Evidence for a third genetic locus causing familial hypercholesterolemia. A non-LDLR, non-APOB kindred.

Monogenically inherited hypercholesterolemia is most commonly caused by mutations at the low density lipoprotein receptor (LDLR) locus causing familial hypercholesterolemia (FH) or at the apolipoprotein B (APOB) locus causing the disorder familial defective apoB (FDB). Probands from 47 kindreds with a strict clinical diagnosis of FH were selected from the Cardiovascular Genetics Research Lipid Clinic, Utah, for molecular genetic analysis. Using a combination of single-strand conformation polymorphism (SSCP) and direct sequencing, 12 different LDLR gene mutations were found in 16 of the probands. Three of the probands were carriers of the APOB R3500Q mutation. In five of the remaining 28 pedigrees where no mutation had been detected, samples from enough relatives were available to examine co-segregation with the LDLR region using the microsatellite marker D19S221, which is within 1 Mb centromeric of the LDLR locus, and D19S394, sited within 150 kb telomeric of the LDLR locus. In four of the families there was strong evidence for co-segregation between the LDLR locus and the phenotype of hypercholesterolemia, but in one large family with 18 living affected members and clear-cut bimodal hypercholesterolemia, there were numerous exclusions of co-segregation. Using length polymorphic markers within and outside the APOB gene, linkage of phenotype in this family to the APOB region was similarly excluded. In this large family, the degree of hypercholesterolemia, prevalence of tendon xanthomata, and occurrence of early coronary disease were indistinguishable from the other families studied. In summary, the data provide unequivocal evidence that a third locus can be etiological for monogenic familial hypercholesterolemia and should be reinvigorating to research in this field.     

Localization of H+-ATPases in soybean root nodules

The localization of H⁺-ATPases in soybean (Glycine max L. cv. Stevens) nodules was investigated using antibodies against both P-type and V-type enzymes. Immunoblots of peribacteroid membrane (PBM) proteins using antibodies against tobacco and Arabidopsis H⁺-ATPases detected a single immunoreactive band at approximately 100 kDa. These antibodies recognized a protein of similar relative molecular mass in the crude microsomal fraction from soybean nodules and uninoculated roots. The amount of this protein was greater in PBM from mature nodules than in younger nodules. Immunolocalization of P-type ATPases using silver enhancement of colloidal-gold labelling at the light-microscopy level showed signal distributed around the periphery of non-infected cells in both the nodule cortex and nodule parenchyma. In the central nitrogen-fixing zone of the nodule, staining was present in both the infected and uninfected cells. Examination of nodule sections using confocal microscopy and fluorescence staining showed an immunofluorescent signal clearly visible around the periphery of individual symbiosomes which appeared as vesicles distributed throughout the infected cells of the central zone. Electron-microscopic examination of immunogold-labelled sections shows that P-type ATPase antigens were present on the PBM of both newly formed, single-bacteroid symbiosomes just released from infection threads, and on the PBM of mature symbiosomes containing two to four bacteroids. Immunogold labelling using antibody against the B-subunit of V-type ATPase from oat failed to detect this protein on symbiosome membranes. Only a very faint signal with this antibody was detected on Western blots of purified PBM. During nodule development, fusion of small symbiosomes to form larger ones containing multiple bacteroids was observed. Fusion was preceded by the formation of cone-like extensions of the PBM, allowing the membrane to make contact with the adjoining membrane of another symbiosome. We conclude that the major H⁺-ATPase on the PBM of soybean is a P-type enzyme with homology to other such enzymes in plants. In vivo, this enzyme is likely to play a critical role in the regulation of nutrient exchange between legume and bacteroids. Received: 25 November 1998 / Accepted: 6 January 1999     

Variation in photorespiration. The effect of genetic differences in photorespiration on net photosynthesis in tobacco

The hypothesis that net photosynthesis is diminished in many plant species because of a high rate of CO₂ evolution in the light has been tested further. High rates of CO₂ output in CO₂-free air in comparison with dark respiration were found in Chlamydomonas reinhardi, wheat leaves, tomato leaves, and to a lesser extent in Chlorella pyrenoidosa by means of the ¹⁴C-photorespiration assay. In tobacco leaves high photorespiration was characteristic of a standard variety, Havana Seed, and a possibly still higher rate was found in a yellow heterozygous mutant, JWB Mutant. However, the dark homozygous sibling of the latter, JWB Wild, had a low photorespiration for the tobacco species. The relative rates of photorespiration were in the same sequence when measured by the ¹⁴CO₂ released in normal air from leaf disks supplied with glycolate-1-¹⁴C in the light.

As would be predicted by the hypothesis, the maximal net rate of photosynthesis at 300 ppm of CO₂ in the air in JWB Wild leaves was greater (24%) than in Havana Seed, while JWB Mutant had less CO₂ uptake than the standard variety (21%). At 550 ppm of CO₂ the differences in net photosynthesis were not as great between the 2 siblings as at 200 ppm. The relative leaf expansion rates of seedlings of the 3 tobacco varieties in a greenhouse had the same relationship as their rates of CO₂ assimilation.

Thus within the tobacco species, as in a comparison between tobacco and maize, low photorespiratory CO₂ evolution was correlated with higher photosynthetic efficiency. Therefore it seems that increased CO₂ uptake should be achieved by genetic interference with the process of photorespiration.

     

Tissue-specific expression of the alternative oxidase in soybean and siratro

Alternative oxidase activity (cyanide-insensitive respiration) was measured in mitochondria from the shoots, roots, and nodules of soybean (Glycine max L.) and siratro (Macroptilium atropurpureum) plants. Activity was highest in the shoots and lowest in the nodules. Alternative oxidase activity was associated with one (roots) or two (shoots) proteins between 30 and 35 kilodaltons that were detected by western blotting with a monoclonal antibody against Sauromatum guttatum alternative oxidase. No such protein was detected in nodule mitochondria. Measurements of oxygen uptake by isolated soybean root and nodule cells in the presence of cyanide and salicylhydroxamic acid indicated that alternative oxidase activity was confined to the uninfected cortex cells of the nodule. Immunoprecipitation of translation products of mRNA isolated from soybean shoots revealed a major band at 43 kilodaltons that is assumed to be the precursor of an alternative oxidase protein. This band was not seen when mRNA from nodules was treated in the same fashion. The results indicate that tissue-specific expression of the alternative oxidase occurs in soybean and siratro.     

Epigenetic mechanisms in cognition

Although the critical role for epigenetic mechanisms in development and cell differentiation has long been appreciated, recent evidence reveals that these mechanisms are also employed in postmitotic neurons as a means of consolidating and stabilizing cognitive-behavioral memories. In this review, we discuss evidence for an "epigenetic code" in the central nervous system that mediates synaptic plasticity, learning, and memory. We consider how specific epigenetic changes are regulated and may interact with each other during memory formation and how these changes manifest functionally at the cellular and circuit levels. We also describe a central role for mitogen-activated protein kinases in controlling chromatin signaling in plasticity and memory. Finally, we consider how aberrant epigenetic modifications may lead to cognitive disorders that affect learning and memory, and we review the therapeutic potential of epigenetic treatments for the amelioration of these conditions.     

Microtubule Motors Power Plasma Membrane Tubulation in Clathrin‐Independent Endocytosis

How the plasma membrane is bent to accommodate clathrin‐independent endocytosis remains uncertain. Recent studies suggest Shiga and cholera toxin induce membrane curvature required for their uptake into clathrin‐independent carriers by binding and cross‐linking multiple copies of their glycosphingolipid receptors on the plasma membrane. But it remains unclear if toxin‐induced sphingolipid crosslinking provides sufficient mechanical force for deforming the plasma membrane, or if host cell factors also contribute to this process. To test this, we imaged the uptake of cholera toxin B‐subunit into surface‐derived tubular invaginations. We found that cholera toxin mutants that bind to only one glycosphingolipid receptor accumulated in tubules, and that toxin binding was entirely dispensable for membrane tubulations to form. Unexpectedly, the driving force for tubule extension was supplied by the combination of microtubules, dynein and dynactin, thus defining a novel mechanism for generating membrane curvature during clathrin‐independent endocytosis.      

Inactivation of a peroxiredoxin by hydrogen peroxide is critical for thioredoxin-mediated repair of oxidized proteins and cell survival

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Highlights? Tpx1, Pap1, and Mxr1 are all substrates for S. pombe thioredoxin Trx1 ? In H₂O₂-treated cells, Tpx1 competitively inhibits reduction of Pap1 and Mxr1 ? H₂O₂-induced hyperoxidation of Tpx1 allows Trx1 to reduce other oxidized proteins ? Inhibition of Tpx1 by H₂O₂ is essential for Trx1-mediated repair and cell survival     

Social interactions among captive brushtail possums (Trichosurus vulpecula)

A biological control strategy relying on a self-disseminating agent may provide the only affordable long-term technique for reducing brushtail possum (Trichosurus vulpecula) numbers throughout New Zealand. The objective of this study was to determine the frequency and patterns of social interactions in single and mixed-sex groups of possums, in order to identify interactions that may assist in the dissemination of biocontrol agents. Thirty-two sexually mature wild-caught possums (16 female, 16 male) were housed in captive groups (of four) in enclosures during the breeding and non-breeding seasons. Groups consisted of either all females, females and males or all males. Four types of social interactions were defined: threats, fights, affiliative and sexual interactions. Interactions only occurred between two animals at one time and were most frequent in the non-breeding season. Within all female groups, possums readily engaged in interactions that had either an agonistic or affiliative nature. Mixed-sex groups interacted less frequently than females, but also engaged in both agonistic and affiliative interactions. In contrast, possums in all male groups rarely interacted, with only a few fights and no affiliative interactions observed. Some mixed-sex dyads appeared to 'associate' during the breeding period. Young were produced by three females that regularly associated with a male and one female that showed little associative behaviour. Given the different interaction patterns observed in each group type, biological control agents that rely on specific interaction patterns for dissemination, are likely to spread at different rates among different possum groups and in different seasons.     

Physiological responses to short-term fasting among herbivorous,omnivorous, and carnivorous fishes

We explored the integrated role of dietary specialization and feeding periodicity on the response of the gastrointestinal tract of teleosts fishes to short-term (7–10 days) fasting and refeeding. Fasted and fed herbivorous grass carp (Ctenopharyngodon idella), omnivorous channel catfish (Ictalurus punctatus), and carnivorous largemouth bass (Micropterus salmoides) were compared for digestive organ masses, intestinal morphology, gastrointestinal pH, and the specific activities and total intestinal capacities of the intestinal hydrolases aminopeptidase (APN) and maltase and intestinal nutrient transporters. All three species experience intestinal hypertrophy with feeding as noted by significant increases in enterocyte dimensions. Of the three, only I. punctatus experienced a postprandial increase in intestinal length, and only C. idella experienced significant modulation of intestinal microvillus length. Feeding resulted in acidification of the stomachs of I. punctatus and M. salmoides. Predicted to exhibit a relatively modest set of postprandial responses because of their more frequent feeding habits, C. idella only experienced increases in APN and maltase activity with feeding and no significant regulation of nutrient uptake. Significant regulation of hydrolase activities and nutrient uptake were exhibited by I. punctatus and M. salmoides, with I. punctatus experiencing the most comprehensive set of responses. As predicted by food habits, there was an interspecific gradient in intestinal length and glucose uptake extending from longer intestines and greater glucose uptake for the herbivorous C. idella, intermediate lengths and glucose uptake for the omnivorous I. punctatus, and shorter intestines and reduced glucose uptake for the carnivorous M. salmoides. Among teleosts fishes, short episodes of fasting lead to significant alterations in intestinal form and function that are rapidly restored with feeding.     

Contrasting geographic structure in evolutionarily divergent Lake Tanganyika catfishes

Geographic isolation is suggested to be among the most important processes in the generation of cichlid fish diversity in East Africa's Great Lakes, both through isolation by distance and fluctuating connectivity caused by changing lake levels. However, even broad scale phylogeographic patterns are currently unknown in many non‐cichlid littoral taxa from these systems. To begin to address this, we generated restriction‐site‐associated DNA sequence (RADseq) data to investigate phylogeographic structure throughout Lake Tanganyika (LT) in two broadly sympatric rocky shore catfish species from independent evolutionary radiations with differing behaviors: the mouthbrooding claroteine, Lophiobagrus cyclurus, and the brood‐parasite mochokid, Synodontis multipunctatus. Our results indicated contrasting patterns between these species, with strong lake‐wide phylogeographic signal in L. cyclurus including a deep divergence between the northern and southern lake basins. Further structuring of these populations was observed across a heterogeneous habitat over much smaller distances. Strong population growth was observed in L. cyclurus sampled from shallow shorelines, suggesting population growth associated with the colonization of new habitats following lake‐level rises. Conversely, S. multipunctatus, which occupies a broader depth range, showed little phylogeographic structure and lower rates of population growth. Our findings suggest that isolation by distance and/or habitat barriers may play a role in the divergence of non‐cichlid fishes in LT, but this effect varies by species.