Leaf malformation during early development in Sorghum. Evidence for an embryonic developmental window

Salt adaptation was induced in two successive generations of Sorghum bicolor , and the germination of their seeds was compared. When germinated in the absence of NaCl, the progeny of adapted plants displayed a specific malformation at the first two leaves, which was never observed in progeny of control plants. The frequency of leaf malformation was enhanced in progeny of the second generation of adapted plants, indicating a cumulative influence of salt adaptation. When germinated in the presence of 75 m M NaCl, seedlings from seeds of salt-adapted plants never displayed the leaf malformation, whereas it was observed on seedlings from seeds of control plants germinated in the presence of 75 m M NaCl. The occurrence of leaf malformation was analyzed for progeny of 20 salt-adapted plants germinated in the absence of NaCl. The link with the reproductive characters of the parents indicates a strong parental control on the expression of the leaf malformation. A comparison with previous data relative to the leaf malformation in Sorghum suggests the existence of a developmental window which 'opens'during embryo morphogenesis. This enables the imprinting of the embryo by the parent's physiological environment. This conclusion is related to other data describing a long-term maternal influence in plants.     

Studying Early Lethality of 45,XO (Turner's Syndrome) Embryos Using Human Embryonic Stem Cells

Turner''s syndrome (caused by monosomy of chromosome X) is one of the most common chromosomal abnormalities in females. Although 3% of all pregnancies start with XO embryos, 99% of these pregnancies terminate spontaneously during the first trimester. The common genetic explanation for the early lethality of monosomy X embryos, as well as the phenotype of surviving individuals is haploinsufficiency of pseudoautosomal genes on the X chromosome. Another possible mechanism is null expression of imprinted genes on the X chromosome due to the loss of the expressed allele. In contrast to humans, XO mice are viable, and fertile. Thus, neither cells from patients nor mouse models can be used in order to study the cause of early lethality in XO embryos. Human embryonic stem cells (HESCs) can differentiate in culture into cells from the three embryonic germ layers as well as into extraembryonic cells. These cells have been shown to have great value in modeling human developmental genetic disorders. In order to study the reasons for the early lethality of 45,XO embryos we have isolated HESCs that have spontaneously lost one of their sex chromosomes. To examine the possibility that imprinted genes on the X chromosome play a role in the phenotype of XO embryos, we have identified genes that were no longer expressed in the mutant cells. None of these genes showed a monoallelic expression in XX cells, implying that imprinting is not playing a major role in the phenotype of XO embryos. To suggest an explanation for the embryonic lethality caused by monosomy X, we have differentiated the XO HESCs in vitro an in vivo. DNA microarray analysis of the differentiated cells enabled us to compare the expression of tissue specific genes in XO and XX cells. The tissue that showed the most significant differences between the clones was the placenta. Many placental genes are expressed at much higher levels in XX cells in compare to XO cells. Thus, we suggest that abnormal placental differentiation as a result of haploinsufficiency of X-linked pseudoautosomal genes causes the early lethality in XO human embryos.     

Early Response of Willow to Increasing Silver Concentration Exposure

This is a preliminary hydroponic study to test willow sensitivity to silver nitrate, a highly toxic chemical compound. We grew willow cuttings for a period of three weeks in the presence of increasing AgNO₃ concentrations and assessed the response in terms of growth and physiology. We found that AgNO₃ is generally extremely harmful to willow. AgNO₃ concentration as high as 0.027 μM may result in a significant reduction of biomass productivity and a decrease in stomatal conductance over the first week of exposure. However, willows seem able to adapt to high AgNO₃ concentrations on a longer timeline.     

Increased hexokinase activity, of either ectopic or endogenous origin, protects renal epithelial cells against acute oxidant-induced cell death.

Glucose (Glc) metabolism protects cells against oxidant injury. By virtue of their central position in both Glc uptake and utilization, hexokinases (HKs) are ideally suited to contribute to these effects. Compatible with this hypothesis, endogenous HK activity correlates inversely with injury susceptibility in individual renal cell types. We recently reported that ectopic HK expression mimics the anti-apoptotic effects of growth factors in cultured fibroblasts, but anti-apoptotic roles for HKs have not been examined in other cell types or in a cellular injury model. We therefore evaluated HK overexpression for the ability to mitigate acute oxidant-induced cell death in an established epithelial cell culture injury model. In parallel, we examined salutary heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) treatment for the ability to 1) increase endogenous HK activity and 2) mimic the protective effects of ectopic HK expression. Both HK overexpression and HB-EGF increased Glc-phosphorylating capacity and metabolism, and these changes were associated with markedly reduced susceptibility to acute oxidant-induced apoptosis. The uniform Glc dependence of these effects suggests an important adaptive role for Glc metabolism, and for HK activity in particular, in the promotion of epithelial cell survival. These findings also support the contention that HKs contribute to the protective effects of growth factors.     

Conservation from rat to human of cytosolic phosphoenolpyruvate carboxykinase and the control of its gene expression

Structural conservation of cytosolic phosphoenolpyruvate carboxykinase protein and mRNA sequence was found in all species examined from rodents to human. The mitochondrial isoenzyme, in all species tested, represents a distinct protein. Moreover, irrespective of the ratio of cytosolic to mitochondrial isoenzyme, cytosolic phosphoenolpyruvate carboxykinase activity in the human as in the rat is controlled at the level of gene expression and through the same multiple hormonal stimulation. This evolutionary conservation of the cytosolic phosphoenolpyruvate carboxykinase structure and mode of regulation supports the enzymes' physiological importance in mammals.     

Astrocyte Leucine Metabolism: Significance of Branched-Chain Amino Acid Transamination

Abstract: We studied astrocytic metabolism of leucine, which in brain is a major donor of nitrogen for the synthesis of glutamate and glutamine. The uptake of leucine into glia was rapid, with a V _max of 53.6 ± 3.2 nmol/mg of protein/min and a K _m of 449.2 ± 94.9 µ M . Virtually all leucine transport was found to be Na⁺ independent. Astrocytic accumulation of leucine was much greater (3×) in the presence of α-aminooxyacetic acid (5 m M ), an inhibitor of transamination reactions, suggesting that the glia rapidly transaminate leucine to α-ketoisocaproic acid (KIC), which they then release into the extracellular fluid. This inference was confirmed by the direct measurement of KIC release to the medium when astrocytes were incubated with leucine. Approximately 70% of the leucine that the glia cleared from the medium was released as the keto acid. The apparent K _m for leucine conversion to extracellular KIC was a medium [leucine] of 58 µ M with a V _max of ∼2.0 nmol/mg of protein/min. The transamination of leucine is bidirectional (leucine + α-ketoglutarate ↮ KIC + glutamate) in astrocytes, but flux from leucine → glutamate is more active than that from glutamate → leucine. These data underscore the significance of leucine handling to overall brain nitrogen metabolism. The release of KIC from glia to the extracellular fluid may afford a mechanism for the "buffering" of glutamate in neurons, which would consume this neurotransmitter in the course of reaminating KIC to leucine.