RESUMO
In the classical model of the basal ganglia, direct pathway striatal projection neurons (dSPNs) send projections to the substantia nigra (SNr) and entopeduncular nucleus to regulate motor function. Recent studies have re-established that dSPNs also possess axon collaterals within the globus pallidus (GPe) (bridging collaterals), yet the significance of these collaterals for behavior is unknown. Here we use in vivo optical and chemogenetic tools combined with deep learning approaches in mice to dissect the roles of dSPN GPe collaterals in motor function. We find that dSPNs projecting to the SNr send synchronous motor-related information to the GPe via axon collaterals. Inhibition of native activity in dSPN GPe terminals impairs motor activity and function via regulation of Npas1 neurons. We propose a model by which dSPN GPe axon collaterals (striatopallidal Go pathway) act in concert with the canonical terminals in the SNr to support motor control by inhibiting Npas1 neurons.
Assuntos
Axônios , Neurônios , Camundongos , Animais , Neurônios/metabolismo , Axônios/metabolismo , Globo Pálido/fisiologia , Corpo Estriado/metabolismo , Gânglios da Base/metabolismo , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismoRESUMO
Adult-born granule cells (abGCs) have been implicated in memory discrimination through a neural computation known as pattern separation. Here, using in vivo Ca2+ imaging, we examined how chronic ablation or acute chemogenetic silencing of abGCs affects the activity of mature granule cells (mGCs). In both cases, we observed altered remapping of mGCs. Rather than broadly modulating the activity of all mGCs, abGCs promote the remapping of place cells' firing fields while increasing rate remapping of mGCs that represent sensory cues. In turn, these remapping deficits are associated with behavioral impairments in animals' ability to correctly identify new goal locations. Thus, abGCs facilitate pattern separation through the formation of non-overlapping representations for identical sensory cues encountered in different locations. In the absence of abGCs, the dentate gyrus shifts to a state that is dominated by cue information, a situation that is consistent with the overgeneralization often observed in anxiety or age-related disorders.
Assuntos
Giro Denteado , Neurogênese , Animais , Neurônios , Sinais (Psicologia)RESUMO
In vivo brainstem imaging with miniature microscopy has been challenging due to surgical difficulty, high motion, and correlated activity between neurons. Here, we present a protocol for brainstem imaging in freely moving mice using the dorsal raphe nucleus as an example. We describe surgical procedures to inject a virus encoding GCaMP6m and securely implant a GRIN lens in the brainstem. We then detail motion correction and cell segmentation from the data to parse single-cell activity from correlated networks. For complete details on the use and execution of this protocol, please refer to Paquelet et al. (2022).1.
Assuntos
Tronco Encefálico , Núcleo Dorsal da Rafe , Camundongos , Animais , Tronco Encefálico/diagnóstico por imagem , Neurônios/fisiologia , MicroscopiaRESUMO
The serotonin system modulates a wide variety of emotional behaviors and states, including reward processing, anxiety, and social interaction. To reveal the underlying patterns of neural activity, we visualized serotonergic neurons in the dorsal raphe nucleus (DRN5-HT) of mice using miniaturized microscopy during diverse emotional behaviors. We discovered ensembles of cells with highly correlated activity and found that DRN5-HT neurons are preferentially recruited by emotionally salient stimuli as opposed to neutral stimuli. Individual DRN5-HT neurons responded to diverse combinations of salient stimuli, with some preference for valence and sensory modality. Anatomically defined subpopulations projecting to either a reward-related structure (the ventral tegmental area) or an anxiety-related structure (the bed nucleus of the stria terminalis) contained all response types but were enriched in reward- and anxiety-responsive cells, respectively. Our results suggest that the DRN serotonin system responds to emotional salience using ensembles with mixed selectivity and biases in downstream connectivity.
Assuntos
Núcleo Dorsal da Rafe , Serotonina , Animais , Núcleo Dorsal da Rafe/fisiologia , Camundongos , Recompensa , Neurônios Serotoninérgicos , Área Tegmentar Ventral/fisiologiaRESUMO
During exploration, animals form an internal map of an environment by combining information about landmarks and the animal's movement, a process that depends on the hippocampus. The dentate gyrus (DG) is the first stage of the hippocampal circuit where self-motion ("where") and sensory cue information ("what") are integrated, but it remains unknown how DG neurons encode this information during cognitive map formation. Using two-photon calcium imaging in mice running on a treadmill along with online cue manipulation, we identify robust sensory cue responses in DG granule cells. Cue cell responses are stable, stimulus-specific, and accompanied by inhibition of nearby neurons. This demonstrates the existence of "cue cells" in addition to better characterized "place cells" in the DG. We hypothesize that the DG supports parallel channels of spatial and non-spatial information that contribute distinctly to downstream computations and affect roles of the DG in spatial navigation and episodic memory.
Assuntos
Sinais (Psicologia) , Giro Denteado/fisiologia , Neurônios/fisiologia , Aprendizagem Espacial/fisiologia , Navegação Espacial/fisiologia , Animais , CamundongosRESUMO
The increasing interest in manipulating neural circuits in developing brains has created a demand for reliable and accurate methods for delivering viruses to newborn mice. Here we describe a novel 3D-printed mouse neonatal stereotaxic adaptor for intracerebral viral injection that provides enhanced precision and reliability. Using this device, we injected A2a-Cre mice with a Cre-dependent hM4D-mCherry viral construct at postnatal day 1 (P1) and demonstrated selective expression in the striatal indirect pathway neurons on days P7, P11 and P25. Similarly, dopaminergic midbrain neurons were selectively targeted with a Cre-dependent green fluorescent protein virus in Dat-IRES-Cre neonates and expression examined at P25. Our open-source neonatal stereotaxic mouse adaptor facilitates neonatal neuronal targeting, which should improve the ability to label and modify neural circuits in developing mouse brains.
Assuntos
Encéfalo/virologia , Técnicas de Transferência de Genes , Técnicas Estereotáxicas/instrumentação , Vírus/genética , Animais , Animais Recém-Nascidos , Camundongos , Neurônios/virologia , Impressão Tridimensional/instrumentaçãoRESUMO
The mammalian brain can form associations between behaviorally relevant stimuli in an animal's environment. While such learning is thought to primarily involve high-order association cortex, even primary sensory areas receive long-range connections carrying information that could contribute to high-level representations. Here, we imaged layer 1 apical dendrites in the barrel cortex of mice performing a whisker-based operant behavior. In addition to sensory-motor events, calcium signals in apical dendrites of layers 2/3 and 5 neurons and in layer 2/3 somata track the delivery of rewards, both choice related and randomly administered. Reward-related tuft-wide dendritic spikes emerge gradually with training and are task specific. Learning recruits cells whose intrinsic activity coincides with the time of reinforcement. Layer 4 largely lacked reward-related signals, suggesting a source other than the primary thalamus. Our results demonstrate that a sensory cortex can acquire a set of associations outside its immediate sensory modality and linked to salient behavioral events.
Assuntos
Dendritos/fisiologia , Reforço Psicológico , Córtex Somatossensorial/fisiologia , Animais , Sinalização do Cálcio , Dendritos/metabolismo , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Células Receptoras Sensoriais/metabolismo , Células Receptoras Sensoriais/fisiologia , Córtex Somatossensorial/citologia , Vibrissas/fisiologiaRESUMO
People aging with HIV face social stressors which may negatively affect their overall nutrition. Here, we assess relationships between self-reported measures of depression, perceived stress, social support, and food insecurity with diet quality in older adults with HIV. A retrospective analysis of self-reported data from parent study at The University of Alabama at Birmingham 1917 HIV Clinic was performed. The study sample consisted of sixty people living with HIV (PLWH) with controlled HIV infection (<50 copies/mL), aged 50 years or older who participated in a cross-sectional microbiome study. Dietary intake was measured using the NHANES 12-month Food Frequency Questionnaire (FFQ) and three Automated Self-Administered (ASA) 24-hr diet recalls to calculate diet quality scores using the Mediterranean Diet Score (MDS); alternative Healthy Eating Index (aHEI); and the Recommended Food Score (RFS) indices. Food insecurity was measured with the Food Security Questionnaire (FSQ). Participants completed the following psychosocial scales: (1) depression - Patient Health Questionnaire-8 (PHQ8); (2) perceived stress - Perceived Stress Scale (PSS-10); (3) social support - Multidimensional Scale of Perceived Social Support (MSPSS). Linear regression models were used to investigate relationships among variables controlling for gender and income. The cohort was characterized as follows: Mean age 56 ± 4.6 years, 80% African-American, and 32% women. Mean body mass index (BMI) was 28.4 ± 7.2 with 55% reporting food insecurity. Most participants reported having post-secondary education (53%), although 77% reported annual incomes <$20,000. Food insecurity was independently associated with measures of poor dietary intake: aHEI (ß = -0.08, p = .02) and MDS (ß = -0.23, p < 0.01) and with low dietary intake of fibre (ß = -0.27, p = .04), vitamin E (ß = -0.35, p = .01), folate (ß = -0.31, p = .02), magnesium (ß = -0.34, p = .01) and copper (ß = -0.36, p = .01). These data indicate food insecurity is associated with poor diet quality among PLWH. Clinical interventions are needed to improve food access for PLWH of low SES.
Assuntos
Dieta , Comportamento Alimentar , Abastecimento de Alimentos/estatística & dados numéricos , Infecções por HIV/psicologia , Estresse Psicológico , Idoso , Alabama , Fármacos Anti-HIV/uso terapêutico , Estudos de Coortes , Depressão , Fibras na Dieta , Feminino , Infecções por HIV/tratamento farmacológico , Humanos , Masculino , Pessoa de Meia-Idade , Avaliação Nutricional , Inquéritos Nutricionais , Estado Nutricional , Estudos Retrospectivos , Apoio Social , Inquéritos e QuestionáriosRESUMO
For many of our senses, the role of the cerebral cortex in detecting stimuli is controversial1-17. Here we examine the effects of both acute and chronic inactivation of the primary somatosensory cortex in mice trained to move their large facial whiskers to detect an object by touch and respond with a lever to obtain a water reward. Using transgenic mice, we expressed inhibitory opsins in excitatory cortical neurons. Transient optogenetic inactivation of the primary somatosensory cortex, as well as permanent lesions, initially produced both movement and sensory deficits that impaired detection behaviour, demonstrating the link between sensory and motor systems during active sensing. Unexpectedly, lesioned mice had recovered full behavioural capabilities by the subsequent session. This rapid recovery was experience-dependent, and early re-exposure to the task after lesioning facilitated recovery. Furthermore, ablation of the primary somatosensory cortex before learning did not affect task acquisition. This combined optogenetic and lesion approach suggests that manipulations of the sensory cortex may be only temporarily disruptive to other brain structures that are themselves capable of coordinating multiple, arbitrary movements with sensation. Thus, the somatosensory cortex may be dispensable for active detection of objects in the environment.
Assuntos
Aprendizagem/fisiologia , Movimento/fisiologia , Sensação/fisiologia , Animais , Fenômenos Biomecânicos , Feminino , Masculino , Camundongos , Camundongos Transgênicos , Neurônios/metabolismo , Optogenética , Recompensa , Córtex Somatossensorial/citologia , Córtex Somatossensorial/fisiologia , Córtex Somatossensorial/cirurgia , Tato/fisiologia , Vibrissas/fisiologiaRESUMO
In vivo calcium imaging is an incredibly powerful technique that provides simultaneous information on fast neuronal events, such as action potentials and subthreshold synaptic activity, as well as slower events that occur in the glia and surrounding neuropil. Bulk-loading methods that involve multiple injections can be used for single-cell as well as wide-field imaging studies. However, multiple injections result in inhomogeneous loading as well as multiple sites of potential cortical injury. We used convection-enhanced delivery to create smooth, continuous loading of a large area of the cortical surface through a solitary injection site and demonstrated the efficacy of the technique using confocal microscopy imaging of single cells and physiological responses to single-trial events of spontaneous activity, somatosensory-evoked potentials, and epileptiform events. Combinations of calcium imaging with voltage-sensitive dye and intrinsic signal imaging demonstrate the utility of this technique in neurovascular coupling investigations. Convection-enhanced loading of calcium dyes may be a useful technique to advance the study of cortical processing when widespread loading of a wide-field imaging is required.
RESUMO
Throughout the adult life of most mammals, new neurons are continuously generated in the dentate gyrus of the hippocampal formation. Recent work has documented specific cognitive deficits after elimination of adult hippocampal neurogenesis in rodents, suggesting that these neurons may contribute to information processing in hippocampal circuits. Young adult-born neurons exhibit enhanced excitability and have altered capacity for synaptic plasticity in hippocampal slice preparations in vitro. Still, little is known about the effect of adult-born granule cells on hippocampal activity in vivo. To assess the impact of these new neurons on neural circuits in the dentate, we recorded perforant-path evoked responses and spontaneous network activity from the dentate gyrus of urethane-anesthetized mice whose hippocampus had been focally X-irradiated to eliminate the population of young adult-born granule cells. After X-irradiation, perforant-path responses were reduced in magnitude. In contrast, there was a marked increase in the amplitude of spontaneous γ-frequency bursts in the dentate gyrus and hilus, as well as increased synchronization of dentate neuron firing to these bursts. A similar increase in gamma burst amplitude was also found in animals in which adult neurogenesis was eliminated using the GFAP:TK pharmacogenetic ablation technique. These data suggest that young neurons may inhibit or destabilize recurrent network activity in the dentate and hilus. This unexpected result yields a new perspective on how a modest number of young adult-generated granule cells may modulate activity in the larger population of mature granule cells, rather than acting solely as independent encoding units.
Assuntos
Giro Denteado/fisiologia , Rede Nervosa/fisiologia , Neurogênese/fisiologia , Plasticidade Neuronal/fisiologia , Neurônios/fisiologia , Animais , Grânulos Citoplasmáticos/fisiologia , Grânulos Citoplasmáticos/efeitos da radiação , Giro Denteado/citologia , Giro Denteado/efeitos da radiação , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Rede Nervosa/citologia , Rede Nervosa/efeitos da radiação , Vias Neurais/citologia , Vias Neurais/fisiologia , Vias Neurais/efeitos da radiação , Neurogênese/efeitos da radiação , Plasticidade Neuronal/efeitos da radiação , Neurônios/citologia , Neurônios/efeitos da radiaçãoRESUMO
Carefully designed animal models of genetic risk factors are likely to aid our understanding of the pathogenesis of schizophrenia. Here, we study a mouse strain with a truncating lesion in the endogenous Disc1 ortholog designed to model the effects of a schizophrenia-predisposing mutation and offer a detailed account of the consequences that this mutation has on the development and function of a hippocampal circuit. We uncover widespread and cumulative cytoarchitectural alterations in the dentate gyrus during neonatal and adult neurogenesis, which include errors in axonal targeting and are accompanied by changes in short-term plasticity at the mossy fiber/CA3 circuit. We also provide evidence that cAMP levels are elevated as a result of the Disc1 mutation, leading to altered axonal targeting and dendritic growth. The identified structural alterations are, for the most part, not consistent with the growth-promoting and premature maturation effects inferred from previous RNAi-based Disc1 knockdown. Our results provide support to the notion that modest disturbances of neuronal connectivity and accompanying deficits in short-term synaptic dynamics is a general feature of schizophrenia-predisposing mutations.
Assuntos
Axônios/metabolismo , Hipocampo/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Plasticidade Neuronal , Potenciais de Ação , Animais , Animais Recém-Nascidos , Proliferação de Células , Células Cultivadas , AMP Cíclico/metabolismo , Nucleotídeo Cíclico Fosfodiesterase do Tipo 4/metabolismo , Dendritos/metabolismo , Dendritos/fisiologia , Giro Denteado/citologia , Giro Denteado/crescimento & desenvolvimento , Giro Denteado/metabolismo , Hipocampo/citologia , Hipocampo/crescimento & desenvolvimento , Imuno-Histoquímica , Potenciação de Longa Duração , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Fibras Musgosas Hipocampais/metabolismo , Proteínas do Tecido Nervoso/genética , Neurogênese , Neurônios/citologia , Neurônios/metabolismo , Neurônios/fisiologia , Técnicas de Patch-ClampRESUMO
It has been suggested that chemotherapy treatment for cancer may contribute to cognitive decline in older cancer survivors. This issue is particularly important given that subtle cognitive impairment, particularly in cognitive processing speed, can affect functional status and quality of life for older adults. Multivariate regression of data from a longitudinal randomized controlled trial of older adults revealed a trend towards decreased performance after cancer treatment with chemotherapy on several functional measures associated with processing speed (as compared with matched individuals who did not have cancer). Additional analyses revealed that a subset of the chemotherapy-treated adults demonstrated a reliable negative change on several measures of processing speed. While inconclusive, this hypothesis generating work suggests that cognitive dysfunction following cancer treatment may contribute to disability observed in older cancer survivors. Further research is needed to determine the significance of the relationship between cognitive and functional impairment in older cancer survivors.
Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Transtornos Cognitivos/induzido quimicamente , Neoplasias/tratamento farmacológico , Atividades Cotidianas , Idoso , Idoso de 80 Anos ou mais , Quimioterapia Adjuvante/efeitos adversos , Transtornos Cognitivos/fisiopatologia , Função Executiva/efeitos dos fármacos , Função Executiva/fisiologia , Feminino , Humanos , Estudos Longitudinais , Masculino , Neoplasias/complicações , Neoplasias/fisiopatologia , Testes Neuropsicológicos , Análise de Regressão , Índice de Gravidade de DoençaRESUMO
Mice lacking the serotonin 1A receptor (5-HT(1A)R) show increased levels of anxiety-related behavior across multiple tests and background strains. Tissue-specific rescue experiments, lesion studies, and neurophysiological findings all point toward the hippocampus as a potential mediator of the phenotype. Serotonin, acting through 5-HT(1A)Rs, can suppress hippocampal theta-frequency oscillations, suggesting that theta oscillations might be increased in the knock-outs. To test this hypothesis, local field potential recordings were obtained from the hippocampus of awake, behaving knock-outs and wild-type littermates. The magnitude of theta oscillations was increased in the knock-outs, specifically in the anxiety-provoking elevated plus maze and not in a familiar environment or during rapid eye movement sleep. Theta power correlated with the fraction of time spent in the open arms, an anxiety-related behavioral variable. These results suggest a possible role for the hippocampus, and theta oscillations in particular, in the expression of anxiety in 5-HT(1A)R-deficient mice.
Assuntos
Transtornos de Ansiedade/fisiopatologia , Hipocampo/fisiopatologia , Receptor 5-HT1A de Serotonina/deficiência , Animais , Transtornos de Ansiedade/genética , Eletrodos Implantados , Eletroencefalografia , Comportamento Exploratório/fisiologia , Análise Fatorial , Aprendizagem em Labirinto , Camundongos , Camundongos Knockout , Células Piramidais/fisiologia , Receptor 5-HT1A de Serotonina/genética , Serotonina/fisiologia , Método Simples-Cego , Sono REM/fisiologiaRESUMO
Interneuronal networks in neocortex underlie feedforward and feedback inhibition and control the temporal organization of pyramidal cell activity. We previously found that lower layer neocortical interneurones can reach action potential threshold in response to the stimulation of a single presynaptic cell. To better understand this phenomenon and the circuit roles of lower layer neocortical interneurones, we combined two-photon calcium imaging with whole cell recordings and anatomical reconstructions of low threshold spiking (LTS) interneurones from mouse neocortex. In both visual and somatosensory cortex, LTS interneurones are somatostatin-positive, concentrated in layer 5 and possess dense axonal innervation to layer 1. Due to the LTS properties, these neurones operate in burst and tonic modes. In burst mode, dendritic T-type calcium channels boosted small synaptic inputs and triggered low threshold calcium spikes, while in tonic mode, sodium-based APs evoked smaller calcium influxes. In both modes, the entire dendritic tree of LTS interneurones behaved as a 'global' single spiking unit. This, together with the fact that synaptic inputs to layer 5 LTS cells are facilitating, and that their axons target the dendritic region of the pyramidal neurones where bursts are generated, make these neurones ideally suited to detect and control burst generation of individual lower layer pyramidal neurones.
Assuntos
Potenciais de Ação/fisiologia , Cálcio/metabolismo , Dendritos/fisiologia , Interneurônios/fisiologia , Células Piramidais/fisiologia , Animais , Canais de Cálcio/fisiologia , Interneurônios/ultraestrutura , Camundongos , Camundongos Endogâmicos C57BL , Técnicas de Cultura de Órgãos , Periodicidade , Receptores de AMPA/fisiologia , Limiar Sensorial/fisiologia , Córtex Somatossensorial/citologia , Córtex Somatossensorial/fisiologia , Somatostatina/metabolismo , Sinapses/fisiologia , Córtex Visual/citologia , Córtex Visual/fisiologiaRESUMO
The pathology of trisomy 21/Down syndrome includes cognitive and memory deficits. Increased expression of the dual-specificity protein kinase DYRK1A kinase (DYRK1A) appears to play a significant role in the neuropathology of Down syndrome. To shed light on the cellular role of DYRK1A and related genes we identified three DYRK/minibrain-like genes in the genome sequence of Caenorhabditis elegans, termed mbk-1, mbk-2, and hpk-1. We found these genes to be widely expressed and to localize to distinct subcellular compartments. We isolated deletion alleles in all three genes and show that loss of mbk-1, the gene most closely related to DYRK1A, causes no obvious defects, while another gene, mbk-2, is essential for viability. The overexpression of DYRK1A in Down syndrome led us to examine the effects of overexpression of its C. elegans ortholog mbk-1. We found that animals containing additional copies of the mbk-1 gene display behavioral defects in chemotaxis toward volatile chemoattractants and that the extent of these defects correlates with mbk-1 gene dosage. Using tissue-specific and inducible promoters, we show that additional copies of mbk-1 can impair olfaction cell-autonomously in mature, fully differentiated neurons and that this impairment is reversible. Our results suggest that increased gene dosage of human DYRK1A in trisomy 21 may disrupt the function of fully differentiated neurons and that this disruption is reversible.
Assuntos
Caenorhabditis elegans/genética , Síndrome de Down/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Tirosina Quinases/genética , Animais , Dosagem de Genes , Neurônios Aferentes/metabolismo , Filogenia , Proteínas Serina-Treonina Quinases/metabolismo , Olfato/genética , Quinases DyrkRESUMO
Relationships between life events and psychological distress were investigated for 197 dementia caregivers and 218 non-caregivers. Participants indicated which events on the Louisville Older Persons Events Scale they had experienced over the past six months. Life events were then classified as associated or unassociated with care-giving using differences in incidence rates between caregivers and non-caregivers. Primary care-giving stressors and associated life events were most predictive of psychological distress among caregivers. Among non-caregivers, unassociated negative life events were the strongest predictors of depression and life satisfaction. Implications for the assessment of life events and caregiver interventions are discussed.
Assuntos
Cuidadores/psicologia , Demência/psicologia , Acontecimentos que Mudam a Vida , Estresse Psicológico/psicologia , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
The presence of long-range correlations and/or mosaicism in DNA sequences results in GC fluctuations, even within individual isochores that are much larger than expected correlation-free 'random' sequences. Neglecting the presence of such fluctuations can lead to incorrect conclusions regarding relative homogeneity or isochore borders. In this commentary, we address these and other methodological issues raised by the variations in GC level within human isochores. We also discuss some recent misconceptions.
Assuntos
Composição de Bases , DNA/genética , Genoma , Animais , Centrifugação com Gradiente de Concentração , Césio , Cloretos , DNA/química , Sequência Rica em GC/genética , Genes/genética , Variação Genética , Humanos , Análise de Sequência de DNA/métodosRESUMO
GC level distributions of a species' nuclear genome, or of its compositional fractions, encode key information on structural and functional properties of the genome and on its evolution. They can be calculated either from absorbance profiles of the DNA in CsCl density gradients at sedimentation equilibrium, or by scanning long contigs of largely sequenced genomes. In the present study, we address the quantitative characterization of the compositional heterogeneity of genomes, as measured by the GC distributions of fixed-length fragments. Special attention is given to mammalian genomes, since their compartmentalization into isochores implies two levels of heterogeneity, intra-isochore (local) and inter-isochore (global). This partitioning is a natural one, since large-scale compositional properties vary much more among isochores than within them. Intra-isochore GC distributions become roughly Gaussian for long fragments, and their standard deviations decrease only slowly with increasing fragment length, unlike random sequences. This effect can be explained by 'long-range' correlations, often overlooked, that are present along isochores.
Assuntos
Composição de Bases , DNA/genética , Genoma , Animais , Centrifugação com Gradiente de Concentração , Césio , Cloretos , DNA/química , Sequência Rica em GC/genética , HumanosRESUMO
In a DNA sequence that exhibits long-range correlations, standard deviations among the GC levels of its segments can be up to an order of magnitude higher than in a sequence consisting of independent, identically distributed nucleotides. Conversely, plots of inter-segment standard deviations vs. segment length reveal quantitative information about the correlations present in a sequence. We present and discuss formulae that relate long-range (power-law) correlations between the nucleotides of a sequence to the expected standard deviations of the GC levels of its segments, and to the correlations between them.