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Results for “developmental timing”

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PubMed2000

Syntrophin isoforms at the neuromuscular junction: developmental time course and differential localization.

The syntrophins are a family of cytoplasmic adapter proteins that associate with dystrophin family proteins and have putative signaling and structural roles at the neuromuscular junction. We have localized the syntrophin family members within the rodent junction from birth to adulthood. Alpha-syntrophin is the only isoform on the postsynaptic membrane at birth. In the adult, it occurs on the crests of the junctional folds, with utrophin, and in the troughs, with dystrophin. Surprisingly, neuronal nitric oxide synthase (nNOS) does not accompany alpha-syntrophin onto the crests. Beta2-syntrophin, a junction-specific form, is not present at birth and occurs mainly in the troughs in the adult. Beta1-syntrophin is a sarcolemmal form at birth, not concentrated at the junction, and disappears entirely from most fibers by 6 weeks. In positive fibers, junctional beta1-syntrophin occurs exclusively in the troughs. These results suggest that the syntrophin isoforms have distinct functions at the junction and show that the known protein-protein associations of the syntrophins and nNOS in skeletal muscle are not sufficient to explain their localizations.

Animals↗
PubMed2000

The development of Xenopus tropicalis transgenic lines and their use in studying lens developmental timing in living embryos.

The generation of reporter lines for observing lens differentiation in vivo demonstrates a new strategy for embryological manipulation and allows us to address a long-standing question concerning the timing of the onset of differentiation. Xenopus tropicalis was used to make GFP reporter lines with (gamma)1-crystallin promoter elements directing GFP expression within the early lens. X. tropicalis is a close relative of X. laevis that shares the same ease of tissue manipulation with the added benefits of a diploid genome and faster life cycle. The efficiency of the Xenopus transgenic technique was improved in order to generate greater numbers of normal, adult transgenic animals and to facilitate in vivo analysis of the crystallin promoter. This transgene is transmitted through the germline, providing an accurate and consistent way to monitor lens differentiation. This line permitted us to distinguish models for how the onset of differentiation is controlled: by a process intrinsic to differentiating tissue or one dependent on external cues. This experiment would not have been feasible without the sensitivity and accuracy provided by the in vivo reporter. We find that, in specified lens ectoderm transplanted from neural tube stage donors to younger neural-plate-stage hosts, the onset of differentiation, as measured by expression of the crystallin/GFP transgene, is delayed by an average of 4.4 hours. When specified lens ectoderm is explanted into culture, the delay was an average of 16.3 hours relative to control embryos. These data suggest that the onset of differentiation in specified ectoderm can be altered by the environment and imply that this onset is normally controlled by external cues rather than by an intrinsic mechanism.

Animals↗
PubMed1996

Behavioral deficits induced by bingelike exposure to alcohol in neonatal rats: importance of developmental timing and number of episodes.

The importance of the timing and number of episodes of bingelike alcohol exposure in neonatal rats on subsequent behavioral outcomes was evaluated with a parallel bar task and a spatial conditional alternation task. Different groups of Sprague-Dawley rat pups were exposed to alcohol delivered via artificial rearing procedures either on postnatal Days (PD) 4 and 5, on PD 8 and 9, or on both PD 4/5 and 8/9 (Combined), producing daily peak blood alcohol concentrations around 400 mg/dl. Controls included an artificially reared group and a normally reared group. Exposure during PD 4/5 produced significantly more severe motor deficits and significantly more severe reductions in cerebellar and brainstem weights than did exposure on PD 8/9. Combined exposure produced greater deficits on these measures than either of the limited exposures. Significant deficits in the acquisition rates for conditional alternation were found only with the Combined exposure, although both the PD 8/9 and Combined groups committed significantly more within-trial errors. All three alcohol treatments produced significant and comparable reductions in forebrain weight. The type and severity of behavioral and neural deficits induced by neonatal bingelike alcohol exposure depend on the timing and number of exposures.

Alcoholic Intoxication↗
PubMed1988

An analysis of developmental timing in Blastocladiella emersonii sporulation.

We propose a model of time regulation for the expression of the Blastocladiella emersonii sporulation phenotypes based on new methods (Soll, 1986) which analyse the effect of temperature on the rate limiting processes, i.e., "timers" of certain events during development. By using reciprocal shift experiments (transferring sporulating cells from 22 to 27 degrees C and vice versa) we characterized the timers of the phenotypes: septate zoosporangium, papillate zoosporangium, cleavage zoosporangium, and empty zoosporangium, considering the number of the components, sensitivity, duration, and the mutual dependency of each limiting factor. The timers for the first three phenotypes started at zero time of sporulation induction and acted in parallel. The fourth phenotype, empty zoosporangium, has a timer which appears to act sequentially to that of the papillate zoosporangium. We also studied the effects of polyoxin D, calcofluor white, and congo red on sporulation. The first drug prevents the appearance of the septate zoosporangium and the other two prevent the expression of the papillate zoosporangium. In spite of the morphological blockage, the zoosporogenesis proceeds, resulting in the formation of normal zoospores. These results are interpreted as additional evidence for the parallel model of control proposed here.

Benzenesulfonates↗
PubMed1992

Cell lineages, developmental timing, and spatial pattern formation in embryos of free-living soil nematodes.

From soils of various origins we have isolated a number of nematode strains and cultured them on agar plates. We have analyzed their anatomy, reproduction, and particularly their pattern of embryogenesis. With respect to early cleavage we can define six different classes. The basic scheme of embryogenesis is similar in all strains but considerable differences were observed in detail. Embryogenesis is more than five times longer in the slowest strain than in the fastest. The following general correlation was found: The slower embryogenesis proceeds in a strain, the relatively earlier the cleavage of germline cells occurs. In the fastest strain the primordial germ cell P4 is present at the 24-cell stage, while in the slowest strain it is already generated in the 5-cell stage. We hypothesize that germline cleavages have to occur within a certain time limit to preserve germline quality. The typical reversal of cleavage polarity in the division of the germline cell P2 is absent in the slowest, on other grounds apparently more primitive strain. This results in an unusual spatial arrangement of cells transiently. However, prior to gastrulation as a consequence of compensatory cell migrations (which may indicate the necessity for cell interactions), the pattern becomes very similar to that in the other strains. We propose that a standard cellular configuration is required at the beginning of gastrulation to ensure normal further development. Early cell interactions might be necessary to achieve this standard pattern. In about half of the analyzed strains cellular structures can be marked with an antibody raised against germline-specific granules of Caenorhabditis elegans. Our results do not support the notion that the staining pattern for P granules is a useful indicator for phylogenetic relationship.

Animals↗
PubMed1987

Developmental time course of the sympathetic postganglionic innervation of the rat eye.

The time course of the innervation of the rat iris by sympathetic postganglionic axons from the superior cervical ganglion (SCG) has been studied in postnatal rats. A retrogradely transported fluorescent dye, Fast blue (FB) was injected bilaterally into the anterior eye chamber of rats within 3 h of birth or at 7 or 14 days postnatal. Littermates were killed at 24 h intervals, both SCG removed, fixed and sectioned. A substantial number of sympathetic neurones were labelled retrogradely from the eye at birth. The number of labelled cells tripled over the first postnatal week to reach proportions equivalent to those labelled in 3-week-old rats. The degree of sympathetic fibre ingrowth to the iris was examined at 3 postnatal ages, using fluorescence histochemistry. This method showed a small proportion of catecholamine-containing fibres in the iris at birth with a more extensive fibre density over the iris by 7 days after birth. A further increase in fibre density had occurred by the end of the 3rd postnatal week even though the number of cells projecting to the iris at these two ages was similar. This difference in fibre density may arise from ramification of fibres which have reached the iris by 7 days postbirth.

Adrenergic Fibers↗
PubMed1983

Developmental time of the hemoglobin transition in the anuran Bombina orientalis.

The electrophoretic pattern of the larval hemoglobin of the anuran Bombina orientalis presents two bands. In premetamorphic period gradually appear four other bands, corresponding to those of the adult hemoglobin; they substitute, within 15-16 days after metamorphosis, the larval pattern. The percentage of larval and adult fractions during the development is shown. In Bombina orientalis the change of the hemoglobinic fractions from larval to adult type is total as in most anurans. But it starts earlier than in other species studied and develops slower than most of the other species.

Animals↗
PubMed2006

Peripherin- and CGRP-immunoreactive nerve fibers in rat molars have different locations and developmental timing.

UNLABELLED: Developing rat molars gain mature sensitivity to electric stimulation at 4-5 weeks after eruption, but the related mechanisms are incompletely understood. Preliminary studies showed weak co-localization of calcitonin gene-related peptide (CGRP) immunoreactivity (IR) with peripherin (PER) or neurofilament protein (NF) in rat molar nerve fibers, while the latter two co-localized extensively. OBJECTIVE: Our goal was to compare timing and location of PER-IR and CGRP-IR innervation in rat first molars during tooth maturation. METHODS: We used single and double immunocytochemistry to study molars of rats aged 10 days to 1 year. Neural patterns were compared with odontoblast maturation stages, dentinogenesis, formation of cell-free and cell-rich zones, and root closure. RESULTS: Spatial and temporal patterns showed that most CGRP-IR and PER-IR have different terminal domains in teeth. PER-IR fibers were well established among immature odontoblasts prior to tooth eruption, but CGRP-IR fibers were absent. Two weeks after eruption of first molars, many CGRP-IR beaded fibers entered dentin, the larger PER-IR fibers began shifting away from odontoblasts towards the pulp, and the symmetrical PER-IR pulpal pattern was being established. The CGRP-IR fibers continued to increase their asymmetric dentinal innervation until root growth was completed, during which time odontoblasts matured, the cell-free and cell-rich zones appeared, and roots closed. CONCLUSIONS: Sensory maturation of rat molars coincides with closed root apices, extensive innervation of dentin by CGRP-IR nerve fibers, and the appearance of the mature avascular odontoblast layer next to cell-free and cell-rich zones in the pulp horns.

Animals↗
PubMed1998

A biophysical model for the developmental time course of retinal orientation selectivity.

A quantitative study of the time course of development of the percentage of orientationally selective and isotropic ganglion cells in turtle retina has recently been performed. This study revealed that as soon as ganglion cells start responding to light, a large percentage of them are selective to the orientations of moving visual stimuli. This percentage decreases with age to reach a minimum around hatching, increases dramatically after birth and finally, decreases again following the first month of life to reach adult level. Concomitantly, the percentage of cells responding isotropically to the orientation of elongated stimuli increases monotonically until about 30 days after birth, stabilizing afterwards. To account for both time courses, we propose a biophysical model implementing features ubiquitous to developing vertebrate retinas. These features include early dendritic and synaptic spatial polarization, dendritic growth, and waves of activity generated spontaneously or by visual stimulation sweeping across the inner plexiform layer (IPL). The model also assumes a physiologically plausible Hebbian rule, which includes long-term potentiation and depression. Computer simulations of this model yield good fits of the data. The quality of these fits confirms and extends results from an earlier model using computationally-simple mechanisms, which suggested that early dendritic polarization might be the seed for mature orientation selectivity.

Animals↗
PubMed1999

A developmental time line in a retinal slice from rainbow trout.

The retina in teleost fish continues to grow throughout much of the life of the animal, in part by the continuing differentiation of new tissue at the retinal margin, an area termed the peripheral growth zone (PGZ) (Lyall, Q J Micros Sci, 1957:98:101-110). We have developed a retinal slice preparation--including the PGZ--from juvenile rainbow trout (Onchorynchus mykiss), a species in which retinal growth is rapid and the PGZ is correspondingly pronounced. The PGZ slice preparation contains a time line of retinal development, with cells at different stages of maturation present side by side. We present evidence that the birth sequence of the various retinal cell types in the PGZ recapitulates the sequence during embryonic development. We also report data on the rate of growth of the PGZ in juvenile trout in vivo. Finally, we have used the PGZ slice preparation to make whole-cell voltage clamp recordings from individual retinal GCs at both early and late stages of maturation. We report that the amplitude of delayed rectifier and A-type potassium currents increases during GC maturation.

Animals↗
PubMed2001

Translating developmental time across mammalian species.

Conservation of the order in which events occur in developing mammalian brains permits use of regression theory to model the timing of neural development. Following a small adjustment to account for a systematic variability in primate cortical and limbic systems, the model is used to generate a 95-event/nine-species matrix that predicts aspects of neurogenesis and axonal outgrowth in the brains of developing mice, hamsters, rats, spiny mice, rabbits, ferrets, cats, monkeys, and humans. Although data are compiled from species in which the timing of birth and the rate of maturation vary widely, the model proves statistically accurate, with practical implications for improving estimation of milestones of neural development, particularly for humans. Using the three-factor model (species, neural events, and primate adjustments), we produce predictions for the timing of 493 neural occurrences in developing mammalian brains that either have not yet been, or cannot be, empirically derived. We also relate the timing of neural events across the nine species in the form of a reference table calibrated to the development of laboratory rats. This 'translation' table will assist in attempts to equate the neurodevelopmental literature across species with either large or small differences in gestation and maturation, and also permit studies done in a variety of mammals to be applied to better understand human development. The comparative data indicate that humans, although conventionally considered an altricial species, are neurally advanced at birth relative to the other species studied.

Aging↗