Abstract-The advent of conditional and tissue-specific recombination systems in gene-targeted or transgenic mice has permitted an assessment of single gene function in a temporally regulated and cell-specific manner. Here we generated transgenic mice expressing a tamoxifen-inducible Cre recombinase protein fused to two mutant estrogen-receptor ligand-binding domains (MerCreMer) under the control of the ␣-myosin heavy chain promoter. These transgenic mice were crossed with the ROSA26 lacZ-flox-targeted mice to examine Cre recombinase activity and the fidelity of the system. The data demonstrate essentially no Cre-mediated recombination in the embryonic, neonatal, or adult heart in the absence of inducing agent but Ͼ80% recombination after only four tamoxifen injections. Expression of the MerCreMer fusion protein within the adult heart did not affect cardiac performance, cellular architecture, or expression of hypertrophic marker genes, demonstrating that the transgene-encoded protein is relatively innocuous. In summary, MerCreMer transgenic mice represent a tool for temporally regulated inactivation of any loxP-targeted gene within the developing and adult heart or for specifically directing recombination and expression of a loxP-inactivated cardiac transgene in the heart. (Circ Res. 2001;89:20-25.)

Members of the mitogen-activated protein kinase (MAPK) cascade such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 are implicated as important regulators of cardiomyocyte hypertrophic growth in culture. However, the role that individual MAPK pathways play in vivo has not been extensively evaluated. Here we generated nine transgenic mouse lines with cardiac-restricted expression of an activated MEK1 cDNA in the heart. MEK1 transgenic mice demonstrated concentric hypertrophy without signs of cardiomyopathy or lethality up to 12 months of age. MEK1 transgenic mice showed a dramatic increase in cardiac function, as measured by echocardiography and isolated working heart preparation, without signs of decompensation over time. MEK1 transgenic mice and MEK1 adenovirus-infected neonatal cardiomyocytes each demonstrated ERK1/2, but not p38 or JNK, activation. MEK1 transgenic mice and MEK1 adenovirus-infected cultured cardiomyocytes were also partially resistant to apoptotic stimuli. The results of the present study indicate that the MEK1-ERK1/2 signaling pathway stimulates a physiologic hypertrophy response associated with augmented cardiac function and partial resistance to apoptotsis.

The process of dark-induced senescence in plants is relatively poorly understood, but a functional electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex, which supports respiration during carbon starvation, has recently been identified. Here, we studied the responses of Arabidopsis thaliana mutants deficient in the expression of isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase to extended darkness and other environmental stresses. Evaluations of the mutant phenotypes following carbon starvation induced by extended darkness identify similarities to those exhibited by mutants of the ETF/ETFQO complex. Metabolic profiling and isotope tracer experimentation revealed that isovaleryl-CoA dehydrogenase is involved in degradation of the branched-chain amino acids, phytol, and Lys, while 2-hydroxyglutarate dehydrogenase is involved exclusively in Lys degradation. These results suggest that isovaleryl-CoA dehydrogenase is the more critical for alternative respiration and that a series of enzymes, including 2-hydroxyglutarate dehydrogenase, plays a role in Lys degradation. Both physiological and metabolic phenotypes of the isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase mutants were not as severe as those observed for mutants of the ETF/ETFQO complex, indicating some functional redundancy of the enzymes within the process. Our results aid in the elucidation of the pathway of plant Lys catabolism and demonstrate that both isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase act as electron donors to the ubiquinol pool via an ETF/ETFQOmediated route.

The zinc finger-containing transcription factors GATA4 and GATA6 are important regulators of basal and inducible gene expression in cardiac and smooth muscle cell types. Here we demonstrate a direct functional role for GATA4 and GATA6 as regulators of cardiomyocyte hypertrophic growth and gene expression. To model the increase in endogenous GATA4 and GATA6 transcriptional activity that occurs in response to hypertrophic stimulation, each factor was overexpressed in cardiomyocytes using recombinant adenovirus. Overexpression of either GATA4 or GATA6 was sufficient to induce cardiomyocyte hypertrophy characterized by enhanced sarcomeric organization, a greater than 2-fold increase in cell surface area, and a significant increase in total protein accumulation. In vivo, transgenic mice with 2.5-fold overexpression of GATA4 within the adult heart demonstrated a slowly progressing increase in heart to body weight ratio, histological features of cardiomyopathy, and activation of hypertrophy-associated genes, suggesting that GATA factors are sufficient regulators of cardiomyocyte hypertrophy in vitro and in vivo. To evaluate the requirement of GATA factors as downstream transcriptional mediators of hypertrophy, a dominant negative GATA4-engrailed repressor fusionencoding adenovirus was generated. Expression of GATA4-engrailed blocked GATA4-and GATA6-directed transcriptional responses and agonist-induced cardiomyocyte hypertrophy, demonstrating that cardiac-expressed GATA factors are necessary mediators of this process.

Obstructive sleep apnea (OSA) has been shown to be an independent risk factor for cardiovascular disease in adults. However, there are severe limitations in the extent to which the cardiovascular consequences of OSA are being studied in children. To investigate the echocardiographic changes in children with OSA, right and left ventricular (RV, LV) dimensions and LV mass index and geometry were measured in 28 children with OSA and 19 children with primary snoring (PS). The study showed that LV mass index and relative wall thickness were greater in the OSA group compared with those with PS (p = 0.012 and p < 0.0001, respectively). An apnea-hypopnea index of more than 10 per hour was significantly associated with RV dimension above the 95th percentile (odds ratios, 6.7; 95% confidence interval, 1.4-32) and LV mass index above the 95th percentile (odds ratios, 11.2; confidence interval, 1.9-64). Abnormality of LV geometry was present in 15% of children with PS compared with 39% of children with OSA. We conclude that OSA in children is associated with increased LV mass.

Angiotensin II (Ang II), a potent hypertrophic stimulus, causes significant increases in TGFb1 gene expression. However, it is not known whether there is a causal relationship between increased levels of TGF-beta1 and cardiac hypertrophy. Echocardiographic analysis revealed that TGF-beta1-deficient mice subjected to chronic subpressor doses of Ang II had no significant change in left ventricular (LV) mass and percent fractional shortening during Ang II treatment. In contrast, Ang II-treated wild-type mice showed a >20% increase in LV mass and impaired cardiac function. Cardiomyocyte cross-sectional area was also markedly increased in Ang II-treated wild-type mice but unchanged in Ang II-treated TGF-beta1-deficient mice. No significant levels of fibrosis, mitotic growth, or cytokine infiltration were detected in Ang II-treated mice. Atrial natriuretic factor expression was approximately 6-fold elevated in Ang II-treated wild-type, but not TGF-beta1-deficient mice. However, the alpha- to beta-myosin heavy chain switch did not occur in Ang II-treated mice, indicating that isoform switching is not obligatorily coupled with hypertrophy or TGF-beta1. The Ang II effect on hypertrophy was shown not to result from stimulation of the endogenous renin-angiotensis system. These results indicate that TGF-beta1 is an important mediator of the hypertrophic growth response of the heart to Ang II.

Adaptation to abiotic stresses like drought is an important acquirement of agriculturally relevant crops like maize. Development of enhanced drought tolerance in crops grown in climatic zones where drought is a very dominant stress factor therefore plays an essential role in plant breeding. Previous studies demonstrated that corn yield potential and enhanced stress tolerance are associated traits. In this study, we analyzed six different maize hybrids for their ability to deal with drought stress in a greenhouse experiment. We were able to combine data from morphophysiological parameters measured under well-watered conditions and under water restriction with metabolic data from different organs. These different organs possessed distinct metabolite compositions, with the leaf blade displaying the most considerable metabolome changes following water deficiency. Whilst we could show a general increase in metabolite levels under drought stress, including changes in amino acids, sugars, sugar alcohols, and intermediates of the TCA cycle, these changes were not differential between maize hybrids that had previously been designated based on field trial data as either drought-tolerant or susceptible. The fact that data described here resulted from a greenhouse experiment with rather different growth conditions compared to natural ones in the field may explain why tolerance groups could not be confirmed in this study. We were, however, able to highlight several metabolites that displayed conserved responses to drought as well as metabolites whose levels correlated well with certain physiological traits.

The development of abiotic stress-resistant cultivars is of premium importance for the agriculture of developing countries. Further progress in maize (Zea mays) performance under stresses is expected by combining marker-assisted breeding with metabolite markers. In order to dissect metabolic responses and to identify promising metabolite marker candidates, metabolite profiles of maize leaves were analyzed and compared with grain yield in field trials. Plants were grown under well-watered conditions (control) or exposed to drought, heat, and both stresses simultaneously. Trials were conducted in 2010 and 2011 using 10 tropical hybrids selected to exhibit diverse abiotic stress tolerance. Drought stress evoked the accumulation of many amino acids, including isoleucine, valine, threonine, and 4-aminobutanoate, which has been commonly reported in both field and greenhouse experiments in many plant species. Two photorespiratory amino acids, glycine and serine, and myoinositol also accumulated under drought. The combination of drought and heat evoked relatively few specific responses, and most of the metabolic changes were predictable from the sum of the responses to individual stresses. Statistical analysis revealed significant correlation between levels of glycine and myoinositol and grain yield under drought. Levels of myoinositol in control conditions were also related to grain yield under drought. Furthermore, multiple linear regression models very well explained the variation of grain yield via the combination of several metabolites. These results indicate the importance of photorespiration and raffinose family oligosaccharide metabolism in grain yield under drought and suggest single or multiple metabolites as potential metabolic markers for the breeding of abiotic stress-tolerant maize.