Biomedical subjects

Tatiana Boiko

Publications and source records attributed to Tatiana Boiko.

5 recordsLinked to original sources

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

Novel clustering of sodium channel Na(v)1.1 with ankyrin-G and neurofascin at discrete sites in the inner plexiform layer of the retina.

Voltage-gated sodium channels cluster at sites of action potential generation and propagation by interacting with partner proteins such as neurofascin, an adhesion molecule in the L1 family, and ankyrin-G, a spectrin-binding protein required for sodium channel accumulation at axon initial segments. Here, we describe in the inner plexiform layer of the retina a novel site of high-density sodium channel clustering, marked by ankyrin-G and neurofascin. The sodium channel isoform at this site is Na(v)1.1, instead of the Na(v)1.6 channels more commonly found in association with the clustering machinery. During development, Na(v)1.2 channels first associate with ankyrin-G in the inner plexiform layer but are later replaced by Na(v)1.1, similar to the switch from Na(v)1.2 to Na(v)1.6 at nodes of Ranvier and initial segments. This represents the first instance of high-density clustering of Na(v)1.1 channels, which may contribute to synaptic interactions among retinal neurons in the inner plexiform layer.

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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.

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PubMed2003

Functional specialization of the axon initial segment by isoform-specific sodium channel targeting.

Voltage-dependent sodium channels cluster at high density at axon initial segments, where propagating action potentials are thought to arise, and at nodes of Ranvier. Here, we show that the sodium channel Na(v)1.6 is precisely localized at initial segments of retinal ganglion cells (RGCs), whereas a different isoform, Na(v)1.2, is found in the neighboring unmyelinated axon. During development, initial segments first expressed Na(v)1.2, and Na(v)1.6 appeared later, approximately in parallel with the onset of repetitive RGC firing. In Shiverer mice, Na(v)1.6 localization at the initial segment was unaffected, although Na(v)1.6 expression was severely disrupted in the aberrantly myelinated optic nerve. Targeting or retention of Na(v)1.6 requires molecular interactions that normally occur only at initial segments and nodes of Ranvier. Expression at nodes but not initial segments exhibits an additional requirement for intact myelination. Because of their high density at the initial segment, Na(v)1.6 channels may be crucial in determining neuronal firing properties.

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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