Thesis (Ph. D.)--University of Chicago, Committee on Developmental Biology, March 2001. / Includes bibliographical references. Also available on the Internet.

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Thesis (Ph. D.)--University of Missouri--Columbia, 2001. / Typescript. Includes bibliographical references (leaves 109-111). Also available on the Internet.

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International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / The MESSENGER mission to Mercury will downlink data files via a protocol defined by the Consultative Committee for Space Data Systems (CCSDS) called the CCSDS File Delivery Protocol (CFDP). A reduced implementation of the protocol was developed for the spacecraft due to various system constraints and operational requirements. The software operates in conjunction with the playback features of the MESSENGER flight software allowing for the autonomous downlinking of files as well as providing for the management of the file system by the mission operations team. This paper presents the software implementation, metrics, and the lessons learned.

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Cells have evolved the ability to change continuously and adapt to their environment. An important way in which this dynamic modulation is achieved is by reversible phosphorylation, mediated by protein kinases and phosphatases. This thesis focuses on the temporal variations in expression of the proteins protein phosphatase 1 (PP1), protein phosphatase 2A (PP2A) and p53 tumour suppressor protein in proliferating and hexamethylene bisacetamide (HMBA) induced differentiating murine erythroleukaemic (MEL) cells. The study included analysis of variations of p53 mRNA in these cells. Protein variations were analysed in cell extracts using western immunoblotting. The p53 variations were evaluated further using enzyme-linked immunosorbent assay (ELISA); p53 mRNA was determined by reverse transcriptase polymerase chain reaction (RT-PCR). Dynamic variations in protein expression and mRNA were detected in both the untreated and HMBA treated MEL cell preparations. For PP1, an immunospecific band of molecular mass 36 kDa, corresponding to the catalytic subunit, was detected, while for PP2A, two immunospecific bands of 32 and 36 kDa were observed. For the PP2A, the 36 kDa band corresponded to the catalytic subunit of this protein and the 32 kDa band was believed to be a proteolytically cleaved form of the catalytic subunit. The mean values of results showed little significant difference between proliferating and differentiating MEL cells, emphasising that single time-point studies give incomplete and probably misleading information. Multiple time analysis for expression clearly showed evidence of oscillatory behaviour and modulation by the differentiating agent. The influence of HMBA on PP1, PP2A and p53 expression was variable for the different experiments and affected both the frequency and phasing of rhythms. The results add support to the view that dynamic oscillatory control processes play an important role in regulating cellular behaviour. Modulation of the dynamics of key proteins in the cell, such as PP1, PP2A and p53, may be an important mechanism of controlling cellular function and reversing neoplastic transformation.

Eukaryotische messenger-RNAs (mRNAs) müssen diverse Prozessierungsreaktionen durchlaufen, bevor sie der Translationsmaschinerie als Template für die Proteinbiosynthese dienen können. Diese Reaktionen beginnen bereits kotranskriptionell und schließen das Capping, das Spleißen und die Polyadenylierung ein. Erst nach dem die Prozessierung abschlossen ist, kann die reife mRNA ins Zytoplasma transportiert und translatiert werden. mRNAs interagieren in jeder Phase ihres Metabolismus mit verschiedenen trans-agierenden Faktoren und bilden mRNA-Ribonukleoproteinkomplexe (mRNPs) aus. Dieser „mRNP-Code“ bestimmt das Schicksal jeder mRNA und reguliert dadurch die Genexpression auf posttranskriptioneller Ebene. Für das La-verwandte Protein LARP4B (La-related protein 4B) wurde kürzlich eine direkte Interaktion mit den Translationsfaktoren PABPC1 (poly(A) binding protein, cytoplasmic 1) und RACK1 (receptor for activated C kinase) gefunden. Diese Befunde sowie die Assoziation mit aktiv translatierenden Ribosomen lässt vermuten, dass LARP4B zum mRNP-Code beiträgt. Die Domänenstruktur des Proteins legt darüber hinaus nahe, dass LARP4B direkt mRNAs bindet. Um einen Einblick in die Funktion von LARP4B und seiner in vivo RNA-Bindungspartner zu erhalten, wurde die mRNA-Assoziation transkriptomweit mit Hilfe von PAR-CLIP (Photoactivatable-Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation)-Experimenten bestimmt. Diese Daten zeigten, dass LARP4B ein spezifisches Set an zellulären mRNAs über Sequenzbereiche in deren 3’-untranslatierten Regionen bindet. Die bioinformatische Auswertung der PAR-CLIP-Daten identifizierte ein LARP4B-Bindemotiv, welches durch in vitro Bindungsstudien validiert werden konnte. Darüber hinaus belegten pSILAC (pulsed stable isotope labeling with amino acids in cell culture)-Experimente und eine transkriptomweite Analyse der mRNA-Level, dass LARP4B die Expression der Ziel-mRNAs beeinflusst, indem es die Stabilität der gebundenen Transkripte erhöht. LARP4B konnte somit als positiver Faktor der eukaryotischen Genexpression identifiziert werden. / Eukaryotic messenger RNAs (mRNAs) undergo several processing reactions before they can serve as a template for protein biosynthesis. These processing reactions begin co-transcriptionally and include capping, splicing and polyadenylation. Once the processing is complete, the mature mRNA can be exported to the cytoplasm for translation. Throughout the various steps of the metabolism, the mRNAs interact with different sets of trans-acting factors to form mRNA ribonucleoprotein complexes (mRNPs). This “mRNP code” determines the fate of any mRNA and thereby regulates gene expression at the post-transcriptional level. Recently, the La-related protein 4B (LARP4B) was shown to interact directly with two translation factors, the cytoplasmic poly(A) binding protein 1 (PABPC1) and the receptor for activated C kinase (RACK1). These findings as well as its association with actively translating ribosomes suggest that LARP4B contributes to the mRNP code. The domain architecture of LARP4B suggests that LARP4B might bind mRNA directly. To gain insight into the function of LARP4B and its in vivo RNA binding partners, the associated mRNAs were determined using the transcriptome-wide PAR-CLIP (Photoactivatable-Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation) technology. These data show that LARP4B binds to a specific set of cellular mRNAs at the 3’-untranslated regions (3’-UTR). The biocomputational analysis of the PAR-CLIP data identified the LARP4B binding motif which could be validated by in vitro binding studies. Furthermore, taken together, pSILAC (pulsed stable isotope labeling with amino acids in cell culture) data and a transcriptome-wide analysis of mRNA levels demonstrate that LARP4B influences target mRNA expression by stabilizing the bound transcript. In conclusion, LARP4B was identified as a positive regulator for eukaryotic gene expression.

Since the advent of the Internet as a means of communication, more and more people have been using electronic media for a variety of purposes including interpersonal communication, sending and receiving information as well as language learning purposes. Therefore, a line of research in this area seems necessary to gain a better understanding of various aspects involved in this topic and identify its possible advantages. To this end, the present study was an attempt to investigate the effectiveness of an online messaging application, namely WhatsApp Messenger, which is an example of computer-mediated communication tool where both synchronous and asynchronous online communication can occur, on Iranian intermediate EFL learners’ syntactic complexity. This research was an experimental study and had a pretest-posttest design. This study had an experimental and a control group. The participants in the experimental group of this study were 15 adult intermediate language learners. They were asked to participate in eight discussion tasks and post on WhatsApp Messenger for a period of two months. The quantitative analyses were carried out by running independent samples t-tests as well as Mann-Whitney U tests to determine the differences in terms of syntactic complexity. The results revealed that using WhatsApp Messenger for communication practice had significant impacts for this group of learners on eleven measures of syntactic complexity. In addition, a survey questionnaire was administered to further delve into the participants’ perceptions and beliefs about their experience of computer-mediated communication. The results showed that participants found this messaging tool helpful and were satisfied with it in terms of comfort level. Participants also showed positive feedback toward the design and implementation of the study. / Graduate