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At least 253 records · Page 14Linked to original sources

PubMed2000

Impact of UV radiation on the early development of the giant kelp (Macrocystis pyrifera) gametophytes.

The mechanisms and dose-response of UV action on the early development of Macrocystis pyrifera (L.) C. Agardh gametophytes were investigated. Post-release, zoospores undergo germination, germ tube elongation, DNA synthesis, nuclear division and translocation, which were followed for 41 h under laboratory conditions. The spores were exposed to UV radiation before germination (3 h post-release) or before nuclear division (20 h post-release). Biologically effective UV-B doses (BEDDNA300 nm) higher than those used in the experiments are needed for a 50% inhibition in germination (BED50 > 1600 J m-2). Nuclear division/translocation was more sensitive to UV radiation. When the spores were cultured in the dark, UV exposure at both 3 and 20 h post-release resulted in a dose-responsive inhibition of nuclear division/translocation (BED50 64 and 86 J m-2). Culturing in the light indicated recovery in the spores that were irradiated at 3 h post-release (BED50 356 J m-2), whereas no light-dependent recovery occurred within 41 h of culture when irradiated at 20 h post-release (BED50 80 J m-2). The results present a possible mechanism of UV inhibition in early life stages of the giant kelp, suggesting that environmentally relevant UV-B levels can perturb or delay the development and recruitment of the gametophytes by inhibiting nuclear events.

Biological Transport↗

PubMed1991

Segmental expression of an engrailed-class gene during early development and neurogenesis in an annelid.

ht-en protein, an annelid homolog of the Drosophila engrailed protein, is expressed during both early development and neurogenesis in embryos of the leech, Helobdella triserialis. In Helobdella as in Drosophila, early expression is in segmentally iterated stripes of cells within the posterior portion of the segment and later expression is in cells of the segmental ganglia. These findings suggest that dual expression of an en-class gene was present in a common ancestor of annelids and arthropods.

Animals↗

PubMed1992

Differential expression and regulation of two distinct fibroblast growth factor receptors during early development of the urodele amphibian Pleurodeles waltl.

Fibroblast growth factor (FGF) has been shown to be involved in mesoderm induction during amphibian development. Its presence in the embryo suggests that FGF is an endogenous inducer. By polymerase chain reaction (PCR) methods and by screening a Pleurodeles waltl tail-bud cDNA library with a cDNA probe for human FGF receptor, we have isolated two full-length cDNA clones, which we designate PFR1 and PFR4 based on their homology to the human FGF receptors FGFR-1 and FGFR-4. Both cDNA clones encode Pleurodeles FGF receptors that share characteristics common to members of the FGF receptor superfamily. The deduced amino acid sequence of PFR1 is 85% identical overall with the human fms-like-gene (FLG). PFR4 is most closely related to the human FGFR-4 (66% overall identity). The tyrosine kinase catalytic domains of both receptors are remarkably conserved. The two receptors show distinct patterns of regulation during early development. PFR1 first appears as a maternally derived mRNA and mRNA levels remain constant during early developmental stages. However, PFR4 mRNA is first expressed at the late blastula stage, which suggests that its expression is a result of zygotic transcription. Furthermore, northern blot analysis indicates that PFR1 mRNA is distributed evenly in the early gastrula while PFR4 mRNA is predominantly localized to the presumptive ectoderm. At tail-bud stage, PFR1 transcripts are localized primarily to the neural and mesodermal tissues, PFR4 transcripts are most abundantly expressed in neural tissue, and more transcripts are detected in lateral plate mesoderm than in the somites. When animal cap explants of blastulae are cultured in the presence of mesoderm-inducing factors, PFR1 mRNA levels are maintained by bFGF and activin A. In contrast, PFR4 mRNA levels are significantly down-regulated. These observations suggest a differential expression and regulation of FGF receptors in early amphibian development.

Amino Acid Sequence↗

PubMed1994

Early development of the optic chiasm in the gray short-tailed opossum, Monodelphis domestica.

We have studied the early development of the uncrossed retinofugal projection in the gray short-tailed opossum. Axons that form the adult uncrossed retinofugal projection arise from the temporal crescent of the retina and reach the optic chiasm on postnatal day 7. The sites at which the uncrossed fibres segregate from the crossed fibres and the pattern of this segregation are very different from those seen in eutherian mammals. In the opossum, the uncrossed fibres segregate from the crossed fibres within the juxtachiasmatic part of the optic nerve before they have encountered either the fibres of the other eye or midline structures of the ventral diencephalon. The uncrossed fibres turn perpendicular to the axis of the nerve and grow dorsoventrally through the crossed projection to gather as a discrete bundle at the ventral edge of the nerve. The abrupt divergence of the uncrossed fibres occurs at a border between two glial cell types: the interfascicular glia that characterise the main part of the optic nerve and the radial glia of the juxtachiasmatic part of the nerve. At the ventral part of the nerve, the bundle of uncrossed fibres turns caudally across the axis of the nerve and enters the ipsilateral optic tract. When retinofugal fibres encounter the border between the interfascicular and radial glia, a very specific axonal reorganisation occurs in marsupials, and this is strikingly different from the axonal reorganisation that occurs at the same site in eutherians, where essentially all retinofugal fibres reorganise, not just the uncrossed component. We believe this to be an important example of an identified cellular element that has quite distinct axon-guidance properties in different species.

Animals↗

PubMed1987

Nuclear antigens differentially expressed during early development of Drosophila melanogaster.

To obtain specific immunological probes for studying molecular events involved in gene activation during early development of Drosophila, we have produced monoclonal antibodies directed against nuclear proteins differentially expressed in time and space during embryogenesis. Twenty-five antibodies against nuclear antigens detected after the onset of zygotic genome transcription were obtained. These antigens have been distributed into six categories depending on their reactivity in dot-blot, in Western-blot and in immunofluorescence on embryo frozen section assays. Six antigens (fifth and sixth categories) are stage-, but not tissue-specific and are present in all nuclei of the embryo after the blastoderm stage. Ten antigens, the third and fourth categories, did not react on immunofluorescence and have not been characterized for a possible tissue specificity. Antigens of the first and second categories are stage- and tissue- specific. Two of them are of particular interest. The first (250 kd, recognized by the monoclonal antibody GB7) is preferentially expressed in nuclei of the ventral nerve cord, whereas the other (65 kd, recognized by the monoclonal antibody LA9) is located in nuclei of the gut and associated structures.

Animals↗

PubMed2003

Expression of muscle LIM protein during early development in Xenopus laevis.

We have isolated the Xenopus homologue of Muscle LIM protein (MLP, CRP3) and examined its expression during early embryonic development. MLP is only expressed in the differentiated heart during early development and is expressed in a subset of other striated muscles during later stages. There is no MLP expression during primary myogenesis in the somites, although it is found in adult skeletal muscle.

Amino Acid Sequence↗

PubMed1988

A third striated muscle actin gene is expressed during early development in the amphibian Xenopus laevis.

During early embryonic development in the frog Xenopus laevis, several muscle-specific actin genes encoding distinct actin protein isoforms are activated in cells of the embryonic muscle. In addition to the cardiac (or alpha 1) and skeletal (or alpha 2) actin genes, a third muscle-specific actin gene is expressed in the same embryonic tissue. We have determined the complete nucleotide sequence of this third gene and examined its expression in embryonic and adult tissues. During embryogenesis, this femoral (alpha 3) actin gene is activated several hours later than its cardiac and skeletal counterparts and its transcripts are first detected after neurulation. The gene encodes a skeletal-type actin protein and is expressed exclusively in skeletal muscle in the adult frog. Two copies of this gene have been isolated from the tetraploid species Xenopus laevis, differing by only a few nucleotides in their protein-coding sequence. The related, diploid species, Xenopus tropicalis, possesses a single copy of the alpha 3 gene and its transcript is similarly conserved in nucleotide sequence. However, the X. tropicalis gene is expressed exclusively in embryonic stages of development. Comparison of the X. laevis and X. tropicalis alpha 3 gene promoters reveals extensive sequence homology, including several copies of a repeated motif that is common to other vertebrate striated-muscle actin gene promoters.

Actins↗

PubMed1994

Isolation of a novel RXR from Xenopus that most closely resembles mammalian RXR beta and is expressed throughout early development.

In a search for nuclear receptors that may mediate the teratogenic effects of the potential morphogen, retinoic acid, on the early development of Xenopus we have isolated a novel Xenopus RXR that most closely resembles the mammalian beta-type RXR. Xenopus RXR beta mRNA is expressed throughout early embryogenesis, and functions as an accessory protein to enhance the DNA-binding of other members of the nuclear receptor superfamily.

Amino Acid Sequence↗

PubMed2002

Spatial learning and memory is preserved in rats after early development in a microgravity environment.

This study evaluated the cognitive mapping abilities of rats that spent part of their early development in a microgravity environment. Litters of male and female Sprague-Dawley rat pups were launched into space aboard the National Aeronautics and Space Administration space shuttle Columbia on postnatal day 8 or 14 and remained in space for 16 days. These animals were designated as FLT groups. Two age-matched control groups remained on Earth: those in standard vivarium housing (VIV) and those in housing identical to that aboard the shuttle (AGC). On return to Earth, animals were tested in three different tasks that measure spatial learning ability, the Morris water maze (MWM), and a modified version of the radial arm maze (RAM). Animals were also tested in an open field apparatus to measure general activity and exploratory activity. Performance and search strategies were evaluated in each of these tasks using an automated tracking system. Despite the dramatic differences in early experience, there were remarkably few differences between the FLT groups and their Earth-bound controls in these tasks. FLT animals learned the MWM and RAM as quickly as did controls. Evaluation of search patterns suggested subtle differences in patterns of exploration and in the strategies used to solve the tasks during the first few days of testing, but these differences normalized rapidly. Together, these data suggest that development in an environment without gravity has minimal long-term impact on spatial learning and memory abilities. Any differences due to development in microgravity are quickly reversed after return to earth normal gravity.

Animals↗

PubMed2006

Evolutionary origins of Notch signaling in early development.

Notch signaling is known to play key roles in early embryonic development and in the specification or patterning of germ layers in several lower organisms. Thus it is surprising that the removal of maternal and zygotic protein O-fucosyltransferase 1 (Pofut1), an essential component of the canonical Notch signaling pathway, does not affect early embryogenesis in the mouse. Mouse embryos lacking Pofut1 develop normally through blastogenesis to E8.0 when all three germ layers have formed. Here we summarize roles for Notch signaling in early embryonic development of several species, and discuss the potential evolutionary origins of these roles. We propose that Notch signaling might have first been used in the common ancestor of the metazoa for certain advanced developmental processes such as segmentation, and only later in evolution been coopted for use at early stages of embryogenesis in some organisms.

Animals↗

PubMed2003

[The expression of glucose-regulated protein 78 (GRP78) in mouse brain during early development].

The development of a multicellular organism results from the selective expression of genes and the maturation of proteins is dependent on molecular chaperons. However, the functions of molecular chaperones, especially endoplasmic reticulum chaperones, on brain development are unclear. In this article we examined the distribution and level of GRP78 in mouse brain during early development by means of Western blot, RT-PCR and immunohistochemistry. The results demonstrated that the expression of GRP78 was in a time-space specific pattern. High levels of GRP78 were present in early embryo stage, and were decreased during the fetal period, increased gradually during postnatal development, and reached adult mouse after one week. In addition, the expression of GPR78 displayed the levels in tendency to decrease from telencephalon to metencephalon during embryonic period. The distribution for GRP78 appeared to be present earlier in neurons than in glial cells. These results suggested that GRP78 might play a significant role in the early morphogenesis of brain.

Animals↗

PubMed1988

Early development of serotonin-containing neurons and pathways as seen in wholemount preparations of the fetal rat brain.

The early development of serotonin-containing neurons was studied in wholemounts of the fetal rat brain (E12-E18). The wholemounts were treated immunocytochemically according to an immunoperoxidase technique to reveal a panorama of developing serotoninergic neurons. Serotoninergic neurons were localized to two discrete groups or clusters within the brainstem. Serotonin-containing neurons were identified first at E12 forming a rostral cluster of cells just caudal to the mesencephalic flexure. The more caudal cluster of cells first appeared at E14 in the medulla. During the period from E12 to E18, the immunoreactive cells increased in number and acquired a more complex dendritic tree while migrating to their permanent position. At E16, cells of the rostral group exhibited remarkably uniform mediolateral orientation. The rostral group of immunoreactive neurons gave rise to almost all ascending fibers, whereas the caudal group gave rise to the majority of descending fibers. Growing serotoninergic fibers were tipped by prominent growth cones, which were strongly immunoreactive. The fibers demonstrated prominent orientational selectivity with an almost total separation into ascending and descending bundles. Some of the ascending immunoreactive fibers displayed acute changes in their direction of growth, suggesting that the orientation of serotininergic fibers is mediated by directional cues that are specific to particular populations of serotoninergic fibers. Serotoninergic axons within the medial forebrain bundle were demonstrated particularly well and their ascent and rate of growth toward the forebrain could be easily followed. Immunoreactive fibers entered the telencephalon at E17 two portals, one along the lateral border of the hypothalamus and one rostrally, adjacent to the olfactory tubercle. In wholemounts at E18, fibers arising from this latter location could be followed as two distinct bands within the pallium; a basal band located ventrolaterally, adjacent to the lateral olfactory tract, and a dorsal band located at the medial edge of the telencephalon. Both fascicles were directed toward the occipital pole and contained unbranched fibers. At E18, serotoninergic axons arising from these two loosely organized fascicles covered most of the frontal telencephalon. The results of the present study indicate that wholemounts of embryonic brain can provide novel spaciotemporal data on the development of neuro-transmitter systems and may in the future prove to be useful experimental preparations in developmental neurobiology.

Animals↗

PubMed2002

Cytoskeletal responses during early development of the downy mildew of grapevine (Plasmopara viticola).

A host-free system was established to induce the early development of the obligate biotrophic pathogen Plasmopara viticola, the downy mildew of grapevine. This system was used to study cytoskeletal responses during encystation and germ tube formation. During these processes, both the actin and the tubulin cytoskeleton show a stage-specific pattern of distribution. Elimination of the cytoskeleton by the actin drug latrunculin B and the microtubule drug ethyl-N-phenyl-carbamate did not affect the release of mobile zoospores from the sporangia, nor the encystation process, but efficiently inhibited the formation of a germ tube. The data are discussed with respect to a role of both actin and microtubules for the establishment of the cell polarity guiding the emergence and the growth of the germ tube.

Actins↗

PubMed1992

[Early development and cell differentiation of the parasympathetic vagus-glossopharyngeal nucleus in cattle. Light and electron microscopic studies].

The early development, differentiation of the cell and cell migration of the nucleus parasympathicus nervi vagi et glossopharyngei were examined by light microscope in 32 bovine embryos with crown-rump-lengths (CRL) ranging from 1 cm to 53 cm. During this period the nucleus is being enlarged 6 to 7 times and the size of the cell increases to 35-40 microns. The ultrastructure during the differentiation of the cell is shown electron microscopically in embryos with CRL of 2.5 cm and 3.6 cm. Several layers of matrix cells arise from the neuroepithelium of the neural tube by mitosis. They migrate in the shape of dark nucleated cells into the parasympathetic cell column. With advancing age of the embryos the number of cells with light nucleus increases. They represent the presumptive neurons. In embryos of 2.5 cm CRL their cytoplasm surrounds the nucleus on three sides in the shape of a narrow rim while on the fourth side it is enlarged into an outgrowing process. In this process a smaller number of organelles and their preliminary stages appears. Their number is significantly increased in embryos of 3.6 cm CRL and they can be seen throughout the growing process. In the following stages of maturity cytological development proceeds. In embryos of 53 cm CRL topographical and cytological data are comparable to those in adult animals.

Animals↗

PubMed1999

Constitutive and stress-inducible expression of the endoplasmic reticulum heat shock protein 70 gene family member, immunoglobulin-binding protein (BiP), during Xenopus laevis early development.

We have characterized the constitutive and stress-inducible pattern of immunoglobulin-binding protein (BiP) gene expression during Xenopus early development. Whole mount in situ hybridization analysis revealed that BiP mRNA was detected in unfertilized eggs, cleavage and blastula stage embryos. In gastrulae, BiP mRNA was present across the surface of the embryo, while in neurulae BiP mRNA was enriched in the neural plate, neural fold, and around the blastopore. In early and late tailbud embryos, BiP mRNA was found primarily in the dorsal region. Tunicamycin and A23187, the calcium ionophore, enhanced BiP mRNA accumulation first at the neurula stage, while heat shock induced BiP mRNA accumulation first at the gastrula stage. Compared to control, A23187- and heat shock-treated neurulae displayed relatively high levels of BiP mRNA in selected tissues, including the neural plate, neural folds, around the blastopore, and ectoderm. At the early tailbud stage, A23187 and heat shock enhanced BiP mRNA accumulation primarily in the head, somites, tail, and along the spinal cord. A similar situation was found with A23187- and heat shock-treated late tailbud embryos, except that heat-shocked embryos also displayed enhanced BiP mRNA accumulation in the epidermis. These studies demonstrate a preferential accumulation of BiP mRNA in selected tissues during development and in response to stress.

Animals↗

PubMed1992

Effects of cholinergic drugs on cell interactions during fertilization and early development of the sea urchin Paracentrotus lividus.

In the present work we tested the effects of cholinergic drugs on the early development of P. lividus. Fertilization was performed in the presence of cholinergic drugs, and the embryos were fixed after 2 hours, when the controls (untreated) completed the second segmentation cleavage. We identified four classes of stages in the development of the embryos affected by the drugs, i.e.: unhatched zygotes, first cleaved stage, second cleaved stage (= unaffected), and anomalous embryos. Statistical analysis indicated that that drugs with analogous action mechanism caused similar alterations in the distribution of the treated embryos in these four classes. This finding supports the hypothesis of the presence of a complete "pre-nervous" cholinergic system, with a true cholinergic role. It is tempting to speculate that this system is involved in the first cell to cell interactions during early segmentation and possibly in the block to polyspermy.

Acetylcholine↗

PubMed1987

Extra-axonal environment and fibre directionality in the early development of the chick embryo optic chiasm: a light and scanning electron microscopic study.

The events that occur during the early development of the optic chiasm of the chick embryo have been studied by light and scanning electron microscopy. In developmental stages previous to the arrival of the first optic fibres in the floor of the diencephalon, as well as during the arrival of the leading fibres, extracellular spaces can be seen in the diencephalon ventral wall. These spaces are defined by external cell prolongations which end in a foot-shaped formation. During stages 25 and 26 a prechiasmic degenerative centre appears in the area immediately rostral to the early chiasm, leading to a notable degree of disorganization in the diencephalon wall. This centre appears to be related to the reorganization of the system of external cell processes and extracellular spaces which become progressively more irregularly distributed, coinciding with the arrival of the first optic fibre fascicles to the midline of the floor of the diencephalon. The optic fibre fascicles change their latero-medial directionality in the medial-most regions of the ventral diencephalon, where their course becomes rostrocaudal. This reorientation of the optic fibres seems to be mediated by primitive glial cells which first appear in the ventrorostral region of the early chiasm (previously occupied by the system of external cell processes and extracellular spaces) in stage 26, increasing in number from this stage on. The morphology of the primitive glial cells is laminar in nature and the cells are seen to be densely packed together with no large extracellular spaces between them.

Animals↗

PubMed2000

Mathematical model for early development of the sea urchin embryo.

In Xenopus and Drosophila, the nucleocytoplasmic ratio controls many aspects of cell-cycle remodeling during the transitory period that leads from fast and synchronous cell divisions of early development to the slow, carefully regulated growth and divisions of somatic cells. After the fifth cleavage in sea urchin embryos, there are four populations of differently sized blastomeres, whose interdivision times are inversely related to size. The inverse relation suggests nucleocytoplasmic control of cell division during sea urchin development as well. To investigate this possibility, we developed a mathematical model based on molecular interactions underlying early embryonic cell-cycle control. Introducing the nucleocytoplasmic ratio explicitly into the molecular mechanism, we are able to reproduce many physiological features of sea urchin development.

Animals↗