Biomedical subjects

Thomas D Singer

Publications and source records attributed to Thomas D Singer.

3 recordsLinked to original sources

PubMed2006

Tissue-specific modulation of glucocorticoid receptor expression in response to salinity acclimation in rainbow trout.

While studies clearly point to a role for cortisol signaling in seawater adaptation, very little is known about salinity impact on glucocorticoid receptor (GR) expression in fish. To this end, we investigated the temporal GR expression in the gill and liver of rainbow trout (Oncorhynchus mykiss) to salinity exposure. Trout were subjected to gradual salinity increases (11 ppt for 1 d, 17 ppt for 2 d and 23 ppt for 2 d) over a five day period. Gill Na(+), K(+)-ATPase alpha-subunit mRNA showed a transient elevation with salinity exposure, while gill cystic fibrosis transmembrane conductance regulator mRNA was not significantly affected by salinity. Liver PEPCK transcript levels showed a transient increase at day 1, but not at day 3 or day 5 of salinity exposure, while the activity of this enzyme was significantly depressed at all time points. Liver glycogen content was also significantly reduced by salinity exposure compared to the freshwater group. Gill GR transcript levels were 3-fold greater upon salinity exposure and this level was maintained over the 5 day period, while gill GR protein content remained unchanged except for a significant drop at day 1 of salinity exposure. Liver GR transcript levels showed no significant change with salinity exposure, while GR protein content was transiently elevated at day 3, but not at day 1 or day 5 of salinity exposure. The tissue-specific GR transcript response in the gill leads us to hypothesize a role for osmosensory signal transduction pathway in the regulation of GR expression in fish. Collectively, salinity exposure modulates GR expression and glucocorticoid signaling in rainbow trout.

Acclimatization↗

PubMed2004

Salinity acclimation affects the somatotropic axis in rainbow trout.

In this study, we set out to examine the role of the somatotropic axis in the ion-regulation process in rainbow trout. Specifically, our objective was to examine whether plasma insulin-like growth factor-binding proteins (IGFBPs) are modulated by gradual salinity exposure. To this end, freshwater (FW)-adapted rainbow trout were subjected to gradual salinity increases, up to 66% seawater, over a period of 5 days. During this acclimation process, minimal elevations in plasma Ca2+ and Cl- were seen in the salinity-acclimated groups compared with FW controls. There were no changes in plasma Na+ levels, and only a minor transient change in plasma cortisol levels was seen with salinity exposure. The salinity challenged animals responded with elevations in plasma growth hormone (GH) and IGF-I levels and gill Na+-K+-ATPase activity. We identified IGFBPs of 21, 32, 42, and 50 kDa in size in the plasma of these animals, and they were consistently higher with salinity. Despite the overall increase in IGFBPs with salinity, transient changes in individual BPs over the 5-day period were noted in the FW and salinity-exposed fish. Specifically, the transient changes in plasma levels of the 21-, 42-, and 50-kDa IGFBPs were different between the FW and salinity groups, while the 32-kDa IGFBP showed a similar trend (increases with sampling time) in both groups. Considered together, the elevated plasma IGFBPs suggest a key role for these binding proteins in the regulation of IGF-I during salinity acclimation in salmonids.

Acclimatization↗

PubMed2002

Applications of DNA and protein microarrays in comparative physiology.

DNA microarrays have revolutionized gene expression studies and made large-scale parallel measurement of whole genome expression a feasible technique in model species where genomes are well characterized. Such studies are perfectly suited to unraveling the complex regulation and/or interaction of both genes and proteins likely involved in most physiological processes. Gene expression profiles are currently being used to identify genes underlying a range of physiological responses. Characterization of these genes will help to elucidate the pathways and processes regulating physiological processes. Expanding the use of DNA microarrays to non-model species that have been critical in elucidating certain physiological pathways will be valuable in determining the genes associated with these processes. Approaches that do not require complete genome information have recently been applied to "non-model" organisms. As whole genomes are sequenced for non-model organisms, the application of DNA microarrays to comparative physiology will expand even further. The recent development of protein microarrays will be critical in understanding the regulation of physiological processes not accounted for at the genomic level. Together, DNA and protein microarrays provide the most thorough and efficient method of understanding the molecular basis of physiological processes to date. In turn, classical physiological approaches will be vital in characterizing and verifying the function of the novel genes identified by microarray experiments. Ultimately, DNA and protein microarray expression profiles may be used to predict physiological responses.

Journal Article↗