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PubMed1989

Spatial and temporal variation in the structure of the basal lamina in embryonic grasshopper limbs during pioneer neurone outgrowth.

The pioneer neurones of the embryonic grasshopper limb use the basal lamina underlying the limb ectoderm as a substratum over which to grow from the periphery to the CNS (Anderson & Tucker, 1988). In this paper we use transmission electron microscopy to describe the structure of this substratum before, during, and after the time of axon navigation. The organization of the basal lamina varies considerably in different regions and at different times of development of the embryonic limbs, and is unlike that of the fully developed limb at the time of hatching. We suggest that this spatial and temporal variation could play a role in regulating the direction of outgrowth of pioneer neurones.

Animals↗
PubMed1998

Adhesive activity of gicerin, a cell-adhesion molecule, in kidneys and nephroblastomas of chickens.

Gicerin, a cell-adhesion molecule belonging to the immunoglobulin superfamily, has both homophilic and heterophilic binding activities to neurite outgrowth factor, an extracellular matrix molecule in the laminin family. Gicerin is thought to play a role in the normal development of chicken kidney, because it is expressed abundantly in the embryonic organ and only slightly in the mature organ. In this study, we have examined the adhesive activity of gicerin in the kidney to characterize its function in organogenesis. We have also examined the function of gicerin in chicken nephroblastomas ("embryonic nephromas"), which show various structures resembling those in embryonic kidneys. Immunohistochemically, the expression patterns of gicerin and neurite outgrowth factor in nephroblastomas are similar to those of embryonic kidneys. Cell-aggregation assays have shown that primary culture cells from both embryonic kidneys and nephroblastomas have strong aggregation activities, and that each aggregation is partially inhibited by gicerin antibody. In contrast, cells from adult kidney exhibit weak aggregation activity that is not inhibited by the antibody. In addition, ligand blot analysis has revealed that gicerins in embryonic kidney and nephroblastoma bind to purified neurite outgrowth factor, whereas extracts from adult kidney show no positive reaction. These findings suggest that the homophilic and heterophilic adhesive activities of gicerin are involved in the formation of both normal kidney and nephroblastoma.

Animals↗
PubMed1998

Transdifferentiation of chick embryonic retinal pigment epithelial cells to lentoid structure in suspension culture.

To test transdifferentiation of retinal pigment epithelial (RPE) cells in suspension culture, chick embryonic RPE sheets and dissociated RPE cells were cultured for two months in a non-adherent dish for suspension culture. RPE cells, isolated as a sheet, aggregated immediately and remained the same size with their differentiated characteristics for two months. The presence of basic fibroblast growth factor (bFGF) at concentrations of 10 ng/ml or higher induced the formation of a spherical lentoid structure which was positive for crystallin and bFGF receptor. In contrast, dissociated RPE cells did reaggregate but did not develop the lentoid structure even in the presence of bFGF. The transdifferentiation of RPE cells to the lentoid structure in this study was in contrast to their transdifferentiation to the retina, as reported in a previous study.

Animals↗
PubMed1988

Kinetic differences between embryonic- and adult-type acetylcholine receptors in rat myotubes.

1. The burst structures of embryonic-type (low-gamma) and adult-type (high-gamma) nicotinic acetylcholine (ACh) receptors (AChRs) in rat myotubes were investigated with the patch clamp technique. The channels were activated with the agonists ACh and suberyldicholine (SubCh). 2. With either agonist, the distribution of burst durations showed two exponential components for both channel types: a 'long' component that corresponds to bursts of one or more openings and a 'brief' component that includes short, isolated openings. 3. For low-gamma channels, the percentage of all openings associated with the brief component decreased from approximately 40% at 10-100 nM-ACh to less than 10% at 10-100 microM-ACh. 4. Both high-gamma and low-gamma long bursts were interrupted by brief (30-90 microseconds) closures and longer (approximately 1 ms) transitions to a partially open (subconductance) state. The duration of brief closures and partial openings was relatively independent of the agonist, but their frequency within low-gamma bursts was 3-fold higher with SubCh than with ACh. 5. Brief closures are interpreted as transitions to a closed, doubly liganded state from which the channel can reopen. This model predicts that the channel opening rate is greater than 10,000 s-1 for both channel types at room temperature. 6. Estimates of the channel opening rate inferred from the rising phase of miniature end-plate currents recorded from rat soleus fibres are consistent with this interpretation. 7. Both high-gamma and low-gamma channels apparently operate via similar gating mechanisms. Differences in their gating behaviour can be explained in terms of faster kinetic rate constants for high-gamma channels.

Acetylcholine↗
PubMed1988

Chronic ethanol exposure in the embryonic chick heart: effect on myocardial function and structure.

To investigate the effect of chronic ethanol exposure on the embryonic chick heart, chick embryos were exposed daily to one of seven graded doses of ethanol or to saline only (shams) from 0 to 96 hr of incubation. One hour before and after exposure at 72 hr, and 1 hr before and after exposure at 96 hr, embryos were analyzed for changes in heart function, embryo tissue ethanol content, occurrence of anomalies, and embryo weights. At both 71 and 73 hr of incubation (during cardiogenesis), when compared to shams, heart rate (HR) in embryos receiving ethanol doses greater than 0.0375 ml increased significantly (P less than .05) with commensurate increases in injected ethanol. Additionally, at 73 hr, depressed cardiac contractility, measured as shortening fraction, was noted at doses greater than or equal to .0375 when compared to shams. While slight increases in shortening fraction (SF) across dose were noted at 95 and 97 hr, only random doses were statistically significant from shams, with no specific trend in either HR or SF at this postcardiogenesis stage. Within each time group, gas chromatography analysis of embryo tissue ethanol content demonstrated a linear relationship between dose injected and tissue ethanol content retrieved. With increasing dose and stage, viability decreased. Weights of ethanol-injected embryos were not significantly different from shams within each time group. Our studies of the response of the embryonic chick heart to ethanol indicate both dose and stage susceptibility, with greater susceptibility to ethanol injury during active cardiogenesis.

Animals↗
PubMed1989

Progressive restriction in the distribution of the Hox-1.3 homeodomain protein during embryogenesis.

Expression of the murine homeobox containing gene Hox-1.3 was analyzed in mouse embryos using polyclonal antisera to peptides predicted from cDNA and genomic sequences. At the earliest stage examined, 7.5 days gestation, cell nuclei throughout the three embryonic germ layers and in extraembryonic structures derived from the fertilized ovum were strongly immunoreactive. Rostro-caudal gradients or other patterns of regional differentiation in levels of expression could not be seen. Surrounding maternal tissue showed only weak immunoreactivity. At 8.5 days gestation, immunoreactivity was present in all embryonic structures including neural tube, somites and lateral plate mesoderm, ectoderm and endoderm. Immunoreactivity was progressively restricted thereafter. At 17 days gestation, strong immunoreactivity was largely restricted to the nervous system, both central and peripheral. Spinal cord was well stained, with a dramatic reduction in intensity near the junction of spinal cord and brain. In addition to this overall pattern, enhanced immunoreactivity appeared in limited populations of newly-formed neuroblasts of spinal cord and brain, suggesting that Hox-1.3 might serve to regulate the development of specific types of neurons following cessation of precursor cell mitosis.

Animals↗
PubMed2000

Structural dynamics and function of early embryonic coats.

The extracellular embryonic coats (embryo/blastocyst coverings) that surround early mammalian embryos are most often still referred to as zona pellucida. Accumulating evidence from a number of earlier and recent studies clearly indicates that this is an oversimplification which cannot be defended anymore, at least in many species. Structural modifications of the coats occur during cleavage and blastocyst stages; these are most obvious in a number of species with the central type of implantation and, related to this, a high degree of blastocyst expansion, notably the rabbit and the horse. In this contribution, formation and transformation of the various layers of coats (zona pellucida, mucoprotein layer, neozona and gloiolemma in the rabbit, capsule in the horse) will be reviewed, as will be comparable structures seen, e.g., in the fur seal (subzonal layer) and the baboon. These phenomena will be discussed in the context of structurally more subtle changes found in other species, including those with small blastocysts and other types of implantation, in particular with biochemical modifications which may be physiologically quite important. The molecular mechanisms of deposition of coats and their transformation and shedding/dissolution will be briefly addressed. The possible functional significance of the coats and their transformation will be discussed (mechanical, morphogenetic and immunological role, molecular transport control, blastocyst positioning, implantation, trap and reservoir function for signalling molecules).

Animals↗
PubMed1979

Cell-to-cell contacts in primary cultures of dissociated chicken embryonic brain.

The fine structure of intercellular contacts was studied in primary cultures prepared from chicken embryonic brain. Desmosomes were frequently seen between the glial cells. Synaptic contacts were observed among neuronal cell bodies and neural processes after 8 days in vitro. Gap junctions were revealed between glial elements suggesting a functional role in direct cell communication and providing a morphological basis for previous observations on potassium transport in cultures of dissociated brain cells.

Animals↗
PubMed1990

Three-dimensional structure of intracellular membranous organelles in embryonic chick skeletal muscle cells in vitro revealed with scanning electron microscope.

Using the freeze-polishing and osmium-maceration procedures, the ultrastructure of intracellular membranous organelles in embryonic chick skeletal muscle cells in vitro was investigated three-dimensionally with the scanning electron microscope (SEM). T-system tubules followed a tortuous course and possessed many warts. Some of these tubules could be traced to the sarcolemma. The sarcoplasmic reticulum (SR) had elaborate structures of a hexagonal pattern. By comparing the SEM images with those of ultrathin sections of myotubes impregnated with ferritin particles, the distinction between the T-system and SR was confirmed. Late in the culture, these two intracellular membranous systems were arranged periodically at right angles to the longitudinal axis of the myotubes. Round-shaped mitochondria were often arranged in chains connected with slender rods. Long rod-shaped mitochondria exhibited occasional branchings.

Animals↗
PubMedDate not supplied

IFN-tau: a novel subtype I IFN1. Structural characteristics, non-ubiquitous expression, structure-function relationships, a pregnancy hormonal embryonic signal and cross-species therapeutic potentialities.

IFN-tau (IFN-tau) constitutes a new class of type I IFN which is not virus-inducible, unlike IFN-alpha and IFN-beta, but is constitutively produced by the trophectoderm of the ruminant conceptus during a very short period in early pregnancy. It plays a pivotal role in the mechanisms of maternal recognition of pregnancy in ruminants and it displays high antiviral and antiproliferative activities across species with a prominent lack of cytotoxicity at high concentrations in vitro in cell culture and possibly in vivo. It exhibits high antiretroviral activity against HIV and exhibits immunosuppressive activity in a multiple sclerosis model and reduces embryo and fetal mortality by stimulation of IL-10 production. In this review all the biochemical and para-hormonal properties of this novel IFN-tau are described in detail: structural characteristics of proteins and genes, trophoblast expression, regulation of its expression, structure of its gene promoter, its absence in human species and in non-ruminant animals, the evolution of the IFN-tau genes, its structure-function relationships with its three-dimensional structure, structural localization of biological activities, its lack of cytotoxicity and its receptor. Surprisingly, for an IFN, IFN-tau is also a pregnancy-embryonic signal with paracrine antiluteolytic activity. In order to maintain luteal progesterone secretion, IFN-tau inhibits PGF-2alpha pulsatile secretion and oxytocin uterine receptivity in early pregnancy. It is believed to suppress pulsatile release of endometrial PGF-2alpha by preventing oxytocin and estrogen receptor expression. Additionally, it directly regulates prostaglandin metabolism and possibly the PGE:PGF-2alpha ratio.

Animals↗
PubMed1996

Distribution of nitric oxide synthase-immunoreactive neurons in fetal rat brains at embryonic day 15 and day 19.

Although nitric oxide (NO) is hypothesized to play a role in the modelling of neuronal connections in the developing brain, no precise histological information has been reported on nitric oxide synthase immunoreactive (NOS-IR) structures in the embryonic brain. Thus, we examined the distribution of NOS-IR structures in the rat brain at embryonic day 15 (E15) and day 19 (E19), as a stage of early embryonic neurogenesis and active synaptogenesis, respectively. In the brain at E15, a few NOS-IR cell bodies were observed in the diencephalon near the 3rd ventricle and in the pons. By E19, the number of NOS-IR cells was greatly increased. Many NOS-IR cells were distributed throughout the forebrain and the medulla oblongata. NOS-IR cells of the neostriatum were located in its ventrolateral two-thirds. NOS-IR cells in the hypothalamus were distributed densely in the medial part while sparsely in the latero-ventral part, suggesting medio-lateroventral directions of NOS development. In the lower brainstem, on the other hand, NOS-IR cells were distributed in a similar pattern to that reported in adult rat, indicating earlier development of synaptic refinement in this area. The number of NOS-IR cells in the cerebral cortex and the cerebellum was very few.

Animals↗
PubMed1992

Structure-affinity relationships of retinoids with embryonic cellular retinoic acid-binding protein.

Separation and quantitation of cellular retinoic acid-binding protein (CRABP) in embryonic and fetal hamster tissues was accomplished with high-performance size-exclusion chromatography. Binding affinity of 26 retinoids was established by in vitro displacement of high specific activity all-trans-[3H2]retinoic acid from fetal CRABP. The CRABP concentration in presomite-to-early somite (Day 8) hamster embryos was 1.9 pmol/mg cytosolic protein and increased to 7.5 pmol/mg protein in Day 13 fetuses; CRABP concentrations subsequently declined as gestation progressed. CRABP was located primarily in fetal brain and skin (5.8 +/- 0.3 and 2.2 +/- 0.1 pmol/mg protein, respectively), whereas only trace concentrations were found in fetal liver, placenta, and maternal uterus. Retinoids that could displace all-trans-retinoic acid from CRABP had a free acid at the polar terminus (or were carboxylate esters that were readily hydrolyzed to the corresponding free acid) and had a hydrophobic ring at the distal position. The ligand specificity of the CRABP studied here suggests that this protein was analogous to the CRABP I isoform. The in vitro binding affinities of teratogenic retinoids that competed for embryonic CRABP failed to correlate directly with relative teratogenic potency. In some instances, the latter observation can be related to extensive in vivo biotransformation of retinoids to multiple teratogenic metabolites and to retinoid persistence in the embryo. Three analogs containing a free carboxy terminus, SRI 5898-21, SRI 7323-78, and SRI 6153-40, were identified with high teratogenic potency but failed to bind fetal hamster CRABP. The structure-activity and binding data of the analogs studied here indicate that many, if not most, teratogenic retinoids (or their acidic metabolites) bind with embryonic/fetal CRABP, but the present data question the role for CRABP in their teratogenic mechanism of action.

Animals↗
PubMedDate not supplied

[The effect of 5-azacytidine on the cell cycle and chromosome structure in cell cultures of swine embryonal kidney tissue].

Incubation of pig kidney cells (PK-cells) in the presence of 5-azacytidine (5-azaC), a DNA enzymatic methylation inhibitor, at concentration of 20 microM for 6 or 24 h results in a dramatic decrease in the DNA methylation level (5mC/C + m5.100) - from 3.0 in control to 1.0 in experiment. This is accompanied by a virtually complete arrest of mitosis and a decrease in the ratio of labeled interphase cells upon simultaneous introduction of 3H-deoxycytidine. The incubation with 5-azaC block PK-cells mainly in the G2-period. The inhibitory action is reversible, for the cells enter into mitosis after removal of the inhibitor. Metaphase chromosomes, whose DNA was replicated in the presence of the 5-azaC, exhibit certain ultrastructural differences from normal ones. The results are being discussed in connection with the earlier data on the anomalous structure of interphase chromatin formed in the course undermethylated DNA replication.

Animals↗
PubMed1985

[Study of the spatial structure of the protein component of the carcino-embryonic antigen by circular dichroism, Raman spectroscopy and UV-spectroscopy].

The spatial structure features of intact and deglycosylated carcino-embryonic antigen (CEA) have been studied by circular dichroism. Raman and UV-spectroscopy methods in order to elucidate a pattern and localization of CEA immunodominants. The temperature-induced changes in the spatial structure of the protein moiety were compared with data on the CEA immunochemical activity estimated by EIA procedure. A conformational transition was found within the 55-75 degrees range that produced irreversible alterations in the tertiary structure, while the secondary structure could be restored after lowering the temperature to 20 degrees C. Spectral studies of intact and deglycosylated CEA demonstrated that immunochemical activity, at least partly, was associated with the tertiary structure of the CEA protein portion.

Carcinoembryonic Antigen↗
PubMed2004

Basement membrane distortions impair lung lobation and capillary organization in the mouse model for fraser syndrome.

Fras1 is a putative extracellular matrix protein that has been implicated in the structural adhesion of embryonic epidermis to dermis. Moreover, mutations in Fras1/FRAS1 have been associated with the mouse blebbed phenotype and the human rare genetic disorder Fraser syndrome, respectively. Here we report the mapping of Fras1 within the extracellular space and evaluate the effects of Fras1 deficiency on lung development in the mouse. Expression of Fras1 was detected in the mesothelial cells of the visceral pleura and in the conducting airway epithelia. Immunogold histochemistry identified Fras1 as a component of the extracellular matrix localized below the lamina densa of epithelial basement membranes in the embryonic lung. Embryos homozygous for a targeted mutation of Fras1 exhibited fused pulmonary lobes resulting from incomplete separation during development as well as a profound disarrangement of blood capillaries in the terminal air sacs. We demonstrate that loss of Fras1 causes alterations in the molecular composition of basement membranes, concomitant with local disruptions of epithelial-endothelial contacts and extravasation of erythrocytes into the embryonic respiratory lumen. Thus, our findings identify Fras1 as an important structural component of the sub-lamina densa of basement membranes required for lobar septation and the organization of blood capillaries in the peripheral lung.

Animals↗
PubMed2002

Formation and malformation of the vertebrate left-right axis.

Despite an externally symmetric body plan, the internal viscera of all vertebrates are asymmetric with respect to the left-right body axis. Determination of the handedness of this asymmetry is nonrandom and highly conserved among vertebrates. Errors in patterning along the left-right axis, which occur in about 1 in 10,000 human births, may result in significant morbidity and mortality. During early embryonic development, midline structures, in particular the node, coordinate patterning of the three main embryonic axes: anterior-posterior, dorsal-ventral, and left-right. A current model for specification of the handedness of left-right axis asymmetry invokes the activity of embryonic cilia in the node that create a net leftward flow of extraembryonic fluid. This flow is proposed to provide a signal for subsequent asymmetric gene expression. Signaling from the node defines patterns of asymmetric gene expression on the left and right sides of the embryo. These signals for "left" and "right" are ultimately interpreted by organ primordia during later development. Complex activating and inhibiting interactions involving TGF-beta family members, as well as homeobox transcription factors, mediate these asymmetric patterns of gene expression. The identification of the genes regulating left-right axis patterning in model organisms has resulted in the characterization of human mutations associated with left-right axis malformations.

Animals↗
PubMed1992

Structural and ultrastructural pattern of the embryonic and early foetal human liver.

With the aim of stressing the main steps which characterize the early development of the human foetal liver, fragments of hepatic buds of 7-12 weeks of pregnancy have been processed for light and scanning electron microscopy; Vial and Porter technique for isolated cells has been utilized too. The obtained results can be summarized as follows. At the 7th-8th weeks the hepatocytes show a globose shape, their surface is furnished with scattered and irregular evaginations and they are arranged in loose and narrow ribbons, separated by vascular spaces; the hepatocytes are tightly connected with haemopoietic cells, usually furnished with hyperchromatic nuclei. On the other hand, the hepatic parenchyma shows a compact pattern at the 11th-12th weeks. The hepatocytes have acquired a polyhydric shape and their faces are usually interlocked with the plasmatic membrane of the adjoining elements than in three fields: (a) the face projecting to the vascular walls with which they are going to form the Disse spaces; (b) the opposite side in which the membranes of neighbouring cells often appear spaced to line the primitive biliary canaliculi; and (c) the areas in which hemispheric and deep hollows of the hepatocyte surface hold haemopoietic elements. The obtained results demonstrate that the developing hepatic buds undergo deep structural changes, at level of the parenchyma and vascular system, in the studied period.

Fetus↗