The role of extrahepatic retinol binding protein in the mobilization of retinoid stores

Although the major tissue site of retinol binding protein (RBP) synthesis in the body is the liver, other sites of synthesis have been reported. The physiological role(s) of circulating RBP that is produced and secreted extrahepatically has not been systematically investigated. To address this question, we used as a model a mouse strain (hRBP(-/-)) that expresses human RBP (hRBP) cDNA under the control of the mouse muscle creatine kinase promoter in an rbp-null background (RBP(-/-)). By comparing hRBP(-/-), RBP(-/-), and wild-type mice, we asked whether extrahepatic RBP can perform all of the physiological functions of RBP synthesized in the liver. We demonstrate that extrahepatically synthesized hRBP, unlike RBP expressed in liver, cannot mobilize liver retinoid stores. Consistent with this conclusion, we find that circulating hRBP is not taken up by hepatocytes. RBP has been proposed to play an essential role in distributing hepatic retinoids between hepatocytes and hepatic stellate cells. We find, however, that the distribution of retinoid in the livers of the three mouse strains described above is identical. Thus, RBP is not required for intrahepatic transport and storage of retinoid. These and other observations are discussed.     

Responses of the coastal bacterial community to viral infection of the algae Phaeocystis globosa

The release of organic material upon algal cell lyses has a key role in structuring bacterial communities and affects the cycling of biolimiting elements in the marine environment. Here we show that already before cell lysis the leakage or excretion of organic matter by infected yet intact algal cells shaped North Sea bacterial community composition and enhanced bacterial substrate assimilation. Infected algal cultures of Phaeocystis globosa grown in coastal North Sea water contained gamma- and alphaproteobacterial phylotypes that were distinct from those in the non-infected control cultures 5 h after infection. The gammaproteobacterial population at this time mainly consisted of Alteromonas sp. cells that were attached to the infected but still intact host cells. Nano-scale secondary-ion mass spectrometry (nanoSIMS) showed ∼20% transfer of organic matter derived from the infected ¹³C- and ¹⁵N-labelled P. globosa cells to Alteromonas sp. cells. Subsequent, viral lysis of P. globosa resulted in the formation of aggregates that were densely colonised by bacteria. Aggregate dissolution was observed after 2 days, which we attribute to bacteriophage-induced lysis of the attached bacteria. Isotope mass spectrometry analysis showed that 40% of the particulate ¹³C-organic carbon from the infected P. globosa culture was remineralized to dissolved inorganic carbon after 7 days. These findings reveal a novel role of viruses in the leakage or excretion of algal biomass upon infection, which provides an additional ecological niche for specific bacterial populations and potentially redirects carbon availability.     

The Effect of Cucurbitacin E Glycoside, a Feeding Stimulant for Corn Rootworm, on Biocontrol Fungi: Beauveria bassiana and Metarhizium anisopliae

Corn rootworms compulsively feed on cucurbitacins (bitter compounds found in many cucurbits), while most other pest insects are repelled by them. Several hypotheses have been proposed for this activity, but the results have been equivocal. One recent hypothesis suggested that cucurbitacin may provide protection against soil borne fungal entomopathogens, both in the adult corn rootworm and in the eggs laid in the soil. Any antifungal activity would preclude the use of this feeding stimulant to enhance the activity of fungal pathogens used in biocontrol. To test this hypothesis, we exposed two fungal pathogens of corn rootworm, Beauveria bassiana and Metarhizium anisopliae , to an extract from a bitter mutant of Hawkesbury watermelon, which contained about 0.05% cucurbitacin E glycoside. The extract inhibited the growth of both fungi. However, when the extract was sterilized by passing through a 0.45 micron filter, this inhibitory activity disappeared. Purified cucurbitacin E glycoside did not inhibit the growth of either fungus. Four Bacillus isolates (identified as Bacillus subtilis var. globigii and B. amyloliquefaciens ) were isolated from this extract which were able to inhibit the growth of both fungi. All of these bacteria excreted the inhibitory activity into the medium. Thus, the inhibition of fungal growth attributed to cucurbitacin may actually be due to bacteria incidentally associated with cucurbits.     

Spiked Sediment Toxicity Testing of Hydrophobic Organic Chemicals: Bioavailability,Technical Considerations,and Applications

Many evaluations estimating safe levels of hydrophobic organic chemicals in sediments do not account for confounding factors such as physical habitat quality or covariance among chemicals. Controlled experiments demonstrating cause and effect can be conducted with spiked sediment toxicity tests, but application of this methodology has been limited in part by concerns about chemical bioavailability and challenges in achieving target concentrations. Relevant literature was reviewed to assess the utility of standardizing sediment equilibration times; hydrophobicity, complex sediment characteristics, and temperature were identified as potentially equally important factors. Disequilibrium appears likely following limited equilibration time but should yield conservative toxicity test results relative to aged field sediments. Nominal and measured concentrations in over 20 published studies were compared to assess spiked chemical recovery (i.e., measured concentration/nominal concentration). Recovery varied substantially among studies and was not readily predictable based on spiking or extraction method, chemical properties, or measured sediment characteristics, although unmeasured differences between sediments appeared to be important. Factors affecting specific studies included chemical adsorption to glassware, biodegradation, and volatilization. Pre- and post-toxicity test analyses are recommended to confirm exposure concentrations. Studies with 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD) and hexachlorobenzene (HCB) exemplify the utility of verifying results of field studies using spiked sediment tests. Sediments spiked with these chemicals at concentrations greatly exceeding those in associated field studies caused no adverse effects in test organisms, demonstrating that other chemicals co-occurring in test sediment samples caused toxicity initially attributed to 2,3,7,8-TCDD and HCB in the field studies. Another key application of spiked sediment tests has been the investigation of TOC as the primary factor affecting bioavailability of hydrophobic organic chemicals. A review of LC50s for nine chemicals reported in 12 studies shows that comparable LC50s derived in different sediments generally agree within a factor of five when concentrations are normalized to a constant TOC. Additionally, use of spiked sediment toxicity testing to investigate toxicological interactions among chemicals provides a promising approach to improving the ability to predict sediment toxicity in the field.     

Banking brains: a pre-mortem “how to” guide to successful donation

A review of the brain banking literature reveals a primary focus either on the factors that influence the decision to become a future donor or on the brain tissue processing that takes place after the individual has died (i.e., the front-end or back-end processes). What has not been sufficiently detailed, however, is the complex and involved process that takes place after this decision to become a future donor is made yet before post-mortem processing occurs (i.e., the large middle-ground). This generally represents a period of many years during which the brain bank is actively engaged with donors to ensure that valuable clinical information is prospectively collected and that their donation is eventually completed. For the past 15 years, the Essential Tremor Centralized Brain Repository has been actively involved in brain banking, and our experience has provided us valuable insights that may be useful for researchers interested in establishing their own brain banking efforts. In this piece, we fill a gap in the literature by detailing the processes of enrolling participants, creating individualized brain donation plans, collecting clinical information and regularly following-up with donors to update that information, and efficiently coordinating the brain harvest when death finally arrives.