Microarray analysis of relative gene expression stability for selection of internal reference genes in the rhesus macaque brain

Abstract Background Normalization of gene expression data refers to the comparison of expression values using reference standards that are consistent across all conditions of an experiment. In PCR studies, genes designated as "housekeeping genes" have been used as internal reference genes under the assumption that their expression is stable and independent of experimental conditions. However, verification of this assumption is rarely performed. Here we assess the use of gene microarray analysis to facilitate selection of internal reference sequences with higher expression stability across experimental conditions than can be expected using traditional selection methods. We recently demonstrated that relative gene expression from qRT-PCR data normalized using GAPDH, ALG9 and RPL13A expression values mirrored relative expression using quantile normalization in Robust Multichip Analysis (RMA) on the Affymetrix® GeneChip® rhesus Macaque Genome Array. Having shown that qRT-PCR and Affymetrix® GeneChip® data from the same hormone replacement therapy (HRT) study yielded concordant results, we used quantile-normalized gene microarray data to identify the most stably expressed among probe sets for prospective internal reference genes across three brain regions from the HRT study and an additional study of normally menstruating rhesus macaques (cycle study). Gene selection was limited to 575 previously published human "housekeeping" genes. Twelve animals were used per study, and three brain regions were analyzed from each animal. Gene expression stabilities were determined using geNorm, NormFinder and BestKeeper software packages. Results Sequences co-annotated for ribosomal protein S27a (RPS27A), and ubiquitin were among the most stably expressed under all conditions and selection criteria used for both studies. Higher annotation quality on the human GeneChip® facilitated more targeted analysis than could be accomplished using the rhesus GeneChip®. In the cycle study, multiple probe sets annotated for actin, gamma 1 (ACTG1) showed high signal intensity and were among the most stably expressed. Conclusions Using gene microarray analysis, we identified genes showing high expression stability under various sex-steroid environments in different regions of the rhesus macaque brain. Use of quantile-normalized microarray gene expression values represents an improvement over traditional methods of selecting internal reference genes for PCR analysis

Neuroendocrine control of the reproductive axis

RESEARCH THEME: The scientific papers presented in this bound volume reflect 20 years' worth of research that I have performed since obtaining my M.Sc., from the University of Edinburgh. The primary focus of this research has been in the field of reproductive neuroendocrinology, where I have tried to integrate findings from different experimental animal models to help elucidate the neuroendocrine mechanisms that control reproductive function. Inevitably, this has also led me to examine related topics such as glutamatergic and GABA-ergic neurotransmitter systems, circadian neuroendocrine rhythms, and environmental-neuroendocrine interactions. It is hoped that these basic studies will provide new insights into the development of effective therapies for human reproductive disorders.RESEARCH HIGHLIGHTS: (1) Having established a novel remote blood sampling set-up, I was able to clearly demonstrate that sex-steroid-independent diurnal changes in the pulsatile pattern of luteinizing hormone (LH) secretion play a central role in triggering the onset of puberty in female rats; (2) I was subsequently able to show that glutamate receptors represent a fundamental component of the reproductive neuroendocrine axis, and that their manipulation can profoundly influence reproductive function; (3) By developing mouse monoclonal antibodies that are highly specific to gonadotrophin-releasing hormone (GnRH), I made it possible for GnRH-producing neurones to be chemically characterized using multiple-label immunohistochemistry; so far, I have freely distributed these antibodies to >70 investigators around the world; (4) Through a series of photoperiodic and histochemical studies I was able to establish that an area of the brain known as the bed nucleus of the stria terminalis represents a key relay station for environmental signals that impinge on the GnRH neuronal circuits of seasonal breeding species; this finding has also helped to establish the hamster as an experimental model for seasonal affective disorder, (5) Traditionally, the neurotransmitter GABA was thought to exert its influence on the reproductive axis exclusively by its actions at the level of the hypothalamus; but this idea has now been brought into question because of my novel finding that GABA is also highly expressed within the pituitary gland itself; (6) Traditionally, control of gonadotrophin secretion in mammals was thought to be controlled by a single neuropeptide, known as mammalian GnRH or GnRH-l; my recent cloning of a second form of the GnRH (GnRH-ll), and demonstration of its unique expression pattern in the rhesus monkey hypothalamus, has opened up a new way of thinking about how the hypothalamus controls reproductive function.SCIENTIFIC PUBLICATIONS: Altogether, this research has resulted in the publication of 110 abstracts, which were presented either at national or international scientific meetings. A complete list of these abstracts is included in this volume, the most notable being: (1) the keynote address "Seasonal Reproduction" at the Canada West Society for Reproductive Biology, (Edmonton, Canada, 1992) (2) presentation of the Walpole Memorial Lecture "N-methyl-Daspartate receptor gene expression in the hamster hypothalamus and in immortalized luteinizing hormone-releasing hormone neurones" at the annual meeting of the Society for the Study of Fertility (Cambridge, England, 1993); and (3) the invited symposium presentation "Development and Aging of the Neuroendocrine Reproductive Axis of the Rhesus Macaque" at the International Primate Symposium (Inuyama City, Japan, 2000). The research has also resulted in the publication of 70 peer-reviewed papers and book chapters, including "Puberty in the Rat" (In; Physiology of Reproduction. Raven Press) which is considered to be one of the most definitive reviews of sexual maturation in rodents, and "Influence of Light and the Pineal Gland on Biological Rhythms" (In: Neuroendocrinolqy in Physiology and Medicine. Humana Press) which is considered to be one of the most comprehensive texts on the subject written specifically for medical and graduate students. The bound volume contains a collated set of these published papers, together with copies of eleven journal covers which feature original artwork/figures from my research (Journal covers include: Brain Research, Developmental Brain Research, Endocrinology, Journal of Endocrinology, and Molecular Brain Research).GRANT SUPPORT: None of my research would have been possible without financial support, predominantly in the form of competitive grants from the National Institutes of Health. I am extremely grateful for this continued support, which currently exceeds $500,000 per year in direct costs. As a form of scientific reciprocation, I have reviewed numerous grants for various funding agencies during the past two decades, including the National Institutes of Health (NIH). National Science Foundation. Canadian Institutes of Health Research. Natural Sciences and Engineering Research Council of Canada, and Agricultural and Food Research Council of the United Kingdom. I have also been an acf doc reviewer of manuscripts for 20 different scientific journals, and I currently serve on the editorial board of the journal Endocrinology

Age-related increase in the expression of 11β-hydroxysteroid dehydrogenase type 1 in the hippocampus of male rhesus macaques

IntroductionThe hippocampus is especially susceptible to age-associated neuronal pathologies, and there is concern that the age-associated rise in cortisol secretion from the adrenal gland may contribute to their etiology. Furthermore, because 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1) catalyzes the reduction of cortisone to the active hormone cortisol, it is plausible that an increase in the expression of this enzyme enhances the deleterious impact of cortisol in the hippocampus and contributes to the neuronal pathologies that underlie cognitive decline in the elderly.MethodsRhesus macaques were used as a translational animal model of human aging, to examine age-related changes in gene and protein expressions of (HSD11B1/HSD11B1) in the hippocampus, a region of the brain that plays a crucial role in learning and memory.ResultsOlder animals showed significantly (p < 0.01) higher base-line cortisol levels in the circulation. In addition, they showed significantly (p < 0.05) higher hippocampal expression of HSD11B1 but not NR3C1 and NR3C2 (i.e., two receptor-encoding genes through which cortisol exerts its physiological actions). A similar age-related significant (p < 0.05) increase in the expression of the HSD11B1 was revealed at the protein level by western blot analysis.DiscussionThe data suggest that an age-related increase in the expression of hippocampal HSD11B1 is likely to raise cortisol concentrations in this cognitive brain area, and thereby contribute to the etiology of neuropathologies that ultimately lead to neuronal loss and dementia. Targeting this enzyme pharmacologically may help to reduce the negative impact of elevated cortisol concentrations within glucocorticoid-sensitive brain areas and thereby afford neuronal protection