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At least 793 records · Page 44Linked to original sources

PubMed1976

Characterization and levels of the RNA polymerases during the embryogenesis of Artemia salina.

Dormant embryos at the gastrula stage of Artemia salina contain three DNA-dependent RNA polymerases: I, II, and III. The enzymes are solubilized from whole embryos and they are separated by chromatography on DEAE Sephadex. The ratio of activities with native and denatured DNA at the optimal salt concentrations is 3.5 for RNA polymerase I, 0.1 for RNA polymerase II and 1.0 for RNA polymerase III.Mn(i2+) is more efficient than Mg(2+) for the three enzymes. RNA polymerase II is 50% inhibited by 5 ng/ml of alpha-amanitin while RNA polymerases I and III are 10% and 30% inhibited by 1 mg/ml. During the embryonic development there is am independent variation of the levels of the RNA polymerases. RNA polymerase I increases its specific activity 4-5-fold, RNA polymerase III increases 2-fold, and RNA polymerase II less than 2-fold. The increase in RNA polymerase activity may represent a mechanism to control the rate of synthesis of RNA during the embryogenesis of A. salina.

Amanitins↗

PubMed1985

Altered synthesis of glucosamine-labeled glycopeptides during postimplantation embryogenesis of the mouse.

Dissected mouse embryos were examined for the ability to synthesize [3H]glucosamine-labeled embryoglycan, which is the glycoprotein-bound large carbohydrate eluted near the excluded volume of a Sephadex G-50 column. Although the ratio of glucosamine-label incorporated into embryoglycan decreased progressively during embryogenesis, 11- and 12-day-old embryos still synthesized significant amounts of the glycan. Severe inhibition of the glycan synthesis was noticed after the 15th day. Therefore, synthesis of the core portion of embryoglycan was suppressed later than when fucosylation of the glycan was known to be suppressed.

Animals↗

PubMed1987

Ionic currents traversing cell clusters from carrot suspension cultures reveal perpetuation of morphogenetic potential as distinct from induction of embryogenesis.

Patterns of ionic currents accompanying shape and surface changes during growth of cell clusters from carrot suspension cultures were examined using a vibrating probe. Electrical polarity was established in clusters undergoing apparently disorganized proliferation in the presence of 2,4-dichlorophenoxyacetic acid (2,4-D). This electrical polarity is similar to that found in organized somatic embryos which form upon removal of 2,4-D, and implies that the proliferating clusters are actually suppressed embryos. This implication is further supported by observations using scanning electron microscopy. We conclude that the potential to undergo embryogenesis is present even before the 2,4-D is removed, but cannot be realized in the presence of the auxin.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1993

Transforming growth factor-beta in neural embryogenesis and neoplasia.

The transforming growth factor-beta (TGF-beta) family of polypeptides includes three structurally and functionally related mammalian isoforms that influence cell proliferation, differentiation, and extracellular matrix production. Recent identification of these isoforms in the embryonic murine central nervous system suggests that these factors may regulate proliferation and differentiation of meningeal and neuroepithelial cells during development. Predominant expression of TGF-beta 1 in the leptomeninges compared with the brain of the murine and human central nervous system implicates this isoform in regulation of that mesodermal tissue. Thus, defective TGF-beta regulation may contribute to neoplastic transformation. Failure to activate latent TGF-beta s may contribute to the loss of autocrine regulation seen in meningiomas. Expression of TGF-beta 2 and TGF-beta 3 primarily in embryonic murine radial glia and adult human astrocytes suggests other roles for these isoforms, including glioblast differentiation and guidance of neuroblast migration. Although inhibitory to "normal" astrocyte proliferation, TGF-beta s demonstrate autocrine growth stimulation in vitro among hyperdiploid malignant gliomas, medulloblastomas, primitive neuroectodermal tumors, and anaplastic ependymomas. Hence, synthesis and release of active TGF-beta s by malignant brain tumors may create aberrant stimulatory autocrine loops. The mechanism of TGF-beta-induced growth stimulation is poorly understood. Future studies will likely clarify and identify additional roles for the TGF-beta isoforms in neuro-embryogenesis and neoplasia.

Animals↗

PubMed1976

Ultrastructural patterns of RNA synthesis during early embryogenesis of Drosophila melanogaster.

Chromatin was obtained from Drosophila melanogaster during early embryogenesis and examined by transmission electron microscopy. Nuclear contents spread at progressive stages of syncytial development show a low level of only non-nuclear template activity, and very few RNP fibril gradients extending over 2mum in length are observed. At the cellular blastoderm stage, newly activated nucleolar genes appear during the early portion of the first true cell cycle. Variation in the lengths of incomplete rRNP gradients indicates that the activation of each rRNA gene is independently controlled. All rRNA loci, whether having complete or incomplete gradients, exhibit high densities of nascent transcripts per unit length, suggesting that the rate of chromatin transcription, rather than the RNA polymarase I pool size, limits rRNA synthesis on individual genes. No more than half the rRNA genes are derepressed at this stage indicating that total rRNA synthesis is regulated by the number of genes activated. Non-nucleolar RNP fibril gradients covering up to 8 mum of genome are also first observed at the cellular blastoderm stage. Most of these gradients are differentiated from the short gradient first seen during syncytial growth by a lower density of transcribing RNA polymerases.

Animals↗

PubMed1985

Expression during embryogenesis of a mouse gene with sequence homology to the Drosophila engrailed gene.

Regions of the mouse and human genomes with strong homology to the Drosophila engrailed gene have been identified by Southern blot analysis. One mouse engrailed-like region, Mo-en.1, has been cloned and partially sequenced; homology with the engrailed gene is localized to a 180 bp engrailed-like homeo box and 63 nucleotides immediately 3' to it. The protein sequence this region can encode includes 81 amino acids, of which 60 (75%) are identical with those of the putative translation product of the corresponding engrailed sequence. These data suggest that Mo-en.1 represents a mouse homolog of a gene of the Drosophila engrailed gene complex. Mo-en.1 has been mapped to chromosome 1, indicating it is not linked to other homeo box sequences that have been mapped in the mouse genome. Analysis of poly(A)+ RNA extracted from teratocarcinoma cells and whole mouse embryos demonstrates that the conserved homeo box region of Mo-en.1 is expressed differentially during mouse embryogenesis.

Animals↗

PubMed1985

Localization of the fushi tarazu protein during Drosophila embryogenesis.

The fushi tarazu (ftz) gene of Drosophila acts early in embryogenesis to regulate body segmentation. The localization of the ftz protein product in embryos was examined using indirect immunofluorescence microscopy. Antibodies were prepared against a beta-galactosidase-ftz hybrid protein made in E. coli. The ftz protein was first detectable in blastoderm-stage embryos as seven stripes of nuclei encircling the embryos transversely. The stripes persist through the early events of gastrulation, but disappear before overt segmentation is visible. The ftz protein is expressed a second time in some nuclei of the developing nervous system. In contrast to the early pattern, at the later stage, ftz is expressed in each of fifteen metameric subunits of the embryo.

Animals↗

PubMed1990

CeMyoD accumulation defines the body wall muscle cell fate during C. elegans embryogenesis.

We have cloned a gene from the nematode C. elegans that is closely related to the vertebrate MyoD gene family. The nematode gene product, CeMyoD, is a nuclear protein that is expressed specifically in body wall muscle cells. Antibody staining of early embryos shows that CeMyoD accumulates in early blastomeres that will subsequently produce only body wall muscle cells. CeMyoD is not detected in pharyngeal muscle cells or in nonmyogenic lineages. A CeMyoD-beta-galactosidase fusion gene is accurately expressed in myogenic cells that also express CeMyoD. In addition, the beta-galactosidase reporter is expressed as early as the 28 cell stage of embryogenesis in specific blastomeres prior to their clonal commitment to body wall muscle. This early fusion gene activity reveals that part of the specificity for CeMyoD transcription can arise very early in development and that subsequently, negative events may restrict CeMyoD expression in progeny cells not destined to become muscle.

Amino Acid Sequence↗

PubMed1994

Cyclin E controls S phase progression and its down-regulation during Drosophila embryogenesis is required for the arrest of cell proliferation.

Most cells of the dorsal epidermis exit from the mitotic cycle after division 16 in Drosophila embryogenesis. This exit is dependent on the down-regulation of Drosophila cyclin E (DmcycE) during the final mitotic cycle. Ectopic expression of DmcycE after the final mitosis induces entry into S phase and reaccumulation of G2 cyclins and results in progression through a complete additional cell cycle. Conversely, analyses in DmcycE mutant embryos indicate that cyclin E is required for progression through S phase of the mitotic cycle. Moreover, endoreplication, which occurs in late wild-type embryos in the same pattern as DmcycE expression, is not observed in the mutant embryos. Therefore, Drosophila cyclin E, which forms a complex with the Dmcdc2c kinase, controls progression through S phase and its down-regulation limits embryonic proliferation.

Animals↗

PubMed1992

Acetyl-L-carnitine has a neuromodulatory influence on neuronal phenotypes during early embryogenesis in the chick embryo.

Studies from this laboratory and others have demonstrated that neuroblasts in early embryogenesis exhibit a high degree of plasticity with respect to neurotransmitter phenotype. The critical period within which these neuroblasts are sensitive to the effects of endogenous neurotrophins has been defined as 1-3 days of development in the chick embryo. In this study, we examined the influence of acetyl-L-carnitine (ALCAR) administered in ovo during embryonic days 1-3 (E1-E3) and sacrificed at embryonic day 8 (E8) on cholinergic and GABAergic neuronal phenotypes using as neuronal markers the activities of choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD), respectively. Phenotypic expression was assessed in 3 distinct anatomical regions of the embryonic brain: cerebral hemispheres (CH), optic lobes (OL), and diencephalon-midbrain-brainstem (DMBS). A single administration of ALCAR at embryonic day 1 resulted in a dose-dependent increase in ChAT activity and decrease in GAD activity in CH. ChAT activity was again increased and GAD activity decreased in CH from embryos that were administered ALCAR (100 micrograms/50 microliters/day) daily from embryonic day E1 to E3. No change was observed in either ChAT or GAD activity in OL in response to ALCAR administration during the critical period (E1-E3) at doses ranging from 10 to 500 micrograms/day. In the DMBS, the activity of ChAT exhibited a marked increase at lower doses (10 micrograms) followed by a marked decrease at higher doses (500 micrograms) of ALCAR. The decrease in ChAT activity in DMBS was again observed at an ALCAR dose of 100 micrograms/day when administered from E1 to E3.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcarnitine↗

PubMed1994

Reciprocal expression of cell-cell coupling and voltage-dependent Na current during embryogenesis of rat telencephalon.

Using whole-cell patch-clamp techniques in situ (whole-tissue and tissue slices), we have studied two aspects of rat telencephalic cell development during the period of embryogenesis starting at E12. The first aspect was related to junctional coupling as revealed by low input resistance, intercellular dye spread and pharmacologic blockade. Coupling appeared to decrease with time, both in extent and occurrence. The second aspect dealt with cell excitability as revealed by voltage-dependent Na current (INa) expression. Immature action potentials and their underlying INaS were present in a small proportion of E12 cells. These currents were blocked 36% and 78% by 10(-7) M and 10(-6) M tetrodotoxin (TTX), respectively. From then onward, INaS got larger and more prevalent while no obvious changes in kinetics were observed. At E21, INaS were abolished by 10(-7) M TTX and channel density apparently was sufficient to support overshooting yet still immature action potentials.

Animals↗

PubMed1994

Cloning of a brain-type aldolase cDNA and changes in its mRNA level during oogenesis and early embryogenesis in Xenopus laevis.

A full length cDNA clone (cXALD3) for Xenopus laevis aldolase mRNA, which exists abundantly in oocytes, was isolated from Xenopus laevis ovary cDNA library, and its nucleotide sequence was determined. The cDNA was 1.8 kb in length and encoded 363 amino acids. From the deduced amino acid sequence and the Northern blot analysis of the RNAs from several adult tissues, this clone was concluded to be a brain-type aldolase gene. The XALD3 mRNA level per egg or embryo was high during early oogenesis, but was markedly reduced during late oogenesis and was maintained at low level during early embryogenesis until it started to increase at the late neurula stage. The mRNA was also detected in testis. The characteristic change in the temporal pattern of expression and the distribution of XALD3 mRNA among different tissues suggest a possibility that brain type aldolase may play some important roles in gametogenesis and in neurulation.

Amino Acid Sequence↗

PubMed1994

Expression of the glucocorticoid receptor gene is regulated during early embryogenesis of Xenopus laevis.

To study the possible role of the glucocorticoid receptor (GR) in early embryogenesis, we isolated a Xenopus glucocorticoid receptor cDNA from an embryonic stage 17 cDNA library. Overexpression of this Xenopus GR in COS cells confers the ability to transactivate a GRE-tk CAT promoter construct in a ligand dependent manner. Expression of the Xenopus GR gene at the RNA level was analyzed by Northern blot hybridization. Transcripts of 4 and 6 kb are present in oocytes. The 4 kb mRNA is abundant and is degraded together with the 6 kb mRNA during cleavage stages of early development. Between stages 17 and 24, GR messengers are extremely rare. From stage 32 onwards, both GR transcripts start to be expressed again at intermediate levels. These results provide the first evidence that expression of the GR gene is regulated during early embryonic development.

Amino Acid Sequence↗

PubMed1995

The putative Drosophila NMDARA1 gene is located on the second chromosome and is ubiquitously expressed in embryogenesis.

We describe the cDNA sequence of a Drosophila gene located at 49D on the second chromosome. The predicted protein sequence has extensive homology (46% identity, 76% similarity) along its entire length to the central portion of the mammalian brain-specific NMDARA1 glutamate binding protein. While RNA expression studies of the Drosophila protein shown that it is ubiquitously expressed throughout embryogenesis, there appears to be a selective accumulation of transcript in the precursor for the larval brain. The similarity in both expression and sequence suggests that the two proteins may share a conserved function.

Amino Acid Sequence↗

PubMed1990

Appearance during chick embryogenesis of vitamin D-dependent calcium-binding protein (calbindin-D28K).

The appearance of the vitamin D-dependent calcium-binding protein (calbindin-D28K) in embryonic chick tissues was determined using a sensitive immunohistochemical assay to elucidate the possible role of calbindin-D28K during embryogenesis. This protein first occurs in renal, cerebellar and intestinal cells during the final stages of maturation and/or differentiation. It is during this period of their development that these tissues become functional. On the basis of our observations, we suggest that the onset of cell function may be coupled with the appearance of calbindin-D28K.

Animals↗

PubMed1984

Plant growth, development and embryogenesis during Salyut-7 flight.

The growth and geotropic movements of roots and hypocotyls of lettuce have been studied on board the Salyut 7 station in a stationary position and on the centrifuge at 0.01, 0.1 and 1 g. On the centrifuge at 0.1 and 0.01 g as well as under weightlessness, the final length of hypocotyls was by 8-16% greater than in control plants on the centrifuge at 1 g. The length of roots, however, was reduced by 17% at 0.01 g and under weightlessness; at 0.1 g their growth is much the same as at 1 g. On the Earth, while growing in a vertical position, and in space at 0 < or = g, the roots and hypocotyls deviate from the longitudinal axis of the seed. Average values of deviation eagles on the Earth are always equal to zero, while this is not always the case in space, which indicates the biological effect of microgravity conditions on board a spacecraft. The threshold of geotropic sensitiveness of lettuce hypocotyls, calculated from the linear regression parameters of the dependence of the response geotropic reaction upon the value of the centrifugal force, comprised 2.9 x 10(-3) g. In the Fiton 3 micro-greenhouse under spaceflight conditions, the plants of Arabidopsis thaliana (L) Heynh have, for the first time, undergone a full cycle of individual development. The seeds sown during the flight germinated, performed growth processes, formed vegetative and generative organs and, judging by the final result, they succeeded in fecundation, embryogenesis and ripening. Despite the noted modification of growth and development of plants in space, 42% of formed seeds appeared to be valuable biologically.

Arabidopsis↗

PubMed1994

Embryogenesis, hatching and larval development of Artemia during orbital spaceflight.

Developmental biology studies, using gastrula-arrested cysts of the brine shrimp Artemia franciscana, were conducted during two flights of the space shuttle Atlantis (missions STS-37 and STS-43) in 1991. Dehydrated cysts were activated, on orbit, by addition of salt water to the cysts, and then development was terminated by the addition of fixative. Development took place in 5 ml syringes, connected by tubing to activation syringes, containing salt water, and termination syringes, containing fixative. Comparison of space results with simultaneous ground control experiments showed that equivalent percentages of naupliar larvae hatched in the syringes (40%). Thus, reactivation of development, completion of embryogenesis, emergence and hatching took place, during spaceflight, without recognizable alteration in numbers of larvae produced. Post-hatching larval development was studied in experiments where development was terminated, by introduction of fixative, 2 days, 4 days, and 8 days after reinitiation of development. During spaceflight, successive larval instars or stages, interrupted by molts, occurred, generating brine shrimp at appropriate larval instars. Naupliar larvae possessed the single naupliar eye, and development of the lateral pair of adult eyes also took place in space. Transmission electron microscopy revealed extensive differentiation, including skeletal muscle and gut endoderm, as well as the eye tissues. These studies demonstrate the potential value of Artemia for developmental biology studies during spaceflight, and show that extensive degrees of development can take place in this microgravity environment.

Animals↗

PubMed1993

Turing structure during embryogenesis.

A non-linear reaction-diffusion model of the epigenetic system involving the synthesis and simultaneous intercellular self and cross-diffusion of the activator and inhibitor during embryogenesis has been proposed. It has been observed that the system spontaneously emerges into a stationary dissipative (Turing) structure only in the presence of positive cross-diffusion. That the stationary structure, thus evolved, has been shown to be globally asymptotically stable by using a suitable Liapunov's function.

Animals↗