Synchronization of non-identical systems by non-invasive mutual time-delayed feedback.

Inspired by time-delayed feedback control, it is shown that synchronization of non-identical systems can be achieved by mutual time-delayed feedback with an asymptotically vanishing interaction. An analytic perturbation scheme is developed, which uncovers the merits as well as the constraints of such an approach. As an application, the use of the concept for a secure communication channel is considered.

Nonlinear dynamics of delay systems: an overview.

Time delays play an important role in many fields such as engineering, physics or biology. Delays occur due to finite velocities of signal propagation or processing delays leading to memory effects and, in general, infinite-dimensional systems. Time delay systems can be described by delay differential equations and often include non-negligible nonlinear effects. This overview article introduces the theme issue 'Nonlinear dynamics of delay systems', which contains new fundamental results in this interdisciplinary field as well as recent developments in applications. Fundamentally, new results were obtained especially for systems with time-varying delay and state-dependent delay and for delay system with noise, which do often appear in real systems in engineering and nature. The applications range from climate modelling over network dynamics and laser systems with feedback to human balancing and machine tool chatter. This article is part of the theme issue 'Nonlinear dynamics of delay systems'.

[Branchio-oculo-facial syndrome]. / Syndrome branchio-oculo-facial.

BACKGROUND: Branchio-Oculo-Facial Syndrome (BOFS, MIM#113620) is a rare, polymalformational disorder with cutaneous and ocular abnormalities and characteristic facial anomalies. It is an autosomal dominant developmental disorder caused by mutations or deletions in the transcription factor AP-2 alpha gene (TFAP2A, 6p24). We report a new case of atypical BOFS with a unilateral cervical cutaneous defect. PATIENT AND METHODS: A 5-year-old girl was admitted to our dermatology department for a congenital, linear, erythematous cutaneous anomaly on the right side of her neck. There was no family history. She also presented characteristic facial and ocular anomalies. BOFS was suspected. TFAP2A molecular analysis revealed a heterozygous missense mutation c.767C>T (p.Ala256Val). DISCUSSION: BOFS is variable and remains unknown to dermatologists in spite of distinctive cutaneous features. Identification of this syndrome is important to improving medical care (multidisciplinary care, further tests, genetic counselling). We report a case of atypical BOFS with a unilateral cervical cutaneous defect in one patient and bilateral cutaneous anomalies in the other four patients. In agreement with the literature, there did not appear to be mutation-specific genotype-phenotype correlations.

In vitro insertion of the 22-kD peroxisomal membrane protein into isolated rat liver peroxisomes.

The membrane insertion of the 22-kD integral peroxisomal membrane protein (PMP 22) was studied in a system in which peroxisomes isolated from rat liver were incubated with the [35S]methionine-labeled in vitro translation product of PMP 22 mRNA. Membrane insertion of PMP 22 was demonstrated by protease treatment of peroxisomes in the absence and presence of detergent. Approximately 35% of total in vitro translated PMP 22 became protease resistant after a 1-h incubation at 26 degrees C. Import was dependent on time and temperature, did not require ATP or GTP and was not inhibited by N-ethylmaleimide treatment of neither the soluble components of the translation mixture nor of the isolated peroxisomes. In contrast to these results it was recently shown that the import of the peroxisomal marker, firefly luciferase, into peroxisomes of permeabilized cells was dependent on ATP hydrolysis and was blocked by N-ethylmaleimide pretreatment of the cytosol-depleted cells (Rapp et al., 1993; Wendland and Subramani, 1993). Therefore, the present data suggest that insertion of PMP 22 into the peroxisomal membrane and translocation of firefly luciferase into peroxisomes follow distinct mechanisms. At low temperature binding of PMP 22 to the peroxisomal membrane was not influenced whereas insertion was strongly inhibited. Pretreatment of peroxisomes with subtilisin reduced binding to a low level and completely abolished insertion. Therefore it is suggested that binding is prerequisite to insertion and that insertion may be mediated by a proteinaceous receptor.

Peroxisome biogenesis: involvement of ARF and coatomer.

Peroxisomal membrane protein (Pmp)26p (RnPex11p), a major constituent of induced rat liver peroxisomal membrane, was found to contain a COOH-terminal, cytoplasmically exposed consensus dilysine motif with the potential to bind coatomer. Biochemical as well as immunocytochemical evidence is presented showing that peroxisomes incubated with preparations of bovine brain or rat liver cytosol recruit ADP-ribosylation factor (ARF) and coatomer in a strictly guanosine 5'-O-(3-thiotriphosphate)-dependent manner. Consistent with this observation, ldlF cells expressing a temperature-sensitive mutant version of the epsilon-subunit of coatomer exhibit elongated tubular peroxisomes possibly due to impaired vesiculation at the nonpermissive temperature. Since overexpression of Pex11p in Chinese hamster ovary wild-type cells causes proliferation of peroxisomes, these data suggest that Pex11p plays an important role in peroxisome biogenesis by supporting ARF- and coatomer-dependent vesiculation of the organelles.

Rhizomelic chondrodysplasia punctata. Deficiency of 3-oxoacyl-coenzyme A thiolase in peroxisomes and impaired processing of the enzyme.

The rhizomelic form of chondrodysplasia punctata (RCDP) is a peroxisomal disorder characterized biochemically by an impairment of plasmalogen biosynthesis and phytanate catabolism. We have now found that the maturation of peroxisomal 3-oxoacyl-CoA thiolase is impaired in fibroblasts from RCDP patients. To establish the subcellular localization of the 3-oxoacyl-CoA thiolase precursor protein, cultured skin fibroblasts were fractionated on a continuous Nycodenz gradient. Only a small amount of 3-oxoacyl-CoA thiolase activity was present in the catalase-containing (peroxisomal) fractions of RCDP fibroblasts in comparison with control fibroblasts. Moreover, the amount of thiolase protein in immunoblots of the catalase-containing fractions was below the limit of detection. Finally, the beta-oxidation of [14C]palmitoyl-CoA was found to be reduced in these fractions. We conclude that the mutation in RCDP leads to a partial deficiency of 3-oxoacyl-CoA thiolase activity in the peroxisomes and, concomitantly, an impairment in the ability to convert the precursor of this protein to the mature form. The reduction of 3-oxoacyl-CoA thiolase activity results in a decrease in the rate of peroxisomal beta-oxidation of palmitoyl-CoA. However, the capacity of the peroxisomes to oxidize very-long-chain fatty acids must be sufficient to prevent excessive accumulation of these compounds in vivo.

Beyond the odd number limitation: a bifurcation analysis of time-delayed feedback control.

We investigate the normal form of a subcritical Hopf bifurcation subjected to time-delayed feedback control. Bifurcation diagrams which cover time-dependent states as well are obtained by analytical means. The computations show that unstable limit cycles with an odd number of positive Floquet exponents can be stabilized by time-delayed feedback control, contrary to incorrect claims in the literature. The model system constitutes one of the few examples where a nonlinear time delay system can be treated entirely by analytical means.

Peroxisomes of normal morphology but deficient in 3-oxoacyl-CoA thiolase in rhizomelic chondrodysplasia punctata fibroblasts.

Rhizomelic Chondrodysplasia Punctata (RCDP) is an autosomal recessive disorder in which plasmalogen biosynthesis and phytanate catabolism are impaired. Peroxisomal structure and the intracellular localization of catalase, the 69 kDa peroxisomal integral membrane protein (PMP), and 3-oxoacyl-CoA thiolase were studied in cultured skin fibroblasts from control subjects and patients with RCDP. A punctate fluorescence pattern characteristic for peroxisomes was seen in control cells incubated with either anti-(catalase), anti-(69 kDa PMP) or anti-(3-oxoacyl-CoA thiolase). Incubation of mutant cells with anti-(catalase) or anti-(69 kDa PMP) resulted in the same pattern. However, when RCDP fibroblasts were incubated with a monoclonal anti-(3-oxoacyl-CoA thiolase) antibody no punctate fluorescence could be observed. Cryosections from control and RCDP cells were examined by electron microscopy using double immunogold labelling. RCDP fibroblasts contained structures indistinguishable from control peroxisomes, the membranes reacting with anti-(69 kDa PMP) and the matrix with anti-(catalase). However, the matrix of RCDP peroxisomes, unlike control peroxisomes, did not react with anti-(3-oxoacyl-CoA thiolase). We conclude that RCDP fibroblasts contain regularly shaped peroxisomes, comparable to control peroxisomes in number as well as in content of catalase and 69 kDa PMP. However, in RCDP peroxisomes the amount of 3-oxoacyl-CoA thiolase protein proved to be below the limit of detection.

A comparison of the expression pattern of five genes of the family of small leucine-rich proteoglycans during mouse development.

For five members of the family of the small leucine-rich proteoglycans (SLRPs), the expression pattern during fetal development was analyzed. RNA in situ hybridization on whole body sections of mouse embryos was performed for biglycan (Bgn), decorin (Dcn), fibromodulin (Fmod), chondroadherin (Chad), and lumican (Lum). Special attention was given to the question of whether these patterns coincide only with sites of collagen secretion in connective tissue during tissue modeling or if expression can be observed at specific sites of organ differentiation also. In general, Fmod, Lum, and Bgn are expressed at sites of cartilage and bone formation and interstitial tissue deposition; Chad is expressed only at sites of cartilage; and Dcn is expressed only at sites of interstitial tissue deposition. However, there are some distinct developmental stages where no collagen secretion is known to occur. For example, this applies for the expression of Fmod in the forming somites of stage 9.5 postconception (p.c.), for Dcn and Lum in later stage embryos in the pituitary gland and dorsal root ganglia, and for Bgn and Dcn during differentiation in the kidney. These studies provide further evidence for a role of these molecules during connective tissue organization but also for an involvement at specific sites of organ differentiation.

Functional characterization of the human biglycan 5'-flanking DNA and binding of the transcription factor c-Krox.

The transcriptional regulation of human biglycan expression under normal and pathological conditions was studied. The 5'-flanking regions of the human and mouse genes were isolated and analyzed; the two promoter regions share 81% identity. Both promoters are without a TATA and CAT box and contain multiple Sp1 sites. Human dermal fibroblasts were transiently transfected with progressive deletional human biglycan 5'-flanking DNA-CAT constructs, and a significant variation in activity among the individual constructs was found. A small deletion in several cases caused a more than 2-fold increase or decrease in promoter activity, thereby mapping the target sites for repressors or activators. Human biglycan expression is reduced in females with Ullrich-Turner syndrome (45,X) and increased in individuals with supernumerary sex chromosomes, and it has been speculated that biglycan plays a role in the short stature phenotype of Turner syndrome. Analysis of the transcriptional regulation of biglycan in individuals with sex chromosome anomalies showed that a -262 to -218 region of the biglycan promoter was differentially regulated. This region was extensively analyzed by DNAse footprinting and electrophoretic mobility shift assays, and a putative binding site for the transcription factor c-Krox was discovered. The binding of c-Krox to a site located at approximately -248 to -230 in the human biglycan promoter was confirmed by using extracts from COS cells expressing recombinant human c-Krox. The expression of c-Krox in bone was then examined by reverse-transcribed polymerase chain reaction and Northern blotting analysis; an approximately 3.4 kb transcript was detected in primary osteoblastic cells, in MG-63 cells, and in human bone marrow stromal cells. This is the first detection of c-Krox in bone cells, and it suggests that c-Krox, like another member of the Krox family, Krox-20, might play a regulatory role in bone.

Lack of ornithine decarboxylase activity in isolated rat liver parenchymal cells.

Polyamines are associated with fundamental metabolic and functional steps in cell metabolism. The activity of ornithine decarboxylase, the key enzyme in polyamine metabolism, was followed during the preparation of rat liver parenchymal cells and in the isolated cells during incubation. In experiments in which ornithine decarboxylase was not induced in vivo, enzyme activity dropped to barely measurable values during the preparation. An even more drastic loss of enzyme activity was noted in livers in which ornithine decarboxylase activity was stimulated in vivo 20-40fold by previous injection of bovine growth hormone, or thioacetamide or elevated because of circadian rhythmical changes of the enzyme activity. Within the first 20 min of liver perfusion to disintegrate the tissue, ornithine decarboxylase activity decreased by up to 80%. The presence of bovine growth hormone during cell preparation cannot prevent the loss of enzyme activity. Incubation of the isolated cells for periods of up to 240 min did not restore the enzyme activity. Furthermore, incubation of the cells with bovine growth hormone did not induce ornithine decarboxylase, even though the medium was supplemented with amino acids in physiological concentrations. During normal liver perfusion and in contrast to the situation with isolated cells, there is no loss of enzyme activity but a small rise. Following pretreatment of the animals with bovine growth hormone or thioacetamide the highly stimulated activity of ornithine decarboxylase declined slowly during liver perfusion, but never dropped to values lower than normal for perfusion periods of up to 240 min. Moreover, in the intact perfused organ ornithine decarboxylase remains responsive to bovine growth hormone. The experiments demonstrate that enzymatic tissue dispersion by collagenase in particular or the preparation of isolated cells in general drastically alters the metabolic and functional state of rat liver parenchymal cells.

Rat liver peroxisomes. I. New peroxisome population induced by thyroid hormones in the liver of male rats.

The paper presents results that a hyperthyroid state for 5 to 10 days induces a new peroxisome population in the liver of male rats. This assumption is based on the following observations: 1. Treatment of male rats for five consecutive days with 25 micrograms thyroxine per day resulted in an increase of catalase and D-amino acid oxidase activities by 32 and 61%, respectively. On the other hand, urate oxidase activity declined by 20%. Prolonged treatment for ten days raised catalase activity by 68% and lowered urate oxidase activity by 35%. 2. Morphological examinations on the light and electron microscopic level revealed that the increase in peroxisomal enzyme activities was accompanied by an augmentation of peroxisomal profiles. "Microperoxisomes" and peroxisomes lacking the electron dense core were frequently observed. 3. The peroxisomes of the livers of thyroxine-treated animals exhibited an altered centrifugal behaviour in sucrose density gradients. The mean equilibrium density of normal liver peroxisomes was 1.23, whereas peroxisomes of thyroxine-treated livers equilibrated at the density of 1.20. It is discussed that peroxisomal metabolism may contribute considerably to the late biochemical effects of thyroid hormones, that means enhancement of lipid oxidation and heat production. Up to now these late effects were attributed to a stimulated mitochondrial metabolism only.

Turnover of peroxisomal vesicles by autophagic proteolysis in cultured fibroblasts from Zellweger patients.

Previous studies have shown that in fibroblasts from patients with the Zellweger syndrome (ZS) aberrant membrane structures are present which contain peroxisomal membrane proteins (Santos, M. J. et al., Science 239, 1536-1538 (1988)). In order to characterize these structures we have performed double labeling immunoelectron microscopy experiments using antisera directed against the 69 kDa peroxisomal integral membrane protein (PMP) and lysosomal hydrolases. The results indicate that at least 80% of the structures earlier referred to as 'peroxisomal ghosts' contain lysosomal hydrolases. In addition, we have studied the effect of culture of ZS fibroblasts in the presence of 3-methyladenine, an inhibitor of autophagy, on the intracellular distribution of the 69 kDa PMP. Immunofluorescence experiments showed that in the presence of 3-methyladenine there is an increase in fluorescent spots and a change in the distribution of the spots from mainly perinuclear to randomly distributed throughout the cytoplasm. Double labeling immunoelectron microscopy revealed that after culture in the presence of 3-methyladenine the 69 kDa PMP also accumulates mainly in compartments containing lysosomal hydrolases. In one ZS cell line we found that after culture in the presence of 3-methyladenine there was also an accumulation of structures which were as small as normal microperoxisomes. We conclude that in ZS fibroblasts the 69 kDa PMP is mainly present in lysosomal compartments, presumably degradative autophagic vacuoles. Furthermore, in ZS fibroblasts peroxisomes of apparently normal morphology may be synthesized, but they are degraded by autophagic proteolysis.

Presence of peroxisomal membrane proteins in liver and fibroblasts from patients with the Zellweger syndrome and related disorders: evidence for the existence of peroxisomal ghosts.

The presence and intracellular localization of peroxisomal integral membrane proteins (PMP) were investigated in liver and cultured skin fibroblasts from control subjects and patients with the Zellweger syndrome and related disorders in which peroxisomes are virtually absent. Immunoblotting experiments showed that 22, 36 and 69 kDa PMPs were present and were confined to the membranous fraction both in the control liver and in the livers from the Zellweger patients. The 22 and 36 kDa PMPs were present in significantly lower amounts in the patients' livers than in the control liver. A reduced amount of the 69 kDa PMP was found in liver from one Zellweger but not in liver from another. The subcellular localization in fibroblasts of catalase and the 69 kDa PMP was studied by indirect immunofluorescence. A characteristic punctate fluorescence was seen in control cells incubated with either anti-(catalase) or with anti-(69 kDa PMP). Incubation of mutant cells with anti-(catalase) resulted in a diffuse fluorescence, whereas with anti-(69 kDa PMP) fluorescent particles were visualized which, in some cell lines, were larger and fewer in number than in control cells. Cryosections of control and mutant cells were examined by electron microscopy using immunogold labeling. Control cells contained small structures consisting of a single membrane enclosing a homogeneous matrix; the membranes reacted with anti-(69 kDa PMP) and the matrix with anti-(catalase). The mutant cell lines contained spherical or ellipsoidal structures whose membranes reacted with anti-(69 kDa PMP); no labeling was observed with anti-(catalase). We conclude that peroxisomal ghosts, the membranes of which contain the 69 kDa PMP, are present in peroxisome-deficient cell lines from all complementation groups studied so far.

(CAG)nCAA and GGN repeats in the human androgen receptor gene are not associated with prostate cancer in a French-German population.

Alleles of the CAG and the GGC repeat in the first exon of the human androgen receptor (AR) gene have been shown to be associated with the risk of (advanced) prostate cancer. These studies had been carried out in the United States. We have analysed these polymorphisms in a French-German collection of 105 controls, 132 sporadic cases, and a sample of prostate cancer families comprising 85 affected and 46 not affected family members. The allele distributions were very similar in all four groups and chi square statistics on contingency tables did not detect any significant differences. The relative risk (odds ratio, OR) were calculated using logistic regression and did not reach significance despite sufficient numbers of patients and controls. Typical results were OR = 1.007; 95% Confidence Interval (CI) 0.97-1.1, P = 0.87 for CAG as continuous variable and OR = 1.2 (95% CI 0.7-2.0), P = 0.47 for CAG classes < 22 and > = 22 repeats. Similar results were obtained for subgroups defined by age or Gleason score. We conclude that these polymorphisms can not be used as predictive parameters for prostate cancer in the French or German population.

Peroxisomal protein import. In vivo evidence for a novel translocation competent compartment.

In homogeneous of isolated hepatocytes separated by Nycodenz density gradient centrifugation, two peroxisomal populations are identified that differ in buoyant density. Organelles present in a high density fraction (1.22-1.23 g/cm3) represent mature peroxisomes. Vesicles of intermediate density (1.16-1.17 g/cm3) represent mature peroxisomes. Vesicles of intermediate density (1.16-1.17 g/cm3) are present in much lower concentration and seem to play a particular role in the import and distribution of newly synthesized peroxisomal proteins. In a typical pulse-chase experiment with a 7.5 min pulse, peroxisomal acyl-CoA oxidase is first imported into the peroxisomal fraction of intermediate density. After a chase of up to 30 min, the enzyme is found in mature peroxisomes.

Cytosolic factors mediate protein insertion into the peroxisomal membrane.

Following in vitro translation of the 22 kDa peroxisomal membrane protein (Pmp22p), gel filtration analysis of the post-ribosomal supernatant revealed that Pmp22p forms two complexes. Complex I is of high molecular weight, results in a crosslinking product of 80 kDa, and by co-immunoprecipitation with anti-TCP1 antibody was identified as TRiC. In complex II Pmp22p was crosslinked to a yet unknown polypeptide of 40 kDa (P40). This complex exhibited much higher efficiency to insert Pmp22p into the peroxisomal membrane compared to complex I. In a model we suggest that newly synthesized Pmp22p is first bound to TRiC before being transferred to P40 which may function as a cytosolic Pmp22p receptor.

Targeting of the 22 kDa integral peroxisomal membrane protein.

Investigating targeting of the 22 kDa peroxisomal membrane protein (Pmp22p) to the peroxisomal membrane we have confined the targeting signal to amino acid residues 16-37 located in the N-terminal cytoplasmic tail. Comparison of Pmp22p orthologous sequences revealed a conserved motif Y3xL3xP3x(KQN) which might represent the core of this targeting signal not found so far in other Pmps. Fusion of the Pmp22p N-terminal tail to the C-terminal portion of Pmp22p which per se is not targeted to peroxisomes, conveys peroxisomal targeting. These data suggest that Pmp22p is targeted to peroxisomes by a new membrane targeting signal which is necessary and sufficient to target a polypeptide containing two transmembrane spans to peroxisomes.