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PubMed1989

Variance within homogeneous phytoplankton populations, III: Analysis of natural populations.

A theoretical framework for interpreting flow cytometric histograms from homogeneous phytoplankton populations was developed in part I of this series of articles and applied to chlorophyll fluorescence histograms from clonal cultures in part II. In this paper, we demonstrate the application of this framework to the analysis of cell volume distributions found in a natural assemblage of phytoplankton from the Gulf of California. Flow cytometric analyses of a surface water sample incubated for a period of 61 h revealed the sequential growth and decline of three distinct subpopulations. Cell volume distributions for each subpopulation measured at different times were analyzed, and the theoretical density function described in parts I and II was fitted to these distributions. The range of cell volumes within each subpopulation was similar to that predicted for asynchronous populations.

Data Interpretation, Statistical↗
PubMed2005

Impaired activation-induced telomerase activity in PBMC of early but not chronic rheumatoid arthritis patients.

Although telomerase activity is important in normal immune function, it is unclear whether telomerase or telomerase (dys)regulation plays a role in the pathogenic immune response in autoimmune diseases like rheumatoid arthritis (RA). In this study, we evaluated the dynamics of the activation-induced human telomerase reverse transcriptase (hTERT) response in RA patients and non-RA controls. The expression of the catalytic subunit of telomerase, hTERT, was measured in peripheral blood mononuclear cells (PBMC) of RA patients and controls after in vitro stimulation with anti-CD3 monoclonal antibody (mAb) using real-time PCR. Anti-CD3 mAb stimulation induced activation and proliferation of the T cells in all populations studied. In early RA patients with a disease duration of less than 1 year, the activation-induced hTERT mRNA levels were found to be reduced as compared to healthy controls (HC). Chronic RA patients, with a disease duration of more than 1 year, did not show these impaired hTERT mRNA levels after stimulation with anti-CD3 mAb. Decreased hTERT mRNA levels were also found in multiple sclerosis patients and patients suffering from flu-like symptoms, indicating that these deviations are not disease-specific. The impaired activation-induced hTERT response in PBMC may be a general response of the immune cells in cases of acute or chronic immune activation, presumably to control unwanted clonal expansions and to maintain the diversity of the TCR repertoire. Our results also indicate that clonal T cell expansions, described in RA, are probably not mediated by an elevated potency to express hTERT.

Adult↗
PubMed1990

Polymerase chain reaction-aided genomic sequencing of an X chromosome-linked CpG island: methylation patterns suggest clonal inheritance, CpG site autonomy, and an explanation of activity state stability.

The 5' region of the gene encoding human X chromosome-linked phosphoglycerate kinase 1 (PGK1) is a promoter-containing CpG island known to be methylated at 119 of 121 CpG dinucleotides in a 450-base-pair region on the inactive human X chromosome in the hamster-human cell line X8-6T2. Here we report the use of polymerase chain reaction-aided genomic sequencing to determine the complete methylation pattern of this region in clones derived from X8-6T2 cells after treatment with the methylation inhibitor 5-azacytidine. We find (i) a clone showing full expression of human phosphoglycerate kinase is fully unmethylated in this region; (ii) clones not expressing human phosphoglycerate kinase remain methylated at approximately 50% of CpG sites, with a pattern of interspersed methylated (M) and unmethylated (U) sites different for each clone; (iii) singles, defined as M-U-M or U-M-U, are common; and (iv) a few CpG sites are partially methylated. The data are interpreted according to a model of multiple, autonomous CpG sites, and estimates are made for two key parameters, maintenance efficiency (Em approximately 99.9% per site per generation) and de novo methylation efficiency (Ed approximately 5%). These parameter values and the hypothesis that several independent sites must be unmethylated for transcription can explain the stable maintenance of X chromosome inactivation. We also consider how the active region is kept free of methylation and suggest that transcription inhibits methylation by decreasing Em so that methylation cannot be maintained. Thus, multiple CpG sites, independent with respect to a dynamic methylation system, can stabilize two alternative states of methylation and transcription.

Animals↗
PubMed2005

Diversity among 2481 Escherichia coli from women with community-acquired lower urinary tract infections in 17 countries.

OBJECTIVES: In the recently published ECO.SENS survey, the antimicrobial susceptibility of Escherichia coli from urinary tract infections in women in 16 European countries and Canada was investigated. This study reports the diversity among these E. coli. METHODS: The 2481 E. coli, typed with the PhenePlate (PhP) System utilizing the dynamics and end result of 11 biochemical reactions in a microplate system, were clustered and the Simpson's index of diversity calculated. RESULTS: Seventy-four Common PhP Types (CT) comprising 2067 isolates and 414 Single Types (Si) were identified. Of these, 916 isolates (37%) belonged to one of the four most frequent CT (arbitrarily numbered CT48, 10, 26 and 20). CT48 with 400 isolates and 11 different susceptibility patterns, was widely disseminated across Europe and Canada and was the most frequent type in 13 countries and the second most frequent in the remaining four countries. Sixty-four per cent of the E. coli were susceptible to all eight investigated antimicrobials (CT48: 73%, CT10: 77%, CT26: 62% and CT20: 37%). Forty-six different susceptibility patterns were seen, the three most common being isolated resistance to ampicillin, resistance to ampicillin and trimethoprim, and isolated resistance to trimethoprim. Multiresistance, here defined as resistance to four or more of the investigated antibiotics, was distributed among E. coli belonging to several PhP types. CONCLUSIONS: There was no obvious correlation between the phenotypes identified with the PhP System and the susceptibility pattern. The data did not indicate clonal dissemination within or between countries as a major reason for differences in antimicrobial resistance rates.

Adult↗
PubMed1995

Transcriptional control of neuropeptide gene expression in sensory neurons, using the preprotachykinin-A gene as a model.

Control of neuropeptide gene expression in sensory neurons is determined in part by a variety of tissue-specific, developmental, and stimulus-induced transcription factors that interact with the promoters of these genes. We have analysed the regulation of the rat preprotachykinin-A (rPPT) gene, which is expressed in a subset of dorsal root ganglia neurons. A region of the promoter encompassing approximately 1300 base pairs spanning the transcriptional start site has been analysed in detail both by functional analysis of promoter activity in clonal cell lines and dorsal root ganglia neurons grown in culture and by in vitro characterisation of transcription factor interaction with this region. Interestingly our analysis indicates an important role in rPPT gene expression for the E box transcription factor family. This class of transcription factor has been demonstrated to be a major determinant of calcitonin gene related peptide (CGRP) expression, which is also expressed in dorsal root ganglia neurons often under similar conditions as rPPT. In addition, multiple regulatory domains have been identified in the rPPT promoter, which act as activators in a variety of cell types. These elements are silenced in the context of the rPPT promoter in many non-neuronal cells. Therefore, tissue-specific expression of reporter genes directed by the rPPT promoter in transient transfection is determined in part by a variety of silencer elements, which act to repress the function of several domains that act as constitutive enhancers of expression in a wide range of cells. Removal or modulation of silencer elements in the rPPT promoter allows activity in a wider variety of cell types. We postulate that control of rPPT gene expression is the results of dynamic interplay of both positive and negative regulatory elements, a phenomenon observed in several other neuronal-specific genes, including that encoding CGRP.

Animals↗
PubMed1999

Dynamic redistribution of STAT1 protein in IFN signaling visualized by GFP fusion proteins.

STAT proteins (signal transducers and activators of transcription) are a family of transcription factors which are used by many cytokines and cell growth factors for initiating gene expression. They are activated by tyrosine phosphorylation through the cytoplasmic domain of stimulated receptors. Upon phosphorylation STAT proteins dimerize, translocate to the nucleus and activate transcription by binding to specific recognition sites. Different cytokines activate different subsets of STATs and other signaling proteins. We have made use of green fluoresencent protein (GFP) fusion proteins to visualize the subcellular localization and trafficking of STAT1, STAT2 and p48 during interferon (IFN) stimulation and have analysed in detail STAT1-GFP trafficking in living cells. Analysis of GFP fusion proteins allowed the determination of time kinetics of subcellular trafficking in individual living cells. STAT1-GFP is indistinguishable from its wild-type protein displaying strong activity as transcriptional activator as well as the same time kinetics of transport to the nucleus and retreat to the cytoplasm. After prolonged exposure to IFN, STAT1-GFP is no longer retained in the nucleus and relocation to the cytoplasm is observed. Restimulation with the same type of IFN does not lead to repeated nuclear translocation of STAT1-GFP. STAT1 is not subject of inhibition, as restimulation with another type of IFN allows immediate reuse of previously activated STAT1-GFP. However, restimulation with the same type of IFN can be achieved when the primary stimulus is removed after a short induction period. This method of visualizing signal transduction reveals a considerable inhomogeneity with respect to the extent of STAT1-GFP shuttling within a clonal cell population, indicating that competence for full-blasted IFN response is restricted to a cellular subpopulation whereas other cells respond incompletely, retarded or not at all.

Animals↗
PubMed2002

Population changes in Phytophthora infestans in Taiwan associated with the appearance of resistance to metalaxyl.

In recent years, late blight, caused by Phytophthora infestans (Mont) De Bary, has increased in severity in many parts of the world, and this has been associated with migrations which have introduced new, arguably more aggressive, populations of the pathogen. In Taiwan, late blight has been endemic on outdoor tomato crops grown in the highlands since the early 1900s, but recent epidemics have been more damaging. To ascertain the present status of the Taiwanese population of P infestans, 139 isolates of the pathogen collected and maintained by the Asian Vegetable Research and Development Center (AVRDC) were characterized using mating type, metalaxyl sensitivity, allozyme genotype, mitochondrial haplotype and RFLP fingerprinting. Up to 1997, all isolates were found to belong to the old clonal lineage of P infestans (US-1 and variants), but in isolates from 1998 a new genotype appeared, and by 2000 this had apparently completely displaced the old population. This new genotype was an A1 mating type and has the dilocus allozyme genotype 100/100/111, 100/100 for the loci coding for glucose-6-phosphate isomerase and peptidase, respectively. These characters, together with RG57 fingerprinting, indicated that these isolates belonged to the US-11 clonal lineage, a minority (11%) being a previously unreported variant of US-11. Whereas metalaxyl-resistant isolates were not detected in the old population, 96% of the new genotypes proved resistant, with the remainder being intermediate in sensitivity. It may be inferred from this sudden, marked change in the characteristics of the Taiwanese P infestans that a new population of the pathogen was introduced around 1997-98 and that this may well have already been metalaxyl-resistant when it arrived, although a role for in situ selection cannot be excluded.

Alanine↗
PubMed2003

Plastic reproductive strategies in a clonal marine invertebrate.

Plastic reproductive allocation may allow individuals to maximize their fitness when conditions vary. Mate availability is one condition that may determine the fitness of an individual's allocation strategy. Using a variety of methods, I detected evidence of plastic allocation to asexual (clonal) reproduction in response to mate availability in the brittle star Ophiactis savignyi. There were more mature individuals in populations in which both sexes were present, and clones from these populations had fewer clone-mates than clones from single-sex populations. Animals placed with mates in a field experiment divided less frequently than animals without a mate. These findings demonstrate that animals reduce their allocation to asexual reproduction when mates are present and when a loss of fecundity associated with cloning would decrease offspring production. This plasticity is probably adaptive because it maximizes sexual-reproductive potential when fertilization is more likely, but maximizes survival of the clone when mates are absent and gametes are unlikely to be converted to offspring.

Animals↗
PubMed2006

Planktonic replication is essential for biofilm formation by Legionella pneumophila in a complex medium under static and dynamic flow conditions.

Legionella pneumophila persists for a long time in aquatic habitats, where the bacteria associate with biofilms and replicate within protozoan predators. While L. pneumophila serves as a paradigm for intracellular growth within protozoa, it is less clear whether the bacteria form or replicate within biofilms in the absence of protozoa. In this study, we analyzed surface adherence of and biofilm formation by L. pneumophila in a rich medium that supported axenic replication. Biofilm formation by the virulent L. pneumophila strain JR32 and by clinical and environmental isolates was analyzed by confocal microscopy and crystal violet staining. Strain JR32 formed biofilms on glass surfaces and upright polystyrene wells, as well as on pins of "inverse" microtiter plates, indicating that biofilm formation was not simply due to sedimentation of the bacteria. Biofilm formation by an L. pneumophila fliA mutant lacking the alternative sigma factor sigma(28) was reduced, which demonstrated that bacterial factors are required. Accumulation of biomass coincided with an increase in the optical density at 600 nm and ceased when the bacteria reached the stationary growth phase. L. pneumophila neither grew nor formed biofilms in the inverse system if the medium was exchanged twice a day. However, after addition of Acanthamoeba castellanii, the bacteria proliferated and adhered to surfaces. Sessile (surface-attached) and planktonic (free-swimming) L. pneumophila expressed beta-galactosidase activity to similar extents, and therefore, the observed lack of proliferation of surface-attached bacteria was not due to impaired protein synthesis or metabolic activity. Cocultivation of green fluorescent protein (GFP)- and DsRed-labeled L. pneumophila led to randomly interspersed cells on the substratum and in aggregates, and no sizeable patches of clonally growing bacteria were observed. Our findings indicate that biofilm formation by L. pneumophila in a rich medium is due to growth of planktonic bacteria rather than to growth of sessile bacteria. In agreement with this conclusion, GFP-labeled L. pneumophila initially adhered in a continuous-flow chamber system but detached over time; the detachment correlated with the flow rate, and there was no accumulation of biomass. Under these conditions, L. pneumophila persisted in biofilms formed by Empedobacter breve or Microbacterium sp. but not in biofilms formed by Klebsiella pneumoniae or other environmental bacteria, suggesting that specific interactions between the bacteria modulate adherence.

Animals↗
PubMedDate not supplied

[Clonal analysis of some multiple antibiotic resistant E. coli strains isolated from river and polluted waters].

Several multiple antibiotic resistant E. coli strains isolated from river and polluted waters were compared for their genetic relatedness. Antibiotic susceptibility testing was performed for gentamycin, kanamycin, ampicillin, tetracycline, chloramphenicol, ceftazidime and cefotaxime, as described by Kirby-Bauer disk diffusion method following NCCLS recommendations. Minimum inhibitory concentrations (MICs) were performed using dilution method in Mueller-Hinton broth with a 0.06-64 micrograms/ml concentration range for all antimicrobials and bacterial inoculum of about 1-2 x 10(8) CFU/ml. For the data analysis NCCLS breakpoints for resistance and sensitivity were used. Genomic DNA was isolated from E. coli strains by CTAB method and digested to completion with HindIII enzyme. Genetic characterization was performed by agarose gel electrophoresis and spectrophotometric analysis. Genetic similarity and clustering were calculated using NISIS program. All E. coli strains isolated from river and polluted waters show a high incidence of multiple antibiotic resistance phenotype, 16% of them being resistant to 7, 6 and 4 antibiotics, 40% to 5 and 8% to 2 antibiotics, respectively. A moderate resistance was observed to kanamycin (higher than 30%) and cefotaxime (68%). The percentage of resistant E. coli strains ranged from 76% (to ampicillin, gentamicin and chloramphenicol) to 85% (to ceftazidime). The best results (resistance about 99%) were obtained with tetracycline. Screening for plasmids relieved the presence into 4 E. coli strains of several plasmids ranging from 3.8 kpb to more than 50 kpb. The number of fragments produced by HindIII digestion of genomic DNA ranged from 11 to 25, with sizes of approximately 22 to more than 750 kb. The phenotypic data shows the dynamic flow of multiple antibioresistant E. coli strains in aquatic media (river and polluted waters). Electrophoretic patterns analysis reflects the incidence and diversity of analyzed plasmids. DNA fingerprinting with genomic DNA RE suggested that, depending of the isolation source, E. coli strains could be grouped in two distinct populations with a different plasmid diversity.

Aminoglycosides↗
PubMed2026

Lineage-specific adaptation and resistance in Candida albicans.

Candida albicans exhibits substantial phenotypic and ecological diversity; however, the exact relationship between its population structure, adaptation to specific niches, and antifungal resistance remains incompletely understood. To investigate these evolutionary dynamics, we analyzed the whole-genome sequences from 591 publicly available isolates, integrating nuclear and mitochondrial phylogenomics with ecological and resistance-associated genomic analyses. Phylogenomic analyses resolved 18 core nuclear clusters together with multiple admixed lineages. Strong cytonuclear concordance was noted in the majority of the central lineages, contrasting with a higher discordance among the admixed groups, consistent with recurrent genetic exchange. The analysis revealed that geographic origin explains a larger fraction of genetic variance than anatomical niche, supporting a predominantly generalist population structure. A notable exception was Cluster N16 (Candida africana), which presented a strict genital origin in our dataset (n = 34). Additionally, although the mitochondrial genome exhibits strong purifying selection, candidate residues under diversifying selection correlated with specific niches (e.g., bloodstream) have been identified. Analysis of five resistance-associated genes (ERG11, UPC2, FKS1, TAC1 and FUR1) revealed that resistance-associated variants were generally rare but exhibited distinct gene-specific patterns. In case of ERG11 and FUR1 they were concentrated in a specific clade (N11, N17, and their admixed Group A) and exhibit gene-dependent zygosity patterns. In summary, the evolution of C. albicans appears to be driven by a predominantly clonal model punctuated by episodic genetic exchange, where both ecological adaptation and antifungal resistance mutations exhibit genomic signatures marked by lineage specificity.

Antifungal resistance↗
PubMed2003

Phylogenetic diversity, abundance, and axial distribution of bacteria in the intestinal tract of two soil-feeding termites (Cubitermes spp.).

The hindgut of soil-feeding termites is highly compartmentalized and characterized by pronounced axial dynamics of the intestinal pH and microbial processes such as hydrogen production, methanogenesis, and reductive acetogenesis. Nothing is known about the bacterial diversity and the abundance or axial distribution of the major phylogenetic groups in the different gut compartments. In this study, we showed that the variety of physicochemical conditions is reflected in the diversity of the microbial communities in the different gut compartments of two Cubitermes species (TERMITIDAE: Termitinae). 16S rRNA gene clones from the highly alkaline first proctodeal segment (P1) of Cubitermes orthognathus represented almost exclusively gram-positive bacteria with low G+C content (LGC bacteria). In the posterior gut segments, their proportion decreased progressively, and the clone libraries comprised a variety of phyla, including the Cytophaga-Flexibacter-Bacteroides group, various subgroups of Proteobacteria, and the spirochetes. Phylogenetic analysis revealed that many of the clones clustered with sequences from the guts of other termites, and some even formed clusters containing only clones from C. orthognathus. The abundance and axial distribution of major phylogenetic groups in the gut of Cubitermes ugandensis were determined by fluorescence in situ hybridization with group-specific oligonucleotide probes. While the results were generally in good agreement with those of the clonal analysis, direct counts with probes specific for the Planctomycetales revealed a severe underestimation of representatives of this phylum in the clone libraries. Results obtained with newly designed FISH probes directed against two clusters of LGC clones from C. orthognathus indicated that the clones were restricted to specific gut regions. A molecular fingerprinting analysis published in a companion paper (D. Schmitt-Wagner, M. W. Friedrich, B. Wagner, and A. Brune, Appl. Environ. Microbiol. 69:6018-6024, 2003) corroborated the presence of compartment-specific bacterial communities in the gut of different Cubitermes species.

Animals↗
PubMed1998

A restricted T cell response to myelin basic protein (MBP) is stable in multiple sclerosis (MS) patients.

The close resemblance of MS to the animal model experimental autoimmune encephalomyelitis (EAE) has provided compelling data sustaining a pathogenic role of circulating T cells reactive against MBP. T cell antigen receptor (TCR) usage in EAE is commonly considered restricted; nevertheless, dynamic changes of TCR usage correlate with the course of EAE, resulting in a limited repertoire during early stages of disease activity followed by the recruitment of other T cells reactive against new determinants. Although a broader TCR repertoire mediates the response to MBP in humans, a restricted intraindividual heterogeneity may occur in some MS patients. In the present study we characterize the response to MBP in MS subjects with relapsing remitting disease from two sampling time points 12 months apart. MBP-specific T cell lines (TCL) were first generated from eight MS individuals and two healthy subjects. New TCL were obtained after 12 months from one control and three MS patients whose response, at the first time point, was directed against a single epitope. Interestingly, these three subjects had a stable and mild disease. Few TCL obtained at two time points from the MS individuals recognized the same immunodominant epitope and shared identical TCR Vbeta sequences. In the control we could not detect a restriction of the repertoire. These findings suggest that in some MS patients with benign disease a predominant T cell response to a single determinant may be detectable at different moments and is mediated by clonally expanded populations.

Adult↗
PubMed2002

Changes in actin dynamics at the T-cell/APC interface: implications for T-cell anergy?

Over the past 20 years the role of the actin cytoskeleton in the formation of the immunological synapse and in T-cell activation has been the subject of intense scrutiny. T-cell receptor (TCR) signaling leads to tyrosine phosphorylation of numerous adapter proteins whose function is to relay signals to downstream components of the TCR signaling pathway and, in particular, to molecules implicated in remodeling the actin cytoskeleton. Here, we discuss how signals from the TCR converge on two key regulators of the actin cytoskeleton, Ena/vasodilator-stimulated phosphoproteins (VASPs) and the actin-related protein (ARP2/3) complex. We also discuss the implications of TCR signaling in the process of T-cell anergy with particular emphasis on the actin remodeling and molecules involved in the control of T-cell proliferation.

Actins↗
PubMed2025

Impact of the ECM on the Mechanical Memory of Cancer Cells.

Besides genomic and proteomic analyses of bulk and individual cancer cells, cancer research focuses on the mechanical analysis of cancers, such as cancer cells. Throughout the oncogenic evolution of cancer, mechanical inputs are stored as epigenetic memory, which ensures versatile coding of malignant characteristics and a quicker response to external environmental influences in comparison to solely mutation-based clonal evolutionary mechanisms. Cancer's mechanical memory is a proposed mechanism for how complex details such as metastatic phenotypes, treatment resistance, and the interaction of cancers with their environment could be stored at multiple levels. The mechanism appears to be similar to the formation of memories in the brain and immune system like epigenetic alterations in individual cells and scattered state changes in groups of cells. Carcinogenesis could therefore be the outcome of physiological multistage feedback mechanisms triggered by specific heritable oncogenic alterations, resulting in a tumor-specific disruption of the integration of the target site/tissue into the overall organism. This review highlights and discusses the impact of the ECM on cancer cells' mechanical memory during their metastatic spread. Additionally, it demonstrates how the emergence of a mechanical memory of cancer can give rise to new degrees of individuality within the host organism, and a connection to the cancer entity is established by discussing a connection to the metastasis cascade. The aim is to identify common mechanical memory mechanisms of different types of cancer. Finally, it is emphasized that efforts to identify the malignant potency of tumors should go way beyond sequencing approaches and include a functional diagnosis of cancer physiology and a dynamic mechanical assessment of cancer cells.

Humans↗
PubMed2006

Resistance in introduced populations of a freshwater snail to native range parasites.

Introduced species provide an opportunity to examine responses to novel ecological conditions, in particular to the absence of co-evolved enemies. Introduced populations could evolve lower investment in resistance or could down-regulate their immune system as a plastic response to enemy absence. The response might have consequences for the success of introduced species. Assuming a trade-off between resistance and traits related to demographic success, an evolved change or reallocation from resistance could increase the chances of invasions. On the other hand, introduced populations could have increased resistance as a correlate of greater vigour and competitive ability among successful invaders [Sampling Bias hypothesis (SBH)]. These hypotheses make different predictions about investment in resistance in introduced populations. Using a New Zealand clonal snail (Potamopyrgus antipodarum), we examined the resistance of three introduced genotypes (one from the US and two from Europe) to several populations of a native range parasite (Microphallus sp.). One genotype (Euro A) was resistant to all native range parasite populations, consistent with the SBH. However, two remaining genotypes (Euro C and US 1) were less susceptible to parasite populations that were allopatric to their source populations. Furthermore, resistance of one genotype (US 1) collected from the introduced range was indistinguishable from its resistance when collected from the range of the parasite. Hence, there was no evidence for decreased resistance in the absence of native enemies, which is inconsistent with hypotheses that envision reduced allocation to resistance or a trade-off between competitive ability and resistance.

Animals↗
PubMed1999

Variation in clonal diversity in glasshouse infestations of the aphid, Aphis gossypii Glover in southern France.

Aphis gossypii is an aphid species that is found throughout the world and is extremely polyphagous. It is considered a major pest of cotton and cucurbit species. In Europe, A. gossypii is assumed to reproduce exclusively by apomictic parthenogenesis. The present study investigates the genetic diversity of A. gossypii in a microgeographic, fragmented habitat consisting of eight glasshouses of cucurbit crops. This analysis, which was based on the results from seven microsatellite loci, has confirmed that A. gossypii populations in southern France are primarily asexual, as only 12 nonrecombinant genotypic classes (clones) were identified from 694 aphids. Moreover, a high proportion of the aphids (87%) had one of three common genotypes. No significant correlation was found between genotypic class and host plant species. Within a glasshouse population of A. gossypii, a significant reduction in clonal diversity was observed as the spring/summer season progressed. The final predominance of a clone could result from interclonal competition. At the microgeographic level (i.e. glasshouses within a 500-m radius), significant genetic subdivision was detected and could be attributed to founder effects and the limitation of gene flow imposed by the enclosed nature of the glasshouse structure. Finally, the three common clones of A. gossypii detected in 1996 reappeared in spring 1997 following the winter extinction, together with rare clones that had not previously been seen. The probability that A. gossypii overwinters within refuges at a microgeographic scale from which populations are renewed each spring is discussed.

Alleles↗
PubMed1993

Growth factors modulate clonal growth and differentiation of cultured rabbit limbal and corneal epithelium.

PURPOSE: To compare the extent of modulation by various growth factors on clonal growth and differentiation between corneal and stem cell-containing limbal epithelium. METHODS: A reported serum-free clonal growth assay was used. The mitogenic response was measured by colony forming efficiency, colony size, and bromodeoxyuridine labelling index; the differentiation was assessed by AE-5 monoclonal antibody staining. RESULTS: As compared to controls in an insulin-containing basic medium, the addition of epidermal growth factor, acidic fibroblast growth factor, basic fibroblast growth factor, and a high dose of nerve growth factor was mitogenic for both epithelia. Cholera toxin was also mitogenic, but platelet-derived growth factor might not have, and insulin-like growth factor type I lacked an additive mitogenic effect with insulin. The mitogenic effect of epidermal growth factor differed from the others in its dose-dependent down-regulation and in having more migratory cells in epidermal growth factor-stimulated colonies. In contrast to these mitogens, transforming growth factor-beta 1 exhibited a clear inhibitory effect in the controls as well as in epidermal growth factor- or fibroblast growth factor-stimulated cultures. Transforming growth factor-beta 1's inhibitory effect was correlated with strong AE-5 staining, whereas the mitogenic effect of epidermal growth factors, fibroblast growth factors or nerve growth factors was correlated with the presence of negative AE-5 colonies. CONCLUSION: There exist potential dynamic interactions among various growth-modifying cytokines in controlling epithelial growth and differentiation. The lack of specific activation of limbal stem cells in this culture assay also suggests that other unidentified factor(s) might be regulating stem cell functions.

Animals↗