Electromagnetic Polarization Effects due to Axion Photon Mixing

We investigate the effect of axions on the polarization of electromagnetic waves as they propagate through astronomical distances. We analyze the change in the dispersion of the electromagnetic wave due to its mixing with axions. We find that this leads to a shift in polarization and turns out to be the dominant effect for a wide range of frequencies. We analyze whether this effect or the decay of photons into axions can explain the large scale anisotropies which have been observed in the polarizations of quasars and radio galaxies. We also comment on the possibility that the axion-photon mixing can explain the dimming of distant supernovae.Comment: 18 pages, 1 figur

Neurofibromatosis type 1 gene product (neurofibromin) associates with microtubules

The neurofibromatosis type 1 (NF1) gene was recently identified by positional cloning and found to encode a protein with structural and functional homology to mammalian and yeast GTPase-activating proteins (GAPs). Using antibodies directed against the NF1 gene product, a protein of ∼250kDa was identified and termed neurofibromin. Double-indirect immunofluorescent labeling with anti-neurofibromin and anti-tubulin antibodies demonstrates that neurofibromin associates with cytoplasmic microtubules. Immunoblotting of microtubule-enriched cytoplasmic fractions, using antibodies generated against neurofibromin, shows that neurofibromin copurifies with microtubules. When portions of neurofibromin are expressed in Sf9 insect cells they associate with polymerized microtubules; furthermore, the critical residues for this interaction reside within the GAP-related domain of neurofibromin. The unexpected association of neurofibromin with microtubules suggests that neurofibromin is involved in microtubule-mediated intracellullar signal transduction pathways.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45544/1/11188_2005_Article_BF01233074.pd

Pollen tube taxol dependent structures co-assemble with neuronal HMW MAPs (MAP2)

Pollen tube microtubules (MTs) are as dynamic as animal MTs and they may interact with plasma membrane, endoplasmic reticulum, Golgi apparatus, mitocondria and a variety of cytoplasmic proteins. Bridges connecting MTs to each other and to membranes have been documented in pollen tubes by electron microscopy; however, the biochemical and molecular nature of these linkages is not known. In other cell types interaction between organelles and MTs require the participation of Microtubule-Associated Proteins (MAPs) that bridge the cytoskeleton to these organelles. Although biochemical documentation of such bridging MAPs in plant cells is lacking, it is reasonable to assume, by analogy with the animal systems, that specialized MAPs regulate MTs polymerization and dynamic in pollen tube. As a first step toward testing this hypothesis, the ability of Nicotiana tabacum pollen tube taxol-stabilized MTs to bind mammalian brain High Molecular Weight MAPs (HMWMAPs)(MAP2) was tested. This association analysis revealed the presence of mammalian MAP2-binding sites on pollen tube taxol-induced structures suggesting that the association presumably occurs at conserved domains on the tubulin molecules