Role of Notch pathway in terminal follicle cell differentiation during Drosophila oogenesis

 During Drosophila oogenesis the body axes are determined by signaling between the oocyte and the somatic follicle cells that surround the egg chamber. A key event in the establishment of oocyte anterior-posterior polarity is the differential patterning of the follicle cell epithelium along the anterior-posterior axis. Both the Notch and epithelial growth factor (EGF) receptor pathways are required for this patterning. To understand how these pathways act in the process we have analyzed markers for anterior and posterior follicle cells accompanying constitutive activation of the EGF receptor, loss of Notch function, and ectopic expression of Delta. We find that a constitutively active EGF receptor can induce posterior fate in anterior but not in lateral follicle cells, showing that the EGF receptor pathway can act only on predetermined terminal cells. Furthermore, Notch function is required at both termini for appropriate expression of anterior and posterior markers, while loss of both the EGF receptor and Notch pathways mimic the Notch loss-of-function phenotype. Ectopic expression of the Notch ligand, Delta, disturbs EGF receptor dependent posterior follicle cell differentiation and anterior-posterior polarity of the oocyte. Our data are consistent with a model in which the Notch pathway is required for early follicle cell differentiation at both termini, but is then repressed at the posterior for proper determination of the posterior follicle cells by the EGF receptor pathway. Received: 5 November 1998 / Accepted: 14 December 1998     

Light pulses do not induce c-fos or per1 in the SCN of hamsters that fail to reentrain to the photocycle

Circadian activity rhythms of most Siberian hamsters (Phodopus sungorus sungorus) fail to reentrain to a 5-h phase shift of the light-dark (LD) cycle. Instead, their rhythms free-run at periods close to 25 h despite the continued presence of the LD cycle. This lack of behavioral reentrainment necessarily means that molecular oscillators in the master circadian pacemaker, the SCN, were unable to reentrain as well. The authors tested the hypothesis that a phase shift of the LD cycle rendered the SCN incapable of responding to photic input. Animals were exposed to a 5-h phase delay of the photocycle, and activity rhythms were monitored until a lack of reentrainment was confirmed. Hamsters were then housed in constant darkness for 24 h and administered a 30-min light pulse 2 circadian hours after activity onset. Brains were then removed, and tissue sections containing the SCN were processed for in situ hybridization. Sections were probed with Siberian hamster c-fos and per1 mRNA probes because light rapidly induces these 2 genes in the SCN during subjective night but not at other circadian phases. Light pulses induced robust expression of both genes in all animals that reentrained to the LD cycle, but no expression was observed in any animal that failed to reentrain. None of the animals exhibited an intermediate response. This finding is the first report of acute shift in a photocycle eliminating photosensitivity in the SCN and suggests that a specific pattern of light exposure may desensitize the SCN to subsequent photic input.     

A whole-genome scan for obstructive sleep apnea and obesity

Obstructive sleep apnea (OSA) is a common, chronic, complex disease associated with serious cardiovascular and neuropsychological sequelae and with substantial social and economic costs. Along with male gender, obesity is the most characteristic feature of OSA in adults. To identify susceptibility loci for OSA, we undertook a 9-cM genome scan in 66 white pedigrees (n=349 subjects) ascertained on the basis of either an affected individual with laboratory-confirmed OSA or a proband who was a neighborhood control individual. Multipoint variance-component linkage analysis was performed for the OSA-associated quantitative phenotypes apnea-hypopnea index (AHI) and body mass index (BMI). Candidate regions on chromosomes 1p (LOD score 1.39), 2p (LOD score 1.64), 12p (LOD score 1.43), and 19p (LOD score 1.40) gave the most evidence for linkage to AHI. BMI was also linked to multiple regions, most significantly to markers on chromosomes 2p (LOD score 3.08), 7p (LOD score 2.53), and 12p (LOD score 3.41). Extended modeling indicated that the evidence for linkage to AHI was effectively removed after adjustment for BMI, with the exception of the candidate regions on chromosomes 2p (adjusted LOD score 1.33) and 19p (adjusted LOD score 1.45). After adjustment for AHI, the primary linkages to BMI remained suggestive but were roughly halved. Our results suggest that there are both shared and unshared genetic factors underlying susceptibility to OSA and obesity and that the interrelationship of OSA and obesity in white individuals may be partially explained by a common causal pathway involving one or more genes regulating both AHI and BMI levels.     

Carbon isotope fractionation during aerobic biodegradation of trichloroethene by Burkholderia cepacia G4: a tool to map degradation mechanisms

The strain Burkholderia cepacia G4 aerobically mineralized trichloroethene (TCE) to CO(2) over a time period of approximately 20 h. Three biodegradation experiments were conducted with different bacterial optical densities at 540 nm (OD(540)s) in order to test whether isotope fractionation was consistent. The resulting TCE degradation was 93, 83.8, and 57.2% (i.e., 7.0, 16.2, and 42.8% TCE remaining) at OD(540)s of 2.0, 1.1, and 0.6, respectively. ODs also correlated linearly with zero-order degradation rates (1.99, 1.11, and 0.64 micromol h(-1)). While initial nonequilibrium mass losses of TCE produced only minor carbon isotope shifts (expressed in per mille delta(13)C(VPDB)), they were 57.2, 39.6, and 17.0 per thousand between the initial and final TCE levels for the three experiments, in decreasing order of their OD(540)s. Despite these strong isotope shifts, we found a largely uniform isotope fractionation. The latter is expressed with a Rayleigh enrichment factor, epsilon, and was -18.2 when all experiments were grouped to a common point of 42.8% TCE remaining. Although, decreases of epsilon to -20.7 were observed near complete degradation, our enrichment factors were significantly more negative than those reported for anaerobic dehalogenation of TCE. This indicates typical isotope fractionation for specific enzymatic mechanisms that can help to differentiate between degradation pathways.     

Control of resistant pink bollworm (Pectinophora gossypiella) by transgenic cotton that produces Bacillus thuringiensis toxin Cry2Ab

Crops genetically engineered to produce Bacillus thuringiensis toxins for insect control can reduce use of conventional insecticides, but insect resistance could limit the success of this technology. The first generation of transgenic cotton with B. thuringiensis produces a single toxin, Cry1Ac, that is highly effective against susceptible larvae of pink bollworm (Pectinophora gossypiella), a major cotton pest. To counter potential problems with resistance, second-generation transgenic cotton that produces B. thuringiensis toxin Cry2Ab alone or in combination with Cry1Ac has been developed. In greenhouse bioassays, a pink bollworm strain selected in the laboratory for resistance to Cry1Ac survived equally well on transgenic cotton with Cry1Ac and on cotton without Cry1Ac. In contrast, Cry1Ac-resistant pink bollworm had little or no survival on second-generation transgenic cotton with Cry2Ab alone or with Cry1Ac plus Cry2Ab. Artificial diet bioassays showed that resistance to Cry1Ac did not confer strong cross-resistance to Cry2Aa. Strains with >90% larval survival on diet with 10 microg of Cry1Ac per ml showed 0% survival on diet with 3.2 or 10 microg of Cry2Aa per ml. However, the average survival of larvae fed a diet with 1 microg of Cry2Aa per ml was higher for Cry1Ac-resistant strains (2 to 10%) than for susceptible strains (0%). If plants with Cry1Ac plus Cry2Ab are deployed while genes that confer resistance to each of these toxins are rare, and if the inheritance of resistance to both toxins is recessive, the efficacy of transgenic cotton might be greatly extended.     

Juvenile Siberian hamsters display torpor and modified locomotor activity and body temperature rhythms in response to reduced food availability

Siberian hamsters as young as 16 and 28 d displayed torpor in response to treatment with 2,500 mg/kg 2-deoxy-D-glucose and reduced food availability, respectively. In addition, most food-restricted hamsters displayed increased locomotor activity and elevated body temperatures in the 3 h immediately preceding daily food delivery. This anticipatory activity disappeared within a few days of reimposition of ad lib. feeding. Torpor first appeared spontaneously at approximately 13 wk of age in hamsters fed ad lib. and maintained in short day lengths. The onset of this "spontaneous" torpor was unaffected by the hamsters' history of food restriction before age 2 mo. Siberian hamsters born late in the breeding season can conserve energy by undergoing torpor immediately after weaning when they contend with food shortages and concurrent energetic challenges imposed by growth requirements and low ambient temperatures.     

Evidence that acetyl phosphate functions as a global signal during biofilm development

We used DNA macroarray analysis to identify genes that respond to the status of the intracellular acetyl phosphate (acP) pool. Genes whose expression correlated negatively with the ability to synthesize acP (i.e. negatively regulated genes) function primarily in flagella biosynthesis, a result consistent with observations that we published previously (Prüss and Wolfe, 1994, Mol Microbiol 12: 973-984). In contrast, genes whose expression correlated positively with the ability to synthesize acP (i.e. positively regulated genes) include those for type 1 pilus assembly, colanic acid (capsule) biosynthesis and certain stress effectors. To our knowledge, this constitutes the first report that these genes may respond to the status of the intracellular acP pool. Previously, other researchers have implicated flagella, type 1 pili, capsule and diverse stress effectors in the formation of biofilms. We therefore tested whether cells altered in their ability to metabolize acP could construct normal biofilms, and found that they could not. Cells defective for the production of acP and cells defective for the degradation of acP could both form biofilms, but these biofilms exhibited characteristics substantially different from each other and from biofilms formed by their wild-type parent. We confirmed the role of individual cell surface structures, the expression of which appears to correlate with acP levels, in fim or fli mutants that cannot assemble type 1 pili or flagella respectively. Thus, the information gained by expression profiling of cells with altered acP metabolism indicates that acP may help to co-ordinate the expression of surface structures and cellular processes involved in the initial stages of wild-type biofilm development.     

The Arabidopsis TDS4 gene encodes leucoanthocyanidin dioxygenase (LDOX) and is essential for proanthocyanidin synthesis and vacuole development

The anthocyanin and proanthocyanidin (PA) biosynthetic pathways share common intermediates until leucocyanidin, which may be used by leucoanthocyanidin dioxygenase (LDOX) to produce anthocyanin, or the enzyme leucoanthocyanidin reductase (LAR) to produce catechin, a precursor of PA. The Arabidopsis mutant tannin deficient seed 4 (tds4-1) has a reduced PA level and altered pattern PA accumulation. We identified the TDS4 gene as LDOX by complementation of the tds4-1 mutation either with a cosmid encoding LDOX or a 35S:LDOX construct. Independent Arabidopsis lines with a T-DNA insertion in the LDOX gene had a similar phenotype, and one was allelic to tds4-1. The seed phenotype of ban tds4 double mutants showed that LDOX precedes BANYULS (BAN) in the PA pathway, confirming recent biochemical characterisation of BAN as an anthocyanidin reductase. Double mutant analysis was also used to order the other TDS genes. Analysis of the PA intermediates in tds4-1 revealed three dimethylaminocinnamaldehyde (DMACA) reacting compounds that accumulated in extracts from developing seeds. Analysis of Arabidopsis PA and its precursors indicates that Arabidopsis, unlike many other plants, exclusively uses the epicatechin and not the catechin pathway to PA. Transmission electron microscopy (TEM) showed that the pattern observed when seeds of tds4 were stained with DMACA was a result of the accumulation of PA intermediates in the cytoplasm of endothelial cells. Fluorescent marker dyes were used to show that tds4 endothelial cells had multiple small vacuoles, instead of a large central vacuole as observed in the wild types (WT). These results show that in addition to its established role in the formation of anthocyanin, LDOX is also part of the PA biosynthesis pathway.