Rodent Genes Research Articles

Accelerated Evolution after Gene Duplication: A Time-Dependent Process Affecting Just One Copy

Gene duplication is widely regarded as a major mechanism modeling genome evolution and function. However, the mechanisms that drive the evolution of the two, initially redundant, gene copies are still ill defined. Many gene duplicates experience evolutionary rate acceleration, but the relative contribution of positive selection and random drift to the retention and subsequent evolution of gene duplicates, and for how long the molecular clock may be distorted by these processes, remains unclear. Focusing on rodent genes that duplicated before and after the mouse and rat split, we find significantly increased sequence divergence after duplication in only one of the copies, which in nearly all cases corresponds to the novel daughter copy, independent of the mechanism of duplication. We observe that the evolutionary rate of the accelerated copy, measured as the ratio of nonsynonymous to synonymous substitutions, is on average 5-fold higher in the period spanning 4-12 My after the duplication than it was before the duplication. This increase can be explained, at least in part, by the action of positive selection according to the results of the maximum likelihood-based branch-site test. Subsequently, the rate decelerates until purifying selection completely returns to preduplication levels. Reversion to the original rates has already been accomplished 40.5 My after the duplication event, corresponding to a genetic distance of about 0.28 synonymous substitutions per site. Differences in tissue gene expression patterns parallel those of substitution rates, reinforcing the role of neofunctionalization in explaining the evolution of young gene duplicates.

Significance of Population Size on the Fixation of Nonsynonymous Mutations in Genes Under Varying Levels of Selection Pressure

Previous studies observed a higher ratio of divergences at nonsynonymous and synonymous sites (ω = dN/dS) in species with a small population size compared to that estimated for those with a large population size. Here we examined the theoretical relationship between ω, effective population size (Ne), and selection coefficient (s). Our analysis revealed that when purifying selection is high, ω of species with small Ne is much higher than that of species with large Ne. However the difference between the two ω reduces with the decline in selection pressure (s → 0). We examined this relationship using primate and rodent genes and found that the ω estimated for highly constrained genes of primates was up to 2.9 times higher than that obtained for their orthologous rodent genes. Conversely, for genes under weak purifying selection the ω of primates was only 17% higher than that of rodents. When tissue specificity was used as a proxy for selection pressure we found that the ω of broadly expressed genes of primates was up to 2.1-fold higher than that of their rodent counterparts and this difference was only 27% for tissue specific genes. Since most of the nonsynonymous mutations in constrained or broadly expressed genes are deleterious, fixation of these mutations is influenced by Ne. This results in a higher ω of these genes in primates compared to those from rodents. Conversely, the majority of nonsynonymous mutations in less-constrained or tissue-specific genes are neutral or nearly neutral and therefore fixation of them is largely independent of Ne, which leads to the similarity of ω in primates and rodents.

An electroolfactogram study of odor response patterns from the mouse olfactory epithelium with reference to receptor zones and odor sorptiveness

Olfactory sensory neuron (OSN) responses to odors, measured at the population level, tend to be spatially heterogeneous in the vertebrates that have been studied. These response patterns vary between odors but are similar across subjects for a given stimulus. However, few species have been studied making functional interpretation of these patterns problematic. One proximate explanation for the spatial heterogeneity of odor responses comes from evidence that olfactory receptor (OR) genes in rodents are expressed in OSN populations that are spatially restricted to a few zones in the olfactory epithelium (OE). A long-standing functional explanation for response anisotropy in the OE posits that it is the signature of a supplementary mechanism for quality coding, based on the sorptive properties of odor molecules. These theories are difficult to assess because most mapping studies have utilized few odors, provided little replication, or involved but a single species (rat). In fact, to our knowledge, a detailed olfactory response "map" has not been reported for mouse, the species used in most studies of gene localization. Here we report the results of a study of mouse OE response patterns using the electroolfactogram (EOG). We focused on the medial aspect of olfactory turbinates that are accessible in the midsagittal section. This limited approach still allowed us to test predictions derived from the zonal distribution of OSN types and the sorption hypothesis. In 3 separate experiments, 290 mice were used to record EOGs from a set of standard locations along each of 4 endoturbinates utilizing 11 different odors resulting in over 4,400 separate recordings. Our results confirmed a marked spatial heterogeneity in odor responses that varied with odor, as seen in other species. However, no discontinuities were found in the odor-specific response patterns across the OE as might have been predicted given the existence of classical receptor zones nor did we find clear support for the hypothesis that OE response patterns, presumably a reflection of OSN distribution, have been shaped through natural selection by the relative sorptive properties of odors. We propose that receptor zones may be an epiphenomenon of a contingent evolutionary process. In this formulation, constraints on developmental programs for distributing OSN classes within the OE may be minimally related to the odor ligands of specific class members. Further, we propose that odor sorptiveness, which appears to be correlated with the inherent response patterns in the OE of larger species, may be of minimal effect in mice owing to scaling issues.

Near-Universal Prevalence of Pneumocystis and Associated Increase in Mucus in the Lungs of Infants With Sudden Unexpected Death

Pneumocystis without obvious accompanying pathology is occasionally reported in autopsied infant lungs. Its prevalence and significance are unknown. Interestingly, this mild infection induces a strong activation of mucus secretion-related genes in young immunocompetent rodents that has not been explored in infants. Excess mucus is induced by multiple airway offenders through nonspecific pathways and would explain a cofactor role of Pneumocystis in respiratory disease. We undertook characterization of the prevalence of Pneumocystis and associated mucus in infant lungs. Samples from 128 infants (mean age, 101 days) who died suddenly and unexpectedly in Santiago during 1999-2004 were examined for Pneumocystis using nested polymerase chain reaction (nPCR) amplification of the P. jirovecii mtLSU ribosomal RNA gene and immunofluorescence microscopy (IF). Pneumocystis-negative infants 28 days and older and their age-closest positives were studied for MUC5AC expression and Pneumocystis burden by Western blot and quantitative PCR, respectively. Pneumocystis DNA was detected by nPCR in 105 of the 128 infants (82.0%) and Pneumocystis organisms were visualized by IF in 99 (94.3%) of the DNA-positive infants. The infection was commonest at 3-4 months with 40 of 41 (97.6%) infants of that age testing positive. MUC5AC was significantly increased in Pneumocystis-positive tissue specimens (P = .013). Death was unexplained in 113 (88.3%) infants; Pneumocystis was detected in 95 (84.0%) of them vs 10 of 15 (66.7%) with explained death (P = .28). A highly focal Pneumocystis infection associated to increased mucus expression is almost universally present in the lungs of infants dying unexpectedly in the community regardless of autopsy diagnosis.

Truncated variants of pig somatostatin receptor subtype 5 (sst5) act as dominant-negative modulators for sst2-mediated signaling

Somatostatin (SST) and its related peptide cortistatin (CORT) exert their multiple actions through binding to the SST receptor (sst) family, generally considered to comprise five G protein-coupled receptors with seven transmembrane domains (TMD), named sst1-sst5, plus a splice sst2B variant. However, we recently discovered that human and rodent sst5 gene expression also generates, through noncanonical alternative splicing, novel truncated albeit functional sst5 variants with less than seven TMD. Here, we cloned and characterized for the first time the porcine wild-type sst5 (psst5, full-length) and identified two novel truncated psst5 variants with six and three TMD, thus termed psst5TMD6 and psst5TMD3, respectively. In line with that observed in human and rodent truncated sst5 variants, psst5TMD6 and psst5TMD3 are functional (e.g., activate calcium signaling), selectively respond to SST and CORT, respectively, and exhibit specific tissue expression profiles that differ from full-length psst5 and often overlaps with psst2 expression. Moreover, fluorescence resonance energy transfer analysis shows that psst5 truncated variants physically interact with psst2, thereby altering their localization at the plasma membrane and specifically disrupting the cellular response to SST and/or CORT. These results represent the first characterization of a key porcine SST receptor, psst5, and, together with our previous results, provide strong evidence that alternative splicing-derived, truncated sst5 variants with distinct functional capacities exist in the mammalian lineage, where they can act as dominant-negative receptors, by interacting directly with long, seven TMD variants, potentially contributing to modulate normal and pathological SST and CORT signaling.

Genomic Targets of Brachyury (T) in Differentiating Mouse Embryonic Stem Cells

BackgroundThe T-box transcription factor Brachyury (T) is essential for formation of the posterior mesoderm and the notochord in vertebrate embryos. Work in the frog and the zebrafish has identified some direct genomic targets of Brachyury, but little is known about Brachyury targets in the mouse.Methodology/Principal FindingsHere we use chromatin immunoprecipitation and mouse promoter microarrays to identify targets of Brachyury in embryoid bodies formed from differentiating mouse ES cells. The targets we identify are enriched for sequence-specific DNA binding proteins and include components of signal transduction pathways that direct cell fate in the primitive streak and tailbud of the early embryo. Expression of some of these targets, such as Axin2, Fgf8 and Wnt3a, is down regulated in Brachyury mutant embryos and we demonstrate that they are also Brachyury targets in the human. Surprisingly, we do not observe enrichment of the canonical T-domain DNA binding sequence 5′-TCACACCT-3′ in the vicinity of most Brachyury target genes. Rather, we have identified an (AC)n repeat sequence, which is conserved in the rat but not in human, zebrafish or Xenopus. We do not understand the significance of this sequence, but speculate that it enhances transcription factor binding in the regulatory regions of Brachyury target genes in rodents.Conclusions/SignificanceOur work identifies the genomic targets of a key regulator of mesoderm formation in the early mouse embryo, thereby providing insights into the Brachyury-driven genetic regulatory network and allowing us to compare the function of Brachyury in different species.

Novel Murine Norovirus-Like Genes in Wild Rodents in Japan

Novel murine norovirus (MNV)-like sequences were detected in 7 (14.9%) of 47 fecal and intestinal samples obtained from wild rodents in Japan. Sequencing and genetic analyses of the 7 MNV-like genes, 6 derived from Apodemus speciosus and 1 from Rattus rattus, suggested that these sequences form a cluster distinct from known MNV within genogroup V and differed even among clusters of wild rodents. Considering these results, MNV might be genetically diverse depending on the host species or distribution. This is the first report suggesting the prevalence of MNV in A. speciosus and R. rattus.

Genetically Engineered Mesenchymal Stem Cells Influence Gene Expression in Donor Cardiomyocytes and the Recipient Heart

AIMS: Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) or mesenchymal stem cells (MSCs) facilitate post-infarct recovery, but the potential benefit of combination therapy using MSCs and hESC-CMs has not been examined. Our objective was to define the gene expression changes in donor and host-derived cells that are induced in vivo after co-transplantation of cardiomyocytes with and without mesenchymal stem cells expressing the prosurvival gene heme oxygenase 1. METHODS AND RESULTS: Human MSCs were engineered to over-express heme oxygenase-1 (HO-1) following lentiviral vector-mediated transduction. Athymic nude rats were subjected to myocardial infarction and received hESC-CMs alone, hESC-CMs plus human MSCs, hESC-CMs plus MSCs overexpressing HO-1, or saline. Real time PCR identified gene expression changes. Cardiac function was assessed by angiography. Co-transplantation of unmodified MSCs plus hESC-CMs elevated CXCR4, HGF, and IGF expression over levels induced by injection of hESC-derived cardiomyocytes alone. In animals co-transplanted with MSC over-expressing HO-1, the expression of these genes was further elevated. Gene expression levels of VEGF, TGF-β, CCL2, SMAD7, STAT3 and cardiomyocyte transcription factors were highest in the HO-1 MSC plus hESC-CM group at 30 days. Human CD31+, CD34+, isl-1+, NXK2.5 and c-kit+ transcripts were elevated. Rodent genes encoding NKX2.5, troponin T and CD31 were elevated and cell cycle genes were induced. Ejection fraction improved by six to seven percent. CONCLUSIONS: Co-administration of HO-1 MSCs plus hESC-CMs increased expression of pro-survival and angiogenesis-promoting genes in human cells and transcripts of cardiac and endothelial cell markers in rodent cells, consistent with activation of tissue repair in both transplanted hESC-CMs and the host heart.

Das periphere olfaktorische System von Vertebraten: Molekulare, strukturelle und funktionelle Grundlagen des Riechens

Zusammenfassung Der Geruchssinn liefert Menschen und Tieren eine Vielzahl von Informationen über die Umgebung, er trägt zur Orientierung und Warnung bei, steuert die Nahrungsaufnahme, die Wahl des Sexualpartners und beeinflusst maßgeblich das innerartliche Sozialverhalten. Die Wahrnehmung von Geruchsstoffen beginnt mit der Bindung der Geruchsmoleküle an spezialisierte Rezeptormoleküle der Plasmamembran, die fast ausnahmslos zu der Superfamilie der G-Protein-gekoppelten Rezeptoren (GPCR) gehören. Insgesamt sind bisher fünf verschiedene Familien von Geruchsrezeptoren identifiziert worden, darunter die mit Abstand größte Genfamilie überhaupt mit über tausend Genen in Nagern. Für diese Familie ist die Signaltransduktionskaskade mittlerweile gut charakterisiert. Drei Arten von Rezeptorneuronen, die ziliierten, mikrovillären und Kryptneurone lassen sich anatomisch und molekular voneinander unterscheiden. Rezeptorneurone beschränken sich in der Regel auf die Expression eines einzigen Geruchsrezeptorgens, und zudem senden Neurone mit übereinstimmend ausgewähltem Rezeptor ihre Axone in eine gemeinsame Zielstruktur, einen Glomerulus, wodurch in der ersten olfaktorischen Gehirnregion, dem Bulbus olfactorius, eine rezeptotope Karte entsteht. Dieser Review gibt zum einen eine allgemeine Übersicht der peripheren Detektion von Geruchsstoffen und fokussiert zum anderen auf die in den letzten Jahren neu gewonnenen Erkenntnisse, unter anderem zur peripheren Modulierung olfaktorischer Signale.

The peripheral olfactory system of vertebrates: molecular, structural and functional basics of the sense of smell

Abstract The sense of smell provides people and animals with an abundance of information about their environment, helping them to navigate, detect potential threats, control food intake, choose sexual partners and significantly influence intraspecies social behav­ior. The perception of odors begins with the binding of odor molecules to specialized olfactory receptor proteins, which nearly all be­long to the superfamily of G protein-coupled receptors. Altogether, five different olfactory receptor gene families have been described to date, among them the largest gene family in the genome with over 1000 genes in rodents. The signal transduction cascade coupled to the receptors has already been well characterized for this family. Three different classes of receptor neurons-ciliated, microvillous and crypt receptor neurons-can be distinguished by their anatomical and molecular characteristics. Generally, an individual receptor neuron expresses only a single olfactory receptor gene, and olfactory receptor neurons that express the same receptor converge into a common target structure, a glomerulus, which generates a receptotop­ic map in the first olfactory brain region, the olfactory bulb. This review article provides a general overview of the peripheral detection of odorants on the one hand, while on the other it focuses on recent advances in the field, including new findings on the peripher­al modulation of olfactory signals.

Variability of Sequence Surrounding the Xist Gene in Rodents Suggests Taxon-Specific Regulation of X Chromosome Inactivation

One of the two X chromosomes in female mammalian cells is subject to inactivation (XCI) initiated by the Xist gene. In this study, we examined in rodents (voles and rat) the conservation of the microsatellite region DXPas34, the Tsix gene (antisense counterpart of Xist), and enhancer Xite that have been shown to flank Xist and regulate XCI in mouse. We have found that mouse regions of the Tsix gene major promoter and minisatellite repeat DXPas34 are conserved among rodents. We have also shown that in voles and rat the region homologous to the mouse Tsix major promoter, initiates antisense to Xist transcription and terminates around the Xist gene start site as is observed with mouse Tsix. A conservation of Tsix expression pattern in voles, rat and mice suggests a crucial role of the antisense transcription in regulation of Xist and XIC in rodents. Most surprisingly, we have found that voles lack the regions homologous to the regulatory element Xite, which is instead replaced with the Slc7a3 gene that is unassociated with the X-inactivation centre in any other eutherians studied. Furthermore, we have not identified any transcription that could have the same functions as murine Xite in voles. Overall, our data show that not all the functional elements surrounding Xist in mice are well conserved even within rodents, thereby suggesting that the regulation of XCI may be at least partially taxon-specific.

Sp3 transcription factor is crucial for transcriptional activation of the human NOX4 gene

NOX is the catalytic subunit of NADPH oxidase, the superoxide-generating enzyme. Among several isoforms of NOX, NOX4 is abundantly expressed in various tissues. To clarify the mechanisms of constitutive and ubiquitous expression of NOX4, the promoter activities of the human NOX4 gene were analyzed by reporter assays. The 5'-flanking and non-coding regions of the human NOX4 gene are known to contain multiple GC bases. Among them, three GC-boxes containing putative Sp/Klf-binding sites, which were not found in rodent genes, were suggested to be essential for the basal expression of the NOX4 gene in SH-SY5Y and HEK293 cells. Electrophoresis mobility shift assays demonstrated that Sp1 and Sp3 could bind to GC-boxes at positions -239/-227 and +69/+81 in these cells. Chromatin immunoprecipitation assays showed that Sp1 and Sp3 could also bind to GC-boxes at positions -239/-227 and +69/+81 in vivo. The promoter activity of the NOX4 gene was reduced in SH-SY5Y and HEK293 cells by transfection of an anti-Sp3 short hairpin RNA-expression plasmid. Taken together, these results suggest that Sp3 plays a key role in the expression of NOX4 in various cell lineages in humans.

Evolutionary maintenance of filovirus-like genes in bat genomes

BackgroundLittle is known of the biological significance and evolutionary maintenance of integrated non-retroviral RNA virus genes in eukaryotic host genomes. Here, we isolated novel filovirus-like genes from bat genomes and tested for evolutionary maintenance. We also estimated the age of filovirus VP35-like gene integrations and tested the phylogenetic hypotheses that there is a eutherian mammal clade and a marsupial/ebolavirus/Marburgvirus dichotomy for filoviruses.ResultsWe detected homologous copies of VP35-like and NP-like gene integrations in both Old World and New World species of Myotis (bats). We also detected previously unknown VP35-like genes in rodents that are positionally homologous. Comprehensive phylogenetic estimates for filovirus NP-like and VP35-like loci support two main clades with a marsupial and a rodent grouping within the ebolavirus/Lloviu virus/Marburgvirus clade. The concordance of VP35-like, NP-like and mitochondrial gene trees with the expected species tree supports the notion that the copies we examined are orthologs that predate the global spread and radiation of the genus Myotis. Parametric simulations were consistent with selective maintenance for the open reading frame (ORF) of VP35-like genes in Myotis. The ORF of the filovirus-like VP35 gene has been maintained in bat genomes for an estimated 13. 4 MY. ORFs were disrupted for the NP-like genes in Myotis. Likelihood ratio tests revealed that a model that accommodates positive selection is a significantly better fit to the data than a model that does not allow for positive selection for VP35-like sequences. Moreover, site-by-site analysis of selection using two methods indicated at least 25 sites in the VP35-like alignment are under positive selection in Myotis.ConclusionsOur results indicate that filovirus-like elements have significance beyond genomic imprints of prior infection. That is, there appears to be, or have been, functionally maintained copies of such genes in mammals. "Living fossils" of filoviruses appear to be selectively maintained in a diverse mammalian genus (Myotis).

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Tumor-specific imaging through progression elevated gene-3 promoter-driven gene expression

Molecular-genetic imaging is advancing from a valuable preclinical tool to guiding patient management. The strategy involves pairing an imaging reporter gene with a complementary imaging agent in a system that can be used to measure gene expression, protein interaction or track gene-tagged cells in vivo. Tissue-specific promoters can be used to delineate gene expression in certain tissues, particularly when coupled with an appropriate amplification mechanism. Here we show that the progression elevated gene-3 promoter (PEG-Prom), derived from a rodent gene mediating the malignant phenotype, can be used to drive imaging reporters selectively to enable detection of micrometastatic disease in murine models of human melanoma and breast cancer using bioluminescence and radionuclide-based molecular imaging techniques. Because of its strong promoter, tumor specificity and capacity for clinical translation, PEG-Prom-driven gene expression may represent a practical, new system for facilitating cancer imaging and therapy.

Inactivation dates of the human and guinea pig vitamin C genes

The capacity to biosynthesize ascorbic acid has been lost in a number of species including primates, guinea pigs, teleost fishes, bats, and birds. This inability results from mutations in the GLO gene coding for L-gulono-γ-lactone oxidase, the enzyme responsible for catalyzing the last step in the vitamin C biosynthetic pathway. We analyzed available primate and rodent GLO gene sequences to determine their evolutionary history. We used a method based on sequence comparisons of lineages with and without functional GLO genes to calculate inactivation dates of 61 and 14 MYA for the primate and guinea pig genes, respectively. These estimates are consistent with previous phylogeny-based estimates. An analysis of transposable element distribution in the primate and rodent GLO sequences did not reveal conclusive evidence that illegitimate recombination between repeats has contributed to the loss of exons in the primate and guinea pig genes.

Evolution of CD33-related siglecs: regulating host immune functions and escaping pathogen exploitation?

Sialic-acid-binding immunoglobulin-like lectins, siglecs, are important immune receptors expressed widely in mammals. A unique feature of siglecs is their ability to bind sialylated glycans and transmit signals to immune cells. The CD33-related siglecs (CD33rSiglecs) form a major subfamily of the siglecs, containing a large, rapidly evolving group of genes that expanded in mammals through an inverse duplication event involving a primordial cluster of siglec genes over 180 million years ago. Humans express a much larger set of CD33rSiglecs than mice and rats, a feature that can be explained by a dramatic loss of CD33rSiglec genes in rodents. Most CD33rSiglecs have immune receptor tyrosine-based inhibitory motifs and signal negatively. Interestingly, novel DAP-12-coupled 'activating' CD33rSiglecs have been identified, such as siglec-14 and siglec-16, which are paired with the inhibitory receptors, siglec-5 and siglec-11, respectively. The evolution of these activating receptors may have been driven in part by pathogen exploitation of inhibitory siglecs, thereby providing the host with additional pathways by which to combat these pathogens. Inhibitory siglecs seem to play important and varied roles in the regulation of host immune responses. For example, several CD33rSiglecs have been implicated in the negative regulation of Toll-like receptor signalling during innate responses; siglec-G functions as a negative regulator of B1-cell expansion and appears to suppress inflammatory responses to host-derived 'danger-associated molecular patterns'. Recent work has also shown that engagement of neutrophil-expressed siglec-9 by certain strains of sialylated Group B streptococci can suppress killing responses, thereby providing experimental support for pathogen exploitation of host CD33rSiglecs.

Endogenous Retroviruses: From Infectious Elements to Essential Genes.

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and are remnants of ancient exogenous retroviral infections of the host germline transmitted vertically from generation to generation. Syncytins are envelope (env) genes of retroviral origin that have been co-opted by the host to mediate placental development. Two syncytin genes have been identified in primates (HERV-W (ERVWE1) termed syncytin-1 and HERV-FRD termed syncytin-2), as well as distinct, nonorthologous genes in rodents (syncytin-A and -B) and rabbits (syncytin-Ory1). The syncytins can induce cell-cell fusion, and placental development in those mammals requires the fusion of trophoblast cells into a highly specialized, multinucleated syncytiotrophoblast layer, which is essential for absorption of nutrients from the mother. All of the syncytins are expressed in the syncytiotrophoblasts, and null mutation of the syncytin-A gene in mice results in disruption of the syncytiotrophoblast-containing labyrinth placenta. The null placentae exhibit decreased vascularization and poor transport, resulting in fetal growth retardation and ultimately embryo loss between 11.5 and 13.5 days of gestation. In both humans and mice, one of the two syncytins (human syncytin-2 and mouse syncytin-B) is also immunosuppressive, suggesting they may be also involved in immunotolerance of the semiallogeneic fetus. The sheep genome contains 27 JSRV-related endogenous betaretroviruses (enJSRVs) related to the pathogenic Jaagsiekte sheep retrovirus (JSRV) that have been integrating in the host genome for the last 5-7 million years. The exogenous JSRV is a causative agent of a transmissible lung cancer in sheep, and enJSRVs are able to protect their host against JSRV infection by blocking different steps of the viral replication cycle via receptor interference and late replication steps. Indeed, endogenization and positive selection of ERVs acting as restriction factors is a mechanism used by the host to fight exogenous retroviral infections. In sheep, the enJSRVs are most abundantly expressed in the uterine luminal and glandular epithelia as well as in the conceptus (embryo and associated extraembryonic membranes) trophectoderm. Sixteen of the 27 enJSRV loci contain an env gene with an intact open reading frame, and in utero loss-of-function experiments found the enJSRVs envelope (env) to be essential for conceptus elongation and trophoblast growth and differentiation. Collectively, available evidence supports the ideas that genes captured from ancestral retroviruses have been pivotal in the acquisition of new, important functions in mammalian evolution and were positively selected for biological roles in genome plasticity, protection of the host against infection of related pathogenic and exogenous retroviruses, and placental morphogenesis. This work supported by NIH Grant HD052745 and by a Strategic Research Developmental Grant by the Scottish Funding Council. (platform)

HYPOXIA-INDUCED ALTERATION OF MITOCHONDRIAL GENES IN CARDIOMYOCYTES

The hypoxic conditions induced by reduced blood flow decreases oxygen availability in target tissues. Cellular hypoxia leads to mitochondrial dysfunction, decreased energy production, and increased production of reactive oxygen species. To determine the alteration in expression of mitochondrial genes after hypoxia in cardiomyocytes, we developed a rodent mitochondrial gene chip (RoMitoChip). The chip had 1088 probe sets including 46 probe sets representing 37 mouse mitochondrial DNA transcripts and the remaining probe sets representing mouse nuclear genes contributing to the mitochondrial structure and function. Mouse cardiomyocytes isolated from neonatal C57BL/6 mice that were subjected to hypoxia (1% oxygen) for different time intervals demonstrated a dichotomy in the expression profile of tRNA and mRNA transcripts. We report a total of 483 signature genes that were altered by hypoxia in the cardiac myocytes and related to mitochondrial structure and function. This includes 23 transcripts on mitochondrial DNA. Pathway analysis demonstrated predominant changes in the expression of genes involved in oxidative phosphorylation, glucose and fatty acid metabolism, and apoptosis. The most upregulated genes after 24 h of hypoxia included hypoxia-inducible factor 1, alpha subunit, inducible genes Bnip3, Pdk1, and Aldoc. Whereas Bnip3 is important in the cardiomyocyte death pathway, Pdk1 enzyme is critical in conserving mitochondrial function by diverting metabolic intermediates to glycolysis. This study identifies the participation of two important pathways, cell death and glycolytic, and two key proteins, Bnip3 and Pdk1, playing critical roles in these pathways in cardiomyocytes after severe hypoxia.

Induction of the renal stanniocalcin-1 gene in rodents by water deprivation

Stanniocalcin-1 (STC-1) is made by kidney collecting duct cells for targeting of nephron mitochondria to promote respiratory uncoupling and calcium uniport activity. However, the purpose of these actions and how the renal gene is regulated are poorly understood. This study has addressed the latter issue by monitoring renal STC-1 gene expression in different models of kidney function. Unilateral nephrectomy and over-hydration had no bearing on renal gene activity in adult Wistar rats. Dehydration, on the other hand, had time-dependent stimulatory effects in male and female kidney cortex, where STC-1 mRNA levels increased 8-fold by 72 h. Medullary gene activity was significantly increased as well, but muted in comparison (∼2-fold). Gene induction was accompanied by an increase in mitochondrial sequestration of STC-1 protein. Aldosterone and angiotensin II had no bearing on STC-1 gene induction, although there was evidence of a role for arginine vasopressin. Gene induction was unaltered in integrin alpha1 knockout mice, which have an impaired tonicity enhancer binding protein (TonEBP) response to dehydration. The STC-1 gene response could be cytoprotective in intent, as dehydration entails a fall in renal blood flow and a rise in medullary interstitial osmolality. Alternatively, STC-1 could have a role in salt and water balance as dehydration necessitates water conservation as well as controlled natriuresis and kaliuresis.