Unknown,Transcriptomics,Genomics,Proteomics

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The transcriptome of the medullary area postrema: The thirsty rat, the hungry rat and the hypertensive rat

ABSTRACT: The area postrema (AP) is a sensory circumventricular organ characterised by extensive fenestrated vasculature and neurons which are capable of detecting circulating signals of osmotic, cardiovascular, immune and metabolic status. The AP can communicate these messages via efferent projections to brainstem and hypothalamic structures that are able to orchestrate an appropriate response. We have used microarrays to profile the transcriptome of the AP in the Sprague Dawley (SD) and Wistar Kyoto (WKY) rat and present here a comprehensive catalogue of gene expression, focussing specifically on the population of ion channels, receptors and G protein-coupled receptors (GPCRs) expressed in this sensory tissue; of the GPCRs expressed in the rat AP we identified ~36% that are orphans having no established ligand. We have also looked at the ways in which the AP transcriptome responds to the physiological stressors of 72-hours dehydration (DSD) and 48-hours fasting (FSD) and have performed microarrays under these conditions. Comparison between the DSD and SD or between FSD and SD revealed only a modest number of AP genes that are regulated by these homeostatic challenges. The expression levels of a much larger number of genes are altered in the spontaneously hypertensive rat (SHR) AP compared to the normotensive WKY controls however. Finally, analysis of these ‘hypertension-related’ elements revealed genes that are involved in both the regulation of blood pressure and immune function and as such are excellent targets for further study. Using Affymetrix microarrays (Rat 230:2.0) we anaysed the transcriptome of the area postrema. Each microarray in the study represents an independent biological replicate of 5 animals.

ORGANISM(S): Rattus norvegicus

SUBMITTER: DAVID MURPHY

PROVIDER: E-GEOD-26660 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:The supraoptic nucleus (SON) of the hypothalamus is an important integrative brain structure that co-ordinates responses to perturbations in water balance and regulates maternal physiology through the release of the neuropeptide hormones vasopressin and oxytocin into the circulation. Both dehydration and lactation evoke a dramatic morphological remodelling of the SON, a process known as function-related plasticity. We hypothesise that some of the changes seen in SON remodelling are mediated by differential gene expression, and have thus used microarrays to document global changes in transcript abundance that accompany chronic dehydration in female rats, and in lactation. In situ hydridisation analysis has confirmed the differential expression of 3 of these genes, namely Tumour necrosis factor induced protein 6, Gonadotrophin inducible transcription factor 1 and Ornithine decarboxylase antizyme inhibitor 1. Comparison of differential gene expression patterns in male and female rats subjected to dehydration and in lactating rats has enabled the identification of common elements that are significantly enriched in gene classes with particular functions. Two of these are related to the requirement for increased protein synthesis and hormone delivery in the physiologically stimulated SON (translation initiation factor activity and endoplasmic reticulum-Golgi intermediate compartment respectively), whilst others are consistent with concept of SON morphological plasticity (collagen fibril organisation, extracellular matrix organization and biogenesis, extracellular structure organization and biogenesis and homophilic cell adhesion). We suggest that the genes co-ordinately regulated in the SON as a consequence of dehydration and lactation form a network that mediates the plastic processes operational in the physiologically activated SON. Each independent microarray sample represented the SON from either 5 female euhydrated, 5 dehydrated (water restriction for 72hours with food ad libitum) or 11 days lactating. In total, 5 microarrays were performed for the Dehydrated and the Lactation groups and 4 for the euhydrated controls. Samples within each group may be considered to be both biological and technical replicates. The GeneSpring-derived MAS5 data described in the publication is not included in this submission.

Project description:We have addressed the question of how different rodent species cope with the life-threatening homeostatic challenge of dehydration at the level of transcriptome modulation in the supraoptic nucleus (SON), a specialised hypothalamic neurosecretory apparatus responsible for the production of the antidiuretic peptide hormone arginine vasopressin (AVP). AVP maintains water balance by promoting water conservation at the level of the kidney. Dehydration evokes a massive increase in the regulated release of AVP from SON axon terminals located in the posterior pituitary, and this is accompanied by a plethora of changes in the morphology, electrophysiological properties, biosynthetic and secretory activity of this structure. Microarray analysis was used to generate a definitive catalogue of the genes expressed in the mouse SON, and to describe how the gene expression profile changes in response to dehydration. Comparison of the genes differentially expressed in the mouse SON as a consequence of dehydration with those of the rat has revealed many similarities, pointing to common processes underlying the function-related plasticity in this nucleus. In addition we have identified many genes that are differentially expressed in a species-specific manner. However, in many cases, we have found that the hyperosmotic cue can induce species-specific alterations in the expression of different genes in the same pathway. The same functional end can be served by different means, via differential modulation, in different species, of different molecules in the same pathway. We suggest that pathways, rather than specific genes, should be the focus of integrative physiological studies based on transcriptome data. Animals. Adult male C57BL/6 mice (Harlan Sera-Lab, Loughborough, UK) were group housed (4 per cage) under controlled temperature (21+ 2ºC) and diurnal light conditions (14-h light, 10-h dark, lights on at 05.00). Food and water were available ad libitum until the experiment commenced. Complete fluid deprivation was imposed for 48 hours starting at 11.00 a.m. Control animals maintained free access to drinking water, and both groups had access to standard laboratory rodent chow. Experiments on adult male rats described previously (27). All procedures were conducted in strict accordance with the Animal Scientific Procedures Act (1986), UK, and were approved by the local University of Bristol Ethical Review Process. Tissue collection. Mice were killed using cervical dislocation and the brain was carefully removed from the cranium and snap frozen using powdered dry ice and stored at -80oC for no more than 14 days. Sections of brain (14μm) were cut using an RNase free cryostat and mounted onto RNase free membrane coated glass slides (P.A.L.M. Membrane slides; P.A.L.M. Microlaser Technologies). Immediately after sectioning, frozen sections were thawed and fixed (30s; in 95% [v/v] EtOH), rehydrated (30s in each of 75% [v/v] and 50% [v/v] EtOH) before being stained (60s 1% [v/v] cresyl violet). Sections were then dehydrated in a graded EtOH series (30s in each of 50% [v/v], 75% [v/v] and 95% [v/v]. then 2x 30s in 100% [v/v]). Laser microdissection was performed using a P.A.L.M. MicrolaserSystem (P.A.L.M. Microlaser Technologies). The SON was identified with reference to Franklin and Paxinos (28) and the tissue from each animal was independently pooled into collection vials containing RNAlater® (Ambion, Huntingdon, UK). A single operative carried out all dissections. Total RNA was isolated without delay (within 24h) according to standard procedures that accompany the Ambion RNAqueous MicroKit (Ambion). Microarray analysis. Separate microarrays (n=4) were probed using independently generated target. For each completely independent replicate, tissue from 1 mouse was used for RNA extraction.

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The transcriptome of the medullary area postrema: The thirsty rat, the hungry rat and the hypertensive rat

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