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At least 1,117 records · Page 62Linked to original sources
PubMed1999

Aspects of cell proliferation kinetics of the inner dental epithelium during mouse molar and incisor morphogenesis: a reappraisal of the role of the enamel knot area.

First lower E-14 and E-16 mouse molars and E-13 lower incisors were cultured in vitro and either sequentially or continuously labelled with BrdU (5-bromo-2'-deoxyuridine). The behaviour of the non-cycling inner dental epithelial cells emerging from the enamel knot area of the molars was analysed by 3D (three dimensional) reconstructions of serial sections. These cells, as well as slow cycling cells underwent a coordinated temporo-spatial patterning leading to their patchy segregation at the tips of the forming cusps. In incisors (in vitro and in vivo), non-cycling cells were also present in the inner dental epithelium of the enamel knot area. However, these cells were not redistributed during incisor morphogenesis. These non-dividing inner dental epithelium cells of the enamel knot area which are either redistributed or not according to the tooth type specific morphogenesis might represent the organizers of morphogenetic units (OMU), the cusps.

Animals↗
PubMed1999

[Morphogenesis of Mauthner neurons of Xenopus laevis tadpoles following early unilateral eye enucleation].

The connection between Mauthner neuron (CMN) and visual analyzer in Xenopus laevis tadpoles was studied using these neurons capacity to change their morphogenesis during the development in case of interruption of their connections with afferent fibres. In phase 31 of development tadpoles were subjected to unilateral enucleation of eye. Morphogenesis of contralateral (experimental) and ipsilateral (control) MN with respect to the operated eye was followed up. Comparison with intact Mauthner neuron of the tadpole of the same age who were not exposed to operation was conducted. Contralateral MN were found to be delayed in development phases 47 and 50. This was associated with 1.5-3.3 fold difference in neuron body central section area and 2-3 fold differences in nuclear section area. Three-dimensional reconstruction revealed lower number of cell processes in contralateral MN as well as decline in their length and diameter. Control and intact MN showed no difference similar to experimental and control ones in phase 41. The data obtained indicate that MN of Xenopus laevis tadpole possess powerful ipsilateral connections originating from the side of visual analyzer and contralateral ones from the side of the eye. This affects MN development and in contrast to octavolateral system (including vestibular apparatus and organs of lateral line) controls the contralateral neuron.

Animals↗
PubMed1998

Dissecting embryonic and seedling morphogenesis in Arabidopsis by promoter trap insertional mutagenesis.

Development can be considered to comprise the co-ordinated regulation of patterning at different levels: patterning of cells to form tissues, patterning of tissues to form organs, and patterning of organs to generate the characteristic architecture of the organism. These processes are expected, in turn, to be mediated by the precise spatial and temporal regulation of patterns of gene expression during development, which depend on appropriate signalling mechanisms. In order to investigate molecular events of morphogenesis in plants, we have utilized a system of promoter trap insertional mutagenesis in Arabidopsis, to generate both phenotypic mutants and gene fusions that represent markers useful in studying the regulation of patterning. A screen of transgenic seedlings containing a T-DNA promoter trap has led to the identification of mutants defective in seedling shape and embryonic development, and of GUS fusion genes that are expressed in spatially restricted patterns. Mutants have been crossed with marker lines expressing cell type-specific GUS activities, to investigate their cellular organization. For example, the POLARIS marker gene is expressed in the embryonic and seedling root tip. When crossed with hydra, which lacks an embryonic root, and with emb30, which lacks both embryonic and seedling roots, it is nevertheless expressed in the correct relative position, and we hypothesize that it represents a novel marker of root positional information, independent of root morphogenesis.

Arabidopsis↗
PubMed2000

Aposymbiotic culture of the sepiolid squid Euprymna scolopes: role of the symbiotic bacterium Vibrio fischeri in host animal growth, development, and light organ morphogenesis.

The sepiolid squid Euprymna scolopes forms a bioluminescent mutualism with the luminous bacterium Vibrio fischeri, harboring V. fischeri cells in a complex ventral light organ and using the bacterial light in predator avoidance. To characterize the contribution of V. fischeri to the growth and development of E. scolopes and to define the long-term effects of bacterial colonization on light organ morphogenesis, we developed a mariculture system for the culture of E. scolopes from hatching to adulthood, employing artificial seawater, lighting that mimicked that of the natural environment, and provision of prey sized to match the developmental stage of E. scolopes. Animals colonized by V. fischeri and animals cultured in the absence of V. fischeri (aposymbiotic) grew and survived equally well, developed similarly, and reached sexual maturity at a similar age. Development of the light organ accessory tissues (lens, reflectors, and ink sac) was similar in colonized and aposymbiotic animals with no obvious morphometric or histological differences. Colonization by V. fischeri influenced regression of the ciliated epithelial appendages (CEAs), the long-term growth of the light organ epithelial tubules, and the appearance of the cells composing the ciliated ducts, which exhibit characteristics of secretory tissue. In certain cases, aposymbiotic animals retained the CEAs in a partially regressed state and remained competent to initiate symbiosis with V. fischeri into adulthood. In other cases, the CEAs regressed fully in aposymbiotic animals, and these animals were not colonizable. The results demonstrate that V. fischeri is not required for normal growth and development of the animal or for development of the accessory light organ tissues and that morphogenesis of only those tissues coming in contact with the bacteria (CEAs, ciliated ducts, and light organ epithelium) is altered by bacterial colonization of the light organ. Therefore, V. fischeri apparently makes no major metabolic contribution to E. scolopes beyond light production, and post-embryonic development of the light organ is essentially symbiont independent. J. Exp. Zool. 286:280-296, 2000.

Animal Structures↗
PubMedDate not supplied

Occurrence and temporal variation in matrix metalloproteinases and their inhibitors during murine secondary palatal morphogenesis.

Extracellular matrix (ECM) molecules are known to play a pivotal role in morphogenesis of the secondary palate, and changes in their composition and distribution, not attributable to changes in synthesis, are known to occur during palatogenesis. The present study was undertaken to determine if the enzymes responsible for mediating their degradation, the matrix metalloproteinases (MMP), and their specific inhibitors, the tissue inhibitors of metalloproteinases (TIMP), are temporospatially regulated during murine palatal shelf morphogenesis. Palatal shelves were harvested at gestational days (gd) 12, 13 and 14. MMPs were identified by gelatin zymography, with and without inhibitors, and the identity of specific bands confirmed by Western blot analysis. TIMPs were identified by reverse zymography. MMP and TIMP messages were detected using RT-PCR with specific primers to MMPs 2, 3, 7, 9 and 13 and TIMPs 1 and 2. Zymography revealed bands of molecular weights corresponding to MMPs 2, 7, 9 and 13 at all ages examined; the intensity of these bands increased with developmental age. Western blot analysis established the presence of MMP-3 and its developmental variation in expression. RT-PCR demonstrated the presence of mRNA for all MMPs and TIMP at all sampling times and all but MMP-2 showed developmental variation. Whereas increases in mRNA were detected for MMPs 3, 9, and 13, MMP-7 mRNA decreased between gd 12 and 14. The results of this study demonstrate that MMPs 2, 3, 7, 9 and 13 and TIMPs 1 and 2 and their messages are present during the course of palatal shelf remodelling and that their expression is temporally regulated.

Animals↗
PubMed2000

[Experimental angiogenesis : strategy for the functional study of the transcription factors of the Ets family during morphogenesis of the vascular tree].

During morphogenesis of the vascular tree, the massive outgrowth of primitive capillaries is followed by the development and the maturation of some capillary branches whereas others regress. The direct observation and the manipulation of in vivo models, including a series of recent knock-out experiments, allow to delineate the mechanisms controlling this process, and to identify factors involved in the formation of a mature capillary, surrounded with a basal lamina and pericytes. The expression of several members of the Ets family of transcription factors, Ets1, Erg and Fli, correlates with the occurrence of invasive processes, such as angiogenesis during normal and pathological development. The description of the phenotype of cultured endothelial cells expressing the DNA binding domain of Ets1 suggests that members of the Ets family take part in the morphogenesis of the -vascular tree. Although transient transfection experiments allowed the identification of putative targets genes for Ets1 during angiogenesis, deciphering the Ets1 regulation networks remains a major goal for the future.

Animals↗
PubMed2000

Intestinal fatty acid binding protein gene expression reveals the cephalocaudal patterning during zebrafish gut morphogenesis.

Intracellular fatty acid-binding proteins (FABPs) are small and highly conserved cytoplasmic proteins that bind long-chain fatty acids and other hydrophobic ligands. We have examined, as a model for studying intestinal epithelial cell differentiation, the cell-specific and spatio-temporal expression of intestinal fatty acid-binding protein (i-fabp) gene during zebrafish larval development. After molecular cloning of zebrafish I-FABP cDNA, whole-mount in situ hybridization analysis revealed that i-fabp is expressed in the intestinal tube around day 3 postfertilization. By day 4, highest level of i-fabp transcript is encountered in the proximal columnar epithelium. From day 5 onwards, i-fabp is strongly expressed in the anterior intestine and its rostral expansion, slightly expressed in the esophagus mucosa and rectum, while no mRNA could be detected in the posterior intestine. Therefore, the regional differentiation of the intestine precedes first feeding and complete yolk resorption. I-fabp expression in the anterior intestine of the fed larvae is correlated with an intracellular storage of lipid droplets in the enterocytes and the massive synthesis of very low-density lipoprotein particles. In conclusion, the cephalocaudal expression pattern of i-fabp demarcates early during zebrafish gut morphogenesis the anterior fat absorbing to posterior cells of the intestine. This gene could be used as a marker for screening for mutations that affect the events of intestinal epithelial differentiation, cephalocaudal patterning, and asymmetric gut looping morphogenesis.

Amino Acid Sequence↗
PubMed2000

[Molecular cell biology on morphogenesis of the fovea and evolution of the central vision].

Since Charles Darwin wrote "On the Origin of Species by Means of Natural Selection", it had been assumed that various eye types, from the compound eye to the camera eye, had originated independently in at least 40-60 different phyletic lines. However, the finding of Pax 6, the master control gene for eye morphogenesis, and the fact that its sequence is highly conserved throughout the animal kingdom indicated that the prototype eye in a primitive animal originated only once in evolution, and various eye types arose from the same origin. We recently found a Pax 6 mutation in a pedigree with foveal hypoplasia. Thus, the Pax 6 that appeared in light sensory cells of a primitive animal in ancient times may play a role in morphogenesis of the fovea, the most highly developed visual receptor. The fovea first appeared in evolution in the temporal retina of fishes. Then, in birds, the nasal fovea and bifoveal system with nasal and temporal foveas developed. The fovea disappeared in primitive mammals, and reappeared in primates. A residue of the fovea is conserved in the visual streak, and the disappearance and reappearance of the fovea, in primitive mammals and primates respectively, correlates with degeneration and restoration of cone pigment genes in photoreceptors. Humans inherited the temporal fovea that had first originated in fish eyes. Pax 6 is expressed in the entire eyeball at an early stage of development, and is also expressed widely in the retina to determine its differentiation. To determine the position of the fovea, retinal cells are abundant in the visual streak, probably because expression of Pax 6 is regulated by patterning of the dorsoventral axis of the eyeball. Signaling molecules, discharged from the front of the face, also regulate Pax 6 expression, and determine position of the fovea, visual axis, angle gamma, growth of the eyeball, and shape of the visual field. Further investigation of nerve pathfinding system from the fovea to the central nervous system will clarify the origin of the central vision, and contribute to human welfare.

Animals↗
PubMed2000

[Morphogenesis and formation of a pattern in hydra. I. Distribution of morphogenetic potential].

True multicellularity is characterized by complex interactions between individual cells of the organism as well as by organization of cell masses into spatially and functionally determined structures promoting the exchange of information. Morphogenetic processes--genetically programmed generation of structures--always correlate with determination and maintenance of a pattern, i.e. a system of spatial relationships between them. Hydroid polyps provide a wide variety of approaches to study morphogenesis and patterning. Being comparatively simply organized, these animals have nevertheless certain developed mechanisms underlaying such processes as regeneration of missing structures, recovery of normal pattern after dissociation of polyps into single cells, tissue transdifferentiation in non-complementary chimaeras. An important feature of regeneration of hydroid polyps is its independence of the nerve net elements; the basis for regeneration is rather stored in epithelial cells and in their interactions. Phenomenological data, provided in the XVIII-XX centuries, allowed to propose several theoretical models of pattern regulation in hydra. The main goal of this paper is to review contemporary models of morphogenesis and patterning in the hydroid polyps.

Animals↗
PubMed2000

Tumor patterning: analogies of neoplastic morphogenesis with embryogenesis.

Patterning or pattern formation is a spatial and temporal process, by which ordered arrangements of cells and tissue structure are attained. The term is mostly applied to the morphogenesis in developmental biology, but it can also be useful for the neomorphogenesis in tumor biology. Despite increasing data on the proliferation and differentiation of tumor cells, processes of tumor patterning are rarely studied and poorly understood. A fundamental embryonic process of patterning is the gastrulation and a basic example of neoplastic patterning is the colonic adenoma-carcinoma sequence. Both processes exhibit distinct nuclear translocations and expressions of beta-catenin, which is considered to be a decisive transcriptional regulator. Our recent studies demonstrate striking analogies of patterning and nuclear beta-catenin expressions between the colonic adenoma-carcinoma sequence and the gastrulation steps. The shared patterns are dissociation, reassembly, tubular reconstruction and branching of neoplastic cells in association with nuclear beta-catenin expressions. These new findings establish patterning as a relevant concept for tumor biology and link the neoplastic morphogenesis with embryogenesis.

Body Patterning↗
PubMedDate not supplied

Dentition development and budding morphogenesis.

The development of functional teeth in the mouse has been widely used as a model to study general mechanisms of organogenesis. Compared with other mammals, in which three incisors, one canine, four premolars, and three molars may occur even in each dental quadrant, the mouse functional dentition is strongly reduced. It comprises only one incisor separated from three molars by a toothless gap diastema at the location of the missing teeth. However, mouse embryos also develop transient vestigial dental primordia between the incisor and molar germs in both the upper and lower jaws. These rudimental structures regress, and epithelial apoptosis is involved in this process. The existence of the vestigial dental structures allowed a better assessment of the periodicity in the mouse dentition, which extends opportunities for the interpretation of molecular data on tooth development. We compared the dentition development with tentative models of budding morphogenesis in other epithelial appendages lungs and feathers. We suggested how developmental control by signaling molecules, including bone morphogenetic protein (Bmp), sonic hedgehog (Shh), and fibroblast growth factor (Fgf), can be similarly involved during budding morphogenesis of dentition and other epithelial appendages. We propose that epithelial apoptosis plays an important role in achieving specific features of dentition, whose development involves both budding and its more complex variant branching. The failure of segregation of the originating buds supports the participation of the concrescence of several tooth primordia in the evolutionary differentiation of mammalian teeth.

Animals↗
PubMed1993

Embryonic lung morphogenesis in organ culture: experimental evidence for a proteoglycan function in the extracellular matrix.

The lung rudiment, isolated from mid-gestation (11 day) mouse embryos, can undergo morphogenesis in organ culture. Observation of living rudiments, in culture, reveals both growth and ongoing bronchiolar branching activity. To detect proteoglycan (PG) biosynthesis, and deposition in the extracellular matrix, rudiments were metabolically labeled with radioactive sulfate, then fixed, embedded, sectioned and processed for autoradiography. The sulfated glycosaminoglycan (GAG) types, composing the carbohydrate component of the proteoglycans, were evaluated by selective GAG degradative approaches that showed chondroitin sulfate PG principally associated with the interstitial matrix, and heparan sulfate PG principally associated with the basement membrane. Experiments using the proteoglycan biosynthesis disrupter, beta-xyloside, suggest that when chondroitin sulfate PG deposition into the ECM is perturbed, branching morphogenesis is compromised.

Animals↗
PubMed1993

Extracellular matrix and growth factors in branching morphogenesis.

The unifying hypothesis of the NSCORT in gravitational biology postulates that the ECM and growth factors are key interrelated components of a macromolecular regulatory system. The ECM is known to be important in growth and branching morphogenesis of embryonic organs. Growth factors have been detected in the developing embryo, and often the pattern of localization is associated with areas undergoing epithelial-mesenchymal interactions. Causal relationships between these components may be of fundamental importance in control of branching morphogenesis.

Animals↗
PubMed2001

The role of capsulin in the morphogenesis and differentiation of fetal rat gastric mucosa.

The signals that guide the morphogenesis and differentiation of rat fetal gastric mucosa remain largely unknown. We have investigated the role of capsulin in pit/gland formation and epithelial cell differentiation in cultured stomach tissue. Embryonic day 16.5 (E 16.5) stomach tissue cultured for three days in the presence of 1 microM hydrocortisone underwent dramatic transformation, from undifferentiated, stratified cells to differentiated epithelia composed of polarised columnar cells with mucous cells and pit/glands. In the presence of capsulin antisense oligonucleotides directed against capsulin mRNA, tissues do not undergo further development. Significantly, both mucous granules and pit/gland formation were inhibited compared to capsulin sense/scrambled oligonucleotide treated controls. However, in tissues treated with specific anti-rat HGF-antiserum to neutralise secreted HGF, pit/gland formation was inhibited, but the number of mucous granules remained unchanged compared to controls treated with non-specific antiserum (mouse monoclonal cytokeratin 8 antiserum). This data suggests that capsulin may have a role in the morphogenesis of pit/glands and mucin granule formation in the developing rat gastric mucosa. We discuss the possibility that this role of capsulin may be partly mediated through the actions of HGF.

Animals↗
PubMedDate not supplied

[Present views of prenatal morphogenesis of human lung].

Published and original data on human lung morphogenesis during prenatal development are reviewed. Morphofunctional description of the lung at various phases of prenatal morphogenesis is given. Differentiation of various lung structures, surfactant system, development of intrapulmonary fluid, and the onset of breathing movements of the fetus are considered in chronological order. The "critical periods" when the fetal respiratory organs are most sensitive to unfavorable factors are considered. Morphofunctional tests for lung maturity are described applicable for predicting lung pathology of human fetus.

Bronchoalveolar Lavage Fluid↗
PubMedDate not supplied

[Variability of flavonol contents during floral morphogenesis in Papaver somniferum L].

We studied the contents of flavonols (kaempferol and quercetin) in the meristem of vegetative and generative apices of the main plant shoot in floral Papaver somniferum mutants, as well as in the normal plants at successive stages of flower development. Five stages of flower development were distinguished. Flavonols (kaempferol and quercetin) were present in all flower organs at all stages of floral morphogenesis we studied. However, their contents and distribution in different organs and at different stages of flower development markedly varied. No significant differences were found in the contents of flavonols in the meristems of vegetative and generative apices of the main shoot in the lines of floral mutants, as well as between the lines with different amounts of vegetative phytomeres. In the plants with normal flower structure, the contents of flavonols (kaempferol + quercetin) sharply increased with the beginning of differentiation of flower organs, i.e. from stage 3, to reach a maximum in the open flower, when gametogenesis is terminated and fertilization takes place. The level of flavonol contents in the petals (upper part) and stamen was at a maximum at all stages of flower development, while that in the gynaecium was at a minimum. The kaempferol: quercetin ratio shifted towards quercetin at successive stages of flower development, most significantly in the stamens. The involvement of flavonols in the regulation of floral morphogenesis at stages of flower organs differentiation and functioning is discussed.

Flavonols↗
PubMedDate not supplied

[Structurization of cortical layer of loach yolk cell after wounding as a "minimal" model of morphogenesis].

Structural rearrangements of the yolk cell surface were studied in loach embryos using SEM and TEM, which take place within 30 min after a point-like puncture at the late blastula stage. The effects of sucking off or addition of a part of yolk, lowered temperature, and absence of Ca2+ on structurization were studied. Around the area of puncture, the yolk granules were submerged, the number of vesicles increased, and numerous membrane folds were formed. The folds were aggregated to form two sharply distinct types of structures: a group of rounded evaginations around the site of puncture and a system of radial folds in the periphery. Small radial folds are aggregated in radial strands, several dozens folds in each. Sucking off a part of yolk accelerated the above processes, while addition of yolk, cooling, and absence of Ca2+ in the incubation medium slowed down or suppressed these processes. The observed structurization can be considered as self-organization at the level of the yolk cell cortical level, largely similar to that during normal morphogenesis at the level of multicellular sheets. Hence, the membrane dynamics in the yolk cell wall after its damage can be considered as one of simplified ("minimal") models of morphogenesis. A study of this model makes it possible to narrow down the circle of factors essential for self-organization of morphogenetic processes.

Animals↗
PubMedDate not supplied

[Dynamics and variability of early morphogenesis in the loach according to observations of individual developmental trajectories].

The dynamics and variability of quantitative morphological characters (morphological variables), which undergo changes upon epiboly, were studied by means of vital observations and measurements of developing loach (Misgurnus fossilis L.) embryos within equal time intervals. None of morphological variables, which characterize the dynamics of blastoderm shape, had monotonous dependence on time. In each individual embryo, the intervals of changes in morphological variables in the "normal" direction corresponding to the change of their mean values during the normal course of epiboly alternated with arrests, as well as with the changes of morphological variables in the reverse direction. The dynamics of morphological variables in time, which reflect the sequence of morphological states of the same embryo, and those of individual variations (variations of morphological states of different embryos on the same temporal section) had identical structure. This suggests instability of individual trajectories of morphogenesis or, strictly speaking, their actual absence. It was shown for the first time on the basis of analysis of individual trajectories of morphogenesis that its dynamics corresponded to so-called "determined chaos", which was previously discussed only as a theoretical possibility. The data obtained suggest that upon approach to the equatorial area of the embryo, the blastoderm marginal zone was elongated in the longitudinal direction and contracted across the axis of its movement. As a result, a positive feedback arises between the cooperated cell movement and the change of shape of the surface, over which the cells move. This leads, due to unstable radial symmetry of this movement, to the formation of embryonic shield.

Animals↗