Loss of the CONSTITUTIVE PHOTOMORPHOGENIC9 signalosome subunit 5 is sufficient to cause the cop/det/fus mutant phenotype in Arabidopsis

The COP9 signalosome (CSN) was originally identified based on the constitutively photomorphogenic/de-etiolated/fusca (cop/det/fus) mutants from Arabidopsis thaliana. CSN is evolutionary conserved, and its subunit 5 (CSN5) mediates the deconjugation of NEDD8 from the cullin subunit of E3 ubiquitin ligases (deneddylation). Here, we report on Arabidopsis mutants deficient in CSN5 function. We show that these mutants are phenotypically indistinguishable from the previously described cop/det/fus mutants of other CSN subunits. However, we also show that these mutants retain the CSN complex (lacking CSN5), and this finding is in contrast with the previously described CSN subunit mutants, which lack the CSN complex. We therefore conclude that loss of CSN5 as part of CSN is sufficient to cause the cop/det/fus mutant phenotype. Furthermore, we show that mutants defective in CSN5 as well as mutants defective in CSN are unable to deneddylate the Arabidopsis cullins AtCUL1, AtCUL3A, and AtCUL4. Because these are representative cullin subunits of the three cullin-containing E3 families present in Arabidopsis, we postulate that the cop/det/fus mutant phenotype may be the result of the defects caused by impaired CSN5-dependent deneddylation of cullin-containing E3s.     

The Modulation of Mimicry by Ethnic Group-Membership and Emotional Expressions

Mimicry has been ascribed affiliative functions. In three experiments, we used a newly developed social-affective mimicry task (SAMT) to investigate mimicry´s modulation by emotional facial expressions (happy, angry) and ethnic group-membership (White in-group, Black out-group). Experiment 1 established the main consistent effect across experiments, which was enhanced mimicry to angry out-group faces compared to angry in-group faces. Hence the SAMT was useful for experimentally investigating the modulation of mimicry. Experiment 2 demonstrated that these effects were not confounded by general aspects of response conflict, as a Simon task resulted in different response patterns than the SAMT. Experiment 2 and pooled analysis of Experiments 1 and 2 also corroborated the finding of enhanced mimicry to angry out-group faces. Experiment 3 tested whether this effect was related to perceptions of threat, by framing angry persons as physically threatening, or not. Selective enhancement of mimicry to out-group persons framed as physically threatening confirmed this hypothesis. Further support for the role of threat was derived from implicit measures showing, in all experiments, that black persons were more strongly associated with threat. Furthermore, enhanced mimicry was consistently related to response facilitation in the execution of congruent movements. This suggests that mimicry acted as a social congruency signal. Our findings suggest that mimicry may serve as an appeasement signal in response to negative affiliative intent. This extends previous models of mimicry, which have predominantly focused on its role in reciprocating affiliation. It suggests that mimicry might not only be used to maintain and establish affiliative bonds, but also to ameliorate a negative social situation.     

Proposing a solution to the Articulata–Ecdysozoa controversy

Recent studies of animal radiation agree on monophyly of the Bilateria, but there is no consensus about the early radiation of the group. Protostomia and Deuterostomia are usually recognized, with two competing theories regarding the division of the Protostomia: one divides them into Spiralia and Cycloneuralia, the other into Lophotrochozoa and Ecdysozoa. The main discrepancy concerns the Arthropoda, which are placed with the Articulata within the Spiralia by the first group, and with the Cycloneuralia within the Ecdysozoa by the second. Here I propose that this discrepancy can be resolved by regarding the Ecdysozoa as the sister group of the Annelida within the Articulata. This implies that segmentation has been lost in phyla such as Nematoda and Priapula, but the Kinorhyncha may show a 'reduced segmentation' with serially arranged muscles associated with a ringed cuticle. Morphological, palaeontological and molecular implications of this theory are discussed. While many morphological and palaeontological data can be interpreted in accordance with the theory, the molecular data remain inconclusive.     

TNT transformation products are affected by the growth conditions of Raoultella terrigena

High concentrations of 2,4,6-trinitrotoluene (TNT) and related nitroaromatic compounds are commonly found in soil and groundwater at former explosive plants. The bacterium, Raoultella terrigena strain HB, isolated from a contaminated site, converts TNT into the corresponding amino products. Radio-HPLC analysis with [¹⁴C]TNT identified aminodinitrotoluene, diaminonitrotoluene and azoxy-dimers as the main metabolites. Transformation rate and the type of metabolites that predominated in the culture medium and within the cells were significantly influenced by the culture conditions. The NAD(P)H-dependent enzymatic reduction of nitro-substituted compounds by cell-free extracts of R. terrigena was evaluated in vitro.     

Control of introduced species using Trojan sex chromosomes

To control introduced exotic species that have predominantly genetic, but environmentally reversible, sex determination (e.g. many species of fish), Gutierrez and Teem recently modeled the use of carriers of Trojan Y chromosomes--individuals who are phenotypically sex reversed from their genotype. Repeated introduction of YY females into wild populations should produce extreme male-biased sex ratios and eventual elimination of XX females, thus leading to population extinction. Analogous dynamics are expected in systems in which sex determination is influenced by one or a few major genes on autosomes.     

Jasmonate biosynthesis in Arabidopsis thaliana requires peroxisomal beta-oxidation enzymes--additional proof by properties of pex6 and aim1

Jasmonic acid (JA) is an important regulator of plant development and stress responses. Several enzymes involved in the biosynthesis of JA from alpha-linolenic acid have been characterized. The final biosynthesis steps are the beta-oxidation of 12-oxo-phytoenoic acid. We analyzed JA biosynthesis in the Arabidopsis mutants pex6, affected in peroxisome biogenesis, and aim1, disrupted in fatty acid beta-oxidation. Upon wounding, these mutants exhibit reduced JA levels compared to wild type. pex6 accumulated the precursor OPDA. Feeding experiments with deuterated OPDA substantiate this accumulation pattern, suggesting the mutants are impaired in the beta-oxidation of JA biosynthesis at different steps. Decreased expression of JA-responsive genes, such as VSP1, VSP2, AtJRG21 and LOX2, following wounding in the mutants compared to the wild type reflects the reduced JA levels of the mutants. By use of these additional mutants in combination with feeding experiments, the necessity of functional peroxisomes for JA-biosynthesis is confirmed. Furthermore an essential function of one of the two multifunctional proteins of fatty acid beta-oxidation (AIM1) for wound-induced JA formation is demonstrated for the first time. These data confirm that JA biosynthesis occurs via peroxisomal fatty acid beta-oxidation machinery.     

Introduction of Trojan sex chromosomes to boost population growth

Conservation programs that deal with small or declining populations often aim at a rapid increase of population size to above-critical levels in order to avoid the negative effects of demographic stochasticity and genetic problems like inbreeding depression, fixation of deleterious alleles, or a general loss of genetic variability and hence of evolutionary potential. In some situations, population growth is determined by the number of females available for reproduction, and manipulation of family sex ratios towards more daughters has beneficial effects. If sex determination is predominantly genetic but environmentally reversible, as is the case in many amphibia, reptiles, and fish, Trojan sex chromosomes could be introduced into populations in order to change sex ratios towards more females. We analyse the possible consequences for the introduction of XX-males (XX individuals that have been changed to phenotypic males in a XY/XX sex determination system) and ZW males, WW males, or WW females (in a ZZ/ZW sex determination system). We find that the introduction of WW individuals can be most effective for an increase of population growth, especially if the induced sex change has little or no effect on viability.     

Chromatin compaction and cell death by high molecular weight FGF-2 depend on its nuclear localization, intracrine ERK activation, and engagement of mitochondria

Fibroblast growth factor 2 (FGF-2) is produced as CUG-initiated, 22-34 kDa or AUG-initiated 18 kDa isoforms (hi- and lo-FGF-2, respectively), with potentially distinct functions. We report that expression of hi-FGF-2 in HEK293 cells elicited chromatin compaction preceding cell death with apoptotic features. Nuclear localization of the intact protein was required as expression of a non-nuclear hi-FGF-2 mutant failed to elicit chromatin compaction. Equally ineffective, despite nuclear localization, was the over-expression of the 18 kDa core sequence (lo-FGF-2). Chromatin compaction by hi-FGF-2 was accompanied by increased cytosolic cytochrome C, and was attenuated either by over-expression of Bcl-2 or by a peptide inhibitor of the pro-apoptotic protein Bax. In addition hi-FGF-2 elicited sustained activation of total and nuclear extracellular signal regulated kinase (ERK1/2) by an intracrine route, as it was not prevented by neutralizing anti-FGF-2 antibodies. Inhibition of the ERK1/2 activating pathway by dominant negative upstream activating kinase, or by PD 98059, prevented chromatin compaction by hi-FGF-2. ERK1/2 activation was not affected by the Bax-inhibiting peptide suggesting that it occurred upstream of mitochondrial involvement. We conclude that the hi-FGF-2-induced chromatin compaction and cell death requires its nuclear localization, intracrine ERK1/2 activation and mitochondrial engagement.