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PubMed1992

Two classes of vesicles are present and change in relative proportion during post-embryonic development of rectifying electrical synapses in the crayfish.

The size and shape of vesicles at junctional appositions of the rectifying electrical synapses between the medial giant fibre and motor giant neurone of the crayfish were measured during the first 2 months after hatching. Summed data over this period reveal a bimodal distribution in vesicle diameter. From the day of hatching until about 7 days of age, small vesicles (circa 25 nm diameter) predominate. From day 7 onwards, larger vesicles (circa 55 nm diameter) occur in increasing numbers, until at day 56 they constitute about 85% of the population at any one junctional apposition. At intermediate ages (day 7-28) individual junctional appositions may show the same bimodal distribution in size as does the age group as a whole, indicating that large and small vesicles occur together at the same junction. The larger vesicles are mainly circular, while the small vesicles are pleomorphic, with shapes ranging from almost circular down to a shape factor of about 0.6.

Aging↗
PubMed1995

Embryonic development of the antennal lobes of a hemimetabolous insect, the cockroach Periplaneta americana: light and electron microscopic observations.

In the hemimetabolous insect Periplaneta americana, the adult-like organization of the primary olfactory centers, the antennal lobes, is established during the approximately 31 days of embryogenesis. This report describes the temporal sequence of developmental events as viewed in the light and electron microscope by means of histological stains and by DiI labeling of antennal receptor axons with subsequent photoconversion. Glomeruli, characteristic differentiations of the antennal lobe neuropil, are first observed on day 19; their development, which is not synchronous in the various parts of the antennal lobe, lasts until about day 22. From day 10 on, glial cells begin to form a narrow boundary layer between the soma cortex and the central neuropil. They exhibit a lengthening of their processes in parallel with the formation of glomeruli. Marked proliferation or migration of these glial cells into the neuropil between glomeruli has not been observed. Antennal receptor axons could be labeled from stage 15 on. They terminate in an elongated growth cone with numerous filopodia. From day 18 on, some of these become bent or show an initial bifurcation. From day 22 on, the first afferent axons develop an adult-like arborization pattern. Synaptic contacts between receptor axons and unidentified neurons were observed as early as stages 16 and 19, in which the axons still have a growth cone-like form. In stage 27, in which the fibers have adult-like arborizations, many output contacts and few input contacts were found.

Animals↗
PubMed2003

Zebrafish atonal homologue zath3 is expressed during neurogenesis in embryonic development.

Basic helix-loop-helix (bHLH) transcriptional activators function in development of various cell lineages, including the central nervous system. One of the bHLH proteins, Math3/Xath3/NeuroM, was suggested to act as a late proneural gene in the mouse, Xenopus, and chick. Here, we isolated a zebrafish homologue, named zath3, and analyzed its expression pattern in zebrafish embryos. In the neural plate, zath3 is expressed first in the primordia of the tegmentum and trigeminal ganglia and three classes of primary neurons: sensory neurons, interneurons, and motor neurons. During later development, zath3 transcripts were localized along the boundaries of the optic tectum in the midbrain and rhombomeres of the hindbrain. Analyses of zath3 expression in three mid-hindbrain boundary mutants, acerebellar, no isthmus, and spiel-ohne-grensen, indicated that distribution of zath3 mRNAs in the midbrain and hindbrain was dramatically disturbed. In addition, these mutants also affect expression of zath3 in the neuroretina.

Amino Acid Sequence↗
PubMed2005

A Xenopus DNA microarray approach to identify novel direct BMP target genes involved in early embryonic development.

Bone morphogenetic proteins (BMPs), a subgroup of the transforming growth factor-beta (TGF-beta) superfamily, were originally isolated from bone on the basis of their ability to induce ectopic bone development. Although BMPs are involved in a wide range of developmental and physiological functions, very few vertebrate target genes in this pathway have been identified. To identify target genes regulated by the BMP growth factor family in Xenopus, large-scale microarray analyses were conducted to discover genes directly activated by this factor in dissociated animal cap tissues treated with a combination of the protein synthesis inhibitor cycloheximide and BMP2. Consequent expression patterns and behaviors of the most highly induced genes were analyzed by in situ and reverse transcriptase-polymerase chain reaction analyses. Here, we describe two sets of the most highly induced direct BMP target genes identified using microarrays prepared from two different stages of early Xenopus development. A wide variety of genes are induced by BMP2, ranging from cell cycle controllers, enzymes, signal transduction cascade components, and components of the blood and vascular system. The finding reinforces the notion that BMP signals play important roles in a variety of biological processes.

Animals↗
PubMed2005

Expression of a novel zebrafish zinc finger gene, gli2b, is affected in Hedgehog and Notch signaling related mutants during embryonic development.

Gli zinc-finger proteins are known as downstream mediators of the evolutionary conserved Hedgehog pathway. In zebrafish, gli2 functions differently from Gli2 in mammals. This difference could be due to the gli2 duplication in teleosts evolution and partial redundancy between two duplicated genes. Here, we report a novel zebrafish gli2-like cDNA. Its structure, genetic location, and distinct expression pattern in the central nervous system suggested that this gene might represent a second gli2 of teleosts, and we named it gli2b. gli2b was expressed in the neural keel, excluding the forebrain-midbrain boundary, while gli2 expression complemented this pattern. After 24 hours postfertilization, several specific domains of gli2b expression were observed in the lateral and medial hindbrain and hypothalamus. In mutants affecting the Hedgehog and Notch signaling pathways, gli2b expression was either disrupted or extended in different regions.

Amino Acid Sequence↗
PubMed2006

Improved translation efficiency of injected mRNA during early embryonic development.

Injection techniques are a powerful approach to study gene function in fish and frog model systems. In particular, in vitro transcribed mRNA is broadly used for such misexpression experiments. Sequence elements flanking the coding region, such as untranslated repeats and polyadenylation sequences, are known to affect the stability and the translation efficiency of mRNA. Here we show that in early embryos, poly(A) signals strongly contribute to the activity of the injected mRNA. Of interest, they only marginally affect mRNA stability, whereas the translation efficiency is dramatically enhanced. Combination of a poly(A) tail and an SV40 late poly(A) signal leads to highly synergistic effects of the two elements for injected mRNA. Compared with established vector systems, we detected a 20-fold improvement for mRNA derived from the novel transcription vector pMC.

Animals↗
PubMed1980

Differential induction of sister chromatid exchanges by indirect-acting mutagen-carcinogens at early and late stages of embryonic development.

To examine the development of drug-metabolizing enzyme systems in the early chick embryo, the procarcinogens, aflatoxin B1 (AF-B1) and 2-acetylamino-fluorene (2-AAF), and the direct-acting carcinogen, ethyl methanesulfonate (EMS) (positive control), were given to embryos; the sister-chromatid-exchange (SCE) technique was used as an indicator of conversion to active mutagenic metabolites. Chick embryos at two stages of incubation (3-day and 6-day) were exposed to the same graded series of dosages of the compounds for a period of 22 hours. All three mutagens increased the frequency of SCE above the control rate of 1,8 SCEs/cell. While a dose-dependent increase in SCE was obtained for both procarcinogens at each age, the mean SCE frequency was significantly higher in the 6-day embryos for each dosage given. In contrast, the direct-acting mutagen, EMS,. gave a reduced level of SCEs at the older age. These results suggest that the ability of early chick embryos to activate promutagens to forms capable of inducing SCE increases as development advances from three to six days of incubation (DI). In the 6-day embryo, the metabolic conversion is enhanced, resulting in a significant increase in the mutagenicity of the test chemicals.

2-Acetylaminofluorene↗
PubMed2005

Live imaging and morphometric analysis of embryonic development in the ascidian Ciona intestinalis.

The ascidian Ciona intestinalis is one of the model organisms of choice for comparative investigations of chordate development and for unraveling the molecular mechanisms underlying morphogenesis and cell fate specification. Taking advantage of the availability of various genetically encoded fluorescent proteins and of defined cis-regulatory elements, we combined transient transgenesis with laser scanning confocal imaging to acquire and quantitate 3D time-lapse data from living Ciona embryos. We used Ciona tissue-specific enhancers to drive expression of spectrally distinct fluorescent protein reporters to label and simultaneously visualize axially and paraxially positioned mesodermal derivatives, as well as neural precursors in individual embryos. We observed morphogenetic movements, without perturbing development, from the early gastrula throughout the larval stage, including gastrulation, neurulation, convergent extension of the presumptive notochord, and tail elongation. These multidimensional data allowed us to establish a reference system of metrics to quantify key developmental events including blastopore closure and muscle extension. The approach we describe can be used to document morphogenetic cell and tissue rearrangements in living embryos and paves the way for a live digitized anatomical atlas of Ciona.

Animals↗
PubMedDate not supplied

Embryonic development of the head and neck: part 5, the brain and cranium.

The development of the brain is presented with respect to closure of the neural tube, the formation of the five vesicles of the brain and their derivatives, and the cranial flexures. The cranial nerves, meninges, choroid plexuses, and cerebral vasculature are also discussed. The origin and ossification of the bony elements of the head and neck, including the neurocranium, viscerocranium, and cervical vertebrae, are described, as well as major congenital defects of the brain and the cranium.

Brain↗
PubMed1993

Expression of type IV collagen-degrading activity during early embryonal development in the sea urchin and the arresting effects of collagen synthesis inhibitors on embryogenesis.

Type IV collagen-degrading activity was expressed in homogenates of Lytechinus pictus embryos during embryogenesis. Activity was concentrated 1,600-fold by ammonium sulfate fractionation, ion exchange, and gel chromatography and could not be activated further upon trypsin or organomercurial treatment. This enzyme activity could also degrade gelatin but had no affinity for type I, III, and V collagens. Activity was inhibited by addition of excess type IV collagen or gelatin, but was unaffected by addition of excess amounts of non-collagenous proteins of the extracellular matrix. Chelators such as 1,10-phenanthroline or Na2EDTA reduced activity to control levels. Inhibitors of plasmin and of serine and thiol proteases were without effect. Type IV collagen-degrading activity first became apparent at the stage of early mesenchyme blastula. It then increased by a small increment and remained stable up to the stage of late mesenchyme blastula, coinciding with first detection of collagen synthesis and the appearance of the archenteron. Thereafter, a sharp increase in activity was observed, concurrently with remodelling of the archenteron. Maximum activity was attained at prism stage and was retained throughout to pluteus-larva stage. The specific inhibitors of collagen biosynthesis 8,9-dihydroxy-7-methyl-benzo[b]quinolizinium bromide and tricyclodecane-9-yl xanthate arrested sea urchin embryo development at early blastula, prevented the invagination of the archenteron, and reverted the expression of type IV collagen-degrading activity to non-detectable levels. Removal of the inhibitors allowed embryos to gastrulate and express type IV collagen-degrading activity.

2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
PubMed2001

Role of motility in embryonic development I: Embryo movements and amnion contractions in the chick and the influence of illumination.

This study provides a quantitative analysis of the active movements of the chick embryo and of the contractions of the amnion over the entire developmental period of 21 days. Four types of embryo movements are distinguished. The motor activity of the embryo shows two characteristic peaks, with maximum contraction frequencies on the 12th and on the 16th day. In contrast, the amnion activity is higher at earlier stages and decreases as the body activity increases. The amnion activity is largely independent of the body activity. Illumination has a strong influence on embryo movements. It is shown that increases of light intensity affect the patterns of activity of both the embryo and the amnion. While the effect of light on the embryo can be interpreted as being transmitted via the optic system, the mechanism of the amniotic response is unclear. The results suggest that the amnion itself may be sensitive to light. J. Exp. Zool. (Mol. Dev. Evol.) 291:186-194, 2001.

Amnion↗