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S Meier

Publications and source records attributed to S Meier.

At least 73 records · Page 4Linked to original sources
PubMed1984

SEM localization of cell-surface-associated fibronectin in the cranium of chick embryos utilizing immunolatex microspheres.

Fibronectin has been localized to basement membranes and cell surfaces with the light microscope by fluorescent staining of thick sections, and with the TEM by immunoperoxidase reaction. However, these methods are limited because it is difficult to appreciate the patterned distribution of fibronectin from sectioned material. We have developed a probe for fibronectin that facilitates its identification with the SEM. Our probe consists of two parts; the first component is a derivatized methacrylate microsphere 90 nm in diameter, linked to purified sheep anti-rabbit IgG. The second component is anti-fibronectin IgG raised in rabbits. Stage-3 to -12 chick embryos were fixed and the ectoderm covering the cranial mesoderm was removed. Embryos were treated with testicular hyaluronidase, exposed to rabbit anti-fibronectin IgG and finally to sheep anti-rabbit IgG conjugated microspheres. As expected, the basal lamina of surface and neural ectoderm as well as the remaining fibrous ECM were heavily decorated with microspheres, whereas control embryos treated with preimmune serum were beadless. Fibronectin was localized on the cell soma and processes of primary mesenchyme as early as stage 3. In addition, it was possible to decorate to various extents, populations of prosencephalic, mesencephalic, and rhombencephalic cranial neural crest cells. Our studies suggest that fibronectin is present in the cranium of chick embryos at earlier times than heretofore realized, and that fibronectin accumulates in a cranial to caudal gradient that reflects the sequential differentiation of the embryonic axis.

Animals↗
PubMed1983

An experimental study of the somitomeric organization of the avian segmental plate.

The segmental plate mesoderm of chicken and Japanese quail embryos HH stages 9 to 16 was studied with scanning electron microscopy (SEM) imaging. The segmental plates were found to exhibit a metameric pattern consisting of tandemly stacked somitomeres. It was found that the numbers of somitomeres in segmental plates removed from the same embryo were nearly identical. Furthermore, the number of somitomeres in a segmental plate was found to be quite consistent (10.0 +/- 1.5) and independent of the length of the segmental plate. These results are very similar to those obtained in previous experimental studies in which "prospective somites" were detected in avian segmental plates. Further experiments showed that for each somite that is formed by a cultured segmental plate-containing explant, the somitomere complement of the segmental plate is reduced by one. It was concluded that the segmental plate mesoderm is already organized into a metameric pattern consisting of somitomeres and that the somitomeres undergo further morphogenesis to become somites. The specification of the somite pattern in birds may occur at the level of Hensen's node and the cephalic primitive streak.

Animals↗
PubMed1983

A yellow crescent cytoskeletal domain in ascidian eggs and its role in early development.

In this investigation, Triton X-100 extraction was utilized to examine the cytoskeleton of ascidian eggs and embryos. The cytoskeleton contained little carbohydrate or lipid and only about 20-25% of the total cellular protein and RNA. It was enriched in polypeptides of molecular weight (Mr)54, 48, and 43 x 10(3) Mr polypeptide was identified as actin based on its Mr, isoelectric point, and affinity for DNase I. Electron microscopy of the detergent-extracted eggs showed that they contained cytoskeletal domains corresponding to colored cytoplasmic regions of specific morphogenetic fate in the living egg. A yellow crescent cytoskeletal domain in the myoplasm was examined and shown to consist of a plasma membrane lamina (PML) and a deeper lattice of filaments which appeared to connect the yellow crescent pigment granules to the PML. The PML probably consists of integral membrane proteins stabilized by an underlying network of actin filaments since NBD-phallacidin stained this area of the egg cortex and the PML was extracted from the cytoskeleton by DNase I treatment. The yellow crescent cytoskeletal domain was found throughout the cortex of the unfertilized egg. During ooplasmic segregation it progressively receded into the vegetal hemisphere and was subsequently partitioned to the presumptive muscle and mesenchyme cells of the 32-cell embryo. It is suggested that contraction of the actin network in the yellow crescent cytoskeletal domain is the motive force for ooplasmic segregation. This structure may also serve as a framework for the positioning of morphogenetic determinants involved in muscle cell development.

Animals↗
PubMed1983

[Immunohistologic determination of a tumor marker (CEA) in diseases of the gastrointestinal tract].

CEA levels in serum are not reliable markers of tumors. In this paper a method for determination of this antigen for tissue sections is given. Histology, immunohistology and serum levels of CEA were compared. Tissue sections were obtained by surgical and endoscopic techniques. In several cases there was a discrepancy between serological and morphological results. Based on recent investigations elevated CEA levels might be only useful in reflecting a relapse of carcinoma of the colon. Immunohistological determinations were done by IFT and PAP-method. The results of both assay systems were comparable. CEA could be also detected in benign neoplasiogenic tissue, i.e. in tubular type of adenomatose polyps and in ulcerative colitis. Both diseases are known to become malignant at an high degree. By contrast no CEA could be detected in hyperplasiogenic polyps. Detection of CEA in malignant tissue might be useful for final classification of tumors. Occurrence of CEA in non malignant tissue should give rise to control in short regular intervals. Prospective studies might show the reliability of the CEA-bearing cells of non malignant tissue.

Adolescent↗
PubMed1982

Development of a latex-conjugated immunocytological marker for scanning electron microscopic analysis of quail-chick chimeras.

Quail-chick chimeras are created by transplanting pieces of quail tissue to chick. We have used antibodies combined with a cell surface marking technique [modified after Molday et al.('75)], to facilitate scanning electron microscopic (SEM) identification of quail cells in such chimeras. First, antibodies to quail RBCs were raised in rabbits by intravenous injection. Rabbit anti-quail RBC serum was precipitated by ammonium sulfate, purified by DEAE chromatography, and cross-absorbed with chicken RBCs. Second, sheep anti-rabbit IgG was purchased commercially and further purified by affinity chromatography. Third, 900-A-diameter latex beads were synthesized by aqueous emulsion copolymerization of methacrylates. Spheres were bound with diaminoheptane to create an extension arm which was further derivatized in a two-step glutaraldehyde procedure. Purified sheep IgG was bound to the aldehyde-activated spheres, with uncoupled sheep IgG removed by sucrose density centrifugation. To test the marker, rabbit anti-quail IgG was added to 1% diluted quail RBCs. After washing, sheep anti-rabbit IgG bound spheres were introduced. Washed cells were fixed in one-half strength Karnovsky's and processed for SEM. Quail RBCs were uniformly decorated with beads, containing 2,000 beads per cell. Similarly treated chick RBCs show no binding to beads. Likewise, quail RBCs not pre-treated with the rabbit IgG do not bind beads. Prefixed quail RBCs still bind latex-conjugated beads, although at somewhat reduced levels. When mixtures of quail and chick RBCs were processed for identification: (1) sphere labeling was an "all or none" phenomenon; (2) the proportion of bead-decorated cells observable in the SEM was the same as the proportion of quail RBCs provided in the initial mix; and (3) morphologically distinguishable embryonic chick RBCs did not label whereas under the same conditions, quail RBCs do. We further demonstrate that rabbit antibodies prepared by injection of stage 4 quail primitive streaks can be used to specifically label quail epiblast and mesoblast cells, providing markers for at least two germ layers. It is now possible to combine grafting techniques of known success, with SEM analysis of the chimera.

Animals↗
PubMed1982

Effect of hyaluronidase treatment on the distribution of cranial neural crest cells in the chick embryo.

The cranial paraxial mesoblast is patterned into segmental units termed somitomeres. Recently we demonstrated the morphological relationship between the migratory pathways of cranial neural crest cells and the patterned primary mesenchyme of chick embryos (Anderson and Meier, '81). Since extracellular matrix, particularly hyaluronate, is also distributed in cranial crest pathways, embryos were given sub-blastodisc injections of hyaluronidase just prior to neural tube fusion and neural crest migration to remove matrix. Histological sections of enzyme-treated embryos showed that Alcian blue staining of hyaluronate was significantly reduced. Surface ectoderm appeared collapsed on the subjacent mesoderm as well. Examination of embryos with the scanning electron microscope (SEM) revealed that paraxial mesoderm remained segmentally patterned even though it appeared more condensed because of a reduction in intercellular space between mesenchymal cells. In enzyme-treated embryos, the rostral crest cells spread over the dorsal surfaces of the first four somitomeres, as they would do normally. This distribution of neural crest cells occurs even when enzyme treatment interferes with neural tube fusion at that level. We conclude that 1) neural tube fusion is not a prerequisite for the timely release of cranial crest in the chick embryo and 2) that much of the organized hyaluronate-rich matrix that lies in the path of cranial crest is not essential for crest emigration or patterned distribution.

Animals↗
PubMed1982

Experimental studies of the origin and expression of metameric pattern in the chick embryo.

On either side of Hensen's node of the fully extended primitive streak of the chick embryo (stage 4) the mesoderm is already organized into circular domains called somitomeres. As Hensen's node regresses, paraxial somitomeres are added in tandem and are early morphological representatives of metameric pattern in the mesoderm. These organized circular domains of mesenchyme cells are best visualized with stereo pair scanning electron microscopy. Experiments suggested that a prepattern of segmentation exists in and around the fully extended primitive streak. Streaks divested of Hensen's node can generate some paraxial somites, but only if surgically split down the midline. We assessed metameric pattern formation in nodeless streaks, both severed and unsevered down the midline. Operated blastoderms were cultured 15 hours, fixed, dissected, processed for scanning electron microscopy, and photographed in stereo. Split nodeless streaks produced a cranial to caudal sequence of somitomeric development. This sequence is similar to the sequential maturational events seen in the segmental plate of older embryos. The least mature somitomeres, toward the posterior end of the severed edge, appear as circular domains of radially oriented cells, looking much like the first somitomeres to emerge near Hensen's node of the stage 4 streak. More cranially along the severed edge, somitomeres are morphologically more mature, being more condensed, with cells oriented about a central myocoele. At the most cranial end of the severed piece, somitomeres are the most mature, having contracted about their centers to create intersomitomeric gaps that permit their identification with light microscopy as individual "somites." Embryos from which the node was removed, but the streak left intact, generated only the most primitive somitomeric pattern repetitively along either side of the primitive groove. We conclude that regression of Hensen's node provides for the timely initiation of morphogenesis of somitomeres from a prepattern of segmentation that already exists.

Animals↗
PubMed1982

The establishment of a somitomeric pattern in the mesoderm of the gastrulating mouse embryo.

Mesoderm formation in the mouse embryo begins at 6.5-6.75 days p.c. (postcoitum) when a primitive streak is formed along the posterior side of the egg cylinder. Epiblast cells in a localized region separate from one another and spread laterally between the primitive endoderm and the rest of the epiblast. The newly formed mesoderm contributes to both embryonic and extraembryonic regions. When the endoderm is removed, a definitive somitomeric pattern is first observed in the lateral sings of mesoderm of the mid-primitive-streak-stage embryo. The sequential appearance and the placement of somitomeres in the gastrulating mouse embryo are closely related to the general changes in physical dimensions and to the pattern of tissue growth which occur during the maturation of the egg cylinder. By the late-primitive-streak stage, about four somitomeres are present in the paraxial mesoderm on either side of the embryonic axis. These somitomeres will undergo morphogenesis and give rise to the cranial segments and head mesenchyme of neurulating embryos (Meier and Tam, 1982). The midline or axial mesoderm, consisting of prechordal plate and notochord, is derived from the head process mesoderm originating from the anterior end of the primitive streak. Cells of the head process are compact and adherent to the endoderm. The early presence of a somitomeric pattern which persists and is added to throughout subsequent phases of mesoderm formation suggests that spreading mesodermal cells have relatively stable neighbor relationships. This morphological evidence supports the idea that the expansion of the mesoderm during gastrulation results from tissue growth and progressive deposition of cells from the primitive streak. Cell migration may be limited principally to nonsomitomeric mesodermal cells found in the leading edge of the spreading lateral wings.

Animals↗
PubMed1982

Metameric pattern development in the embryonic axis of the mouse. I. Differentiation of the cranial segments.

The overall pattern of the mesoderm in the embryonic axis of the cranial region of mouse embryos was examined with the scanning electron microscope (SEM). A segmental organization was observed first in the paraxial mesodermal wings and midline axis of embryos at the late primitive streak stage. Each segmental unit consists of a somitomere in the paraxial region on each side of an enclosed stretch of midline notochord. Somitomeres appear initially as circular domains of radially arranged cells that swirl about the core center of the unit and are quite similar morphologically to those described recently in chick embryos [12]. Lying in tandem sequence, the segments comprise the chordamesoderm that underlies the neural plate. As additional pairs of somitomeres are added from the primitive streak at the caudal end of the axis, those established in the cranial region remain contiguous and undergo morphogenesis that is coordinate with neurulation. We divide the development of the cranial axis into five phases and associate somitomeres in the mesoderm with neuromeric segmentation in the neural plate. It was found that the first pair of somitomeres comes to underlie the prosencephalon, the second and third pairs underlie the mesencephalon, while the fifth, sixth, and seventh pairs of somitomeres underlie neuromeres of the metencephalon. The eighth pair of somitomeres are the first to separate themselves from the first seven and from the first pair of somites visible at the light microscope level. This study suggests that the cranial axis of the mouse embryo is initially organized into segments like the rest of the body and that subsequent cranial morphology is a consequence of differential development of these segments.

Animals↗
PubMed1982

Differentiation of the metameric pattern in the embryonic axis of the mouse. II. Somitomeric organization of the presomitic mesoderm.

The formation of the embryonic axis is brought about by the continuous recruitment of cells from the primitive streak, and at later stages from the tail bud. Presumptive somitic cells are first incorporated into presomitic mesoderm before they emerge as metamerically arranged somites. When the presomitic mesoderm was examined in stereo with the scanning electron microscope (SEM), mesenchymal cells were found to be already organized into segmental units. These segmental units are called somitomeres because of their striking similarity to structures in the embryonic axis of the chick embryo described by Meier [16]. Cells within the somitomere are arranged in concentric whorls about a core center, bisected by a medio-lateral seam which subdivides the cell population into anterior and posterior halves. The concentric configuration of the cells is most easily observed along the medial face of the presomitic mesoderm when it is generally wedge-shaped. Even tough the units are tandemly contiguous, somitomeric interfaces are distinguished by abrupt change in cellular orientation. Despite a nearly two-fold fluctuation in the overall size of the presomitic mesoderm during embryonic development, a relatively constant number of somitomeres (six) is found in tandem sequence. Somitomeric maturation culminating in somite formation involves compaction of the cell population, more orderly alignment of cells, reduction in extracellular space, and changes in the shape of the somitomere concomitant with neurulation. Though the more mature somitomere is about 70% the size of the most recently formed somitomere at the caudal end of the presomitic mesoderm, the average size of each somitomere is adjusted proportionally to the overall length of the presomitic mesoderm. In vitro culture of the presomitic mesoderm shows a direct developmental lineage between the somitomere and the somite, suggesting that somite formation is a morphologic manifestation of a somitomeric pattern laid down at an earlier stage in development. The somitomeric pattern in the paraxial mesoderm is the earliest recognizable morphologic evidence of metamerism in the embryonic axis. This pattern is later emulated by other tissues that are topographically associated with the paraxial mesoderm.

Animals↗
PubMed1982

Danazol and its principal metabolites interfere with binding of testosterone, cortisol, and thyroxin by plasma proteins.

Danazol and its three principal metabolites (2-hydroxy-methylethisterone, 2-hydroxymethyl-1,2-dehydroethisterone, and ethisterone) competitively displace cortisol and testosterone from plasma proteins. This effect is in addition to the reported inhibition of the production of testosterone-binding globulin and thyroxin-binding globulin. We saw no competitive inhibition of thyroxin binding. Concentrations of total testosterone, total cortisol, and total thyroxin were low, whereas percentages of free testosterone, free cortisol, and free thyroxin were abnormally high in women being treated with danazol. Values for testosterone, cortisol, and thyroxin in danazol-treated patients should therefore be appropriately corrected before interpretation. Protein-binding assays for testosterone or cortisol that involve testosterone- or cortisol-binding globulin may be invalid in danazol-treated subjects because of the competitive binding of danazol and its metabolites to these proteins.

Adult↗
PubMed1982

The distribution of cranial neural crest cells during ocular morphogenesis.

This study describes the mesodermal pattern adjacent to the region of migration of prosencephalic neural crest cells. The paraxial mesoderm is organized into somitomeres, which are composed of extended, radially oriented mesenchyme cells. The mesodermal pattern is mimicked by the cranial neural crest cells as they migrate inthe extracellular space between mesoderm and surface ectoderm. The prosencephalic crest spreads over the dorsal surface of the second somitomere and assumes a swirled configuration. Extending cranially, prosencephalic crest follows the contours of the posterior portion of the first somitomere and also spreads over the posterior and rostral surface of the optic vesicle. It is suggested that the somitomeric (segmental) partitioning of the mesoderm, as well as the surface contours of the somitomeres themselves, may provide topographic information that influences cranial crest migration.

Animals↗
PubMed1980

Development of the chick embryo mesoblast: pronephros, lateral plate, and early vasculature.

The early development of the mesoblast in the intermediate and lateral regions of the chick embryo was examined with the scanning and transmission electron microscope. It was found that primary mesenchyme here becomes condenses into epithelial structures that emerge in a metameric pattern. Viewed in developmental sequence, the intermediate mesoblast condenses into a narrowing cord of axially oriented cells which divert medially at regular intervals into the intersegmental interfaces of somitomeres and somites. These cells give rise to the vascular channels of the posterior cardinal vein as well as to tubular elements of the pronephros. Intermediate mesenchyme cells become epithelial, forming zonular junctional complexes apically and depositing patchy basal lamina over their basal surfaces. The lateral plate mesenchyme organizes similarly into somatic and splanchnic epithelial sheets that utilize the body coelom as their lumenal surface. Cells of the lateral plate extend filopodia basally that interweave with adjacent cells, fibrillar extracellular matrix, as well as with interstitial bodies. The pattern in the lateral plate is subtly ribbed as bands of mesoblast undulate along the axis. The central region of each band is raised while ther are grooves created along lines of band abutment, corresponding to intersegmental clefts in the paraxial region and reflecting an underlying metameric pattern. These grooves are usually demarked medially by the protrusion of short segments of adjacent intermediate mesoblast. Most of the remaining primary mesenchyme develops into a non-metameric vascular epithelium, which forms a prominent anastamosing plexus between splanchnic mesoderm and endoderm. It is proposed that the emergence of primary mesenchyme into patterened epithelial anlage facilitates the distribution of neural crest cells introduced subsequently.

Animals↗