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At least 667 records · Page 37Linked to original sources
PubMed2002

Perturbed turnover of microtubule-based nutritive tubes in ovarioles of virgin and precocene-treated Dysdercus fasciatus.

During early oogenesis in Dysdercus fasciatus, anteriorly positioned nurse cells supply each oocyte with mRNA, ribosomes, and proteins via a microtubule-rich nutritive tube that lengthens as the oocyte is displaced backwards down an ovariole. Nurse cell-dependent development of an oocyte continues until the latter reaches a particular stage of oogenesis after which the nutritive tube supplying it becomes redundant and breaks down. The signal for nutritive tube breakdown is believed to derive from the oocyte, and to be developmental stage-specific. To explore this, nutritive tube turnover has been investigated following the experimental inhibition of oocyte maturation both by the prevention of mating, and also the topical application of precocene II. In each case, the nutritive tubes with their component microtubules continued to extend and failed to show normal tube redundancy, typified by microtubule rearrangement and then depolymerisation. This provided an in vivo demonstration that the dynamics of a large microtubule aggregate are influenced by the developmental state of the cytoplasm.

Animals↗
PubMed1988

Occupation: form and performance.

As used both in everyday language and in the literature of occupational therapy, occupation is an ambiguous term. This article defines occupation unambiguously as the relationship between two things: occupational form and occupational performance. Each occupational form has an objective nature independent of the individual engaged in the occupation; sociocultural as well as physical characteristics constitute each occupational form. Occupational performance, in turn, is the action elicited, guided, or structured by the preexisting occupational form. Although occupational form may be said to predict or explain occupational performance, the nature of occupation is not deterministic. A series of figures in the paper graphically depicts how the individual's interpretation of an occupational form (its meaning) depends on the individual's developmental structure, and how occupational performance depends on the individual's sense of purpose. The dynamics of occupation are such that occupational performance impacts on subsequent occupational forms and promotes adaptations in the individual's own developmental structure. The framework explained here can be applied to different levels of occupation, depending upon the unit of time used by the analyst. A table presents an extensive set of examples oriented to a specific occupation. Recommendations for future scholarly inquiry are made.

Adaptation, Psychological↗
PubMed2003

Population dynamics of male-killing and non-male-killing spiroplasmas in Drosophila melanogaster.

The endosymbiotic bacteria Spiroplasma spp. are vertically transmitted through female hosts and are known to cause selective death of male offspring in insects. One strain of spiroplasma, NSRO, causes male killing in Drosophila species, and a non-male-killing variant of NSRO, designated NSRO-A, has been isolated. It is not known why NSRO-A does not kill males. In an attempt to understand the mechanism of male killing, we investigated the population dynamics of NSRO and NSRO-A throughout the developmental course of the laboratory host Drosophila melanogaster by using a quantitative PCR technique. In the early development of the host insect, the titers of NSRO were significantly higher than those of NSRO-A at the first- and second-instar stages, whereas at the egg, third-instar, and pupal stages, the titers of the two spiroplasmas were almost the same. Upon adult emergence, the titers of the two spiroplasmas were similar, around 2 x 10(8) dnaA copy equivalents. However, throughout host aging, the two spiroplasmas showed strikingly different population growth patterns. The titers of NSRO increased exponentially for 3 weeks, attained a peak value of around 4 x 10(9) dnaA copy equivalents per insect, and then decreased. In contrast, the titers of NSRO-A were almost constant throughout the adult portion of the life cycle. In adult females, consequently, the titer of NSRO was significantly higher than the titer of NSRO-A except for a short period just after emergence. Although infection of adult females with NSRO resulted in almost 100% male killing, production of some male offspring was observed within 4 days after emergence when the titers of NSRO were as low as those of NSRO-A. Based on these results, we proposed a threshold density hypothesis for the expression of male killing caused by the spiroplasma. The extents of the bottleneck in the vertical transmission through host generations were estimated to be 5 x 10(-5) for NSRO and 3 x 10(-4) for NSRO-A.

Animals↗
PubMed2003

Embryonic stem cell differentiation: a chromatin perspective.

Embryonic stem (ES) cells hold immense promise for the treatment of human degenerative disease. Because ES cells are pluripotent, they can be directed to differentiate into a number of alternative cell-types with potential therapeutic value. Such attempts at "rationally-directed ES cell differentiation" constitute attempts to recapitulate aspects of normal development in vitro. All differentiated cells retain identical DNA content, yet gene expression varies widely from cell-type to cell-type. Therefore, a potent epigenetic system has evolved to coordinate and maintain tissue-specific patterns of gene expression. Recent advances show that mechanisms that govern epigenetic regulation of gene expression are rooted in the details of chromatin dynamics. As embryonic cells differentiate, certain genes are activated while others are silenced. These activation and silencing events are exquisitely coordinated with the allocation of cell lineages. Remodeling of the chromatin of developmentally-regulated genes occurs in conjunction with lineage commitment. Oocytes, early embryos, and ES cells contain potent chromatin-remodeling activities, an observation that suggests that chromatin dynamics may be especially important for early lineage decisions. Chromatin dynamics are also involved in the differentiation of adult stem cells, where the assembly of specialized chromatin upon tissue-specific genes has been studied in fine detail. The next few years will likely yield striking advances in the understanding of stem cell differentiation and developmental biology from the perspective of chromatin dynamics.

Animals↗
PubMed2001

Development of bimanual skill: the search for stable patterns of coordination.

In 2 experiments, dynamic systems theory predictions concerning intrinsic dynamics and variability of bimanual coordination were examined at different developmental stages. In Experiment 1, ten 4-, 6-, 7-, 8-, and 10-year-old children and adults performed unimanual dominant, unimanual nondominant, and bimanual continuous circle drawing. All tasks were performed at the participants' preferred rate, size, and mode of coordination. The 4-, 6-, and 7-year-old children produced larger circles with longer durations than those of the 8- and 10-year-olds and the adults. That finding demonstrates that younger children display different intrinsic dynamics than older children and adults. The 4-, 6-, and 7-year-old children also displayed more variability in bimanual coordination (more time in less stable patterns of coordination, higher standard deviation in relative phase) and produced more transitions between coordination patterns than the 8- and 10-year-olds and the adults. In Experiment 2, the same participants performed bimanual circles at increasing rates. Consistent with predictions of the HKB model (H. Haken, J. A. S. Kelso, & H. Bunz, 1985), the number of transitions decreased as speed increased. Some support was found for the notion that age-related variables of attention and rate contribute to the increased variability in young children's bimanual coordination.

Adult↗
PubMed1988

Development of chorda tympani nerve taste responses in the hamster.

To determine whether changes in salt and sugar responses occur during development in the hamster, multifiber responses were recorded from the chorda tympani nerve while stimulating the anterior tongue of preweanling, early postweanling, and adult hamsters. Gustatory stimuli included 0.1 and 0.5 M solutions of NH4Cl, NaCl, LiCl, and KCl, and concentration series (0.01-1.0 M) of glucose, fructose, sucrose, maltose, lactose, and (0.0005-0.01 M) saccharin. Dramatic alterations in hamster peripheral gustatory sensitivities occurred with age, with the direction and magnitude of change dependent on the specific stimulus. Response magnitudes to 0.1 M solutions of NaCl and LiCl decreased with age compared to the NH4Cl response, whereas responses to all other salt stimuli remained constant during development. Responses to all sugars and saccharin compared to the NH4Cl response increased during development across a large concentration range; however, the age at which mature responses were achieved depended on the specific "sweet" stimulus. Whereas these findings demonstrate that the hamster peripheral gustatory system is dynamic during postnatal development, the hamster has a unique developmental pattern of salt taste development compared to other species. Specifically, the effectiveness of NaCl and LiCl decrease during development compared to NH4Cl in the hamster, but increase dramatically in the rat and sheep. Thus, the developmental patterns are opposite in direction for the hamster compared to the rat and sheep and may relate to the environmental pressures imposed upon each species.

Aging↗
PubMed1995

Axial rotation in rat embryos: morphological analysis and microsurgical study on the role of the allantois.

In mouse and rat embryos, the embryonic disc develops within a cup-shaped "egg cylinder" and consists of an inner layer of ectoderm and an outer layer of endoderm. Because of this configuration, the embryo first develops in a dorsally flexed position and then undergoes "axial rotation" to a ventrally flexed position. In the present study, we first analyzed the morphological process of axial rotation in rat embryos using novel reference axes set in the egg cylinder that remained invariant during the process. Our new perspective allowed us to demonstrate that the process consists of three movements which start at different stages of development: twisting of the upper body at stage 12/s7-8, twisting of the middle body at stage 13/s11-12, and twisting of the lower body (so called "tail") at stage 14/s15-16. Axial rotation is an interesting developmental event not only because it is such a dynamic process but also because it is one of the earliest morphological signs of body asymmetry. This asymmetry is strongly biased in that the tail almost always finishes up on the right side of the embryo for reasons that are still unknown. In the second part of the study, we performed microsurgical experiments to extend our previous finding that removal of the allantois results in random determination of tail sidedness. We demonstrated that an allantois transplanted from another embryo can prevent this abnormal sidedness in an embryos whose allantois had been removed and that transecting the allantois did not lead to abnormal tail sidedness. A possible explanation is that the allantois produces a chemical factor that controls tail sidedness.

Allantois↗
PubMed1996

Deletion of integrin alpha 1 by homologous recombination permits normal murine development but gives rise to a specific deficit in cell adhesion.

Integrin alpha 1 is a receptor for laminin and collagen which is expressed widely and dynamically in embryogenesis and has been implicated in various developmental processes including establishment of the placenta and formation of the central and peripheral nervous system. In the adult it is the sole collagen receptor in smooth muscle and liver and is thought to be important for the stability of these tissues. We have generated a null allele of the alpha 1 gene in the germline of mice by homologous recombination in embryonic stem cells. Mice homozygous for the mutation are viable and fertile and have no overt phenotype, demonstrating that the molecule is not required for development. Embryonic fibroblasts derived from mutant animals are unable to spread on or migrate into substrata of collagen IV and are deficient in spreading on and migrating into laminin. Further in vitro analysis of cell spreading and migration suggests that alpha 1 beta 1 is not required for binding to collagen I and implicates a third receptor, possibly integrin alpha 3 beta 1, in collagen I binding.

Alleles↗
PubMed1996

Eggshell assembly in Drosophila: processing and localization of vitelline membrane and chorion proteins.

The Drosophila eggshell consists of three major proteinaceous layers: the vitelline membrane, the inner chorionic layer, and the outer endochorion. During the latter stages of oogenesis, the proteins that comprise these layers are synthesized and secreted by epithelial follicle cells which surround the maturing oocyte. While there is considerable knowledge of the structural units which comprise the eggshell layers, there is little knowledge of how individual proteins function or interact with one another to form the structure. Immunoelectron microscopy was used to follow the distribution of four different eggshell proteins in the assembling and mature eggshell. sV23 and sV17, follicle cell proteins synthesized during the early stages of eggshell formation (stages 8-10), were distributed within the vitelline membrane layer at all stages. Despite marked temporal differences in their accumulation profiles, s36 and s18, putative chorion proteins, were similarly distributed throughout the floor, pillars, and roof of the endochorion. Although the vitelline membrane appears to be morphologically complete by stage 11, developmental Western blots and immunolocalization data indicate that molecular dynamism persists within the layer throughout the subsequent choriogenic stages. During early chorion formation the vitelline membrane appears to act as a reservoir for chorion proteins since s36 was found predominantly in the vitelline membrane layer of stage 12 egg chambers. During the late choriogenic stages (13-14), both sV17 and sV23 are processed to smaller derivatives. Interactions between the eggshell layers were suggested by ultrastructural analysis of a sV23 protein null mutant which showed that the structural integrity of the outer chorion is dependent upon the presence of a vitelline membrane component.

Animals↗
PubMed1992

The role of the frontal lobes in the regulation of cognitive development.

Between the ages of 1.5 and 5 years, and again between the ages of 5 and 10 years, a sequence of changes takes place in children's behavior which indicates a fundamental reorganization of their attentional, executive, and self-reflexive processes. In the present article, these changes are summarized, and evidence is adduced to support the claims (1) that these changes are frontally mediated and (2) that the underlying mechanism that generates them is similar to the one that generates the changes in EEG coherence during the same time period. The psychological model that has been hypothesized to explain the cycles of cognitive development (Case, 1992) is then compared to the physiological model that has been proposed to explain cycles of EEG development (Thatcher, 1992). It is shown that the two models are complementary, both in the underlying developmental sequence that they postulate and in the recursive dynamic they propose for producing movement through this sequence. A number of implications and predictions are derived, which follow from the proposition that the two sets of changes are different manifestations of a common underlying process.

Attention↗
PubMed2025

A mouse organoid platform for modeling cerebral cortex development and cis-regulatory evolution in vitro.

Natural selection has shaped the gene regulatory networks that orchestrate cortical development, leading to structural and functional variation across mammals, but the molecular and cellular mechanisms underpinning these changes have only begun to be characterized. Here, we develop a reproducible protocol for cerebral cortex organoid generation from mouse epiblast stem cells (EpiSCs), which recapitulates the timing and cellular differentiation programs of the embryonic cortex. We generated cortical organoids from F1 hybrid EpiSCs derived from crosses between laboratory mice (C57BL/6J) and four wild-derived inbred strains spanning ∼1 M years of evolutionary divergence to comprehensively map cis-acting transcriptional regulatory variation across developing cortical cell types, using single-cell RNA sequencing (scRNA-seq). We identify hundreds of genes that exhibit dynamic allelic imbalances, providing the first insight into the developmental mechanisms underpinning changes in cortical structure and function between subspecies. These experimental methods and cellular resources represent a powerful platform for investigating gene regulation in the developing cerebral cortex.

Organoids↗
PubMed2006

Chemotactic cell movement during Dictyostelium development and gastrulation.

Many developmental processes involve chemotactic cell movement up or down dynamic chemical gradients. Studies of the molecular mechanisms of chemotactic movement of Dictyostelium amoebae up cAMP gradients highlight the importance of PIP3 signaling in the control of cAMP-dependent actin polymerization, which drives the protrusion of lamellipodia and filopodia at the leading edge of the cell, but also emphasize the need for myosin thick filament assembly and motor activation for the contraction of the back of the cell. These process become even more important during the multicellular stages of development, when propagating waves of cAMP coordinate the chemotactic movement of tens of thousands of cells, resulting in multicellular morphogenesis. Recent experiments show that chemotaxis, especially in response to members of the FGF, PDGF and VEGF families of growth factors, plays a key role in the guidance of mesoderm cells during gastrulation in chick, mouse and frog embryos. The molecular mechanisms of signal detection and signaling to the actin-myosin cytoskeleton remain to be elucidated.

Animals↗
PubMed2004

Small is beautiful: what flies tell us about ERM protein function in development.

Actin dynamics is recognized as being a determinant in many developmental processes and pathologies, such as cell polarity, morphogenesis and tumour metastasis. However, how actin interacts with the plasma membrane is poorly understood. Although numerous studies in cell culture point to the crucial role of Ezrin, Radixin and Moesin (ERM) proteins in the actin-membrane link, genetic approaches in mice have not yet revealed their activity during development. Drosophila has recently become an alternative and promising system for the genetic study of ERM protein function. This article focuses on advances made in flies, providing evidence for the evolutionary conservation of functional properties of ERM proteins, in addition to shedding new light on their importance for development.

Actins↗
PubMedDate not supplied

Pediatric adherence as a multidimensional and dynamic construct, involving a triadic partnership.

OBJECTIVE: The aim of this paper is to integrate and draw attention to research findings that support our conceptualization of adherence as being multidimensional, dynamic, and involving a triadic partnership. METHODS: A review of relevant articles found in Medline, PsychLit, and reference lists provided in pertinent articles was performed. RESULTS: Significant progress has been made in identifying disease-related and psychosocial correlates of pediatric adherence and in developing intervention programs to promote adherence. Both lines of work have proceeded without a unifying framework for conceptualizing and measuring pediatric adherence. We offer a model that views adherence as comprising three defining aspects: (a) multidimensional, in support of the complexity and interrelatedness of treatment components, (b) a triadic partnership, as in mutually influential exchanges within and among the caregiver-medical team, child-medical team, and caregiver-child relationships, and (c) dynamic in relation to the notion of changes in developmental adaptive capacity, contextual characteristics, and disease course. CONCLUSIONS: Much work has yet to be done to validate, refine, and extend our model of adherence. Recommendations are offered for assessing each defining aspect, and a group-based methodology that accommodates longitudinal, prospective data is described.

Caregivers↗
PubMed2004

Conceptual models to understand tissue stem cell organization.

PURPOSE OF REVIEW: Theoretic and, in particular, mathematic models can help biologists to select and design experiments, to highlight general principles, to discriminate similar and to link different phenomena, and to predict novel features. Specifically, they contribute to an understanding of latent mechanisms and crucial parameters of biologic processes. The following review gives an overview of recent developments in the field of hematopoietic tissue stem cell modeling. RECENT FINDINGS: A number of experimental findings on heterogeneity, flexibility, and plasticity of hematopoietic and other tissue stem cells are challenging the classic stem cell concept of a predefined intrinsic stem cell program. Self-organizing systems provide a more elegant and comprehensive alternative to explain experimental data. SUMMARY: Within the last few decades, modeling approaches in stem cell biology have evolved and now encompass a broad spectrum of phenomena, ranging from the cellular level to the tissue level. The application of theoretic models is currently suggesting that we abandon the classic assumption of a strict developmental hierarchy and understand stem cell organization as a dynamic, functional process. Such a perspective has implications for a prospective characterization of tissue stem cells (eg, regarding gene expression profiles and genetic regulation patterns).

Animals↗
PubMed2001

Vowel perception by adults and children with normal language and specific language impairment: based on steady states or transitions?

The current investigation studied whether adults, children with normally developing language aged 4-5 years, and children with specific language impairment, aged 5-6 years identified vowels on the basis of steady-state or transitional formant frequencies. Four types of synthetic tokens, created with a female voice, served as stimuli: (1) steady-state centers for the vowels [i] and [ae]; (2) voweless tokens with transitions appropriate for [bib] and [baeb]; (3) "congruent" tokens that combined the first two types of stimuli into [bib] and [baeb]; and (4) "conflicting" tokens that combined the transitions from [bib] with the vowel from [baeb] and vice versa. Results showed that children with language impairment identified the [i] vowel more poorly than other subjects for both the voweless and congruent tokens. Overall, children identified vowels most accurately in steady-state centers and congruent stimuli (ranging between 94%-96%). They identified the vowels on the basis of transitions only from "voweless" tokens with 89% and 83.5% accuracy for the normally developing and language impaired groups, respectively. Children with normally developing language used steady-state cues to identify vowels in 87% of the conflicting stimuli, whereas children with language impairment did so for 79% of the stimuli. Adults were equally accurate for voweless, steady-state, and congruent tokens (ranging between 99% to 100% accuracy) and used both steady-state and transition cues for vowel identification. Results suggest that most listeners prefer the steady state for vowel identification but are capable of using the onglide/offglide transitions for vowel identification. Results were discussed with regard to Nittrouer's developmental weighting shift hypothesis and Strange and Jenkin's dynamic specification theory.

Adult↗
PubMed2000

Initial and cyclic recruitment of ovarian follicles.

Mammalian ovaries consist of follicles as basic functional units. The total number of ovarian follicles is determined early in life, and the depletion of this pool leads to reproductive senescence. Each follicle develops to either ovulate or, more likely, to undergo degeneration. The dynamics of ovarian follicle development have interested endocrinologists and developmental biologists for many years. With the advent of assisted reproductive techniques in humans, the possibility of regulating follicle development in vivo and in vitro has gained clinical relevance. In this review, we focus upon key branching points during the development of ovarian follicles as well as factors involved in determining the eventual destiny of individual follicles. We discuss inconsistencies in the literature regarding the definitions of follicle recruitment and selection and propose to name the two major steps of follicle development as initial and cyclic recruitment, respectively. Because some of these disparities have arisen due to differences in the animal systems studied, we also compare the development of the ovarian follicles of both humans and rats. We also review the status of knowledge of several puzzling clinical issues that may provide important clues toward unlocking the mechanisms of follicle development.

Aging↗