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Results for “developmental timing”

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At least 127 records · Page 7Linked to original sources
PubMed1991

Developmental time course and ionic dependence of kainate-mediated toxicity in rat cerebellar granule cell cultures.

The mechanisms associated with the neurotoxic response caused by kainate (KA) were examined in cerebellar granule cell cultures. Under the conditions studied, millimolar concentrations of quisqualate, (RS)-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, glutamate and N-methyl-D-aspartate did not cause significant cytolysis. In contrast, KA induced complete cell death, which was antagonized by 6,7-dinitroquinoxaline-2,3-dione, quisqualate, (RS)-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and glutamate. This neurotoxic effect was dependent on the dose of KA and the age of the cultures. Two separate components of KA-induced neurotoxicity were observed and differentiated according to morphological changes, time of onset and ionic dependence. For acute neurotoxicity, release of lactate dehydrogenase measured after 30 min of KA exposure, became apparent between 8 and 11 days in culture and was dependent on both Cl- and Na+. However, vulnerability to acute toxicity did not correlate with [3H]KA receptor expression with receptor-mediated Cl- influx. On the other hand, delayed toxicity, as determined by lactate dehydrogenase release 24 hr after KA exposure, was dependent on Cl-. This delayed neurotoxicity induced by KA shares time course features with N-methyl-D-aspartate-mediated toxicity. Yet in contrast to studies reported for N-methyl-D-aspartate, glutamate was ineffective as an agonist, measured by its ability to elicit a neurotoxic response, and the KA delayed response did not appear to be dependent upon the presence of extracellular Ca++, during the exposure to KA.

Animals↗
PubMed1988

Developmental time and mortality of larvae of Triatoma infestans infected with Trypanosoma cruzi.

Triatoma infestans were infected with Trypanosoma cruzi (zymodeme 1) at the first feed after eclosion from the egg; interstadial development times and mortality rates were then recorded until the imaginal moult and compared with those of uninfected controls. No retardation of development occurred in infected bugs and their mean total mortality rate (9%) was only slightly higher than that (6%) of uninfected controls (due solely to 4 additional deaths). This is the first demonstration, under optimal and standardized rearing conditions, that infection of T. infestans with T. cruzi has little or no effect on development times or mortality rates.

Animals↗
PubMed1986

Assessment of developmental time periods and risks of brain damage in the fetus and neonate.

The life cycles of 18 infants with neurologic morbidity were divided into antepartum, intrapartum, neonatal and infant time periods. Specific events related to risks for each infant were assigned to these periods. In almost all the children multiple, rather than single, fetal, neonatal and infant risks were found, and along with the multiple risks, multiple time periods were found during which the risks occurred. It is difficult, and often impossible, to relate infant neurologic morbidity to a single event or time period.

Brain Damage, Chronic↗
PubMed1994

Hippocampal synaptogenesis in cell culture: developmental time course of synapse formation, calcium influx, and synaptic protein distribution.

The formation of chemical synapses between hippocampal neurons in primary cell culture was studied using electrophysiology, calcium imaging, and immunocytochemical approaches. Inhibitory and excitatory synapses formed within 12 d in cell culture (DIC) that were sensitive to the N-type calcium channel blocker omega-conotoxin GVIA (omega-CgTx). At 4 DIC, immature connections were present in which spontaneous, but rarely evoked, synaptic currents were detected. At both 4 and 12 DIC, the synaptic proteins rab3a, synapsin I, and synaptotagmin were present in hippocampal neurons, but the subcellular distribution changed from one in which immunoreactivity was initially distributed within soma and neurites to a punctate varicose appearance. Correlated with the transformation from immature to mature synaptic states was the onset of omega-CgTx-sensitive calcium influx. Taken together, these data suggest that the expression of functional omega-CgTx-sensitive calcium influx is temporally coincident with synapse formation, and that during the maturation of the synapse there is a redistribution of synaptic proteins.

Animals↗
PubMed1993

The importance of developmental timing in cortical specification.

Environmental control of gene expression can occur early or late during development, and this is relevant to understanding species differences in cortical specification. Experiments in the developing visual system of the primate show that the areal limits of striate cortex are specified by the thalamic inputs, so that afferent specification of cortex appears as a general feature of mammalian development. Primates differ from nonprimates in that thalamic afferents control very early stages of corticogenesis when symmetrical cell division is forming the pool of striate neuron precursors. Other cortical features are specified much later in primates than in nonprimates. We speculate that the early specification of certain features and the late specification of others contribute to the sophistication of the cerebral cortex characteristic of primates.

Afferent Pathways↗
PubMed2001

Life cycle of Ixodes pacificus (Acari: Ixodidae): timing of developmental processes under field and laboratory conditions.

The developmental timing of Ixodes pacficus Cooley & Kohls, the primary vector of the Lyme disease spirochete and the agent of human granulocytic ehrlichiosis in the far-western United States, was determined under field and laboratory conditions. During their seasonal peaks of abundance, each of the three parasitic stages of L. pacificus, both fed and unfed, was placed inside silk-screen packets. These packets were apportioned between four topographic exposures of two hilltop sites in northwestern California. The sites differed in vegetational composition and elevation: the first (elevation 390 m) was dominated by woodland-grass, the second (elevation 914 m) by chaparral. The timing of oviposition, larval eclosion, molting, and mortality were recorded in the field every 2-3 wk for 2.5 yr. Microenvironmental temperatures were measured on all four exposures at both sites. Accelerated developmental rates of all three stages were correlated with warmer soil temperatures and the time of placement in the field. In the laboratory, replete female I. pacificus maintained under uniform environmental conditions sustained constant preovipositional and prehatch periods independent of date-of-feeding. In the field, all unfed stages survived through one active feeding season with most larvae and nymphs remaining in behavioral diapause between late summer and early spring. No life stage survived through two active feeding periods which suggests that cohorts do not overlap. We concluded that I. pacificus takes a minimum of 3 yr to complete its life cycle in northwestern California.

Animals↗
PubMed2026

Heterokairic Genes and the Eco-Evo-Devo of Timing.

Concepts of developmental timing have traditionally been framed under heterochrony as evolved (genetically based) differences in timing, while environmentally induced shifts in timing within genotypes have been treated more loosely. In this article, heterokairy is presented as plasticity in the timing of developmental events, and the term "heterokairic genes" is proposed for environmentally modulated heterochronic genes that underlie this plasticity. Evidence from nematodes, insects, plants, and vertebrates is assembled, with emphasis placed on systems where environmental cues are relayed through endocrine or metabolic pathways to known timing modules/genes. On this basis, a distinction is drawn between validated heterokairic genes, supported by direct mechanistic data, and a broader set of candidates inferred from gene-environment interactions in developmental timing. The eco-evolutionary consequences of such genes are considered, and experimental and genomic strategies for their identification are outlined. It is argued that heterokairic genes provide a useful bridge between environmental variation, developmental mechanisms, and evolutionary change in timing.

Animals↗
PubMed2002

Analyzing developmental sequences within a phylogenetic framework.

Heterochrony is important as a potential mechanism of evolutionary change. However, the analysis of developmental timing data within a phylogenetic framework to identify important shifts has proven difficult. In particular, analytical problems with sequence (event) heterochrony revolve around the lack of an absolute time frame in development to allow standardization of timing data across species. An important breakthrough in this regard is the method of "event-pairing," which compares the relative timing of developmental events in a pairwise fashion. The resulting event-pair-encoded data can be mapped onto a phylogeny, which can provide important biological information. However, event-paired data are cumbersome to work with and lack a rigorous quantitative framework under which to analyze them. Critically, the otherwise advantageous relativity of event-pairing prevents an assessment of whether one or both events in a single event-pair have changed position during evolutionary history. Building on the method of event-pairing, we describe a protocol whereby event-pair transformations along a given branch are analyzed en bloc. Our method of "event-pair cracking" thereby allows developmental timing data to be analyzed quantitatively within a phylogenetic framework to infer key heterochronic shifts. We demonstrate the utility of event-pair cracking through a worked example and show how it provides a set of desired features identified by previous authors.

Animals↗
PubMed1997

Temporal pattern formation by heterochronic genes.

Heterochrony describes the phylogenetic variation in the relative timing of major developmental events. Such heterochronic variation has been noted across phylogeny, including closely related species, suggesting that particular genetic loci control global aspects of developmental timing, and that variation at those loci may play important roles in evolutionary change. Genetic analyses of heterochronic mutations in the nematode Caenorhabditis elegans reveal that control of temporal patterning is analogous to the dedicated genetic pathways that control the patterning of the spatial axes in Drosophila and other metazoans. These pathways generate graded or binary levels of regulatory factors that pattern particular axes of the developing animal. C. elegans heterochronic genes constitute a regulatory cascade that both generates a temporal decrease in the level of the LIN-14 and LIN-28 proteins and responds to the changes in these gene activities to coordinate the temporal sequence of many cell fates as the animal develops. The temporal regulation of lin-14 and lin-28 gene activities is posttranscriptional and mediated by the antisense RNA product of the lin-4 gene. Hormonal control of developmental timing is a common theme throughout phylogeny. Heterochronic genes that involve hormonal signaling have been identified in vertebrates as well as C. elegans.

Animals↗
PubMedDate not supplied

Effect of two solanaceous plants on developmental and population parameters of the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae).

Tuta absoluta (Meyrick) is an important tomato pest that also feeds on other host-plants from the Solanceae family. We studied the effect of two cultivated plants, tomato (Lycopersicum esculentum Mill.) and potato Solanum tuberosum L. on the development and populational parameters of T. absoluta related with host-plant suitability. Larval developmental time, pupal weight, mean fecundity and an index of host-plant quality (IPQ = pupal weight / frass weight) were estimated. Age-specific survivorship and fecundity life tables were constructed in the laboratory to evaluate the following populational parameters: net reproductive rate (Ro), intrinsic rate of increase (r) and generation time (T). Larval developmental time was shorter and pupal weight was higher (P < 0.0001) for larvae reared on tomato (P < 0.0001). Mean fecundity was not significantly different on both plants (P = 0.07) and food quality of host-plant was higher for tomato (P = 0.02). Mean population parameters on tomato were: Ro = 48.92; T = 27.98, r = 0.14; and on potato: Ro = 14.43; T = 32.35, r = 0.08. Although results showed that tomato was a more suitable host-plant and had a better nutritional quality than potato, when T. absoluta fed on potato the potential population increase requires attention. Under appropriate climatic conditions, spatial and temporal coincidence between crop and pest, T. absoluta could become a pest for the potato crop.

Animals↗
PubMed2002

Suitability of transgenic glyphosate-resistant soybeans to green cloverworm (Lepidoptera: Noctuidae).

Host plant suitability to green cloverworm, Hypena scabra (F.), was evaluated on two conventional soybean varieties (Stine 2499-0 and 2972-2) and two RoundUp Ready Soybeans (Stine 2506-4 and 2892-4) with and without exposure to glyphosate. No differences among treatments were detected on developmental time and survivorship. Developmental time from first instar to adult ranged from 24.7 to 25.5 d, and survivorship ranged from 86 to 96%. No sex bias was observed among treatments (proportion of females ranged from 0.41 to 0.50). Morphological differences were observed between sexes; males had a longer and wider thorax, longer wings, and longer body. Females had longer and wider abdomens. Although treatments did not affect size (calculated with principal component analyses), significant differences were observed between males and females. These results suggest that soybean genetic differences (between conventional varieties and analogous transgenic varieties) or plant stress (induced by glyphosate metabolization) do not affect the plant suitability to H. scabra.

Animals↗
PubMed1995

Developmental changes in intestinal glycosylation: nutrition-dependent multi-factor regulation of the fucosylation pathway at weaning time.

Developmental changes in the fucoglycoproteins of the intestinal brush-border membranes were determined by lectin affinoblotting after electrophoresis. Whereas only two alpha(1-6)-fucoglycoproteins were detected in brush-border membranes from suckling rats, a large number of N-fucoglycoproteins with alpha(1-2)- and/or alpha(1-6)-linked fucose residues were detected in rat membranes after weaning. Dietary manipulations at weaning time were used to investigate the effect of nutritional factors in the development of fucosylation in the small intestine of prolonged-nursed rats fed with milk (a high-fat, low-carbohydrate diet) compared to rats weaned normally with a standard high-carbohydrate diet. The fucose content of the mucosa glycoproteins was lower in 22-day-old prolonged-nursed rats than in 22-day-old rats weaned normally with the standard diet. The appearance of fucoglycoproteins in the brush-border membranes, which was delayed by prolonged nursing, was accompanied by a concomitant delay in the increase of intestinal fucosyl-transferase activity and in the decrease of GDP-fucose substrate breakdown. The developmental decrease in the activity of the inhibitory protein which regulates the fucosyl-transferase activity was also delayed by prolonged nursing. The intestinal fucosylation of brush-border membrane glycoproteins (which include many digestive enzymes) displayed ontogenic changes on which were superimposed dietary influences at the time of weaning. The complete maturation of the brush-border membrane glycoproteins, and particularly their terminal fucosylation, is a developmental event which thus seems to be strongly influenced by the manipulation of nutritional factors during the weaning period.

Animal Nutritional Physiological Phenomena↗
PubMedDate not supplied

Citric acid cycle: a mainstream metabolic pathway influencing life span in Drosophila melanogaster?

The role of the citric acid cycle enzyme NADP-dependent isocitrate dehydrogenase (IDH-NADP) and its allele product variants in resisting the oxidative agent paraquat, was analyzed among descendants of reciprocal crosses between fast developmental time short-lived individuals (F-) and slow developmental time long-lived ones (S+), in Drosophila melanogaster. Taking preadult developmental time into account, the data suggested that IDH-NADP differences in enzymatic activity between electrophoretically fast and slow allele product variants could play an important role in paraquat resistance and longevity, because individuals with slow developmental time bearing the fast electrophoretic variant of IDH-NADP ("fast" allele) were the most resistant. The fast electrophoretic variant of this enzyme is known to be the most active one and its activity is related to increased reduction of NADP to NADPH. This process could be very important for an effective balance between several pathways that use NADPH as precursor molecules and the oxidative stress defense system that uses it as an oxygen free radical reductor. We also reported a strong maternal effect on these traits, because survivors of a paraquat bioassay carrying cytoplasm inherited from slow developmental long-lived females (S+ cytoplasm) showed the highest frequency of the fast electrophoretical variant of IDH-NADP.

Alleles↗
PubMed1977

The development of children's understanding of cyclic aspects of time.

Developmental psychological approaches to the study of time have fallen into 3 categories: studies of time perception; studies of logical, reconstructive abilities; and studies of the understanding of conventional time systems. The present work examines problems spanning the latter 2 categories--the development of children's understanding of temporal cycles and the relationship between cyclic concepts and cognitive development. 62 children, ranging in age from 4 to 10 years, were administered Piagetian tests of classification and seriation and a variety of specially designed cyclic tasks. Results show major progress in the representation of cyclic order and recurrence during the age period examined. For a variety of particular cycles, order responses were shown before continuity responses. The ability to produce a correct order is related to seriation performance but not classification performance when the variance attributable to age is partialed out. Continuity responses appear to be unrelated to performance on either of the Piagetian tasks tested when age is controlled.

Age Factors↗
PubMed1977

Variation in the direction of selection applied by pentenol to the alcohol dehydrogenase locus in Drosophila melanogaster.

This paper describes selective effects of pentenol-impregnated media on six genotypes at the alcohol dehydrogenase (Adh) locus in D. melanogaster. In the laboratory population studied, developmental times of pre-adults homozygous for an alcohol dehydrogenase "null" allele increased with increasing pentenol concentrations. The developmental times of the other five genotypes, which produced active alcohol dehydrogenases, increased slightly at pentenol concentrations up to 0-0033%, but above this concentration they decreased markedly. In fact on 0-067% pentenol, the highest concentration tested, developmental times of these five genotypes were between 9 and 24 h less than their developmental times on media lacking pentenol. The magnitude of the reduction in developmental time differed significantly between genotypes and was positively correlated with alcohol dehydrogenase activity. Pentenol had toxic effects on adults and significant differences were found between survival percentages of adults of different genotypes on pentenol-impregnated media. These survival percentages were negatively correlated with alcohol dehydrogenase activities. Therefore selective differences between genotypes in adult survival were negatively correlated with those in developmental times. The variations in the direction of selection are discussed in terms of their possible biochemical basis and their effects on the maintenance of Adh polymorphisms.

Alcohol Oxidoreductases↗
PubMed1985

Perinatal development of the small intestine and pancreas in rat and spiny mouse. Its relation to altricial and precocial timing of birth.

Rat (Rattus norvegicus) and spiny mouse (Acomys cahirinus) are closely related species that mainly differ in the developmental timing of birth. A comparison between the developmental profiles of some characteristic enzymes of the small intestine (lactase and sucrase) and of the pancreas (amylase) of both species was carried out to elucidate the question to what extent these enzymic profiles and hence the maturation of these organs was related to the process of birth. It was found that these organ-specific enzymes become first detectable at the same developmental stage in both species. Likewise, the weaning phase of the enzymic profiles occurred at the same developmental time point in both species. It is argued that both the first appearance and the weaning increase in enzyme activity follow an inherent biological program that can only be modulated by hormones. In contrast, the perinatal phase of the enzymic profile is completely dependent on the developmental timing of birth, and therefore appears not to be anchored to a particular developmental time point but rather to be dependent on birth-associated (hormonal) adaptation. In accordance with this hypothesis it was found that the development of the microscopic anatomy of the small intestine proceeded independently of the functional adaptation of the intestine to the process of birth.

Animals↗
PubMed2006

The timing of developmental transitions in plants.

Plants rely heavily on environmental cues to control the timing of developmental transitions. We are beginning to better understand what determines the timing of two of these transitions, the switch from juvenile to adult vegetative development and the transition to flowering. In this review, we discuss how RNA silencing mechanisms may influence the juvenile-to-adult vegetative switch. We also describe the discovery and regulation of a component of "florigen," the mobile flowering promotion signal that is involved in the transition to flowering. Parallel themes are beginning to emerge from a molecular comparison of these two developmental transitions.

Biological Clocks↗