Biomedical subjects

Bettina Winckler

Publications and source records attributed to Bettina Winckler.

7 recordsLinked to original sources

PubMed2006

Role of Pur alpha in targeting mRNA to sites of translation in hippocampal neuronal dendrites.

Using genetic inactivation in the mouse, PURA, encoding Pur alpha, is demonstrated to be essential for developmentally-timed dendrite formation in the cerebellum and hippocampus. Comparison of RNA species bound by Pur alpha prompts the hypothesis that Pur alpha functions with non-coding RNA in transport of certain mRNA molecules to sites of translation in dendrites. Pur alpha binds to human BC200 RNA, implicated in dendritic targeting, and this has homologies to 7SL RNA, implicated in compartmentalized translation. Results using hippocampal rat neurons in situ show that Pur alpha binds to BC1 RNA, implicated in dendritic targeting as a mouse counterpart of BC200, and to mRNA molecules translated in dendrites; Pur alpha is specifically located in dendrites, where it is colocalized with Map2, but not in axons, where it fails to colocalize with Ankyrin G. Pur alpha and Staufen are colocalized at dendritic sites of mRNA translation. Microtubule disruptors inhibit Pur alpha dendritic targeting and allow its mislocalization to axons. Using mouse brain, double-RNA immunoprecipitation places Pur alpha together with Staufen or FMRP on BC1 RNA and specific mRNA species in vivo. These results help define a mechanism by which Pur alpha targets specific mRNA molecules to sites of dendritic translation.

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PubMed2006

Myelin under construction -- teamwork required.

Myelinating glial cells synthesize specialized myelin proteins and deposit them in the growing myelin sheath that enwraps axons multiple times. How do axons and myelinating glial cells coordinate this spectacular cell-cell interaction? In this issue, Trajkovic et al. show that neuronal signaling regulates cell surface expression of the myelin proteolipid protein in cultured oligodendrocytes in unexpected ways that may also contribute to myelination in situ.

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PubMed2005

Inhibition of sphingolipid synthesis affects kinetics but not fidelity of L1/NgCAM transport along direct but not transcytotic axonal pathways.

Glycosphingolipids are constituents of lipid rafts which might function in sorting apical and axonal cargoes in the trans-Golgi network. In fact, two GPI-linked proteins, Thy1 and PrPC, require lipid raft lipids for sorting to the axon. It was previously shown that inhibition of glycosphingolipid synthesis by FumonisinB1 (FB1) impairs axon outgrowth but not axon specification, leading to the hypothesis that formation of axonally-targeted vesicles is coupled to sphingolipid synthesis. Since the axonal cell adhesion molecule L1/NgCAM can partition into membrane rafts biochemically, we asked whether correct targeting to the axon is FB1-sensitive, similarly to GPI-linked proteins. We previously showed that cultured hippocampal neurons use more than one trafficking pathway to the axon: a transcytotic pathway and a direct pathway. We show here that reducing raft lipid levels does not disrupt axonal targeting of L1/NgCAM along either pathway. Unexpectedly, FB1 selectively slowed the kinetics of surface expression of a truncated NgCAM using the direct pathway, but not of NgCAM using the transcytotic pathway. Therefore, the formation and/or transport of a subset of axonally-targeted vesicles are coupled to sphingolipid synthesis. Our results yield a mechanism for the axon outgrowth defect observed in FB1.

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PubMed2005

Transcytosis of NgCAM in epithelial cells reflects differential signal recognition on the endocytic and secretory pathways.

NgCAM is a cell adhesion molecule that is largely axonal in neurons and apical in epithelia. In Madin-Darby canine kidney cells, NgCAM is targeted to the apical surface by transcytosis, being first inserted into the basolateral domain from which it is internalized and transported to the apical domain. Initial basolateral transport is mediated by a sequence motif (Y(33)RSL) decoded by the AP-1B clathrin adaptor complex. This motif is a substrate in vitro for tyrosine phosphorylation by p60src, a modification that disrupts NgCAM's ability to interact with clathrin adaptors. Based on the behavior of various NgCAM mutants, it appears that after arrival at the basolateral surface, the AP-1B interaction site is silenced by phosphorylation of Tyr(33). This slows endocytosis and inhibits basolateral recycling from endosomes, resulting in NgCAM transcytosis due to a cryptic apical targeting signal in its extracellular domain. Thus, transcytosis of NgCAM and perhaps other membrane proteins may reflect the spatial regulation of recognition by adaptors such as AP-1B.

Adaptor Protein Complex 1↗

PubMed2004

Scientiae forum / models and speculations pathways for axonal targeting of membrane proteins.

The distribution of proteins to the correct domains of neurons is crucial for neuronal functioning. Here I discuss possible mechanisms underlying sorting to the axonal plasma membrane which differ with respect to the steps providing selectivity for axonal vs. somatodendritic cargo. Selectivity can be executed at one or more than one step, including sorting into distinct carriers in the Golgi, preferential transport along axonal microtubules, fusion with the plasma membrane, and importantly retrieval by endocytosis. A protein might in fact be sorted multiple times at different places to achieve axonal localization.

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PubMed2003

Uncovering multiple axonal targeting pathways in hippocampal neurons.

Neuronal polarity is, at least in part, mediated by the differential sorting of membrane proteins to distinct domains, such as axons and somata/dendrites. We investigated the pathways underlying the subcellular targeting of NgCAM, a cell adhesion molecule residing on the axonal plasma membrane. Following transport of NgCAM kinetically, surprisingly we observed a transient appearance of NgCAM on the somatodendritic plasma membrane. Down-regulation of endocytosis resulted in loss of axonal accumulation of NgCAM, indicating that the axonal localization of NgCAM was dependent on endocytosis. Our data suggest the existence of a dendrite-to-axon transcytotic pathway to achieve axonal accumulation. NgCAM mutants with a point mutation in a crucial cytoplasmic tail motif (YRSL) are unable to access the transcytotic route. Instead, they were found to travel to the axon on a direct route. Therefore, our results suggest that multiple distinct pathways operate in hippocampal neurons to achieve axonal accumulation of membrane proteins.

Animals↗

PubMed2003

Picket and other fences in biological membranes.

Nakada et al. revisit the controversial question of whether membrane lipids are able to diffuse from the axon of a neuron into the soma. Using single molecule imaging of a fluorescent phospholipid, the authors show that a diffusion barrier in the axon initial segment blocks the diffusion of lipids.

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