EFFECTS OF ETHEPHON,ITS NONETHYLENE-GENERATING ANALOG ETHYLPHOSPHONIC ACID,AND PHOSPHOROUS ACID IN ASEPTIC CULTURE OF ORCHID SEEDLINGS

Seeds of Cattleya aurantiaca (Orchidaceae) were germinated and grown aseptically on Knudson C medium containing 2.5, 5, 10, 20, and 50 mg l^-1 of 2-chloroethylphosphonic acid (Ethephon), ethylphosphonic acid, or the inorganic acid moiety of both, phosphosphorous (phosphonic) acid. 2-Chloroethylphosphonic acid, an ethylene precursor, reduced leaf length at 5–50 mg l^-1 proportional to increasing concentrations. Seedlings produced fewer leaves within the range of 20–50 mg l^-1 Ethephon compared to lower concentrations (2.5–10 mg l^-1). Germination was not affected adversely. Cultures containing the homologous, but not ethylene-generating ethylphosphonic acid in the same concentrations brought about similar but generally less severe reductions in leaf length and number. Phosphorous acid at the same concentration levels did not reduce the number and length of leaves. Our observation suggests that the intact organic phosphonates contribute to the inhibition of leaf growth caused by ethylene, which is released slowly from Ethephon in the culture medium and/or plant tissue, following uptake.     

The helix-loop-helix inhibitor of differentiation (ID) proteins induce post-mitotic terminally differentiated Sertoli cells to re-enter the cell cycle and proliferate

Prior to puberty the Sertoli cells undergo active cell proliferation, and at the onset of puberty they become a terminally differentiated postmitotic cell population that support spermatogenesis. The molecular mechanisms involved in the postmitotic block of pubertal and adult Sertoli cells are unknown. The four known helix-loop-helix ID proteins (i.e., Id1, Id2, Id3, and Id4) are considered dominant negative regulators of cellular differentiation pathways and act as positive regulators of cellular proliferation. ID proteins are expressed at low levels by postpubertal Sertoli cells and are transiently induced by serum. The hypothesis tested was that ID proteins can induce a terminally differentiated postmitotic Sertoli cell to reenter the cell cycle if they are constitutively expressed. To test this hypothesis, ID1 and ID2 were stably integrated and individually overexpressed in postmitotic rat Sertoli cells. Overexpression of ID1 or ID2 allowed postmitotic Sertoli cells to reenter the cell cycle and undergo mitosis. The cells continued to proliferate even after 300 cell doublings. The functional markers of Sertoli cell differentiation such as transferrin, inhibin alpha, Sert1, and androgen binding protein (ABP) continued to be expressed by the proliferating Sertoli cells, but at lower levels. FSH receptor expression was lost in the proliferating Sertoli cell-Id lines. Some Sertoli cell genes, such as cyclic protein 2 (cathepsin L) and Sry-related HMG box protein-11 (Sox11) increase in expression. At no stage of proliferation did the cells exhibit senescence. The expression profile as determined with a microarray protocol of the Sertoli cell-Id lines suggested an overall increase in cell cycle genes and a decrease in growth inhibitory genes. These results demonstrate that overexpression of ID1 and ID2 genes in a postmitotic, terminally differentiated cell type have the capacity to induce reentry into the cell cycle. The observations are discussed in regards to potential future applications in model systems of terminally differentiated cell types such as neurons or myocytes.     

Synthesis of N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids

The synthesis of 10 N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids that are amenable to solid-phase synthesis is described. The general synthetic strategy involves initial incorporation of the protected amine, followed by selective TEMPO oxidation of C-6 hydroxyl groups to give the corresponding Fmoc-protected sugar amino acids. Amine incorporation may be accomplished from aminolysis of the free sugar or from glycosyl azide reduction. The reactions can be carried out on multigram scale, providing access to unique monomer units for future incorporation into combinatorial library syntheses.     

Chemical and structural diversity in cyclooxygenase protein active sites

A major pharmaceutical problem is designing diverse and selective lead compounds. The human genome sequence provides opportunities to discover compounds that are protein selective if we can develop methods to identify specificity determinants from sequence alone. We have analyzed sequence and structural diversity of sheep COX-1 and mouse COX-2 proteins by Active Site Profiling (ASP). Eleven residues that should serve as specificity determinants between COX-1 and COX-2 were identified; however, the literature suggests that only one has been utilized in structure-based discovery. ASP was used to create a position-specific scoring matrix, which was used to identify possible cross-reacting proteins from the human sequences. This method proved selective for cyclooxygenases, comparing well with results using BLAST. The methods identify a probable misannotation of a cyclooxygenase in which there is high sequence similarity scores using BLAST, but ASP shows it does not contain the residues necessary for cyclooxygenase function. ASP Analysis of human COX proteins suggests that some specificity determinants that distinguish COX-1 and COX-2 proteins are similar between sheep COX-1/mouse COX-2 and human COX-1/COX2; however, residue identities at those positions are not necessarily conserved. Our results lay groundwork for development of family-specific pattern recognition methods to selectively match compounds with proteins.     

Metal-induced toxicity, carcinogenesis, mechanisms and cellular responses

A wide variety of metals have been reported to act as mutagenic and carcinogenic agents in both human and animal studies. The underlying mechanisms are being extensively investigated. Recently, a new sub-discipline of molecular carcinogenesis has surfaced and new techniques and instruments are being developed which allow exploration of the complex biological relationships and signaling pathways involved in response to metal exposure at the molecular level. The 2nd Conference on Molecular Mechanisms of Metal Toxicity and Carcinogenesis was held at NIOSH in Morgantown, West Virginia, Sept. 8-11, 2002. One hundred thirty scientist from sixteen countries presented their novel findings and investigations of metal-induced carcinogenesis. The conference focused on state-of-the-art research and developments in metal toxicity and carcinogenesis. Emphasis was placed on delineating molecular mechanisms involved in free radical effects, cellular uptake, signaling pathways/interaction, dose response, biomarkers, and resistance mechanisms. This article reviews some of the novel information presented at the conference and discusses future avenues of research in this field.     

Sexual responses of the male rat medial preoptic area and medial amygdala to estrogen I: site specific suppression of estrogen receptor alpha

Male rat copulation is mediated by estrogen-sensitive neurons in the medial preoptic area (MPO) and medial amygdala (MEA); however, the mechanisms through which estradiol (E(2)) acts are not fully understood. We hypothesized that E(2) acts through estrogen receptor α (ERα) in the MPO and MEA to promote male mating behavior. Antisense oligodeoxynucleotides (AS-ODN) complementary to ERα mRNA were bilaterally infused via minipumps into either brain area to block the synthesis of ERα, which we predicted would reduce mating. Western blot analysis and immunocytochemistry revealed a knockdown of ERα expression in each brain region; however, compared to saline controls, males receiving AS-ODN to the MPO showed significant reductions in all components of mating, whereas males receiving AS-ODN to the MEA continued to mate normally. These results suggest that E(2) acts differently in these brain regions to promote the expression of male rat sexual behavior and that ERα in the MPO, but not in the MEA, promotes mating.     

Trafficking defects in WASH-knockout fibroblasts originate from collapsed endosomal and lysosomal networks

The Arp2/3-activator Wiskott-Aldrich syndrome protein and Scar homologue (WASH) is suggested to regulate actin-dependent membrane scission during endosomal sorting, but its cellular roles have not been fully elucidated. To investigate WASH function, we generated tamoxifen-inducible WASH-knockout mouse embryonic fibroblasts (WASHout MEFs). Of interest, although EEA1(+) endosomes were enlarged, collapsed, and devoid of filamentous-actin and Arp2/3 in WASHout MEFs, we did not observe elongated membrane tubules emanating from these disorganized endomembranes. However, collapsed WASHout endosomes harbored segregated subdomains, containing either retromer cargo recognition complex-associated proteins or EEA1. In addition, we observed global collapse of LAMP1(+) lysosomes, with some lysosomal membrane domains associated with endosomes. Both epidermal growth factor receptor (EGFR) and transferrin receptor (TfnR) exhibited changes in steady-state cellular localization. EGFR was directed to the lysosomal compartment and exhibited reduced basal levels in WASHout MEFs. However, although TfnR was accumulated with collapsed endosomes, it recycled normally. Moreover, EGF stimulation led to efficient EGFR degradation within enlarged lysosomal structures. These results are consistent with the idea that discrete receptors differentially traffic via WASH-dependent and WASH-independent mechanisms and demonstrate that WASH-mediated F-actin is requisite for the integrity of both endosomal and lysosomal networks in mammalian cells.     

4,5-dihydropyridazin-3-one derivatives as histamine H₃ receptor inverse agonists

H(3)R structure-activity relationships for a new class of 4,5-dihydropyridazin-3-one H(3)R antagonists/inverse agonists are disclosed. Modification of the 4,5-dihydropyridazinone moiety to block in vivo metabolism identified 4,4-dimethyl-6-{4-[3-((R)-2-methyl-pyrrolidin-1-yl)-propoxy]-phenyl}-4,5-dihydro-2H-pyridazin-3-one 22 as a lead candidate demonstrating potent in vivo functional H(3)R antagonism in the rat dipsogenia model and robust wake promoting activity in the rat EEG/EMG model.