Analysis of Hepatocyte Secretion Pathways: A Case Study on Hepatic Apolipoproteins, Serum Albumin, and Hepatitis C Virus

The hepatocyte is one of the major secretory cell types in the body. It fulfills many of the liver\u27s essential functions in protein secretion, lipid storage and transport, and excretion. Some of these functions are carried out via polarized secretion of simple protein cargo, such as serum albumin, or large macromolecular lipid-protein complexes, the lipoproteins. The hepatocyte is also the site of infection of several hepatotropic viruses. Of these, hepatitis C virus (HCV) is peculiar due to its close structural and functional association with the hepatic lipoproteins. All these cargoes are transported from the endoplasmic reticulum (ER) to the cell surface by the vesicular secretory pathway, yet insufficient knowledge exists regarding the molecular regulation of their secretion by the hepatocyte. Furthermore, differential modalities of regulation may be involved in the shuttling of such a diverse set of cargoes as albumin, the lipoproteins and HCV. The work presented here head-starts a comprehensive examination of how the hepatocyte regulates the secretion of the following cargoes: serum albumin, the apolipoproteins E and B100 (ApoE and ApoB100, respectively, both lipoprotein components, and surrogate markers for these complex macromolecular particles), and HCV, a lipoprotein-associated virus. I propose to combine genetic, biochemical, virological and imaging approaches to identify which vesicular secretory pathways are utilized by each of these cargoes. These approaches include inactivation of specific vesicular transport pathways, accompanied by measurements of their effects on cargo secretion efficiencies, and establishment of functional fluorescent protein-tagged cargo markers to be used in live cell imaging experiments. I begin by describing a dominant negative (DN) Rab GTPase screen that I performed to identify Rab proteins involved in ApoE, ApoB100 or albumin secretion. The small Rab GTPases control individual steps of vesicular transport. I analyzed how expression of individual dominant negative Rab proteins affected cargo secretion compared to expression of their wild type (WT) counterparts. I identified several Rabs that caused significant changes in secretion, many of which had previously been described as regulators of various exocytic vesicular transport steps. I next present ongoing work that aims to define the involvement of the Rabs 11a, 11b, 8a, and 8b in hepatic cargo secretion. Their dominant negative mutants exhibited some of the largest secretion phenotypes in my dominant negative Rab screen. These Rabs have been implicated in various aspects of post-Golgi secretion in polarized and non-polarized cell types. I thus discuss the implications of their involvement in cargo secretion in the polarized hepatocyte and outline my ongoing efforts to define the parameters of this involvement. I also investigated the function of Rab1b in hepatic secretion. I show that inactivation of Rab1 function, by expression of a set of dominant negative mutants, or by expression of a bacterial effector which affects Rab1 function, led to impairment of albumin, ApoE, ApoB100 and HCV secretion. I implicate Rab1, for the first time to my knowledge, in the transport of these cargoes. I also document differences in the sensitivity of cargo secretion to the various means of Rab1 inactivation. ApoE secretion, in particular, was insensitive to several means of transport inactivation, consistent with existing models of differential regulation of hepatic cargo transport. Lastly, I functionally characterize an ApoE-green fluorescent protein fusion (ApoE-GFP). I show that while ApoE-GFP does not support infectious HCV release, a hallmark function of untagged ApoE, ApoE-GFP nevertheless reproduces several known behaviors of ApoE that have been associated with lipoprotein release. I thus conclude that ApoE-GFP may be a useful marker for live cell imaging of lipoprotein release. This work therefore identifies potential regulators of hepatic cargo transport, establishes molecular tools useful for the continued study of cargo secretion in hepatocytes and elsewhere, and advances the understanding of the involvement of Rabs 11, 8, and, in particular, Rab1, in the regulation of hepatic cargo transport. I propose that this work forms a solid foundation for extensive studies on how these biomedically relevant hepatic cargoes are secreted

Experiences of aiding autobiographical memory using the sensecam

Human memory is a dynamic system that makes accessible certain memories of events based on a hierarchy of information, arguably driven by personal significance. Not all events are remembered, but those that are tend to be more psychologically relevant. In contrast, lifelogging is the process of automatically recording aspects of one's life in digital form without loss of information. In this article we share our experiences in designing computer-based solutions to assist people review their visual lifelogs and address this contrast. The technical basis for our work is automatically segmenting visual lifelogs into events, allowing event similarity and event importance to be computed, ideas that are motivated by cognitive science considerations of how human memory works and can be assisted. Our work has been based on visual lifelogs gathered by dozens of people, some of them with collections spanning multiple years. In this review article we summarize a series of studies that have led to the development of a browser that is based on human memory systems and discuss the inherent tension in storing large amounts of data but making the most relevant material the most accessible

Baby Blue

https://digitalcommons.library.umaine.edu/mmb-vp/5935/thumbnail.jp

Exact Maximal Height Distribution of Fluctuating Interfaces

We present an exact solution for the distribution P(h_m,L) of the maximal height h_m (measured with respect to the average spatial height) in the steady state of a fluctuating Edwards-Wilkinson interface in a one dimensional system of size L with both periodic and free boundary conditions. For the periodic case, we show that P(h_m,L)=L^{-1/2}f(h_m L^{-1/2}) for all L where the function f(x) is the Airy distribution function that describes the probability density of the area under a Brownian excursion over a unit interval. For the free boundary case, the same scaling holds but the scaling function is different from that of the periodic case. Numerical simulations are in excellent agreement with our analytical results. Our results provide an exactly solvable case for the distribution of extremum of a set of strongly correlated random variables.Comment: 4 pages revtex (two-column), 1 .eps figure include

A parallel multigrid solver for multi-patch Isogeometric Analysis

Isogeometric Analysis (IgA) is a framework for setting up spline-based discretizations of partial differential equations, which has been introduced around a decade ago and has gained much attention since then. If large spline degrees are considered, one obtains the approximation power of a high-order method, but the number of degrees of freedom behaves like for a low-order method. One important ingredient to use a discretization with large spline degree, is a robust and preferably parallelizable solver. While numerical evidence shows that multigrid solvers with standard smoothers (like Gauss Seidel) does not perform well if the spline degree is increased, the multigrid solvers proposed by the authors and their co-workers proved to behave optimal both in the grid size and the spline degree. In the present paper, the authors want to show that those solvers are parallelizable and that they scale well in a parallel environment.Comment: The first author would like to thank the Austrian Science Fund (FWF) for the financial support through the DK W1214-04, while the second author was supported by the FWF grant NFN S117-0

Boundary form factors of the sinh-Gordon model with Dirichlet boundary conditions at the self-dual point

In this manuscript we present a detailed investigation of the form factors of boundary fields of the sinh-Gordon model with a particular type of Dirichlet boundary condition, corresponding to zero value of the sinh-Gordon field at the boundary, at the self-dual point. We follow for this the boundary form factor program recently proposed by Z. Bajnok, L. Palla and G. Takaks in hep-th/0603171, extending the analysis of the boundary sinh-Gordon model initiated there. The main result of the paper is a conjecture for the structure of all n-particle form factors of two particular boundary operators in terms of elementary symmetric polynomials in certain functions of the rapidity variables. In addition, form factors of boundary "descendant" fields have been constructedComment: 14 pages LaTex. Version to appear in J. Phys.

Evidence of hybridization between Galatella villosa and G. linosyris, and a taxonomic reappraisal of the hybrid G. xsubvillosa

At the westernmost distribution of the steppe herbaceous plant, Galatella villosa, in Hungary, Serbia and Ukraine, we recently observed intermediate specimens between this species and its close relative, G. linosyris. We were able to demonstrate the hybrid origin of these individuals by sequencing the biparentally inherited nuclear ribosomal internal transcribed spacer (nrITS) region and checking additive polymorphism in the hybrids. In addition, examination of the maternally inherited plastid regions (trnH-psbA and trnL-trnF intergenic spacers) revealed that G. villosa is likely to be the maternal parent in the Hungarian and Ukrainian populations and G. linosyris in the Serbian population. The intermediate forms produced only sterile seeds. The alleged hybrid between the above two species has already been described as G. xsubvillosa based on a very brief diagnosis. Still, the analysis of the morphological characters using linear discriminant analyses clearly separated the holotype of G. xsubvillosa from individuals of G. linosyris x G. villosa. The latter appeared to be morphologically intermediate between populations of G. villosa and G. linosyris. Contrary to the originally stated hybrid origin of the type plants of G. xsubvillosa, morphological evidence indicates the involvement of G. divaricata not G. linosyris. The hybrid G. linosyris x G. villosa is thus described here, as a new nothospecies G. xfeketegaborii. This study highlights the power of easily available molecular phylogenetic tools for demonstrating the hybrid origin of plants and illustrates how additive polymorphism can be distinguished from other types of intraindividual polymorphism in nuclear DNA sequences.Peer reviewe