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PubMed1988

Secretory activity in the floor plate neuroepithelium of the developing human spinal cord: morphological evidence.

The developing spinal cord at the cervical and thoracic levels in 14 human embryos ranging from Carnegie stages 14 to 20 were examined with the electron microscope. The floor plate-forming cells contained numerous cytoplasmic organelles, such as rough endoplasmic reticulum (ER), Golgi apparatus, and well-developed junctional complexes between the adjacent cells. Microvilli and cilia were numerous at the apical surface of neuroepithelial cells in the floor plate, but few were found in the lateral walls. Periodic acid-Schiff-positive substances were predominantly present in the neuroepithelial cells of the floor plate. In all specimens examined, multivesicular structures were observed in the floor plate neuroepithelium, but not in other regions of the spinal cord. The number of multivesicular structures appeared to increase with embryonic age. These structures contained numerous small and translucent vesicles within an electron-dense matrix; most vesicles were 40-70 nm in diameter. It appeared that the envelope of the multivesicular structures was first formed by the fusion of smooth ER-like cisterns, followed by invagination of the envelope by the vesicular contents. Presumably, the mature multivesicular structures were subsequently translocated to peduncular processes and their contents released into the central canal lumen in an exocytotic manner. This morphological evidence suggests that the floor plate cells of the spinal cord may have secretory activity during embryonic development.

Epithelium↗

PubMed2006

Regulation of urogenital smooth muscle patterning by testosterone and estrogen during prostatic induction.

BACKGROUND: Smooth muscle (SM) has been proposed to play an important role in controlling prostate organogenesis by regulating signaling between inductive mesenchyme and developing epithelial prostatic buds. METHODS: We have examined the effects of testosterone and estrogen upon SM patterning in the embryonic rat urogenital tract (UGT) using in vitro organ cultures, immunohistochemistry, and Western blotting. RESULTS: We observed that testosterone elicited a sexually dimorphic difference in SM structure of embryonic UGTs, in cultures grown with testosterone. The addition of estrogen led to an increase in the rate of SM closure, in both males and females. To quantify the effects of steroids upon SM we used Western blotting of SM actin, which showed that estrogen stimulated SM content, while testosterone reduced SM content. Finally, we examined the expression of ERalpha, ERbeta, PR, and SM actin under different hormonal treatments of UGTs grown in vitro. The expression patterns of ERalpha and ERbeta were largely unchanged by hormonal treatment, while PR showed a much broader expression pattern in response to estradiol. CONCLUSIONS: Our results indicate that testosterone can directly regulate SM patterning and content in the UGT, and that SM is sensitive to both androgens and estrogens.

Animals↗

PubMed2007

Specification of primordial germ cells in medaka (Oryzias latipes).

BACKGROUND: Primordial germ cells (PGCs) give rise to gametes that are responsible for the development of a new organism in the next generation. Two modes of germ line specification have been described: the inheritance of asymmetrically-localized maternally provided cytoplasmic determinants and the induction of the PGC fate by other cell types. PGCs specification in zebrafish appears to depend on inheritance of germ plasm in which several RNA molecules such as vasa and nanos reside. Whether the specification mode of PGCs found in zebrafish is general for other fish species was brought into question upon analysis of olvas expression--the vasa homologue in another teleost, medaka (Oryzias latipes). Here, in contrast to the findings in zebrafish, the PGCs are found in a predictable position relative to a somatic structure, the embryonic shield. This finding, coupled with the fact that vasa mRNA, which is localized to the germ plasm of zebrafish but does not label a similar structure in medaka opened the possibility of fundamentally different mechanisms governing PGC specification in these two fish species. RESULTS: In this study we addressed the question concerning the mode of PGC specification in medaka using embryological experiments, analysis of RNA stability in the PGCs and electron microscopy observations. Dramatic alterations in the somatic environment, i.e. induction of a secondary axis or mesoderm formation alteration, did not affect the PGC number. Furthermore, the PGCs of medaka are capable of protecting specific RNA molecules from degradation and could therefore exhibit a specific mRNA expression pattern controlled by posttrancriptional mechanisms. Subsequent analysis of 4-cell stage medaka embryos using electron microscopy revealed germ plasm-like structures located at a region corresponding to that of zebrafish germ plasm. CONCLUSION: Taken together, these results are consistent with the idea that in medaka the inheritance of maternally provided asymmetrically-localized cytoplasmic determinants directs cells to assume the germ line fate similar to zebrafish PGCs.

Animals↗

PubMed2003

Thymus, kidney and craniofacial abnormalities in Six 1 deficient mice.

Six genes are widely expressed during vertebrate embryogenesis, suggesting that they are implicated in diverse differentiation processes. To determine the functions of the Six1 gene, we constructed Six1-deficient mice by replacing its first exon by the beta-galactosidase gene. We have previously shown that mice lacking Six1 die at birth due to thoracic skeletal defects and severe muscle hypoplasia affecting most of the body muscles. Here, we report that Six1(-/-) neonates also lack a kidney and thymus, as well as displaying a strong disorganisation of craniofacial structures, namely the inner ear, the nasal cavity, the craniofacial skeleton, and the lacrimal and parotid glands. These organ defects can be correlated with Six1 expression in the embryonic primordium structures as revealed by X-Gal staining at different stages of embryogenesis. Thus, the fetal abnormalities of Six1(-/-) mice appear to result from the absence of the Six 1 homeoprotein during early stages of organogenesis. Interestingly, these Six1 defects are very similar to phenotypes caused by mutations of Eya 1, which are responsible for the BOR syndrome in humans. Close comparison of Six1 and Eya 1 deficient mice strongly suggests a functional link between these two factors. Pax gene mutations also lead to comparable phenotypes, suggesting that a regulatory network including the Pax, Six and Eya genes is required for several types of organogenesis in mammals.

Animals↗

PubMed1980

Properties of purified papain-solubilized rat AgB antigens and reactivity of a xenoantiserum against the isolated antigens.

Rat AgB transplantation antigens were isolated after papain digestion of spleens from the inbred strain Hooded Lister. Both subunits of the AgB antigens were present in the purified material. Some physical characteristics of the antigens have been determined. An antiserum, raised in a rabbit, against the purified material reacted exclusively with AgB antigens on splenocytes but detected novel structures on both adult and embryonic fibroblasts. These structures, antigenically related to AgB antigens, were not detected on plasmacytoma or hepatoma cells, nor did they display any antigenic similarity with rat beta 2-microglobulin. Radioimmunoassays specific for the AgB antigen heavy chain and for beta 2-microglobulin, respectively, were used to estimate the contents of these antigens in several tissues. Spleen and thymus exhibit the largest density, while brain is almost devoid of these antigens.

Animals↗

PubMed1976

[Discovery of the nature of the process of fertilization and of the role of nuclear structures in this process (on the centenary of the discovery)].

The history of the discovery by O. Hertwig (1875-1878) of the very nature of fertilization--the fusion of the egg's and spermatozoon's nuclei--is presented. In result, the principle of continuity of the nuclear structures in embryonic development was proclaimed. It is noticed that the correct understanding of such phenomena as maturation of the egg, meiosis and fertilization as well the role played by the nuclear structures in these processes was achieved not at once but gradually due to joint efforts of the number of scientists (E. van Beneden, O. Bütschli, H. Fol, W. Flemming and others).

Amphibians↗

PubMed1995

Structure and function of DNA methyltransferases.

In prokaryotes, the major role of DNA methylation is to protect host DNA against degradation by restriction enzymes. In eukaryotes, DNA methylation has been implicated in the control of several cellular processes, including differentiation, gene regulation, and embryonic development. Structural work on HhaI DNA methyltransferase demonstrates that the substrate nucleotide is completely flipped out of the helix during the modification reaction and has provided much insight into the enzymatic properties of S-adenosyl-L-methionine (SAM)-dependent DNA-modifying enzymes. Structural comparison of three enzymes, HhaI C5-cytosine methyltransferase, TaqI N6-adenine methyltransferase, and catechol O-methyltransferase, reveals a striking similarity in protein folding and indicates that many SAM-dependent methyltransferases have a common catalytic-domain structure. This feature permits the prediction of tertiary structure for other DNA, RNA, protein, and small-molecule methyltransferases from their amino acid sequences, including the eukaryotic CpG methyltransferases.

Adenine↗

PubMed1997

Expression of alpha 2 adrenoceptors during rat brain development--I. Alpha 2A messenger RNA expression.

The distribution of alpha 2A adrenoceptor messenger RNA expression in developing rat brain was characterized using in situ hybridization with 35S-labeled riboprobes. Intense hybridization signal was detected as early as embryonic day 14 in several areas adjacent to the forebrain and hindbrain germinal zones and in central noradrenergic neurons. A marked increase in messenger RNA expression was observed throughout the brain during late prenatal development, consistent with the migration and maturation of neurons in developing brain structures. In embryonic brain, there was a temporal and spatial correspondence in the appearance of alpha 2A messenger RNA expression and binding sites labeled with [3H]idazoxan or p-[125I]iodoclonidine, indicating translation into receptor protein at an early stage of development. Whereas the presynaptic expression remained constant throughout development, there was an early postnatal decline of alpha 2A receptor expression in many brain regions, including the olfactory bulb, cortex, caudate-putamen, hippocampus, thalamus, hypothalamus and medulla. Thereafter, messenger RNA expression increased, establishing an adult-like pattern during the second postnatal week, but remained low in areas such as the caudate-putamen, thalamus and hippocampus, which do not exhibit extensive expression in the adult. The transient perinatal expression of this alpha 2 adrenoceptor type, which coincides with a period of hyperreactivity to sensory stimuli in the locus coeruleus, may indicate a specific functional role for the alpha 2A receptor in the developing rat brain. The early and intense expression in olfactory structures suggests an involvement in early olfactory learning. The pattern of widespread, transient expression of alpha 2A receptors in the fetal brain is in marked contrast to the postnatal development of the alpha 2C receptor type.

Aging↗

PubMed1977

Monosomy 21 in a human spontaneous abortus. Morphogenetic disturbances and phenotype at the cellular level.

Complex investigation of a spontaneous abortus with monosomy 21 was carried out. Phenotypic expression at the organism and tissue level was characterized by the pathology of the external form of the embryo and by abnormalities of the embryonic facial structures, the stomodeum, the anterior part of the primary gut, and neural tube development. The anomalies found in the embryo indicate primary morphogenetic disturbances arising at the initial stage of organogenesis. Investigation of LHC-431 strain cells derived from musculocutaneous embryonic fragments revealed a complex of cytophenotypic alterations similar to the cellular syndrome of trisomic cells and indicating an insufficient biologic maturity of the mutant cells (alterations of cellular form, disturbances in their contact orientation, underdevelopment of fibrillar apparatus and decreased collagen formation, changes in the accumulation of intracellular metabolic products, decreased growth capacity and alterations of mitotic cycle parameters). It was found that the single chromosome 21 takes part in assocations twice as frequently as would theoretically be expected.

Abortion, Missed↗

PubMed2005

Crucial transcription factors in endoderm and embryonic gut development are expressed in gut-like structures from mouse ES cells.

Mouse embryonic stem (ES) cells are pluripotent and retain the potential to form an organ similar to the gut showing spontaneous contractions in vitro. The morphological features of these structures and their formation, as assessed using the hanging drop method to produce embryoid bodies (EBs), seem to be similar to those in vivo. To determine whether the same molecular mechanisms are involved in the formation process, the expression pattern of transcription factors regulating endoderm and gut development in the mouse embryo was examined by in situ hybridization and compared with in vivo expression. Expression of gene products was also examined by immunohistochemistry, and expression colocalization was analyzed with double staining. The results showed that all factors examined, that is, Sox17, Id2, HNF3beta/Foxa2, and GATA4, were expressed in both EBs and gut-like structures. Moreover, their expression patterns were similar to those in the mouse embryo. EBs after the hanging drop period and before outgrowth already expressed all factors that were colocalized with each other in EB epithelial structures. These findings suggest that the origin of the gut-like structure is determined during the hanging drop period and that the gut-like structure is formed as the epithelial structure in EBs during the hanging drop period. They also indicate that the in vitro system using mouse ES cells mimics in vivo development and should prove useful in the study of molecular mechanisms for endoderm and gut development.

Animals↗

PubMed2005

Structural development of PGP9.5-immunopositive myenteric plexus in embryonic rats.

To investigate relationships between changes in the 3-dimensional structure of the myenteric plexus and the time at which functional movement of intestine begins in mammalian embryos, whole mounts of embryonic rat intestine were examined under confocal laser scanning microscopy on spacer-equipped glass slides after immunostaining with antiprotein gene product 9.5 antibody. At embryonic day 12.5, very few nerve cells were scattered throughout the small intestine, but no immunostained structures were apparent on the anal side of the large intestine. At embryonic day 13.5, immunostained fibers appeared on the oral side of the large intestine. Nerve cells and associated fiber bundles formed neuronal networks with large meshes in both intestines. Marked increases in number of nerve fibers and decreases in mesh size were seen in the small intestine between embryonic days 13.5 and 15.5. Similar changes were found in the large intestine between embryonic days 13.5 and 16.5. After embryonic day 16.5, nerve cells were arranged parallel to circular muscle fibers, and networks formed by cell fibers elongated until the neonatal period in both intestines. Meconium passed through the large intestine from embryonic day 17.5. Thin fiber bundles extended from the ganglion to the inner side of the myenteric layer, parallel (and occasionally extending) to the circular muscle fibers. Formation of nerve fiber networks and arrangement of nerve cells parallel to circular muscle fibers probably relate to movement coordination for inner circular muscle fibers in the intestinal wall, and development of this neural network may be important for acquiring intestinal movements before birth.

Animals↗

PubMed1997

Liver development in the rat during the embryonic period (Carnegie stages 15-23).

Hepatic and biliary structures appearing during embryonic Carnegie stages 15-23 were analyzed in OFA rat embryos. The group of rats with crown rump length 7.5-16 mm and 12.8-16 days after coitus yielded 55 specimens (23 of stages 15-16, 20 of stages 17-18, 9 of stages 19-22 and 3 of stage 23). The embryos were submitted to serial histological sections with graphic reconstructions. From stage 15 to the end of the embryonic period, the hepatic gland and its vascular channels (transverse portal sinus and hepatocardiac veins) presented considerable enlargement while hematopoietic function appeared. At stage 17, occlusion due to epithelial proliferation was evident in the hepatic duct. At stage 18, the duct became recanalized and assured the continuity between liver cells and gut. From stage 18 to 23, biliary ductules developed in periportal connective tissue forming ductal plates which received biliary caniculi. Except for the gall-bladder which is never present in the rat, similarity and presence of the same hepatic structures in man and in the rat during the embryonic period stages 15-23 suggest that the rat is a good experimental model for liver development and will be useful in the understanding of congenital anomalies.

Animals↗

PubMed2001

Differentiation of embryonic stem cells to insulin-secreting structures similar to pancreatic islets.

Although the source of embryonic stem (ES) cells presents ethical concerns, their use may lead to many clinical benefits if differentiated cell types can be derived from them and used to assemble functional organs. In pancreas, insulin is produced and secreted by specialized structures, islets of Langerhans. Diabetes, which affects 16 million people in the United States, results from abnormal function of pancreatic islets. We have generated cells expressing insulin and other pancreatic endocrine hormones from mouse ES cells. The cells self-assemble to form three-dimensional clusters similar in topology to normal pancreatic islets where pancreatic cell types are in close association with neurons. Glucose triggers insulin release from these cell clusters by mechanisms similar to those employed in vivo. When injected into diabetic mice, the insulin-producing cells undergo rapid vascularization and maintain a clustered, islet-like organization.

Animals↗

PubMed1998

Nuclear envelope removal/maintenance determines the structural and functional remodelling of embryonic red blood cell nuclei in activated mouse oocytes.

Nuclei of embryonic red blood cells (e-RBC) from 12-day mouse fetuses are arrested in G0 phase of the cell cycle and have low transcriptional activity. These nuclei were transferred with help of polyethylene glycol (PEG)-mediated fusion to parthenogenetically activated mouse oocytes and heterokaryons were analysed for nuclear structure and transcriptional activity. If fusion proceeded 25-45 min after oocyte activation, e-RBC nuclei were induced to nuclear envelope breakdown and partial chromatin condensation, followed by formation of nuclei structurally identical with pronuclei. These 'pronuclei', similar to egg (female) pronuclei, remained transcriptionally silent over several hours of in vitro culture. If fusion was performed 1 h or later (up to 7 h) after activation, the nuclear envelope of e-RBC nuclei remained intact and nuclear remodelling was less spectacular (slight chromatin decondensation, formation of nucleolus precursor bodies). These nuclei, however, reinforced polymerase-II-dependent transcription within a few hours of in vitro culture. Our present experiments, together with our previous work, demonstrate that nuclear envelope breakdown/maintenance are critical events for nuclear remodelling in activated mouse oocytes and that somatic dormant nuclei can be stimulated to renew transcription at a time when the female pronucleus remains transcriptionally silent.

Animals↗

PubMed1993

[Idiopathic asymmetric heart hypertrophy in a newborn infant].

A sporadic case of idiopathic asymmetric heart hypertrophy in a newborn infant is reported. Despite drug therapy the baby died in progressive heart failure at 23 days of age. At necropsy there was cardiac hypertrophy with features similar to those of the usual asymmetric from observed in adults. On gross examination the myocardium of the ventricular septum and the free wall of the left ventricle showed a disorganized structure. Microscopically, the changes consisted of an abnormal arrangement of muscle cells and muscle bundles with areas of hypertrophied myofibers. In agreement with other authors myocardial disorganization ("disarray") is interpreted as a form of dysplasia, hypertrophy being a secondary phenomenon. The hypothesis that these abnormalities represent the persistence of the embryonic myocardial structure is discussed. The pathogenetic significance of focal myocardial dysplasias is apparently related to the amount of myocardium involved.

Cardiomyopathy, Hypertrophic↗

PubMed1975

Structure of rat ultimobranchial bodies after birth.

The evolution of ultimobranchial bodies in Holtzman rats during the first 64 weeks after birth was studied by reconstructing three-dimensional models from serial sections stained by the periodic acid-Schiff technique.Radio-autography with 125I was made to see if ultimobranchial cells and/or follicular cells lining the lumen of mixed follicles were able to iodinate proteins. The term ultimobranchial body designates herein an embryonic vesicular structure (derived from the third pharyngeal pouch) whose wall is made of stratified squamous epithelium. During the first week after birth, the vesicular ultimobranchial body elongates rapidly and becomes a canal or a duct. During the second week, cell desquamation brings about local dilatations in the lumen of these ducts; with further enlargement ultimobranchial follicles will appear. In one-day-old rats, mixed follicles are present. Only the follicular component of mixed follicles iodinates proteins as is shown by radioautography. The reconstructed models enlarge rapidly up to the 56th day after birth at which time their weight has increased nineteenfold. These same models show that the three morphological components of ultimobranchial parenchyma, namely ducts, follicles and mixed follicles, are in continuity within the thyroid parenchyma. The formation of new thyroid follicles after birth and the possiblility that the ultimobranchial parenchyma may function as an endocrine gland of holocrine type are discussed.

Age Factors↗

PubMed2006

Differential role of FGF9 on epithelium and mesenchyme in mouse embryonic lung.

Mesothelial Fibroblast Growth Factor 9 (Fgf9) has been demonstrated by inactivation studies in mouse to be critical for the proliferation of the mesenchyme. We now show that Fgf9 is also expressed at significant levels in the distal epithelium from the mid-pseudoglandular stages. Using mesenchymal-free lung endoderm culture, we show that FGF9 triggers the proliferation of the distal epithelium leading to the formation of a cyst-like structure. On embryonic Fgfr2b-/- lungs, FGF9 induces proliferation of the mesenchyme but fails to trigger a similar effect on the epithelium, therefore involving the FGFR2b receptor in the proliferative response of the epithelium to FGF9. While FGF9 inhibits the differentiation of the mesenchyme, the epithelium appears to differentiate normally. At the molecular level, FGF9 up-regulates Fgf10 expression in the mesenchyme likely via increased expression of Tbx4 and 5 and controls the transcription of Hedgehog targets Ptc and Gli-1 in a Hedgehog-independent manner. We also show that FGF9 inhibits the activation of the canonical Wnt pathway in the epithelium by increasing Dkk1 expression, a canonical Wnt antagonist. Our work shows for the first time that FGF9 acts on the epithelium involving FGFR2b to control its proliferation but not its differentiation and contributes to the regulation of canonical Wnt signaling in the epithelium.

Animals↗

PubMed1997

Le(X) structure enhances myocardial differentiation from embryonic stem cells.

alpha-1,3-Fucosyltransferase (Fuc T IV) cDNA was placed under the control of beta-actin, cytomegalovirus enhancer/promoter and transfected into embryonic stem cells. The transfected cell clones with integrated cDNA (positive clones) differentiated more efficiently into myocardial cell clones without integrated cDNA (negative clones) or parental cells. Furthermore, myocardial cells differentiated from the positive clones survived longer than those differentiated from the negative clones or parental cells. These results indicate that Lewis X structure, the product of Fuc T IV, enhances myocardial differentiation. The mechanism of the phenomenon is discussed on relation to integrin action.

Animals↗