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B Christ

Publications and source records attributed to B Christ.

At least 127 records · Page 7Linked to original sources
PubMed1994

Kinetics and differentiation of somite cells forming the vertebral column: studies on human and chick embryos.

We have studied the kinetics of somite cells with an antibody against proliferating cell nuclear antigen (PCNA/cyclin) in human and chick embryos, and with the BrdU anti-BrdU method in chick embryos, to investigate whether the metameric pattern of the developing vertebral column can be explained by different proliferation rates. Furthermore we applied antibodies against differentiation markers of chondrogenic and myogenic cells of the somites in order to study the correlation between proliferation and differentiation. There are no principal differences in the proliferation pattern of the vertebral column between human and chick embryos. In all stages examined, the cell density is higher in the caudal sclerotome halves than in the cranial halves. Laterally, the caudal sclerotome halves, which give rise to the neural arches, are characterized by a higher proliferative activity than the cranial halves. Although there is a high variability, the labelling indices show significant differences between the two halves with both proliferation markers. With the onset of chondrogenic differentiation, only the perichondrial cells retain a high proliferation rate. During fetal development, the neural arches and their processes grow appositionally. Even at the earliest stages, there is practically no immunostaining for PCNA or BrdU in the desmin-positive myotome cells of human and chick embryos. Axially, a higher proliferation rate is found in the condensed mesenchyme of the anlagen of the intervertebral discs than in the anlagen of the vertebral bodies. During fetal development, cells at the borders between vertebral bodies and intervertebral discs proliferate, indicating appositional growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The fate of somitocoele cells in avian embryos.

The early somite of avian embryos is made up of an epithelial wall and mesenchymal cells located within the somitocoele. We have studied the fate of somitocoele cells for a period of up to 6 days, using the quail-chick marker technique. We also applied the QH-1 antibody, which specifically stains hemangiopoietic cells of quail origin, and studied the proliferative activity of epithelial somites with the BrdU anti-BrdU method. Our results show that somitocoele cells mainly give rise to the ribs and peripheral parts of the intervertebral discs. After 1 and 2 days of reincubation, the grafted somitocoele cells were located in the lateral part of the sclerotome, and only a few cells migrated axially towards the notochord. In frontal sections, the cells were located in a triangular area within the cranial part of the caudal sclerotome half. After 3 days of reincubation, some of the cells had migrated cranially along the myotome. After longer reincubation periods, cells grafted into one somite could be found in two adjacent ribs. The studies with the QH-1 antibody show that a subpopulation of somitocoele cells has angiogenic potency. Endothelial cells originating from the mesenchyme of the somitocoele migrated actively and even invaded the ipsilateral half of the neural tube. In the epithelial wall of the somite, BrdU-labelled nuclei were found basally, whereas more apically the nuclei were not stained, but mitotic figures were frequently present. The somitocoele cells also showed a high proliferative activity with about 26% of nuclei labelled with BrdU.

Animals↗
PubMed1994

Distribution of extracellular matrix components in nuchal skin from fetuses carrying trisomy 18 and trisomy 21.

We have investigated histologically the elevations of the skin in dorsal and lateral neck (nuchal) regions of human fetuses carrying karyotypes of trisomy 18 (Edwards' syndrome) and trisomy 21 (Down's syndrome). Cavities filled with interstitial fluid were found in the dermis, epidermal basement membrane and occasionally in the epidermis of trisomy-18 fetuses, but were not delineated by an epithelium or basement membrane as judged by the absence of immunostaining for laminin, collagen IV and collagen VII. Dilated vessels were also found at the interface between dermis and subcutis. Neither normal fetal skin nor that of trisomy-21 fetuses contained cavities or dilated vessels. In order to detect possible alterations of the extracellular matrix in trisomy-18 and trisomy-21 skin, the distribution of glycoproteins, glycosaminoglycans and proteoglycans was studied immunohistochemically. In trisomy-21 and control skin, the dermis stained intensely for fibronectin, whereas the subcutis reacted only weakly. In trisomy-18 skin, the stronger staining for fibronectin appeared in the subcutis, and the prevailing collagen type was collagen III, collagen type I being absent. In the skin of trisomy-21 fetuses, collagen VI was more irregularly arranged and densely packed, whereas collagen I was more widely spaced than in normal fetuses. More hyaluronan was present in the dermis and subcutis of trisomy-21 fetuses than in that of trisomy-18 and control fetuses. A correlation seems to exist between undelimited cavities and collagen III in trisomy-18 skin, and between hyaluronan and the specific arrangement of collagen in trisomy-21 skin.

Chromosomes, Human, Pair 18↗
PubMed1994

Alterations of the fetal extracellular matrix in the nuchal oedema of Down's syndrome.

Elevations in the lateral and dorsal neck region are known to be highly correlated with chromosomal aberrations in human fetuses. However, the morphology of the elevations is poorly described. Only in the case of Turner's syndrome has lymphatic vessel formation been shown to be deficient leading to swellings in the nuchal area. In Down's syndrome, non-echogenic nuchal oedemata can be visualized in ultrasound scan between the 10th and 15th week of gestation. In the present study, alterations in the extracellular matrix (ECM) of the skin in trisomy 21 fetuses were found to be the morphological basis of the nuchal oedema. The distribution of collagen type VI differs from that in normal fetuses, both in nuchal and leg skin. Collagen VI forms a denser mesh in trisomy 21 than in normal fetal skin, hyaluronan (HA) being the main glycosaminoglycan (GAG) component as judged from the appearance of the TEM precipitate after fixation in the presence of tannic acid. Nuchal oedema in Down's syndrome is therefore found to be an interstitial oedema. The interstitial fluid is bound to HA, leading to a swelling of the fetal dermis. No cysts or dilated vessels were found in the oedematous tissue. The presence of a high amount of HA during development can influence the behaviour of migrating cell populations, which might have a bearing on the pathogenesis of Down's syndrome.

Abortion, Induced↗
PubMed1994

Principles of ontogenesis of leg and foot in man.

Human leg and foot anlagen of different developmental stages were studied by means of light and scanning electron microscopy. The findings were compared with principles of human arm and hand development and results obtained experimentally from chicken limbs. The limbs studied have in common the shaping, cell differentiation, and spatial arrangement of different cells as basic processes of development. On the other hand, upper and lower limbs are very different in human and avian embryos with regard to their position, form, and function. We found that the different positions in relation to the dorsal and ventral surfaces and maintenance of the apical ectodermal ridge (AER) are important factors leading to the different orientations and forms of limbs. The unequal length of the fingers and toes might also be explained in this way. Differences in the position of the most distal muscles in the hand and foot could be a consequence of the cranio-caudal sequence of development. The factors controlling the developmental differences between arm and leg are discussed.

Animals↗
PubMed1994

Initial steps of myogenesis in somites are independent of influence from axial structures.

Formation of paraxial muscles in vertebrate embryos depends upon interactions between early somites and the neural tube and notochord. Removal of both axial structures results in a complete loss of epaxial myotomal muscle, whereas hypaxial and limb muscles develop normally. We report that chicken embryos, after surgical removal of the neural tube at the level of the unsegmented paraxial mesoderm, start to develop myotomal cells that express transcripts for the muscle-specific regulators MyoD and myogenin. These cells also make desmin, indicating that the initial steps of axial skeletal muscle formation can occur in the absence of the neural tube. However, a few days following the extirpation, the expression of MyoD and myogenin transcripts gradually disappears, and becomes almost undetectable after 4 days. From these observations we conclude that the neural tube is not required for the generation of the skeletal muscle cell lineage, but may support the survival or maitenance of further differentiation of the myotomal cell compartment. Notochord transplanted medially or laterally to the unsegmented paraxial mesoderm leads to a ventralization of axial structures but does not entirely prevent the early appearance of myoblasts expressing MyoD transcripts. However, the additional notochord inhibits subsequent development and maturation of myotomes. Taken together, our data suggest that neural tube promotes, and notochord inhibits, the process of myogenesis in axial muscles at a developmental step following the initial expression of myogenic bHLH regulators.

Animals↗
PubMed1994

The role of Pax-1 in axial skeleton development.

Previous studies have identified a single amino-acid substitution in the transcriptional regulator Pax-1 as the cause of the mouse skeletal mutant undulated (un). To evaluate the role of Pax-1 in the formation of the axial skeleton we have studied Pax-1 protein expression in early sclerotome cells and during subsequent embryonic development, and we have characterized the phenotype of three different Pax-1 mouse mutants, un, undulated-extensive (unex) and Undulated short-tail (Uns). In the Uns mutation the whole Pax-1 locus is deleted, resulting in the complete absence of Pax-1 protein in these mice. The other two genotypes are interpreted as hypomorphs. We conclude that Pax-1 is necessary for normal vertebral column formation along the entire axis, although the severity of the phenotype is strongest in the lumbar region and the tail. Pax-1-deficient mice lack vertebral bodies and intervertebral discs. The proximal part of the ribs and the rib homologues are also missing or severely malformed, whereas neural arches are nearly normal. Pax-1 is thus required for the development of the ventral parts of vertebrae. Embryonic analyses reveal that although sclerotomes are formed in mutant embryos, abnormalities can be detected from day 10.5 p.c. onwards. The phenotypic analyses also suggest that the notochord still influences vertebral body formation some days after the sclerotomes are formed. Furthermore, the notochord diameter is larger in mutant embryos from day 12 p.c., due to increased cell proliferation. In the strongly affected genotypes the notochord persists as a rod-like structure and the nucleus pulposus is never properly formed. Since the notochord is Pax-1-negative these findings suggest a bidirectional interaction between notochord and paraxial mesoderm. The availability of these Pax-1 mutant alleles permitted us to define an early role for Pax-1 in sclerotome patterning as well as a late role in intervertebral disc development. Our observations suggest that Pax-1 function is required for essential steps in ventral sclerotome differentiation, i.e. for the transition from the mesenchymal stage to the onset of chondrogenesis.

Animals↗
PubMed1993

The glucagon-insulin antagonism in the regulation of cytosolic protein binding to the 3' end of phosphoenolpyruvate carboxykinase mRNA in cultured rat hepatocytes. Possible involvement in the stabilization of the mRNA.

Since protein binding to the 3' end of mRNA is believed to be involved in the control of mRNA stability, the time course of alterations in glucagon-induced phosphoenolpyruvate-carboxykinase-mRNA (PCK) levels, in the absence and presence of insulin, was correlated with the time course of changes in the binding of cytosolic protein from 24-h cultured rat hepatocytes to the 3' end of PCK mRNA. PCK-mRNA levels were monitored by Northern blot analysis and protein binding was analyzed by an electrophoretic mobility-shift assay. In 24-h cultured rat hepatocytes, binding of cytosolic protein to the PCK-mRNA 3' end and PCK-mRNA levels were increased to a transient maximum at 2 h and 2-4 h, respectively, by a 1-nM glucagon treatment, added with a change of medium. 100 nM insulin, added simultaneously with glucagon, reduced the glucagon-induced maximum of protein binding by 80% and the increase of PCK mRNA by about 30%. In controls without hormonal treatment protein binding at 1 h was also increased; this increase was prevented by insulin. 100 nM insulin, added 1 h after glucagon, reversed protein binding to the 3' end of PCK mRNA to nearly initial levels within 1 h and impaired the glucagon-induced increase in PCK-mRNA levels by 30%. The transcriptional inhibitor cordycepin, added 1 h after glucagon, did not prevent the further increase in glucagon-enhanced protein binding nor its reversal by insulin. It did, however, prevent a further significant increase in PCK mRNA. Hormonally regulated protein binding could be localized to the 256 distal bases of the PCK-mRNA 3' end. The proximal 466 bases of the PCK-mRNA 3' end as well as the 1050 bases of the histone-H1(0)-mRNA 3' end and the 1200 bases of the arylsulfatase-A-mRNA 3' end also bound cytosolic protein(s), but this protein binding was not altered by treatment with glucagon or insulin. The 3' end of PCK, arylsulfatase A and H1(0) mRNA exhibited strong binding of cytosolic protein(s) from diverse rat tissues such as heart, liver and lung as well as Fao rat hepatoma cells. Cytosolic protein(s) from spleen showed weak binding and proteins from HeLa and U937 tumor cells did not bind. Protein binding was most prominent with the 3' end of PCK mRNA and cytosolic extracts from liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The ventralizing effect of the notochord on somite differentiation in chick embryos.

The dorso-ventral pattern formation of the somites becomes manifest by the formation of the epithelially organized dorsal dermomyotome and the mesenchymal ventrally situated sclerotome. While the dermomyotome gives rise to dermis and muscle, the sclerotome differentiates into cartilage and bone of the axial skeleton. The onset of muscle differentiation can be visualized by immunohistochemistry for proteins associated with muscle contractility, e.g. desmin. The sclerotome cells and the epithelial ventral half of the somite express Pax-1, a member of a gene family with a sequence similarity to Drosophila paired-box-containing genes. In the present study, changes of Pax-1 expression were studied after grafting an additional notochord into the paraxial mesoderm region. The influence of the notochord and the floor-plate on dermomyotome formation and myotome differentiation has also been investigated. The notochord is found to exert a ventralizing effect on the establishment of the dorso-ventral pattern in the somites. Notochord grafts lead to a suppression of the formation and differentiation of the dorsal somitic derivatives. Simultaneously, a widening of the Pax-1-expressing domain in the sclerotome can be observed. In contrast, grafted roof-plate and aorta do not interfere with dorso-ventral patterning of the somitic derivatives.

Animals↗
PubMed1993

Differences in the fibronectin-dependence of migrating cell populations.

In avian embryos, the migration behaviour of several cell populations, melanoblasts, Schwann cells, myogenic cells and axons after application of antibodies directed against the cell-attachment fragment of fibronectin (alpha-CAF) was investigated. The migration of the different cell types was influenced in different ways. 1. Epidermal melanoblasts did not colonize areas into which the antibody had been injected, i.e. distal to the grafting site. They frequently spread proximally to the back and neck, sometimes even as far as to the ipsilateral leg. When grafted to the dorsal side of the wing bud, melanoblasts never spread to the ventral side after injection of the antibody. Non-epidermal melanoblasts continued to migrate distally. 2. Grafted Schwann cells and host axons were not noticeably affected by the antibody injections. Both were found proximally and far distally to the grafting site, i.e. also within the injected area. 3. Myogenic cells were immobilized near the grafting site, where they differentiated biochemically, but sometimes only partially underwent fusion into myotubes. They participated in the formation of host muscle blastemas only immediately adjacent to the non-migratory cell population of the graft such as fibroblasts and cartilage. 4. The injected antibody could be localized up to 5 h after the application in the distal third of the limb bud. We conclude that migrating cell populations show differences in their fibronectin-dependence which probably reflect their use of fibronectin during migration.

Animals↗
PubMed1993

In vivo effects of vascular endothelial growth factor on the chicken chorioallantoic membrane.

The effect of vascular endothelial growth factor (VEGF165) on the chorioallantoic membrane (CAM) of 13-day-old chick embryos was studied. The factor was applied in doses of 0.5-4 micrograms for a period of up to 4 days. Macroscopical, histological and immunohistological studies were carried out. The localization of the factor was examined with an anti-VEGF antibody. The mitogenicity of VEGF165 and basic fibroblast growth factor (bFGF) were studied by means of the BrdU-anti-BrdU method. Furthermore, the effect of heparin alone and in combination with VEGF165 was investigated. VEGF165 specifically induces angiogenesis in doses of 0.5 microgram and more. A brush-like formation of blood vessels can be seen in the region of the precapillary vessels. Angiogenesis also takes place in the region of the capillaries and the venules. Histologically we found indications of sprouting as well as of intussusceptive capillary growth. The presence of the factor in the application area could be demonstrated with the anti-VEGF antibody for a period of 3 days. The factor is located in the chorionic epithelium and the intraepithelial capillaries. The BrdU-studies show that VEGF165 induces strong endothelial cell proliferation, whereas bFGF elicits fibrocyte proliferation and minor endothelial cell proliferation. Heparin induces squamous metaplasia of the chorionic and allantoic epithelium in combination with an aggregation of fibrocytes. We could not detect any enhancement of VEGF165 by heparin.

Allantois↗
PubMed1993

Effects of vascular endothelial growth factor and basic fibroblast growth factor: application with corneal grafts on the chorioallantoic membrane.

The corneae of 17- to 19-day-old chick embryos were dissected and grafted on the chorioallantoic membrane (CAM) of 10- to 14-day-old embryos with reincubation periods of 3-9 days. After fixation, serial semithin or paraffin sections were made. Furthermore, two growth factors were applied together with the corneae. The 165-amino-acid vascular endothelial growth factor (VEGF165) or basic fibroblast growth factor (bFGF) was either pipetted onto the corneae, or pieces of shell membrane were soaked in a factor solution, dried and inserted into an incision in the corneae. After a reincubation of 4-6 days, serial paraffin sections were made. The controls show that the viability of the grafts decreases with increasing age of the host CAM. Furthermore, with prolonged reincubation, the viable corneae become more and more spherical. Due to this movement, necrotic tissue of the CAM is shifted into the center of the sphere. After 9 days, blood vessels can be seen growing in the direction of the necrosis. bFGF pipetted onto the grafts induces marked proliferation of the stroma of the CAM beneath the corneae. Additionally, bFGF carriers inserted into the corneae induce fibrocyte ingrowth in the grafts together with a few blood vessels. VEGF165 specifically induces vascular growth in the CAM beneath the cornea but did not induce blood vessel growth into the grafts. The pros and cons of the method are discussed.

Allantois↗
PubMed1993

A role for Pax-1 as a mediator of notochordal signals during the dorsoventral specification of vertebrae.

The notochord plays an important role in the differentiation of the paraxial mesoderm and the neural tube. We have analyzed the role of the notochord in somite differentiation and subsequent formation of the vertebral column using a mouse mutant, Danforth's short-tail (Sd). In this mutant, the skeletal phenotype is most probably a result of degeneration and subsequent loss of the notochord. The Sd gene is known to interact with undulated (un), a sclerotome mutant. Double mutants between Sd and un alleles show an increase in the severity of the defects, mainly in the ventral parts of the vertebrae. We also show that part of the Sd phenotype is strikingly similar to that of the un alleles. As un is known to be caused by a mutation in the Pax-1 gene, we analyzed Pax-1 expression in Sd embryos. In Sd embryos, Pax-1 expression is reduced, providing a potential molecular basis for the genetic interaction observed. A complete loss of Pax-1 expression in morphologically intact mesenchyme was found in the lower thoracic-lumbar region, which is phenotypically very similar to the corresponding region in a Pax-1 null mutant, Undulated short-tail. The sclerotome developmental abnormalities in Sd coincide closely, both in time and space, with notochordal changes, as determined by whole-mount T antibody staining. These findings indicate that an intact notochord is necessary for normal Pax-1 expression in sclerotome cells, which is in turn required for the formation of the ventral parts of the vertebrae. The observed correlation among structural changes of the notochord, Pax-1 expression levels and skeletal phenotypes, suggests that Pax-1 might be an intrinsic mediator of notochordal signals during the dorsoventral specification of vertebrae.

Animals↗
PubMed1993

Neural crest cell migration into the limb bud of avian embryos.

The colonization of limb buds by neural crest cells was studied in quail-chick chimeras and in chick embryos using HNK-1 and DiI staining and the LD-DOPA reaction. Two populations of neural crest cells were found to colonize the limb bud. They migrate successively and use different routes of migration. The first population migrates within the limb bud subectodermally at stages before the limb is innervated. In the wing bud the migration route is localized postaxially and in the leg bud preaxially. Two cell types were identified differentiating from this first population: melanoblasts and Merkel cells. The second population of crest cells invades the limb bud at a later stage. These cells follow the routes of ingrowing nerves and migrate along a dorsal and a ventral path which correspond to the position of nerves for extensor and flexor muscles. Crest cells were found here also in the absence of nerves. Schwann cells and terminal glial cells develop from this second population of neural crest cells.

Animals↗
PubMed1992

The effects of growth factors on the day 13 chorioallantoic membrane (CAM): a study of VEGF165 and PDGF-BB.

The in vivo effects of two growth factors, VEGF165 and PDGF-BB, were studied in the chick chorioallantoic membrane (CAM). The factors were air-dried on Thermanox discs and the inverted discs were placed on the day-13 CAM for a period of 3 days. The specimens were then fixed, examined under a stereomicroscope and processed for semi- and ultrathin sectioning. VEGF165 induces marked vascular growth. Many new blood vessels emerge from the precapillary arterioles, and a brush-like formation of vessels can be seen in this region. In the venous part of the vascular system, the formation of sinusoidal or lacunar vessels can be seen. Edema does not develop. PDGF-BB induces thickening of the CAM due to extracellular-matrix production and the proliferation or immigration of fibrocytes. These lie just beneath the ectodermal epithelium and are oriented parallel to it. Out of the four factors we have already studied (PDGF-BB, VEGF165, Angiogenin, bFGF), only VEGF165 specifically induces the growth of blood vessels.

Allantois↗
PubMed1992

Local signalling in dermomyotomal cell type specification.

The development and differentiation of the avian myotome was studied after removal of the neural tube, including neural crest, and after replacement of dorsal half-somites by ventral half-somites. Results show that in the absence of neural tissue myoblast differentiation within the somites does not take place. Ventral half-somites are able to undergo muscle differentiation if they were grafted in place of dorsal half somites. It is suggested that local signals must be responsible for the dorsalisation of the newly formed somite including myoblast differentiation. Neural crest cells are discussed as possible sources of these signals.

Animals↗
PubMed1992

Cytokinetic studies on the aortic endothelium and limb bud vascularization in avian embryos.

Cytokinetic studies on the aortic endothelium using the BrdU/anti-BrdU-method were carried out on 2.5- to 6-day chick and quail embryos. The mitotic activity of the aortic endothelium is related temporally to the age of the avian embryo and spatially to the embryonic region where the aorta originates. The mitotic activity of the aortic endothelium decreases with increasing age of the embryos. In the limb buds, however, the mitotic rate of the aortic endothelial cells increases independently of the age of the embryo. This increase in the mitotic activity of the aortic endothelium at the appropriate levels coincides with the vascularization of the outgrowing limb buds. We concluded therefore that the aortic endothelium probably supplies endothelial cells for the formation of limb vessels at this stage. Thus our results suggest that angiogenesis (sprouting of capillaries from pre-existing vessels) takes place during limb vascularization in avian embryos. On the other hand, immunohistochemical studies with QH-1 or MB-1 antibody show, beside a capillary network in the central core of the wing bud, individual immunolabelled cells of mesenchymal character within the primarily avascular subectodermal region from the onset of vascularization onwards. We suggest that these cells have partly to be regarded as endothelial precursor cells, which have differentiated in situ from the local limb mesenchyme, and which will contribute to the developing vascular plexus. This means that not only angiogenesis, but also vasculogenesis (in situ from mesenchymal precursors differentiated endothelial cells) appears to be involved in limb vessel formation.

Animals↗