junctional belt of the sustentacular cells. We further examined JN expression and functional roles in the retina using fluorescence histochemistry, confocal microscopy, immuno-electron microscopy, molecular biology, and cell culture. Prominent JN expression was found in the photoreceptor-supporting retinal pigment epithelium (RPE), especially in a zone corresponding to the apices of RPE cells, at the roots of the RPE microvilli, and at the base of RPE cells next to the Bruch's membrane. Partial co-localization of JN immunoreactivity with F-actin (labeled with phalloidin) was observed at the apices and bases of RPE cells. No JN was detected in other cell types of the retina. In cultured human RPE cell line ARPE-19, expression of extrinsic JN up-regulated formation of actin cytoskeleton stress fibers, caused redistribution of more F-actin fibers to the cell periphery, and promoted spreading/enlargement of transfected cells. These findings suggest possible roles of JN in RPE molecular transport, phagocytosis and formation of outer blood-retinal barrier, or possible involvement of JN expression perturbations in pathogenesis of such retinal disorders as proliferative vitreoretinopathy and age-related macular degeneration.

Olfactory receptor neuronal dendrites become mostly intra‐sustentacularly enwrapped upon maturity

“…; Liang et al. ). In view of possible functions of JN in oligodendrogia differentiation, myelination and formation of the node of Ranvier in the CNS (Zhang et al.…”

“…Juxtanodin (JN, also known as ermin/ERMN) was identified previously as an actin cytoskeleton-related protein of oligodendroglia and myelin sheath in the central nervous system (CNS) (Zhang et al 2005;Brockschider et al 2006), and subsequently also found in rat OE sustentacular cells, especially at the apical junctional belt, and retinal pigment epithelial cells (Tang et al 2009;Liang et al 2018). In view of possible functions of JN in oligodendrogia differentiation, myelination and formation of the node of Ranvier in the CNS (Zhang et al 2005;Brockschider et al 2006;Meng et al 2010), it was hypothesized that JN in the OE may similarly regulate sustentacular cell interaction with olfactory receptor neurons, and facilitate differentiation/maturation of related OE cell types.…”

Flexible Players within the Sheaths: The Intrinsically Disordered Proteins of Myelin in Health and Disease

“…The inhibition is abolished by removal of the ERM domain, or by removal of the N-terminal half of Jux [163]. A prominent effect of Jux was recently observed in Jux-transfected retinal pigment epithelial cells, whereby the expression of Jux reorganized the actin cytoskeleton in a manner that affected cell morphology and size [168]. At the sequence level, Jux is not as conserved as MBP or MOBP, as e.g.…”

“…Cells 2020, 9, 470 10 of 34Jux[163]. A prominent effect of Jux was recently observed in Jux-transfected retinal pigment epithelial cells, whereby the expression of Jux reorganized the actin cytoskeleton in a manner that affected cell morphology and size[168].…”

Flexible Players within the Sheaths: The Intrinsically Disordered Proteins of Myelin in Health and Disease

“…The inhibition is abolished by removal of the ERM domain, or by removal of the N-terminal half of Jux [160]. A prominent effect of Jux was recently observed in Jux-transfected retinal pigment epithelial cells, whereby the expression of Jux reorganized the actin cytoskeleton in a manner that affected cell morphology and size [165]. At the sequence level, Jux is not as conserved as MBP or MOBP, as e.g.…”