Modeling and identification of a gene regulatory network programming erythropoiesis (1)

The development of mature blood cells of distinct lineages from the hematopoietic stem cells (hematopoiesis) involves a progressive restriction of differentiation potential and the establishment of lineage-specific gene expression profiles. The establishment of these profiles relies on lineage-specific transcription factors to modulate the expression of their target genes. This work is embedded in a wider ErasmusMC/CWI collaboration that develops the informatics and mathematics to underpin studies on gene expression regulation by mapping and analyzing the regulatory pathways and networks of transcription factors that control cellular functions (so called 'Gene Regulatory Networks' or 'GRNs'). This project is concerned with the mathematical part and concentrates on a GRN central to erythropoiesis. Among the many housekeeping and tissue-specific genes involved in the differentiation and the commitment of hematopoietic stem cells to erythrocytes (erythropoiesis), we focus on a small pool of genes (Gata-1, Gata-2, Pu.1, EKLF, FOG-1, alpha/beta-globin) known to be critically involved in an intricate but well-less investigated regulatory circuit. Based on the regulatory interactions in the GRN we have developed models in the form of a system to account for the dynamics of gene expression and regulation involved in this process. Because of the lack of information about a significant number of model parameters, our focus is on system identification. In this first report some preliminary results are presented based on synthetic data. However, time series of the levels of all relevant mRNA’s are available from micro-array analysis of G1E cells, a murine cell line which recapitulates erythropoiesis. In the follow-up report a detailed account will be given of the parameter estimation and identifiability analysis with respect to these data. This will eventually allow for a thorough evaluation of the role of various characterized as well as hypothetical regulatory mechanisms. In depth characterization of the necessary expression patterns and gene regulatory interactions responsible for the the set of commitments all along the erythroid lineage is essential to gain fundamental insight into the behaviour of these complex networks and to design further experiments. Ultimately, this may lead to ways to rescue erythroid differentiation in several anemic diseases

Information seeking about the psychological contract: the impact on newcomers' evaluations of their employment relationship

Both socialization and psychological contract literature demonstrate that the first months of employment are critical for the development of a positive psychological contract with organizational newcomers (e.g. Bauer et al., 1994, Robinson et al., 1994, Thomas & Anderson, 1998). For this reason, it is the objective of this study to explicate newcomers' psychological contract perceptions and evaluations during the socialization process, using information seeking as the central antecedent variable. Based upon socialization and psychological contract literature, hypotheses are formulated that address the relationship between newcomer information seeking and (1) changes in newcomers' perceptions of promises exchanged with their employer, and (2) newcomers' evaluations of their employment relationship one year after entry. To test our hypotheses, a four-wave longitudinal survey among 333 newcomers has been conducted, covering the first year of their new employment relationship. These newcomers, all white-collar level, belonged to six large organizations located in Belgium. Data collections took place at four moments: (T1) at entry, (T2) three months after entry, (T3) six months after entry, and (T4) one year after entry. Results suggest that during the socialization process newcomers change their perceptions of promises but that, contrary to our expectations, these changes are not related to their information-seeking behaviors. On the other hand, and in line with our hypotheses, the frequency of contract-related information seeking during the socialization process significantly affects newcomers' evaluations of their employment relationship one year after entry. Newcomers who engage more frequently in information seeking make up a more positive evaluation of psychological contract fulfillment and they are also more satisfied with their employment relationship in general. Our findings are discussed in view of the available literature on newcomer socialization and psychological contract development and implications for theories on psychological contract development are drawn

Effects of random RF disturbances on aeronautical communication systems

Air Traffic Control (ATC) and their responsible authorities have been always very sensitive to safety of the systems they are using to guarantee a fool-proof and environmentally safe operation of the facilities to provide air traffic services and guidance for the airplanes. This paper deals with the influence of random systems like badly shielded ignition systems of cars and motorbikes on standard air-ground aviation communication systems. Following a series of theoretical simulations, a measurement campaign quantifying this influence is described. This campaign is shedding some light on the fundamental behaviour and mechanisms of the RF disturbances caused by (shielded and unshielded) spark plug systems. It will be investigated both in the time domain and in the frequency domain. An analysis of the inaccuracies of those measurements is performed and the influence of (shielded and unshielded) spark plug systems on aviation communication systems (still based on A(mplitude)M(odulation)) is explained in detail

Effects of pulsed RF disturbances on aeronautical communication systems

Air Traffic Control (ATC) and their responsible authorities have been always very sensitive to safety of the systems they are using to guarantee a fool-proof and environmentally safe operation of the facilities to provide guidance for the airplanes. This paper deals with the influence of a pulsed systems on standard air-ground aviation communication systems. A measurement campaign is described. An analysis of the inaccuracies of those measurements is performed and the influence of (shielded and unshielded) spark plug systems on aviation communication systems (still based on A(mplitude) M(odulation)) is explained in detai

Modeling Lewis acid catalyzed reactions in MOFs : how to solve the challenges?

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The role of career-self-management in determining employees' perceptions and evaluations of their psychological contract and their esteemed value of career activities offered by the organization

The development of a career is subject to an interaction and exchange process between employer and employee. In addition, the changing nature and meaning of a career in today's competitive labor market has stimulated researchers to relate this with the psychological contract theory (e.g. Herriot, 1998, Sparrow & Cooper, 1998). However, the research domain of career self-management and the potential influence on the perception and evaluation of the psychological contract and on career activities offered by the organization in particular, has not been explicitly explored yet. Studies of Kossek et al. (1998) and Sturges et al. (2000) show that employees who actively manage their own career, hold higher expectations towards their employer, since they develop a clear idea on what their career objectives are and on how they want to achieve them. Hence, hypotheses are formulated that address the relationship between career self-management and (1) the perception and evaluation of the psychological contract, (2) the esteemed value and perception of career activities offered by the employer. To test our hypotheses, a cross-sectional survey among 491 employees of six Belgian organizations has been conducted. Our results suggest that the extent to which employees manage their own career has a significant impact on (1) the perception and evaluation of promises exchanged with their employer and (2) the importance they attach to career activities and the evaluation they make of the career activities offered by the company. First, employees who actively manage their own career, believe their employer has made more promises to them relating to different content domains of the psychological contract. Secondly, employees who actively manage their own career, are more positive on the fulfillment of their psychological contract. More specifically, this conclusion can be applied to the two dimensions of the psychological contract that are job-related, i.e. career development opportunities, job content. Thirdly, employees who actively manage their own career, attach more importance to the career activities offered by the company. In particular those career activities that consist of real guidance and steering from the organization. Furthermore, these employees also evaluate the provision of career management practices in the organization more positively. Our findings are discussed in view of the literature on career self-management and psychological contracts and they add new important insights

Modeling Lewis catalyzed reactions in Metal Organic Frameworks

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