Distortion of the three-dimensional structure of the vnd/NK-2 homeodomain bound to DNA induced by an embryonically lethal A35T point mutation

The three-dimensional solution structure obtained by NMR of the A35T mutant vnd/NK-2 homeodomain bound to the vnd/NK-2 consensus 16 bp DNA sequence was determined. This mutation to threonine from alanine in position 35 in helix II of the vnd/NK-2 homeodomain is associated with early embryonic lethality in Drosophila melanogaster. Although the unbound mutant protein is not structured, in the DNA-bound state it adopts the three-helix fold characteristic of all known homeodomains, but with alterations relative to the structure of the wild-type analogue. These structural modifications occur, and are accompanied by a 50-fold reduction in the DNA binding affinity, even though most of the protein-DNA interactions originally seen for the wild-type homeodomain are found likewise in the threonine analogue. Alterations include torsional angle changes in the loop between helix I and helix II, and in the turn between helix II and helix III, as well as in a distortion of the usual antiparallel orientation of helix I with respect to helix II. The alteration of the position of leucine 40 in the A35T mutant is proposed to explain the observed 1.27 ppm upfield shift of the corresponding amide proton resonance relative to the value observed for the wild-type analogue. A detailed comparison of the structures of the mutant A35T and wild-type vnd/NK-2 homeodomains bound to the cognate DNA is presented. The consequences of the structural alteration of the DNA-bound A35T mutant vnd/NK-2 protein may constitute the basis of the observed early embryonic lethality.     

Effect of a pharmacological activation of PPAR on the expression of RAR and TR in rat liver

It has recently been shown that high-fat diets induce the expression of peroxisome proliferator-activated receptor (PPAR) with a concomitant decrease in expression of retinoic acid (RAR) and triiodothyronine (TR) receptors in rat liver. The authors have suggested that PPAR activation may be responsible for these modifications in nuclear receptor expression. With the aim of gaining further insight into a possible relationship between the patterns of expression of these receptors, we have examined, using a pharmacological model, the effect of a strong and specific PPAR activation induced by bezafibrate, a peroxisome proliferator agent. Activation of PPAR was evaluated by quantifying PPARα mRNA and acyl-CoA oxidase mRNA. The expression of RAR and TR was determined by assaying the binding properties of these nuclear receptors and by quantifying the mRNA level of RARβ and TRα₁,β₁ isoforms. After a 10 day treatment of young rats, induction of PPAR (PPARα mRNA was increased by 40% [P< 0.05 and acyl-CoA oxidase mRNA by 411% [P<0.001]) and a concomitant decrease of RAR and TR expression (Maximal Binding Capacity was decreased by 21 and 26%, respectively [P<0.05]) in the liver was observed. RXRα mRNA expression was unchanged by treatment. Cross-talk between RAR, TR and PPAR signalling pathways may be implicated in the new patterns of nuclear receptor expression observed. The decreased expression of RAR and TR reported here could provide a novel element for the understanding of the link between PPAR and tumorigenesis in rat liver.     

The consequences of crowned eagle central-place foraging on predation risk in monkeys

The African crowned eagle (Stepahnoaetus coronatus) is the primary predator for arboreal primates throughout sub-Saharan forests. Monkeys typically respond with alarm calls when they are aware of the presence of crowned eagles and such calls can be considered a corollary of predation risk within primate groups. Alarm calls from six species of monkeys were recorded across the home range of an eagle pair in Taï National Park, Côte d''Ivoire. Spatial and temporal variation in primate alarm calling was found to be related to eagle ranging behaviour according to the predictions of central-place foraging models. Radio-tracking data indicate that eagle activity is higher in the centre of their home range and monkey alarm-calling rates are correspondingly elevated near eagle nests as opposed to farther away. Alarm-calling rates are also temporally coupled with measures of eagle activity. There were considerable differences between the species in both rates and spatial patterns of alarm calling. The variation we measure in predation risk is expected to have consequences at the behavioural and population level.     

Conjugated linoleic acid isomers in mitochondria: evidence for an alteration of fatty acid oxidation

The beneficial effects exerted by low amounts of conjugated linoleic acids (CLA) suggest that CLA are maximally conserved and raise the question about their mitochondrial oxidizability. Cis-9,trans-11-C(18:2) (CLA1) and trans-10,cis-12-C(18:2) (CLA2) were compared to cis-9,cis-12-C(18:2) (linoleic acid; LA) and cis-9-C(16:1) (palmitoleic acid; PA), as substrates for total fatty acid (FA) oxidation and for the enzymatic steps required for the entry of FA into rat liver mitochondria. Oxygen consumption rate was lowest when CLA1 was used as a substrate with that on CLA2 being intermediate between it and the respiration on LA and PA. The order of the radiolabeled FA oxidation rate was PA > LA > CLA2 > CLA1. Transesterification to acylcarnitines of the octadecadienoic acids were similar, while uptake across inner membranes of CLA1 and, to a lesser extent, of CLA2 was greater than that of LA or PA. Prior oxidation of CLA1 or CLA2 made re-isolated mitochondria much less capable of oxidising PA or LA under carnitine-dependent conditions, but without altering the carnitine-independent oxidation of octanoic acid. Therefore, the CLA studied appeared to be both poorly oxidizable and capable of interfering with the oxidation of usual FA at a step close to the beginning of the beta-oxidative cycle.     

Indirect effects of lemming cycles on sandpiper dynamics: 50 years of counts from southern Sweden

The bird-lemming hypothesis postulates that breeding success of tundra-nesting geese and waders in Siberia follows the cyclic pattern of lemming populations, as a result of predators switching from lemmings to birds when the lemming population crashes. We present 50 years of data on constant-effort catches of red knot Calidris canutus and curlew sandpiper C. ferruginea at an autumn migratory stopover site (Ottenby) at the Baltic Sea, supplemented with literature data on winter censuses of dark-bellied brent goose Branta b. bernicla and white-fronted goose Anser albifrons in northwestern Europe, and waders in Germany and Southern Africa. Number and proportion of juveniles in these bird populations (both our own and literature data) were compared with an index of predation pressure (calculated from the abundance of lemmings on the Taimyr peninsula), and climate indices for the North Eurasia and the North Atlantic regions. The index of predation pressure correlated significantly with the number of juveniles of red knot and curlew sandpiper, but not with number of adults. Also, this index correlated with the reproductive performance of geese and waders reported in the literature. Fourier analysis revealed a significant deviation from random noise with the maximum spectral density at the period length of 3 years for number of juvenile red knots and curlew sandpipers captured at Ottenby, abundance of lemmings, reproduction in arctic fox Alopex lagopus, and reproductive performance in geese on the Siberian tundra. Also, the date of passage at Ottenby for adult red knot and curlew sandpiper showed a spectral density peak at a period length of 3 years, the latter species also showing a peak at a period length of 5-6 years. Passage dates for adult red knot and curlew sandpiper were earlier in years of high predation pressure compared with years of low predation pressure. The fluctuations in reproductive success of the studied Siberian goose and wader species appear to be primarily influenced by biotic factors in the breeding area, rather than by abiotic factors, such as climate oscillations. Annual variations in migratory arctic bird populations may have far reaching effects in habitats along their migration routes and in their wintering areas. We suggest a link between lemming cyclicity in the Northern Hemisphere and predation pressure on Southern Hemisphere benthos, in which the signal is carried between continents by long distance migrating waders.     

Response of recombinant Chinese hamster ovary cells to hyperosmotic pressure: effect of Bcl-2 overexpression

In an attempt to use the hyperosmotic pressure for improved foreign protein production in recombinant Chinese hamster ovary (rCHO) cells, the response of rCHO cells producing a humanized antibody (SH2-0.32-(Delta)bcl-2 cells) to hyperosmotic pressure was determined in regard to cell growth and death, and antibody production. Further, the feasibility of Bcl-2 overexpression in improving rCHO cell viability under hyperosmotic pressure was also determined by comparing control cells (SH2-0.32-(Delta)bcl-2) with Bcl-2 overexpressing cells (14C6-bcl-2). After 3 days of cultivation in the standard medium (294 mOsm x kg(-1)), the spent medium was exchanged with the fresh media with various osmolalities (294-640 mOsm x kg(-1)). The results obtained show that hyperosmotic pressure inhibited cell growth in a dose-dependent manner, though 14C6-bcl-2 cells were less susceptible to hyperosmotic pressure than SH2-0.32-(Delta)bcl-2 cells. At 522 mOsm x kg(-1), SH2-0.32-(Delta)bcl-2 cells underwent a gradual cell death mainly through apoptosis due to the cytotoxic effect of hyperosmotic pressure. In contrast, Bcl-2 overexpression in 14C6-bcl-2 cells could delay the apoptosis induced by 522 mOsm x kg(-1) by inhibiting caspase-3 activation. Bcl-2 overexpression could also improve the cellular membrane integrity of 14C6-bcl-2 cells. When subjected to hyperosmotic pressure, the specific antibody productivity of SH2-0.32-(Delta)bcl-2 cells and 14C6-bcl-2 cells was increased in a similar extent. As a result, the final antibody concentration achieved in 14C6-bcl-2 cells at 522 mOsm x kg(-1) was 2.5-fold higher than that at 294 mOsm x kg(-1). At 580 mOsm x kg(-1), acute hyperosmotic pressure induced the rapid loss of viability in both SH2-0.32-(Delta)bcl-2 and 14C6-bcl-2 cells through necrosis rather than through apoptosis. Taken together, Bcl-2 overexpression and optimized hyperosmotic pressure could improve the antibody production of rCHO cells.     

Familiarity and dominance relations among female sooty mangabeys in the Taï National Park

Dominance relationships of female sooty mangabeys have thus far been studied exclusively in captive groups. In captivity, adult females form a stable linear hierarchy as would be expected in species exhibiting strong contest competition. However, the same individuals do not exhibit other aspects of behavior that would be expected where contest competition occurs. For example, they show no kin‐based alliances leading to hierarchies in which the members of each matriline occupy adjacent ranks. The goal of this study was to provide the first data on dominance relationships of sooty mangabey females in their natural environment in the Taï National Park, Ivory Coast. In our study group, adult females formed a linear dominance hierarchy. Aggression over food increased in food patches, as would be expected for species that experience contest competition. Moreover, females formed highly differentiated social relationships, showing particular affinities with females of adjacent rank. Am. J. Primatol. 56:137–153, 2002. © 2002 Wiley‐Liss, Inc.