Balance between maternal and paternal alleles sets the timing of resource accumulation in the maize endosperm

Key aspects of seed development in flowering plants are held to be under epigenetic control and to have evolved as a result of conflict between the interests of the male and female gametes (kinship theory). Attempts to identify the genes involved have focused on imprinted sequences, although imprinting is only one mechanism by which male or female parental alleles may be exclusively expressed immediately post-fertilization. We have studied the expression of a subset of endosperm gene classes immediately following interploidy crosses in maize and show that departure from the normal 2 : 1 ratio between female and male genomes exerts a dramatic effect on the timing of expression of some, but not all, genes investigated. Paternal genomic excess prolongs the expression of early genes and delays accumulation of reserves, while maternal genomic excess foreshortens the expression period of early genes and dramatically brings forward endosperm maturation. Our data point to a striking interdependence between the phases of endosperm development, and are consonant with previous work from maize showing progression from cell proliferation to endoreduplication is regulated by the balance between maternal and paternal genomes, and from Arabidopsis suggesting that this ‘phasing’ is regulated by maternally expressed imprinted genes. Our findings are discussed in context of the kinship theory.     

Malaria and urbanization in sub-Saharan Africa

There are already 40 cities in Africa with over 1 million inhabitants and the United Nations Environmental Programme estimates that by 2025 over 800 million people will live in urban areas. Recognizing that malaria control can improve the health of the vulnerable and remove a major obstacle to their economic development, the Malaria Knowledge Programme of the Liverpool School of Tropical Medicine and the Systemwide Initiative on Malaria and Agriculture convened a multi-sectoral technical consultation on urban malaria in Pretoria, South Africa from 2nd to 4th December, 2004. The aim of the meeting was to identify strategies for the assessment and control of urban malaria. This commentary reflects the discussions held during the meeting and aims to inform researchers and policy makers of the potential for containing and reversing the emerging problem of urban malaria.     

Antenna organization and evidence for the function of a new antenna pigment species in the green photosynthetic bacterium Chloroflexus aurantiacus

Whole cells and isolated chlorosomes (antenna complex) of the green photosynthetic bacterium Chloroflexus aurantiacus have been studied by absorption spectroscopy (77 K and room temperature), fluorescence spectroscopy, circular dichroism, linear dichroism and electron spin resonance spectroscopy. The chlorosome absorption spectrum has maxima at 450 (contributed by carotenoids and bacteriochlorophyll (BChl) a Soret), 742 (BChl c) and 792 nm (BChl a) with intensity ratios of 20:25. The fluorescence emission spectrum has peaks at 748 and 802 nm when excitation is into either the 742 or 450 nm absorption bands, respectively. Whole cells have fluorescence peaks identical to those in chlorosomes with the addition of a major peak observed at 867 nm. The CD spectrum of isolated chlorosomes has an asymmetric-derivative-shaped CD centered at 739 nm suggestive of exciton interaction at least on the level of dimers. Linear dichroism of oriented chlorosomes shows preferential absorption at 742 nm of light polarized parallel to the long axis of the chlorosome. This implies that the transition dipoles are also oriented more or less parallel to the long axis of the chlorosome. Treatment with ferricyanide results in the appearance of a 2.3 G wide ESR spectrum at g 2.002. Whole cells grown under different light conditions exhibit different fluorescence behavior when absorption is normalized at 742 nm. Cells grown under low light conditions have higher fluorescence intensity at 748 nm and lower intensity at 802 nm than cells grown under high light conditions. These results indicate that the BChl c in chlorosomes is highly organized, and transfers energy from BChl c (742 nm) to a connector of baseplate BChl B792 (BChl a) presumably located in the chlorosome baseplate adjacent to the cytoplasmic membrane.     

Visual-Olfactory Integration in the Human Disease Vector Mosquito Aedes aegypti

1. Download : Download high-res image (194KB)
2. Download : Download full-size image

     

α-Catenin and IQGAP Regulate Myosin Localization to Control Epithelial Tube Morphogenesis in Dictyostelium

Apical actomyosin activity in animal epithelial cells influences tissue morphology and drives morphogenetic movements during development. The molecular mechanisms leading to myosin II accumulation at the apical membrane and its exclusion from other membranes are poorly understood. We show that in the nonmetazoan Dictyostelium discoideum, myosin II localizes apically in tip epithelial cells that surround the stalk, and constriction of this epithelial tube is required for proper morphogenesis. IQGAP1 and its binding partner cortexillin I function downstream of α- and β-catenin to exclude myosin II from the basolateral cortex and promote apical accumulation of myosin II. Deletion of IQGAP1 or cortexillin compromises epithelial morphogenesis without affecting cell polarity. These results reveal that apical localization of myosin II is a conserved morphogenetic mechanism from nonmetazoans to vertebrates and identify a hierarchy of proteins that regulate the polarity and organization of an epithelial tube in?a simple model organism.     

Hydrogen sulfide mediates vasoactivity in an O2-dependent manner

Hydrogen sulfide (H(2)S) has recently been shown to have a signaling role in vascular cells. Similar to nitric oxide (NO), H(2)S is enzymatically produced by amino acid metabolism and can cause posttranslational modification of proteins, particularly at thiol residues. Molecular targets for H(2)S include ATP-sensitive K(+) channels, and H(2)S may interact with NO and heme proteins such as cyclooxygenase. It is well known that the reactions of NO in the vasculature are O(2) dependent, but this has not been addressed in most studies designed to elucidate the role of H(2)S in vascular function. This is important, since H(2)S reactions can be dramatically altered by the high concentrations of O(2) used in cell culture and organ bath experiments. To test the hypothesis that the effects of H(2)S on the vasculature are O(2) dependent, we have measured real-time levels of H(2)S and O(2) in respirometry and vessel tension experiments, as well as the associated vascular responses. A novel polarographic H(2)S sensor developed in our laboratory was used to measure H(2)S levels. Here we report that, in rat aorta, H(2)S concentrations that mediate rapid contraction at high O(2) levels cause rapid relaxation at lower physiological O(2) levels. At high O(2), the vasoconstrictive effect of H(2)S suggests that it may not be H(2)S per se but, rather, a putative vasoactive oxidation product that mediates constriction. These data are interpreted in terms of the potential for H(2)S to modulate vascular tone in vivo.     

Stress causes decrease in vascular relaxation linked with altered phosphorylation of heat shock proteins

Cyclic nucleotide-dependent vascular relaxation is associated with increases in the phosphorylation of a small heat shock protein (HSP), HSP20. An increase in phosphorylation of another small HSP, HSP27, is associated with impaired cyclic nucleotide-dependent vascular relaxation. Expression of HSPs is altered by exposure to several types of cellular stress in vitro. To determine if behavioral stress in vivo alters vascular expression and phosphorylation of the small HSPs and cyclic nucleotide-dependent vascular relaxation, borderline hypertensive rats were stressed by restraint and exposure to air-jet stress 2 h/day for 10 days or remained in their home cage. Stress impaired relaxation of aorta to forskolin, which activates adenylyl cyclase, and sodium nitroprusside, which activates guanylyl cyclase. This was associated with an increase in the aortic expression and phosphorylation of HSP27, which was localized to the vascular smooth muscle, but a decrease in the amount of phosphorylated (P)-HSP20. To determine if P-HSP27 inhibits phosphorylation of HSP20, P-HSP27 was added to a reaction mixture containing recombinant HSP20 and the catalytic subunit of cAMP-dependent protein kinase. P-HSP27 inhibited phosphorylation of HSP20 in a concentration-dependent manner. These data demonstrate that P-HSP27 can inhibit phosphorylation of HSP20. The increase in P-HSP27 and decrease in P-HSP20 were associated with reduced cyclic nucleotide-dependent vascular smooth muscle relaxation in response to behavioral stress in vivo, an effect similar to that observed previously in response to cellular stress in vitro.