Gene expression profiles highlight adaptive brain mechanisms in corticotropin releasing factor overexpressing mice.

Corticotropin-releasing factor (CRF) plays an important role in mediating central and peripheral responses to stress. Alterations in CRF system activity have been linked to a number of psychiatric disorders, including anxiety and depression. Aim of this study was to elucidate homeostatic mechanisms induced by lifelong elevated CRF levels in the brain. We therefore profiled gene expression in several brain areas of transgenic mice overexpressing CRF (CRF-OE), a model for chronic stress. Several genes showed altered expression levels in CRF-OE mice when compared to their wild type littermates and were confirmed by quantitative PCR. Differences in gene expression profiles revealed the presence of previously unrecognized homeostatic mechanisms in CRF-OE animals. These included changes in glucocorticoid signaling, as exemplified by changes in 11beta-hydroxysteroid dehydrogenase type 1, FK506 binding protein 5 and serum/glucocorticoid kinase. Alterations in expression of genes involved in myelination (myelin, myelin-associated glycoprotein), cell proliferation and extracellular matrix formation (Edg2, Fgfr2, decorin, brevican) suggest changes in the dynamics of neurogenesis in CRF-OE. Pronounced changes in neurotensin (NT) receptors 1 and 2 mRNA were identified. Overall downregulation of NT receptors in CRF-OE animal was substantiated by receptor binding studies. Pronounced neurotensin receptor downregulation was observed for NT type 1 receptors in limbic brain areas, suggesting that NT could be implicated in some of the effects attributed to CRF overexpression. These data show that lifelong exposure to excessive CRF leads to adaptive changes in the brain which could play a role in some of the behavioral and physiological alterations seen in these animals.

Transcriptional response to corticotropin-releasing factor in AtT-20 cells.

Corticotropin-releasing factor (CRF) plays a central role in the regulation of the hypothalamic-pituitary-adrenal axis, mediating endocrine and behavioral responses to various stressors. Two high-affinity receptors for CRF have been described. Although many of the intracellular signaling pathways activated by CRF have been studied extensively, our knowledge of transcriptional responses downstream of the CRF receptor 1 (CRFR1) is still limited. To elucidate gene networks regulated by CRF and CRFR1, we applied microarray technology to explore transcriptional response to CRF stimulation. Therefore, mouse pituitary-derived AtT-20 cells were exposed continuously to CRF either in the presence or absence of the specific CRFR1 antagonist R121919. Transcriptional responses to different treatments were studied in a time course ranging from 0.5 to 24 h. Microarray data were analyzed using classic microarray data analysis tools such as correspondence factor analysis, cluster analysis, and fold-change filtering. Furthermore, spectral map analysis was applied, a recently introduced unsupervised multivariate analysis method. A broad and transient transcriptional response to CRF was identified that could be blocked by the antagonist. This way, several known CRF-induced target genes and novel CRF responsive genes were identified. These include transcription factors such as cAMP-responsive element modulator (7x increased), secreted peptides such as cholecystokinin (1.5x), and proteins involved in modulating intracellular signaling, such as regulator of G-protein signaling 2 (11x). Up-regulation of many of these genes can be explained as negative feedback, attenuating CRF-activated pathways. In addition, spectral map analysis proved to be a promising new tool for microarray data analysis.

Sensory deficits in mice hypomorphic for a mammalian homologue of unc-53.

The migration of cells and the extension of cellular processes along pathways to their defined destinations are crucial in the development of higher organisms. Caenorhabditis elegans unc-53 plays an important role in cell migration and the outgrowth of cellular processes such as axons. To gain further insight into the biological function of unc53H2, a recently identified mammalian homologue of unc-53, we have generated mice carrying a mutation of unc53H2 and provide evidence that unc53H2 is involved in neuronal development and, more specifically, the development of different sensory systems. The unc53H2 hypomorphic mouse showed a general impaired acuity of several sensory systems (olfactory, auditory, visual and pain sensation) which in case of the visual system was corroborated by the morphological observation of hypoplasia of the optic nerve. We hypothesize that in analogy with its C. elegans homologue, unc53H2 may play a role in the processes of cellular outgrowth and migration.

Graphical exploration of gene expression data: a comparative study of three multivariate methods.

This article describes three multivariate projection methods and compares them for their ability to identify clusters of biological samples and genes using real-life data on gene expression levels of leukemia patients. It is shown that principal component analysis (PCA) has the disadvantage that the resulting principal factors are not very informative, while correspondence factor analysis (CFA) has difficulties interpreting distances between objects. Spectral map analysis (SMA) is introduced as an alternative approach to the analysis of microarray data. Weighted SMA outperforms PCA, and is at least as powerful as CFA, in finding clusters in the samples, as well as identifying genes related to these clusters. SMA addresses the problem of data analysis in microarray experiments in a more appropriate manner than CFA, and allows more flexible weighting to the genes and samples. Proper weighting is important, since it enables less reliable data to be down-weighted and more reliable information to be emphasized.