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Results for “developmental timing”

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At least 235 records · Page 13Linked to original sources
PubMed1998

Role of PKA in the timing of developmental events in Dictyostelium cells.

The cyclic AMP (cAMP)-dependent protein kinase, PKA, is dispensable for growth of Dictyostelium cells but plays a variety of crucial roles in development. The catalytic subunit of PKA is inhibited when associated with its regulatory subunit but is activated when cAMP binds to the regulatory subunit. Deletion of pkaR or overexpression of the gene encoding the catalytic subunit, pkaC, results in constitutive activity. Development is independent of cAMP in strains carrying these genetic alterations and proceeds rapidly to the formation of both spores and stalk cells. However, morphogenesis is aberrant in these mutants. In the wild type, PKA activity functions in a circuit that can spontaneously generate pulses of cAMP necessary for long-range aggregation. It is also essential for transcriptional activation of both prespore and prestalk genes during the slug stage. During culmination, PKA functions in both prespore and prestalk cells to regulate the relative timing of terminal differentiation. A positive feedback loop results in the rapid release of a signal peptide, SDF-2, when prestalk cells are exposed to low levels of SDF-2. The signal transduction pathway that mediates the response to SDF-2 in both prestalk and prespore cells involves the two-component system of DhkA and RegA. When the cAMP phosphodiesterase RegA is inhibited, cAMP accumulates and activates PKA, leading to vacuolation of stalk cells and encapsulation of spores. These studies indicate that multiple inputs regulate PKA activity to control the relative timing of differentiations in Dictyostelium.

Animals↗
PubMed2004

Control of sawtoothed grain beetles (Coleoptera: Silvanidae) in stored oats by using an entomopathogenic fungus in conjunction with seed resistance.

We tested the hypothesis that the entomopathogenic fungus Beauveria bassiana would be more efficacious on oat cultivars that prolonged the immature developmental period of sawtoothed grain beetle, Oryzaephilus surinamensis (L.), a storage pest. However, percentage of reduction in progeny production was similar on whole 'Don' and 'Paul' oats treated with fungus, even though immature developmental time was longer on whole 'Don' than on 'Paul' oats. In our initial test at 10 mg of conidia per kilogram of oats, the number of beetle progeny produced was reduced by 38-67% in whole oats, and there was no effect of the fungus on insects developing on cracked oats. Therefore, we conducted two dose-response studies that showed that adding 150 mg of conidia per kilogram to cracked or whole 'Paul' oats resulted in a 70 and 98% reduction, respectively, in number of progeny produced. No further reduction was obtained by adding 200 mg of conidia per kilogram of cracked or whole 'Paul' oats. Presence of the fungus did not affect developmental time in any of our tests. A previous study showed that cleaned oats should limit insect population growth to allow long-term storage of oats without insect damage. However, the current study shows that if the oats are not cleaned, and not cleaning oats is the normal storage practice, then B. bassiana could be used to help control sawtoothed grain beetles.

Animals↗
PubMed2000

Virulence variability of the Drosophila C virus and effects of the microparasite on demographic parameters of the host (Drosophila melanogaster).

We carried out experiments with the Drosophila C virus (DCV), a nonhereditary virus acting on demographic parameters of infected Drosophila host populations. It is well known that DCV increases mortality rate, decreases developmental time, and increases daily fecundity. As usual for Drosophila viruses, the DCV was multiplied in vivo. In this study we tested the hypothesis of virulence variability in DCV strains by isolating different stocks of the virus. The flies were tested for susceptibility to injection of such isolates and for virulence variability. Possible interactions between demographic parameters in three Drosophila host populations and injected isolates were studied under two egg densities (low and high). The hypothesis of virulence variability of DCV was supported by significant differences in mortality rates, depending on whether virus isolates were ingested or injected. When DCV was ingested, differences between host mortality rates were independent of the Drosophila host populations. Nevertheless, the developmental time was equally decreased by each virus isolate, independent of the host population. Moreover, the two viral stocks strongly increased the egg production of the flies. This experimental approach clearly showed that DCV could be considered a polymorphic virus. The phenotypic interactions between DCV and host flies varied according to parasite genotype.

Animals↗
PubMed2003

Conservation of the heterochronic regulator Lin-28, its developmental expression and microRNA complementary sites.

The heterochronic gene lin-28 is a regulator of developmental timing in the nematode Caenorhabditis elegans. It must be expressed in the first larval stage and downregulated by the second stage for normal development. This downregulation is mediated in part by lin-4, a 21-nt microRNA. If downregulation fails due to a mutation in a short sequence in the lin-28 3' UTR that is complementary to lin-4, then a variety of somatic cell lineages fail to progress normally in development. Here, we report that Lin-28 homologues exist in diverse animals, including Drosophila, Xenopus, mouse, and human. These homologues are characterized by the LIN-28 protein's unusual pairing of RNA-binding motifs: a cold shock domain (CSD) and a pair of retroviral-type CCHC zinc knuckles. Conservation of LIN-28 proteins shows them to be distinct from the other conserved family of CSD-containing proteins of animals, the Y-box proteins. Importantly, the LIN-28 proteins of Drosophila, Xenopus, and mouse each appear to be expressed and downregulated during development, consistent with a conserved role for this regulator of developmental timing. In addition, the extremely long 3' UTRs of mouse and human Lin-28 genes show extensive regions of sequence identity that contain sites complementary to the mammalian homologues of C. elegans lin-4 and let-7 microRNAs, suggesting that microRNA regulation is a conserved feature of the Lin-28 gene in diverse animals.

3' Untranslated Regions↗
PubMed1998

Time out: developmental regulation of heterochromatic silencing in Drosophila.

Transcriptional silencing by heterochromatin represents a model for developmental gene silencing. Current models of heterochromatin envision DNA-protein complexes that prevent access by euchromatic transcription factors. Here, we summarize the evidence that heterochromatin acts at the chromatin level to silence genes and the status of current models of heterochromatin silencing, and we highlight some recent progress in understanding the composition and regulation of heterochromatin in Drosophila.

Animals↗
PubMed2006

Casein kinases I of the silkworm, Bombyx mori: their possible roles in circadian timing and developmental determination.

Doubletime (DBT), a homolog of casein kinase Iepsilon (CKIepsilon), is an essential circadian clock component and developmental regulator in Drosophila melanogaster. The authors cloned a dbt homolog from the silkworm, Bombyx mori(Bmdbt), and examined its spatial and temporal expression in comparison to a CKI[alpha] homolog (BmCKIalpha). Four Bmdbt splice variants and 2 BmCKIalpha splice variants were detected, and their expression patterns varied in different tissues. The level of Bmdbt transcript in the brain was constant under LD 12:12 while those of BmCKIalpha transcripts fluctuated with a decrease at ZT12. In situ hybridization showed presumably identical distribution of dbt, CKIalpha, and per transcripts in the putative clock neurons of the head ganglia, as well as in the retina, where CKI-and PER-like immunoreactivities were colocalized, suggesting a possible involvement of both CKIs in the B. mori circadian system. Signals were detected at 4 Ia(1) neurons in each dorsolateral protocerebrum, 6 to 8 cells in the pars intercerebralis, about 6 cells in the suboesophageal ganglion, 2 neurons in the frontal ganglion, and most of the photoreceptors. All these cells contained dbt, CKIalpha, and per antisense transcripts. The Northern analysis of dbtand CKIalpha transcripts at different developmental stages showed that both genes were expressed at relatively high levels during early embryogenesis and in the ovary. The levels of CKIalpha transcripts were also high in the late larval stages until the mid-fifth instar and then suddenly disappeared before larval-pupal ecdysis. In contrast, the transcriptional activity of both genes was low in diapausing eggs.

Alternative Splicing↗
PubMed2006

[Development of auditory-visual spatial integration using saccadic response time as the index].

We measured saccadic response time (SRT) to investigate developmental changes related to spatially aligned or misaligned auditory and visual stimuli responses. We exposed 4-, 5-, and 11-month-old infants to ipsilateral or contralateral auditory-visual stimuli and monitored their eye movements using an electro-oculographic (EOG) system. The SRT analyses revealed four main results. First, saccades were triggered by visual stimuli but not always triggered by auditory stimuli. Second, SRTs became shorter as the children grew older. Third, SRTs for the ipsilateral and visual-only conditions were the same in all infants. Fourth, SRTs for the contralateral condition were longer than for the ipsilateral and visual-only conditions in 11-month-old infants but were the same for all three conditions in 4- and 5-month-old infants. These findings suggest that infants acquire the function of auditory-visual spatial integration underlying saccadic eye movement between the ages of 5 and 11 months. The dependency of SRTs on the spatial configuration of auditory and visual stimuli can be explained by cortical control of the superior colliculus. Our finding of no differences in SRTs between the ipsilateral and visual-only conditions suggests that there are multiple pathways for controlling the superior colliculus and that these pathways have different developmental time courses.

Acoustic Stimulation↗
PubMed2004

A general rule for the dependence of developmental rate on temperature in ectothermic animals.

In animals that do not regulate their body temperature by the production of heat, the proportion of the total developmental time spent in a particular developmental stage does not change with temperature. In the quasi-linear region of the relationship between developmental rate and temperature, all of the developmental stages appear to have the same species-specific lower developmental threshold. This trait, which is called developmental isomorphy, constrains developmental adaptations of ectotherms to their environments and facilitates the precise timing of life-history events.

Amphibians↗
PubMed1986

Hormones in perinatal rat and spiny mouse: relation to altricial and precocial timing of birth.

Rat (Rattus norvegicus) and spiny mouse (Acomys cahirinus) are closely related murine species that, due to their altricial (rat) and precocial (spiny mouse) modes of development, differ in the developmental timing of birth. A comparison between the developmental profiles of plasma glucagon, insulin, thyroxine, triiodothyronine, and glucocorticosteroid hormone was carried out to elucidate the question to what extent these hormonal profiles were related to the timing of birth. Although corticosterone is the major circulating glucocorticosteroid in rat, only cortisol was found in the spiny mouse. The onset of increases in glucocorticosteroid and thyroid hormone levels occurred at the same developmental time points in both species. A neonatal increase in triiodothyronine levels was observed in the spiny mouse only. In both species the immediate perinatal period was characterized by decreases in the ratio of insulin and glucagon levels and the level of glucocorticosteroids. The observed developmental patterns of hormonal levels were found to be consistent with the observed developmental pattern of enzymic maturation in the respiratory and gastrointestinal tract, which play a critical role in the adaptation to the extrauterine environment.

Animals↗
PubMed2006

Psychiatric disorders among foreign-born and US-born Asian-Americans in a US national survey.

BACKGROUND: Among Hispanics, Non-Hispanic Whites and Non-Hispanic Blacks studies have found lower risk for psychiatric disorders among the foreign-born than among the US-born. We examine the association of nativity and risk for psychiatric disorder in a national sample of the Asian-American (AA) population. METHODS: Data on 1,236 AAs from the National Epidemiological Survey of Alcohol and Related Conditions (NESARC) are analyzed using logistic regression and discrete time survival models to specify differences between the foreign-born and US-born in the lifetime occurrence of mood, anxiety and substance use disorders. RESULTS: Foreign-born AAs had significantly lower risk for all classes of disorder compared with US-born AAs (OR = 0.16-0.59). Risk for all classes of disorder was lowest for those foreign-born AAs who arrived in the US as adults. Among foreign-born AAs risk of first onset was lowest relative to the US-born in years prior to their arrival in the US and tended to rise to levels equal to that of the US-born with longer duration of residence in the US. CONCLUSIONS: Among AAs, risk for psychiatric disorders is lower among the foreign-born than among the US-born. The pattern of change in risk over time suggests that both the developmental timing and the duration of experience in the US contribute to increases in risk.

Adult↗
PubMed1987

Changing spatial patterns of DNA replication in the developing wing of Drosophila.

Using an antibody against bromodeoxyuridine we have analyzed the distribution of S-phase nuclei in the wing disc of Drosophila as the larval disc transforms into the adult wing during metamorphosis. On the basis of the timing of replication three cell populations can be distinguished: the cells of the presumptive wing margin, the precursor cells of the longitudinal veins, and those of the intervein regions. In each of these populations the cell cycle is first arrested and later resumes at a specific time, so that at each developmental time point a characteristic spatial pattern of S-phase nuclei is seen. An interpretation of these changing patterns in terms of vein formation, compartments, and neural development is offered.

Animals↗
PubMed1995

Identification of a sequence-specific single-stranded DNA binding protein that suppresses transcription of the mouse myelin basic protein gene.

The myelin basic protein (MBP) gene is expressed only in oligodendrocytes and Schwann cells, and expression follows a tightly regulated developmental time course. Cell type- and developmental stage-specific expression of the MBP gene appears to be regulated by a series of cis-acting elements located upstream of the transcription start site. The proximal element of the MBP regulatory region (MB1), located between nucleotides -14 and -50, is one of several elements participating in the programmed expression of MBP. In this report, we describe the molecular cloning and characterization of myelin gene expression factor-2 (Myef-2), a protein isolated from mouse brain that binds specifically to single-stranded DNA derived from the MB1 element and represses transcription of the MBP gene in transient transfection assay. Myef-2 mRNA is developmentally regulated in mouse brain; its peak expression occurs at postnatal day 7, prior to the onset of MBP expression. The developmental pattern of Myef-2 mRNA expression coincides with that previously described for SCIP, a POU domain transcription factor that also represses myelin basic protein expression. The myef-2 gene maps to mouse chromosome 2. The relevance of these findings for regulation of MBP gene expression and oligodendrocyte differentiation is discussed.

Aging↗
PubMed1999

Distinct synaptic and extrasynaptic NMDA receptors in developing cerebellar granule neurons.

In rat cerebellar granule neurons, mRNA and protein levels of the NR2A and NR2C subunits of the NMDA receptor increase during the second postnatal week. At this time, mRNA and protein levels of the NR2B subunit begin to fall. To investigate targeting of NMDA receptor subunits, we performed whole-cell recordings from rat cerebellar granule neurons at different times during development and investigated the pharmacological and biophysical properties of mossy fiber-evoked NMDA EPSCs. Isolated NMDA EPSCs from newly formed synapses in the first postnatal week exhibited partial block by the NR2B subunit-specific antagonist (1S, 2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP 101,606). By the end of the second postnatal week, NMDA EPSCs were virtually unaffected by the NR2B antagonist. In parallel, NMDA EPSC decay times decreased over a similar developmental time course. We compared properties of synaptic NMDA receptors with extrasynaptic receptors that are present on the cell body with rapid application of glutamate to excised nucleated patches. Deactivation of patch responses accelerated with development and closely resembled evoked NMDA EPSCs in rats of the same age. However, patch responses were highly sensitive to CP 101,606 through the second postnatal week, and sensitivity was seen in some neurons up to the fourth postnatal week. Spermine potentiated peak NMDA patch responses from postnatal days 10-14 rats but had little effect on evoked NMDA EPSCs. Our data suggest selective targeting of a distinct NMDA receptor subtype to synaptic receptor populations in cerebellar granule neurons. Later in development, similar changes occur in the extrasynaptic receptor population.

Aging↗
PubMed1995

Developmental expression of elements of hepatic cholesterol metabolism in the rat.

The expression of several key enzymes and receptors of rat hepatic cholesterol metabolism was studied during development. Among major findings were: acyl coenzyme A:cholesterol acyltransferase, the cholesteryl ester hydrolases, cholesterol-7 alpha-hydroxylase and the alpha 2-macroglobulin receptor (LRP) were very low in fetal livers, but all were induced shortly before birth, suggesting that these elements are important for extrauterine life. Although the other elements continued to increase, by day 6 of postnatal life, cholesterol-7 alpha-hydroxylase had reached undetectable levels. It reappeared by day 12 of suckling, placing it in the group of late-appearing activities necessary for the fully mature hepatic phenotype. Changes in acyl coenzyme A:cholesterol acyltransferase activity appeared due predominantly to changes in amount of active protein. The cholesteryl ester hydrolase (CEH) activities all showed different developmental patterns, suggesting that each was a unique activity. The bile salt-dependent CEH activity was much higher in the suckling period than in the adult where it was almost undetectable, suggesting that this CEH may have its major importance in the suckling period of development. Low density lipoprotein receptors exhibited a pattern very different from that of the alpha 2-macroglobulin receptors and did not show consistent correlation with any other elements. At some developmental time points, the relationships amongst the elements differed significantly from the adult pattern. These studies provide for the first time an integrated picture of developmental expression of key elements of hepatic cholesterol metabolism and set the stage for further studies on their modes of regulation.

Animals↗
PubMedDate not supplied

The dynamic gene expression from different genetic systems for protein and lysine contents of indica rice.

The dynamic expression of genes for protein and lysine contents of rice grain under different environments was carried out with time-dependent measures by using the developmental genetic models for quantitative traits of triploid endosperm in cereal crops. The results showed that the genetic effects, especially genotype x environment (GE) interaction effects from the genes expression of different genetic systems including triploid endosperm, cytoplasm and diploid maternal plant were important for the performance of both nutrient quality traits at all developmental times/stages of rice grain. The conditional genetic variance analysis found that the activation of quantitative genes especially from endosperm and maternal plant genetic systems for protein and lysine contents was gradually carried through the developmental process of rice grain. The net genetic effects showed that the new expression of quantitative genes for protein and lysine contents was more active at late filling stage (15-21 days after flowering) and maturity stage (22-28 days) of rice grain. Also the sequential expression of cytoplasmic genes cannot be ignorable for the development of nutrient quality traits. The phenomena that some genes could continuously express for several developmental stages or the genes expression could be interrupted among developmental stages of rice grain was detected especially for net endosperm additive main effects or maternal additive main effects. The differences of genetic relationships from different genetic systems were found for protein and lysine contents among developmental times of rice grain.

Diploidy↗
PubMed1999

Differential changes in the subcellular distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate and N-methyl-D-aspartate receptors in neonate and adult rat cortex.

We compared the distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors and their individual subunits in synaptosomal and microsomal fractions prepared from 2-day-old (P2) and adult rat cortex. In P2 cortex more [3H]-(S)-fluorowillardiine ([3H]FW) binding to AMPA receptors was in the intracellular microsomal fraction than in the synaptosomal fraction whereas in adult rats the reverse was observed. Immunoblots with GluR1, GluR2/3, GluR4 and pan-AMPA antibodies showed the same profile. In contrast, the majority of [3H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor and NR1 subunit immunoreactivity was present in the synaptosomal fraction at both developmental time points. These results suggest a developmental rearrangement of the distribution of AMPA receptors within neurons, a process which is likely to be important in synaptic stabilization and plasticity.

Aging↗
PubMed2003

Role of microRNAs in plant and animal development.

Small RNAs, including microRNAs (miRNAs) and short interfering RNAs (siRNAs), are key components of an evolutionarily conserved system of RNA-based gene regulation in eukaryotes. They are involved in many molecular interactions, including defense against viruses and regulation of gene expression during development. miRNAs interfere with expression of messenger RNAs encoding factors that control developmental timing, stem cell maintenance, and other developmental and physiological processes in plants and animals. miRNAs are negative regulators that function as specificity determinants, or guides, within complexes that inhibit protein synthesis (animals) or promote degradation (plants) of mRNA targets.

Animals↗
PubMedDate not supplied

Gearing balint group leadership to resident professional development.

This paper discusses the sequential phases of typical Balint training groups. The cases presented reflect the presenters' professional developmental time line and serve the participants' developmental needs: exploring professional boundaries and intragroup intimacy. The activities and issues arising in the meetings stem from these developmental needs and help the group members acquire specific skills. Knowing where the group members are in their professional development should help group leaders give a seminar its focus, decide on group membership, and recognize when a group is not developing appropriately.

Family Practice↗