Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels

Mitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion

Biogenesis of the mitochondrial phosphate carrier

The mitochondrial phosphate carrier (PiC) is a member of the family of inner-membrane carrier proteins which are generally synthesized without a cleavable presequence. Surprisingly, the cDNA sequences of bovine and rat PiC suggested the existence of an amino-terminal extension sequence in the precursor of PiC. By expressing PiC in vitro, we found that PiC is indeed synthesized as a larger precursor. This precursor was imported and proteolytically processed by mitochondria, whereby the correct amino-terminus of the mature protein was generated. Import of PiC showed the characteristics of mitochondrial protein uptake, such as dependence on ATP and a membrane potential and involvement of contact sites between mitochondrial outer and inner membranes. The precursor imported in vitro was correctly assembled into the functional form, demonstrating that the authentic import and assembly pathway of PiC was reconstituted when starting with the presequence-carrying precursor. These results are discussed in connection with the recently postulated role of PiC as an import receptor located in the outer membrane

Biogenesis of mitochondrial porin

We review here the present knowledge about the pathway of import and assembly of porin into mitochondria and compare it to those of other mitochondrial proteins. Porin, like all outer mitochondrial membrane proteins studied so far is made as a precursor without a cleavble lsquosignalrsquo sequence; thus targeting information must reside in the mature sequence. At least part of this information appears to be located at the amino-terminal end of the molecule. Transport into mitochondria can occur post-translationally. In a first step, the porin precursor is specifically recognized on the mitochondrial surface by a protease sensitive receptor. In a second step, porin precursor inserts partially into the outer membrane. This step is mediated by a component of the import machinery common to the import pathways of precursor proteins destined for other mitochondrial subcompartments. Finally, porin is assembled to produce the functional oligomeric form of an integral membrane protein wich is characterized by its extreme protease resistance

Anoxia begets anoxia: a positive feedback to the deoxygenation of temperate lakes

Declining oxygen concentrations in the deep waters of lakes worldwide pose a pressing environmental and societal challenge. Existing theory suggests that low deep-water dissolved oxygen (DO) concentrations could trigger a positive feedback through which anoxia (i.e., very low DO) during a given summer begets increasingly severe occurrences of anoxia in following summers. Specifically, anoxic conditions can promote nutrient release from sediments, thereby stimulating phytoplankton growth, and subsequent phytoplankton decomposition can fuel heterotrophic respiration, resulting in increased spatial extent and duration of anoxia. However, while the individual relationships in this feedback are well established, to our knowledge, there has not been a systematic analysis within or across lakes that simultaneously demonstrates all of the mechanisms necessary to produce a positive feedback that reinforces anoxia. Here, we compiled data from 656 widespread temperate lakes and reservoirs to analyze the proposed anoxia begets anoxia feedback. Lakes in the dataset span a broad range of surface area (1–126,909 ha), maximum depth (6–370 m), and morphometry, with a median time-series duration of 30 years at each lake. Using linear mixed models, we found support for each of the positive feedback relationships between anoxia, phosphorus concentrations, chlorophyll a concentrations, and oxygen demand across the 656-lake dataset. Likewise, we found further support for these relationships by analyzing time-series data from individual lakes. Our results indicate that the strength of these feedback relationships may vary with lake-specific characteristics: For example, we found that surface phosphorus concentrations were more positively associated with chlorophyll a in high-phosphorus lakes, and oxygen demand had a stronger influence on the extent of anoxia in deep lakes. Taken together, these results support the existence of a positive feedback that could magnify the effects of climate change and other anthropogenic pressures driving the development of anoxia in lakes around the world

Feeding Behaviour, Swimming Activity and Boldness Explain Variation in Feed Intake and Growth of Sole (Solea solea) Reared in Captivity

The major economic constraint for culturing sole (Solea solea) is its slow and variable growth. The objective was to study the relationship between feed intake/efficiency, growth, and (non-) feeding behaviour of sole. Sixteen juveniles with an average (SD) growth of 2.7 (1.9) g/kg0.8/d were selected on their growth during a 4-week period in which they were housed communally with 84 other fish. Selected fish were housed individually during a second 4-week period to measure individual feed intake, growth, and behaviour. Fish were hand-fed three times a day during the dark phase of the day until apparent satiation. During six different days, behaviour was recorded twice daily during 3 minutes by direct observations. Total swimming activity, frequency of burying and of escapes were recorded. At the beginning and end of the growth period, two sequential behavioural tests were performed: “Novel Environment” and “Light Avoidance”. Fish housed individually still exhibited pronounced variation in feed intake (CV = 23%), growth (CV = 25%) and behavior (CV = 100%). Differences in feed intake account for 79% of the observed individual differences in growth of sole. Fish with higher variation in feed intake between days and between meals within days had significantly a lower total feed intake (r = −0.65 and r = −0.77) and growth. Active fish showed significantly higher feed intake (r = 0.66) and growth (r = 0.58). Boldness during both challenge tests was related to fast growth: (1) fish which reacted with a lower latency time to swim in a novel environment had significantly higher feed intake (r = −0.55) and growth (r = −0.66); (2) fish escaping during the light avoidance test tended to show higher feed intake (P<0.1) and had higher growth (P<0.05). In conclusion, feeding consistency, swimming activity in the tank, and boldness during behavioral tests are related to feed intake and growth of sole in captivity

Synapsin I is structurally similar to ATP-utilizing enzymes.

Synapsins are abundant synaptic vesicle proteins with an essential regulatory function in the nerve terminal. We determined the crystal structure of a fragment (synC) consisting of residues 110-420 of bovine synapsin I; synC coincides with the large middle domain (C-domain), the most conserved domain of synapsins. SynC molecules are folded into compact domains and form closely associated dimers. SynC monomers are strikingly similar in structure to a family of ATP-utilizing enzymes, which includes glutathione synthetase and D-alanine:D-alanine ligase. SynC binds ATP in a Ca2+-dependent manner. The crystal structure of synC in complex with ATPgammaS and Ca2+ explains the preference of synC for Ca2+ over Mg2+. Our results suggest that synapsins may also be ATP-utilizing enzymes

Shared and Unique Abnormalities in Sleep and Rest- Activity Rhythms in Residential and Outpatient Schizophrenia Spectrum Disorder Patients

Background: Sleep and rest-activity-rhythm (RAR) abnormalities are commonly reported in schizophrenia spectrum disorder (SSD) patients. However, an extensive characterization of RAR alterations in SSD patients relative to healthy control subjects is currently lacking. Furthermore, differences in RAR parameters between residential and outpatient SSD individuals, including their relationships with the SSD clinical symptoms, have not been thoroughly examined. Methods: Two hundred and fifty participants, including one hundred and thirty-seven patients diagnosed with Schizophrenia Spectrum Disorders (SSD, seventy-nine residential patients, and fifty-eight outpatients) and one hundred and thirteen healthy comparison (HC) subjects, were recruited at ten different mental health centers in Northern Italy Ras as part of the DiAPAson project. To monitor habitual sleep-wake patterns, study participants were instructed to wear an ActiGraph GT9X on the nondominant wrist for seven consecutive days. Data from 20 participants were excluded due to having either less than 3 days of actigraphy data or being detected as an outlier. Therefore, 68 residential SSD patients, 54 SSD outpatients, and 108 HC individuals were included in further analyses. RAR parameters, including M10, L5 relative amplitude (RA), intra-daily variability (IV), inter-daily stability (IS), alpha, beta, F-statistic (F-stat), and sleep parameters (i.e., total sleep time [TST], wake after sleep onset [WASO]) were computed for each study participant. Moreover, negative symptoms were assessed in residential and outpatient SSD patients with the Brief Negative Symptom Scale (BNSS). Analysis of covariance (ANCOVA) was performed to identify differences in RAR and sleep parameters between HC, outpatient SSD, and residential SSD groups after controlling for age and sex. Statistical significance was determined by applying Bonferroni's correction for multiple comparisons. For RAR/sleep parameters showing significant ANCOVA differences across the three groups, the Tukey HSD test was used for pairwise comparison, including differences between each SSD population with HC and between the two SSD samples. Finally, correlation analyses between BNSS scores and RAR parameters were performed. Results: Among sleep parameters, TST (F(2, 225) = 79.43, p < 0.001), but not WASO, was different between groups after Bonferroni's correction for multiple comparisons. Furthermore, except RA and F-stat, all RAR parameters, including IV (F(2, 225) = 8.35, p = 0.003), M10 (F(2, 225) = 31.13, p < 0.001), L5 (F(2, 225) = 7.91, p = 0.005), alpha (F(2, 225) = 46.092, p < 0.001), beta (F(2, 225) = 27.68, p < 0.001), and IS (F(2, 225) = 14.33, p < 0.001) were significantly different across the three groups. Specifically, TST was higher in both SSD groups compared to HC (t = 11.18, p < 0.001, t = 9.28, p < 0.001; for residential and outpatients SSD vs HC, respectively). Both SSD groups showed also lower M10 (residential vs control: t = -7.71 and p < 0.001; outpatients vs control: t = -4.2 and p < 0.001) and L5 (residential vs control: t = -3.79 and p < 0.001; outpatients vs control: t = -2.43 and p = 0.048), along with higher alpha (residential vs control: t = 7.43 and p < 0.001; outpatients vs control: t = 8.25 and p < 0.001) compared to HC. Residential SSD patients had higher IV (residential vs control: t = 2.98 and p = 0.010), IS (residential vs control: t = 5.35 and p < 0.001), and beta (residential vs control: t = 7.16 and p < 0.001) relative to HC. In contrast, SSD outpatients showed no differences in any of those three measures compared to HC. We also observed that M10 (t = 2.67, p = 0.024) was higher in SSD outpatients compared to residential patients, whereas IV (t = -3.95, p < 0.001), beta (t = -5.51, p < 0.001), and IS (t = -2.73, p = 0.020) were higher in residential compared to SSD outpatients. Furthermore, residential patients had worse negative symptoms compared to outpatients (t = 2.6299, p = 0.010), and IS correlated with the severity of negative symptoms across all SSD patients (R = 0.248, p = 0.024). Conclusions: In this study, we found that compared to healthy controls, residential and outpatient SSD individuals had both unique (IV, beta, IS) and shared (e.g., TST, M10, L5, alpha) abnormalities in RAR/sleep measures, and IS was associated with the severity of the SSD clinical symptoms