THE INFLUENCE OF BACE1 EXPRESSION ON THE RECRUITMENT OF MACROPHAGES TO THE INJURED PERIPHERAL NERVE

Macrophages play a critical role in regeneration following peripheral nerve injury. Hematogenous macrophages are recruited to the distal nerve segment and shape the injured nerve microenvironment to be more conducive to regeneration through the clearance of cellular debris and the production of neurotrophic factors. Enhanced macrophage recruitment and debris clearance has been observed in BACE1 KO mice. This phenotype could be the result of BACE1 activity in macrophages, other nerve resident cells (neurons, Schwann cells), or it could also be the result of the hypomyelination phenotype that is also observed in BACE1 KO mice. To date it is uncertain what potential mechanisms may be driving this enhanced recruitment and debris clearance phenotype. Further, it is unknown which cell types in the peripheral microenvironment contribute most towards this phenotype when BACE1 is deleted. BACE1 is a promiscuous enzyme and has many substrates, thus may play a role in a variety pathways that could result in this enhanced macrophage recruitment and debris clearance phenotype. This thesis discusses several known BACE1 substrates and how they could impact macrophages in the context of peripheral nerve regeneration. Previous work done in our lab suggests that elimination of expression of BACE1 in cells derived from bone marrow may recapitulate the enhanced macrophage recruitment and activity phenotype. This thesis utilizes a mouse model with macrophage specific deletion of BACE1 to investigate whether BACE1 expression by macrophages mediates the immumodulatory phenotype observed in global BACE1 KO mice. This thesis demonstrates that there is not enhanced recruitment of macrophages to the injured peripheral nerve following injury. This suggests that the elimination of BACE1 expression by macrophages is not essential for the increased recruitment phenotype observed in global BACE1 KO mice

An Imprint of Molecular Cloud Magnetization in the Morphology of the Dust Polarized Emission

We describe a morphological imprint of magnetization found when considering the relative orientation of the magnetic field direction with respect to the density structures in simulated turbulent molecular clouds. This imprint was found using the Histogram of Relative Orientations (HRO): a new technique that utilizes the gradient to characterize the directionality of density and column density structures on multiple scales. We present results of the HRO analysis in three models of molecular clouds in which the initial magnetic field strength is varied, but an identical initial turbulent velocity field is introduced, which subsequently decays. The HRO analysis was applied to the simulated data cubes and mock-observations of the simulations produced by integrating the data cube along particular lines of sight. In the 3D analysis we describe the relative orientation of the magnetic field $\mathbf{B}$ with respect to the density structures, showing that: 1.The magnetic field shows a preferential orientation parallel to most of the density structures in the three simulated cubes. 2.The relative orientation changes from parallel to perpendicular in regions with density over a critical density $n_{T}$ in the highest magnetization case. 3.The change of relative orientation is largest for the highest magnetization and decreases in lower magnetization cases. This change in the relative orientation is also present in the projected maps. In conjunction with simulations HROs can be used to establish a link between the observed morphology in polarization maps and the physics included in simulations of molecular clouds.Comment: (16 pages, 11 figures, submitted to ApJ 05MAR2013, accepted 07JUL2013

Delayed crystallization of ultrathin Gd2O3 layers on Si(111) observed by in situ X-ray diffraction

We studied the early stages of Gd2O3 epitaxy on Si(111) in real time by synchrotron-based, high-resolution X-ray diffraction and by reflection high-energy electron diffraction. A comparison between model calculations and the measured X-ray scattering, and the change of reflection high-energy electron diffraction patterns both indicate that the growth begins without forming a three-dimensional crystalline film. The cubic bixbyite structure of Gd2O3 appears only after a few monolayers of deposition

Tracing H2 column density with atomic carbon (CI) and CO isotopologues

We present first results of neutral carbon ([CI], 3P1 - 3P0 at 492 GHz) and carbon monoxide (13CO, J = 1 - 0) mapping in the Vela Molecular Ridge cloud C (VMR-C) and G333 giant molecular cloud complexes with the NANTEN2 and Mopra telescopes. For the four regions mapped in this work, we find that [CI] has very similar spectral emission profiles to 13CO, with comparable line widths. We find that [CI] has opacity of 0.1 - 1.3 across the mapped region while the [CI]/13CO peak brightness temperature ratio is between 0.2 to 0.8. The [CI] column density is an order of magnitude lower than that of 13CO. The H2 column density derived from [CI] is comparable to values obtained from 12CO. Our maps show CI is preferentially detected in gas with low temperatures (below 20 K), which possibly explains the comparable H2 column density calculated from both tracers (both CI and 12CO underestimate column density), as a significant amount of the CI in the warmer gas is likely in the higher energy state transition ([CI], 3P2 - 3P1 at 810 GHz), and thus it is likely that observations of both the above [CI] transitions are needed in order to recover the total H2 column density.Comment: accepted for publication in ApJ Letter