Autotaxin in Central Nervous System Development and Disease

During development, oligodendrocytes (OLGs), the myelinating cells of the central nervous system (CNS), undergo a stepwise progression during which OLG progenitors, specified from neural stem/progenitor cells, differentiate into fully mature myelinating OLGs. This progression along the OLG lineage is characterized by well-synchronized changes in morphology and gene expression patterns. The studies presented in this dissertation identified the extracellular factor Autotaxin (ATX) as a novel upstream signal modulating HDAC1/2 activity and gene expression in cells of the OLG lineage. Using the zebrafish as an in vivo model system, as well as rodent primary OLG cultures, this functional property of ATX was found to be mediated by its lysoPLD activity, which has been well-characterized to generate the lipid signaling molecule lysophosphatidic acid (LPA). LPA binds to Gprotein-coupled LPA receptors (LPARs) on the surface of OLGs to initiate downstream signaling events. ATX’s lysoPLD activity was found to modulate HDAC1/2 regulated gene expression during a time window coinciding with the transition from OLG progenitor to early differentiating OLG. When looking further downstream of the ATX-LPA axis, down-regulation of LPA receptor 6 (LPA6) was found to reduce the expression of OLG differentiation genes as well as the overall process network area of OLGs. Thus, LPA6 plays a role in both the gene expression and morphology changes seen in OLG differentiation. These findings prove useful for future therapeutic targets needed for demyelinating diseases of the CNS such as Multiple Sclerosis (MS), in which OLGs fail to differentiate into mature OLGs, needed for remyelination. Additionally, white matter injury has been frequently reported in HIV+ patients. Previous studies showed that HIV-1 Tat (transactivator of transcription), a viral protein that is produced and secreted by HIV-infected cells, is a toxic factor to OLGs. We show here that Tat treatment reduces the expression of OLG differentiation genes and the overall process network area of OLGs. Additionally, Tat-treated OLGs have reduced ATX lysoPLD activity and there is a physical interaction between Tat and ATX. Together, these data strongly suggest functional implications of Tat blocking ATX’s lysoPLD activities and thus the ATX-LPA signaling axis proves to play a significant role in the development of OLGs

Molecular and Atomic Confinement in Large Core Photonic Microcells for Slow Light and Laser Metrology Applications

This thesis describes developments in the fabrication and applications of photonic microcells (PMCs). A PMC is a length of gas-filled hollow core-photonic crystal fibre (HC-PCF) that is hermetically sealed by splicing both ends to standard single mode fibre. A PMC enables integration of gas-filled HC-PCF into all-fibre systems with low insertion loss. PMCs have applications in coherent optics and metrology, where specific HC-PCF designs are advantageous. Two types of state-of-the-art HC-PCF, double bandgap HCPCF and large-pitch Kagome fibre, are fabricated. The double bandgap HC-PCF extends the usable bandwidth of the fibre by providing low loss guidance across two transmission bands. The large-pitch Kagome HC-PCF has a record low attenuation of 0.3 dB/m at 800 nm, while maintaining broadband guidance, which is partially attributed to the core shape. Three distinct developments in the field of PMCs are described. Firstly, a record length 20 metre acetylene-filled PMC is fabricated which is the key component in the first demonstration of an all-fibre slow and fast light system based on electromagnetically induced transparency. Secondly, a technique based on fibre tapering is presented which enables low loss integration of large core Kagome HC-PCFs into PMC form. Thirdly, micromirrors are developed and integrated with HC-PCF to confine light in the longitudinal dimension, providing a means to fabricate multi-pass PMCs. Two uncoated micromirrors are used to form a low finesse microcavity in Kagome HC-PCF, with record high fringe visibility using reflections from a silica/air junction. In collaboration with Kansas State University, an acetylene optical reference with sub-10 KHz accuracy and the first acetylene laser based on population inversion are demonstrated using Kagome HC-PCF.Finally, this thesis reports on rubidium vapour loading in HC-PCF with the ultimate aim being the production of a rubidium-filled PMC for applications in metrology. Preliminary results highlight the limited loading distance of the current technique and modified loading schemes are outlined accordingly.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Is fish predation on Enallagma selective pressure?

Natural History & EvolutionAttempts to explain female color polymorphism in various species of damselfly—particularly Enallagma—have failed to yield convincing data. Increased risk of fish predation on the more conspicuous female Enallagma morph is a worthwhile hypothesis to test because Enallagma are found co-existing with species of fish that are able to detect differences in UV reflection, such as rock bass (Ambloplites rupestris). Rock bass caught in Douglas Lake, Michigan were tested for the ability to differentiate between a conspicuous blue male Enallgama carunculatum damselfly, a male E. carunculatum whose UV reflectance had been diminished with sunscreen (in order to mimic the UV reflectance of a female heteromorph) and male Ishnura, whose color morphology is similar to the female E. carunculatum heteromorph. Attempts to mimic a natural setting failed at obtaining data due to no reactivity from the fish being tested. Rock bass were responsive to a line and hook test. No trend in the reaction time of the rock bass to each of the morphs tested was observed. This does not sufficiently accept the null hypothesis, and more testing should be done on how much UV reflection has an effect on fish prey choice, and also how that relates to polymorphic damselflies.http://deepblue.lib.umich.edu/bitstream/2027.42/57476/1/Hubbard_Kalash_Wheeler_2007.pd

Two coastal upwelling domains in the northern California Current system

A pair of hydrographic sections, one north and one south of Cape Blanco at 42.9N, was sampled in five summers (1998–2000 and 2002–2003). The NH line at 44.6N lies about 130 km south of the Columbia River, and spans a relatively wide shelf off Newport, Oregon. The CR line at 41.9N off Crescent City, California, lies 300 km farther south and spans a narrower shelf. Summer winds are predominantly southward in both locations but the southward winds are stronger on the CR line. Sampling included CTD/rosette casts (to measure temperature, salinity, dissolved oxygen, nutrients, chlorophyll), zooplankton net tows and continuous operation of an Acoustic Doppler Current Profiler. We summarize and compare July-August observations from the two locations. We find significant summer-season differences in the coastal upwelling domains north and south of Cape Blanco. Compared to the domain off Newport, the domain off Crescent City has a more saline, cooler, denser and thicker surface mixed layer, a wider coastal zone inshore of the upwelling front and jet, higher nutrient concentrations in the photic zone and higher phytoplankton biomass. The southward coastal jet lies near the coast (about 20–30 km offshore, over the shelf) on the NH line, but far from shore (about 120 km) on the CR line; a weak secondary jet lies near the shelf-break (35 km from shore) off Crescent City. Phytoplankton tend to be light-limited on the CR line and nutrient-limited on the NH line. Copepod biomass is high (15 mg C m−3) inshore of the mid-shelf on both NH and CR lines, and is also high in the core of the coastal jet off Crescent City. The CR line shows evidence of deep chlorophyll pockets that have been subducted from the surface layer. We attribute these significant differences to stronger mean southward wind stress over the southern domain, to strong small-scale wind stress curl in the lee of Cape Blanco, and to the reduced influence of the Columbia River discharge in this region

Dual hollow-core anti-resonant fibres

While hollow core-photonic crystal fibres are now a well-established fibre technology, the majority of work on these speciality fibres has been on designs with a single core for optical guidance. In this paper we present the first dual hollow-core anti-resonant fibres (DHC-ARFs). The fibres have high structural uniformity and low loss (minimum loss of 0.5 dB/m in the low loss guidance window) and demonstrate regimes of both inter-core coupling and zero coupling, dependent on the wavelength of operation, input polarisation, core separation and bend radius. In a DHC-ARF with a core separation of 4.3 µm, we find that with an optimised input polarisation up to 65% of the light guided in the launch core can be coupled into the second core, opening up applications in power delivery, gas sensing and quantum optics

Modal content in hypocycloid Kagomé hollow core photonic crystal fibers

The modal content of 7 and 19 cell Kagomé anti resonant hollow core fibers (K-ARF) with hypocycloid core surrounds is experimentally investigated through the spectral and spatial (S2) imaging technique. It is observed that the 7 and 19 cell K-ARF reported here, support 4 and 7 LP mode groups respectively, however the observation that K-ARF support few mode groups is likely to be ubiquitous to 7 and 19 cell K-ARFs. The transmission loss of the higher order modes (HOMs) was measured via S2 and a cutback method. In the 7 cell K-ARF it is found that the LP11 and LP21 modes have approximately 3.6 and 5.7 times the loss of the fundamental mode (FM), respectively. In the 19 cell it is found that the LP11 mode has approximately 2.57 times the loss of the FM, while the LP02 mode has approximately 2.62 times the loss of the FM. Additionally, bend loss in these fibers is studied for the first time using S2 to reveal the effect of bend on modal content. Our measurements demonstrate that K-ARFs support a few mode groups and indicate that the differential loss of the HOMs is not substantially higher than that of the FM, and that bending the fiber does not induce significant inter modal coupling. A study of three different input beam coupling configurations demonstrates increased HOM excitation at output and a non-Gaussian profile of the output beam if poor mode field matching is achieved

Low loss kagome fiber in the 1µm wavelength region

We present a Kagome hollow core fiber with record low loss (12.3dB/km at 1010nm), a wide 3dB bandwidth (150nm), low bend sensitivity and large mode field diameter (~30µm), tailored for high power delivery applications

Recent advances in hollow fiber technology for telecoms applications

We review our recent work on the modelling, fabrication and characterization of hollow-core photonic bandgap fibers. We discuss the modal content of these fibers, as well as the opportunities and challenges presented by modal interactions in space division multiplexed transmission applications