Non-overlapping Patterns Research Articles

Cocaine abstinence alters nucleus accumbens firing dynamics during goal‐directed behaviors for cocaine and sucrose

Distinct subsets of nucleus accumbens (NAc) neurons differentially encode goal-directed behaviors for natural vs. drug rewards [R. M. Carelli et al. (2000)The Journal of Neuroscience, 20, 4255-4266], and the encoding of cocaine-seeking is altered following cocaine abstinence [J. A. Hollander & R. M. Carelli (2007) The Journal of Neuroscience, 27, 3535-3539]. Here, electrophysiological recording procedures were used to determine if the selective encoding of natural vs. cocaine reward by NAc neurons is: (i) maintained when the natural reinforcer is a highly palatable sweet tastant and (ii) altered by cocaine abstinence. Rats (n = 14) were trained on a multiple schedule of sucrose reinforcement and cocaine self-administration (2-3 weeks) and NAc activity was recorded during the task before and after 30 days of cocaine abstinence. Of 130 cells recorded before abstinence, 82 (63%) displayed patterned discharges (increases or decreases in firing rate, termed phasic activity) relative to operant responding for sucrose or cocaine. As in previous reports, the majority of those cells displayed nonoverlapping patterns of activity during responding for sucrose vs. cocaine. Specifically, only 17 (21%) showed similar patterns of activity (i.e. overlapping activity) across the two reinforcer conditions. After abstinence, this pattern was largely maintained, 23 of 70 phasic cells (33%) were overlapping. However, cocaine abstinence altered the overall percentage of selectively active neurons across reinforcer conditions. Specifically, significantly more neurons became selectively activated during cocaine-directed behaviors than during sucrose-directed behaviors. The results indicate that, although the selective encoding of cocaine and natural rewards is maintained even with a highly palatable substance, 30 days of cocaine abstinence dynamically alters the overall population encoding of natural and drug rewards by NAc neurons.

Social Network Concordance in Food Choice Among Spouses, Friends, and Siblings

We investigated whether eating behaviors were concordant among diverse sets of social ties. We analyzed the socioeconomic and demographic distribution of eating among 3418 members of the Framingham Heart Study observed from 1991 to 2001. We used a data-classification procedure to simplify choices into 7 nonoverlapping patterns that we matched with information on social network ties. We used correlation analysis to examine eating associations among 4 types of peers (spouses, friends, brothers, and sisters). Longitudinal multiple logistic regression was used to evaluate evidence for peer influences on eating. Of all peer types, spouses showed the strongest concordances in eating patterns over time after adjustment for social contextual factors. Across all peers, the eating pattern most likely to be shared by socially connected individuals was "alcohol and snacks." Models estimating one's current eating pattern on the basis of a peer's prior eating provided supportive evidence of a social influence process. Certain eating patterns appeared to be socially transmissible across different kinds of relationships. These findings represent an important step in specifying the relevant social environment in the study of health behaviors to include eating.

Functional diversity of melanopsins and their global expression in the teleost retina.

Melanopsin (OPN4) is an opsin photopigment that, in mammals, confers photosensitivity to retinal ganglion cells and regulates circadian entrainment and pupil constriction. In non-mammalian species, two forms of opn4 exist, and are classified into mammalian-like (m) and non-mammalian-like (x) clades. However, far less is understood of the function of this photopigment family. Here we identify in zebrafish five melanopsins (opn4m-1, opn4m-2, opn4m-3, opn4x-1 and opn4x-2), each encoding a full-length opsin G protein. All five genes are expressed in the adult retina in a largely non-overlapping pattern, as revealed by RNA in situ hybridisation and immunocytochemistry, with at least one melanopsin form present in all neuronal cell types, including cone photoreceptors. This raises the possibility that the teleost retina is globally light sensitive. Electrophysiological and spectrophotometric studies demonstrate that all five zebrafish melanopsins encode a functional photopigment with peak spectral sensitivities that range from 470 to 484nm, with opn4m-1 and opn4m-3 displaying invertebrate-like bistability, where the retinal chromophore interchanges between cis- and trans-isomers in a light-dependent manner and remains within the opsin binding pocket. In contrast, opn4m-2, opn4x-1 and opn4x-2 are monostable and function more like classical vertebrate-like photopigments, where the chromophore is converted from 11-cis to all-trans retinal upon absorption of a photon, hydrolysed and exits from the binding pocket of the opsin. It is thought that all melanopsins exhibit an invertebrate-like bistability biochemistry. Our novel findings, however, reveal the presence of both invertebrate-like and vertebrate-like forms of melanopsin in the teleost retina, and indicate that photopigment bistability is not a universal property of the melanopsin family. The functional diversity of these teleost melanopsins, together with their widespread expression pattern within the retina, suggests that melanopsins confer global photosensitivity to the teleost retina and might allow for direct "fine-tuning" of retinal circuitry and physiology in the dynamic light environments found in aquatic habitats.

Abstract 4846: Genomic analysis of high grade bladder cancer: Defining genetic subtypes and therapeutic targets

Abstract Background: Genomic instability, as manifested by copy number alteration (CNA) and mutation, is a hallmark of cancer. We sought to characterize the spectrum of CNAs in 97 high-grade bladder tumors (HGBT) using high-resolution comparative genomic hybridization (CGH). We then performed an integrated analysis of CNA and targeted mutation testing to construct a comprehensive profile of genomic alterations in these tumors and to identify any correlation with clinical outcome. Methods: Genomic DNA from 97 frozen HGBTs (tumor content>70% or greater) and commercially available normal human DNA (Roche) were labeled with cyanine-based fluorescent dyes and hybridized onto a one-million oligonucleotide microarray (Agilent) followed by scanning and image analysis. High-throughput Sanger sequencing of select genes was performed with validation of hotspot oncogene mutations using a mass spectrometry based multiplex Sequenom assay. Results: We found that 47% of HGBT samples possessed a high degree of CNA with widespread amplifications and deletions while 53% contained markedly fewer numbers of events. A non-overlapping pattern of mutations and amplifications was observed when events were grouped within the context of specific signal transduction or cell cycle pathways. Preliminary survival analysis suggests that patients in the high CNA group have a worse prognosis than those in the low CNA group: fifteen out of 46 patients (33%) in the high CNA group have died of their disease vs. 9 of 51 (18%) in the low CNA group. Highly focal amplification events were noted within HER2 (5% of samples), E2F3 (11%), and CCND1 (10%). Immunohistochemistry (IHC) confirmed 3+ overexpression of HER2 in 5 of 5 samples exhibiting genetic amplification. Deletion events were most frequent in CDKN2A (13%). A subset of 11 tumors with small-cell histologic features was included within the samples analyzed and 45% of these tumors possessed E2F3 amplification vs. only 8% within the non-small cell tumor set. Targeted sequencing of select genes revealed that the majority of mutation events occurred within the high-CNA HGBTs. Conclusions: Distinct genetic subsets exist within HGBT and can be classified based on CNA and mutational analysis. The finding of focal amplification events within genes known to drive tumorigenesis in other contexts, such as HER2, underscores the need for global genomic approaches in identifying targets for therapy in bladder cancer. Small-cell bladder cancer may possess a distinct genetic signature characterized by E2F3 amplification. The non-overlapping pattern of CNAs and mutations seen within specific mitogenic pathways suggests that focal driver lesions can be identified for targeted therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4846. doi:10.1158/1538-7445.AM2011-4846

Peripheral blood gene expression profiles in metabolic syndrome, coronary artery disease and type 2 diabetes

To determine if individuals with metabolic disorders possess unique gene expression profiles, we compared transcript levels in peripheral blood from patients with coronary artery disease, type 2 diabetes and their precursor state, metabolic syndrome to those of control subjects and subjects with rheumatoid arthritis. The gene expression profile of each metabolic state was distinguishable from controls and correlated with other metabolic states more than with rheumatoid arthritis. Of note, subjects in the metabolic cohorts over-expressed gene sets that participate in the innate immune response. Genes involved in activation of the pro-inflammatory transcription factor, NF-κB, were over-expressed in coronary artery disease while genes differentially expressed in type 2 diabetes play key roles in T cell activation and signaling. RT-PCR validation confirmed microarray results. Furthermore, several genes differentially expressed in human metabolic disorders have been previously shown to participate in inflammatory responses in murine models of obesity and Type 2 diabetes. Taken together, these data demonstrate that peripheral blood from individuals with metabolic disorders display overlapping and non-overlapping patterns of gene expression indicative of unique, underlying immune processes.

Drosophila gustatory preference behaviors require the atypical soluble guanylyl cyclases

The intracellular messenger cGMP has been suggested to play a role in taste signal transduction in both vertebrates and invertebrates. In the present study, we have examined the role of the Drosophila atypical soluble guanylyl cyclases (sGCs), Gyc-89Da and Gyc-89Db, in larval and adult gustatory preference behaviors. We showed that in larvae, sucrose attraction requires Gyc-89Db and caffeine avoidance requires Gyc-89Da. In adult flies, sucrose attraction is unaffected by mutations in either gene whereas avoidance of low concentrations of caffeine is eliminated by loss of either gene. Similar defective behaviors were observed when cGMP increases were prevented by the expression of a cGMP-specific phosphodiesterase. We also showed that both genes were expressed in gustatory receptor neurons (GRNs) in larval and adult gustatory organs, primarily in a non-overlapping pattern, with the exception of a small group of cells in the adult labellum. In addition, in adults, several cells co-expressed the bitter taste receptor, Gr66a, with either Gyc-89Da or Gyc-89Db. We also showed that the electrophysiological responses of a GRN to caffeine were significantly reduced in flies mutant for the atypical sGCs, suggesting that at least part of the adult behavioral defects were due to a reduced ability to detect caffeine.

Seasonal variability of sleep‐disordered breathing in children

Snoring and sleep-disordered breathing (SDB) are frequent pediatric conditions. Although allergies and respiratory viruses have been pathophysiologically implicated in these conditions, their seasonal distribution has not been examined. The records of all children participating in a prospective, cross-sectional community-based research study that included a questionnaire on snoring frequency and loudness and an overnight sleep study were retrospectively assessed for seasonal patterns based on the day the children were evaluated. A total of 1,051 children were included with a mean age of 7 years. There were no seasonal differences in the number of children evaluated or in their demographic characteristics. However, the odds of increased snoring frequency and loudness were significantly higher in spring and summer and lowest in fall (P < 0.001). However, the mean AHI was highest and the nadir SaO(2) was lowest in winter and spring compared to summer and fall (P < 0.001 and P < 0.03, respectively). Snoring and the severity of SDB exhibit distinct and essentially non-overlapping patterns of seasonal variation, with peaks in spring-summer for snoring and peaks in winter-spring for SDB severity. These findings suggest that both seasonal viral and allergen burdens may contribute to SDB severity and may prompt differing clinical referral patterns throughout the year.

Functional Redundancy of Paralogs of an Anaphase Promoting Complex/Cyclosome Subunit in Caenorhabditis elegans Meiosis

The anaphase promoting complex/cyclosome (APC/C) mediates the metaphase-to-anaphase transition by instructing the ubiquitination and turnover of key proteins at this stage of the cell cycle. We have recovered a gain-of-function allele in an APC5 subunit of the anaphase promoting complex/cyclosome. This finding led us to investigate further the role of APC5 in Caenorhabditis elegans, which contains two APC5 paralogs. We have shown that these two paralogs, such-1 and gfi-3, are coexpressed in the germline but have nonoverlapping expression patterns in other tissues. Depletion of such-1 or gfi-3 alone does not have a notable effect on the meiotic divisions; however, codepletion of these two factors results in meiotic arrest. In sum, the two C. elegans APC5 paralogs have a redundant function during the meiotic divisions.

The neurexin superfamily of Caenorhabditis elegans

The neurexin superfamily is a group of transmembrane molecules mediating cell–cell contacts and generating specialized membranous domains in polarized epithelial and nerves cells. We describe here the domain organization and expression of the entire, core neurexin superfamily in the nematode Caenorhabditis elegans, which is composed of three family members. One of the superfamily members, nrx-1, is an ortholog of vertebrate neurexin, the other two, itx-1 and nlr-1, are orthologs of the Caspr subfamily of neurexin-like genes. Based on reporter gene analysis, we find that nrx-1 is exclusively expressed in most if not all cells of the nervous system and localizes to presynaptic specializations. itx-1 and nrx-1 reporter genes are expressed in non-overlapping patterns within and outside the nervous system. ITX-1 protein co-localizes with β-G-spectrin to a subapical domain within intestinal cells. These studies provide a starting point for further functional analysis of this family of proteins.

Comparative expression pattern analysis of the highly conserved chemokines SDF1 and CXCL14 during amniote embryonic development

Chemokines are secreted proteins with essential roles in leukocyte trafficking and cell migration during embryogenesis. CXCL14 displays a degree of evolutionary conservation unmatched by any other chemokine except for SDF1(CXCL12). However, its role during embryogenesis has not been studied. Here we describe the expression pattern of mouse and chicken CXCL14 during embryogenesis and compare it with that of SDF1. CXCL14 is widely expressed in embryonic ectoderm and shows a restricted and dynamic expression pattern in paraxial mesoderm, mesonephros, neural tube, and limbs. During limb development, CXCL14 marks a unique connective tissue subset that surrounds developing tendons. Comparison of CXCL14 and SDF1 reveals mostly non-overlapping or complementary expression patterns, suggesting an interactive regulation of developmental processes by these two chemokines. Our study identifies CXCL14 as a novel marker of tendon connective tissue and provides a conceptual framework for the coordinated action of two highly conserved chemokines in embryonic development.

Factors influencing the temporal patterns of dyadic behaviours and interactions between domestic cats and their owners

Human-cat dyads may be similar in interaction structure to human dyads because many humans regard their cats as being social companions. Consequently, we predict that dyadic structure will be contingent on owner and cat personalities, sex, and age as well as duration of cohabitation of the partners. Forty owner-cat dyads were visited in their homes, on four occasions, during which their behaviours and interactions were video-taped. Behaviour was coded from tape and was analysed for temporal (t)-patterns using Theme (Noldus; Magnusson, 1996). Owner personality was assessed using the NEO-FFI. Five cat personality axes were identified by Principal Component Analysis (PCA) based on observer-rated items and on coded behaviours. We found that the higher the owner in neuroticism, the fewer t-patterns occurred per minute. The higher the owner in extraversion, the higher was the number of non-overlapping patterns per minute. The more "active" the cat, the fewer non-overlapping patterns occurred per minute, but the higher was the event type complexity. The older the cat, the lower was dyadic event type complexity. We suggest that basic temporal structures similar to those of human-cat dyads may also be found in other long-term and complex dyadic relationships, including those between humans.

Robust In Vivo Transduction of Nervous System and Neural Stem Cells by Early Gestational Intra Amniotic Gene Transfer Using Lentiviral Vector

Presently, in vivo methods to efficiently and broadly transduce all major cell types throughout both the central (CNS) and peripheral adult nervous system (PNS) are lacking. In this study, we hypothesized that during early fetal development neural cell populations, including neural stem cells (NSCs), may be accessible for gene transfer via the open neural groove. To test this hypothesis, we injected lentiviral vectors encoding a green fluorescent protein (GFP) marker gene into the murine amniotic cavity at embryonic day 8. This method (i) efficiently and stably transduced the entire nervous system for at least 80% of the lifespan of the mice, (ii) transduced all major neural cell types, and (iii) transduced adult NSCs of the subventricular zone (SVZ) and subgranular zones (SGZs). This simple approach has broad applications for the study of gene function in nervous system development and adult NSCs and may have future clinical applications for treatment of genetic disorders of the nervous system.

Expression and distribution of voltage-gated ion channels in ferret sinoatrial node

Spontaneous diastolic depolarization in the sinoatrial (SA) node enables it to serve as pacemaker of the heart. The variable cell morphology within the SA node predicts that ion channel expression would be heterogeneous and different from that in the atrium. To evaluate ion channel heterogeneity within the SA node, we used fluorescent in situ hybridization to examine ion channel expression in the ferret SA node region and atrial appendage. SA nodal cells were distinguished from surrounding cardiac myocytes by expression of the slow (SA node) and cardiac (surrounding tissue) forms of troponin I. Nerve cells in the sections were identified by detection of GAP-43 and cytoskeletal middle neurofilament. Transcript expression was characterized for the 4 hyperpolarization-activated cation channels, 6 voltage-gated Na(+) channels, 3 voltage-gated Ca(2+) channels, 24 voltage-gated K(+) channel α-subunits, and 3 ancillary subunits. To ensure that transcript expression was representative of protein expression, immunofluorescence was used to verify localization patterns of voltage-dependent K(+) channels. Colocalizations were performed to observe any preferential patterns. Some overlapping and nonoverlapping binding patterns were observed. Measurement of different cation channel transcripts showed heterogeneous expression with many different patterns of expression, attesting to the complexity of electrical activity in the SA node. This study provides insight into the possible role ion channel heterogeneity plays in SA node pacemaker activity.

A complex interplay of three R2R3 MYB transcription factors determines the profile of aliphatic glucosinolates in Arabidopsis.

While R2R3 MYB transcription factors are a large gene family of transcription factors within plants, comprehensive functional data in planta are still scarce. A model for studying R2R3 MYB control of metabolic networks is the glucosinolates (GLSs), secondary metabolites that control plant resistance against insects and pathogens and carry cancer-preventive properties. Three related members of the R2R3 MYB transcription factor family within Arabidopsis (Arabidopsis thaliana), MYB28, MYB29, and MYB76, are the commonly defined regulators of aliphatic GLS biosynthesis. We utilized new genotypes and systems analysis techniques to test the existing regulatory model in which MYB28 is the dominant regulator, MYB29 plays a minor rheostat role, and MYB76 is largely uninvolved. We unequivocally show that MYB76 is not dependent on MYB28 and MYB29 for induction of aliphatic GLSs and that MYB76 plays a role in determining the spatial distribution of aliphatic GLSs within the leaf, pointing at a potential role of MYB76 in transport regulation. Transcriptional profiling of knockout mutants revealed that GLS metabolite levels are uncoupled from the level of transcript accumulation for aliphatic GLS biosynthetic genes. This uncoupling of chemotypes from biosynthetic transcripts suggests revising our view of the regulation of GLS metabolism from a simple linear transcription factor-promoter model to a more modular system in which transcription factors cause similar chemotypes via nonoverlapping regulatory patterns. Similar regulatory networks might exist in other secondary pathways.

Functional redundancy of EGF-CFC genes in epiblast and extraembryonic patterning during early mouse embryogenesis

During early mouse embryogenesis, multiple patterning and differentiation events require the activity of Nodal, a ligand of the transforming growth factor-beta (TGFβ) family. Although Nodal signaling is known to require activity of EGF-CFC co-receptors in many contexts, it has been unclear whether all Nodal signaling in the early mouse embryo is EGF-CFC dependent. We have investigated the double null mutant phenotypes for the EGF-CFC genes Cripto and Cryptic, which encode co-receptors for Nodal, and have found that they have partially redundant functions in early mouse development. Expression of Cripto and Cryptic is non-overlapping prior to gastrulation, since Cripto is expressed solely in the epiblast whereas Cryptic is expressed in the primitive endoderm of the late blastocyst and the visceral endoderm after implantation. Despite these non-overlapping expression patterns, Cripto; Cryptic double mutants display severe defects in epiblast, extraembryonic ectoderm, and anterior visceral endoderm (AVE), resulting in phenotypes that are highly similar to those of Nodal null mutants. Our results indicate that both Cripto and Cryptic function non-cell-autonomously during normal development, and that most if not all Nodal activity in early mouse embryogenesis is EGF-CFC-dependent.

Capillary Based Patterning of Cellular Communities in Laterally Open Channels

In order to offer an easier way to study interactions between multiple cellular populations, we have developed a novel method to precisely place cells in a variety of nonoverlapping patterns using surface tension in laterally open microchannels. Our design is fundamentally different from previous strategies such as compartmentalization, stamping, stenciling, or mechanical approaches. It relies on capillary action or the propensity for liquid to move more readily through narrow spaces as a result of surface tension. Until now, capillary based patterning has been limited to coating chemically isolated areas. Here, we demonstrate, through use of surface tension and controlled flooding, that it is possible to pattern multiple cells and proteins using laterally open channels in a variety of designs. We demonstrate the relevance of the concept by coculturing different mammalian cell types and evaluating the behavior of engineered quorum sensing circuits in E. coli. In the future, we believe the laterally open channel designs shown here can be useful for rapidly creating and studying cellular ecologies using simple pipetting.

Systematic image‐driven analysis of the spatial Drosophila embryonic expression landscape

Discovery of temporal and spatial patterns of gene expression is essential for understanding the regulatory networks and development in multicellular organisms. We analyzed the images from our large-scale spatial expression data set of early Drosophila embryonic development and present a comprehensive computational image analysis of the expression landscape. For this study, we created an innovative virtual representation of embryonic expression patterns using an elliptically shaped mesh grid that allows us to make quantitative comparisons of gene expression using a common frame of reference. Demonstrating the power of our approach, we used gene co-expression to identify distinct expression domains in the early embryo; the result is surprisingly similar to the fate map determined using laser ablation. We also used a clustering strategy to find genes with similar patterns and developed new analysis tools to detect variation within consensus patterns, adjacent non-overlapping patterns, and anti-correlated patterns. Of the 1800 genes investigated, only half had previously assigned functions. The known genes suggest developmental roles for the clusters, and identification of related patterns predicts requirements for co-occurring biological functions.

MiR319a targeting of TCP4 is critical for petal growth and development in Arabidopsis

In a genetic screen in a drnl-2 background, we isolated a loss-of-function allele in miR319a (miR319a(129)). Previously, miR319a has been postulated to play a role in leaf development based on the dramatic curled-leaf phenotype of plants that ectopically express miR319a (jaw-D). miR319a(129) mutants exhibit defects in petal and stamen development; petals are narrow and short, and stamens exhibit defects in anther development. The miR319a(129) loss-of-function allele contains a single-base change in the middle of the encoded miRNA, which reduces the ability of miR319a to recognize targets. Analysis of the expression patterns of the three members of the miR319 gene family (miR319a, miR319b, and miR319c) indicates that these genes have largely non-overlapping expression patterns suggesting that these genes have distinct developmental functions. miR319a functions by regulating the TCP transcription factors TCP2, TCP3, TCP4, TCP10, and TCP24; the level of RNA expression of these TCP genes is down-regulated in jaw-D and elevated in miR319a(129). Several lines of evidence demonstrate that TCP4 is a key target of miR319a. First, the tcp4(soj6) mutant, which contains a mutation in the TCP4 miRNA-binding site complementary to the miR319a(129) mutation, suppresses the flower phenotype of miR319a(129). Second, expression of wild-type TCP4 in petals and stamens (i.e., AP3:TCP4) has no effect on flower development; by contrast, a miRNA-resistant version of TCP4, when expressed in petals and stamens (i.e., pAP3:mTCP4) causes these organs not to develop. Surprisingly, when AP3:TCP4 is present in a miR319a(129) background, petal and stamen development is severely disrupted, suggesting that proper regulation by miR319a of TCP4 is critical in these floral organs.

The Roles and Acting Mechanism of Caenorhabditis elegans DNase II Genes in Apoptotic DNA Degradation and Development

DNase II enzymes are acidic endonucleases that have been implicated in mediating apoptotic DNA degradation, a critical cell death execution event. C. elegans genome contains three DNase II homologues, NUC-1, CRN-6, and CRN-7, but their expression patterns, acting sites, and roles in apoptotic DNA degradation and development are unclear. We have conducted a comprehensive analysis of three C. elegans DNase II genes and found that nuc-1 plays a major role, crn-6 plays an auxiliary role, and crn-7 plays a negligible role in resolving 3′ OH DNA breaks generated in apoptotic cells. Promoter swapping experiments suggest that crn-6 but not crn-7 can partially substitute for nuc-1 in mediating apoptotic DNA degradation and both fail to replace nuc-1 in degrading bacterial DNA in intestine. Despite of their restricted and largely non-overlapping expression patterns, both CRN-6 and NUC-1 can mediate apoptotic DNA degradation in many cells, suggesting that they are likely secreted nucleases that are retaken up by other cells to exert DNA degradation functions. Removal or disruption of NUC-1 secretion signal eliminates NUC-1's ability to mediate DNA degradation across its expression border. Furthermore, blocking cell corpse engulfment does not affect apoptotic DNA degradation mediated by nuc-1, suggesting that NUC-1 acts in apoptotic cells rather than in phagocytes to resolve 3′ OH DNA breaks. Our study illustrates how multiple DNase II nucleases play differential roles in apoptotic DNA degradation and development and reveals an unexpected mode of DNase II action in mediating DNA degradation.

Geographical parthenogenesis, genome size variation and pollen production in the arctic-alpine species Hieracium alpinum

Hieracium alpinum L. (Asteraceae) is an arctic-alpine species distributed throughout Europe with both diploid and triploid cytotypes. We determined the ploidy levels of plants from 23 populations from Austria, Bosnia and Herzegovina, Finland, Italy, Norway, Romania, Slovakia, Switzerland and Ukraine. Data showed a non-overlapping pattern of cytotype distribution: sexually reproducing diploids (2n = 2x = 18) occur solely in the Eastern and Southern Carpathians, while apomictic triploids (2n = 3x = 27) cover the rest of the range. Such clear-cut allopatry is rather rare in vascular plants with geographical parthenogenesis. Comparison of absolute genome size indicates genome downsizing (by on average 3.7%) of haploid DNA amount in triploids relative to diploids. Genome size further correlated with longitude and latitude in the Alps, with decreasing absolute DNA content from west to east, and from south to north. While previously published data indicated complete male sterility of triploid plants, we found that plants from the Alps and Bosnia and Herzegovina commonly produced some pollen, whereas populations from the Western Carpathians and Scandinavia seemed to be almost completely pollen sterile. Scenarios about the evolution of geographical parthenogenesis in H. alpinum are discussed.