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Biomedical subjects

B Christ

Publications and source records attributed to B Christ.

At least 181 records · Page 10Linked to original sources
PubMed1986

Principles of hand ontogenesis in man.

Human hand anlagen of different developmental stages are studied light and scanning electron microscopically. The findings are compared with experimental and ultrastructural results obtained from avian limb anlagen. Shaping, cell differentiation and the spatial arrangement of different cells are found to be the basic processes of hand development. The shaping of the arm and hand seems to anticipate future grasping movements. Factors controlling this developmental process are on the one hand the apical ectodermal ridge (AER) that maintains in the underlying mesoderm a high level of mitotic activity, and on the other hand a species-specific pattern of cell death in different zones of arm and hand. Interdigital cell death, microfilament bundles included in the basal compartment of AER cells, and local anchorings of the AER ectoderm by collagen fibrils are involved in finger separation. The flexion creases are genetically fixed and their development cannot be explained by mechanical factors. It is found that the early hand anlage is already composed of relatively autonomous founder cells committed to different lineages. This is true for the muscle precursor cells which originate from the brachial somites. These migrating somite cells are determined to belong to the myogenic lineage. However, their distribution, mitotic activity and later arrangement in single muscles are controlled by factors localized within the hand itself. Tendons develop autonomously from somatopleural cells. Other already committed cells are the angioblasts forming the endothelial lining of the blood vessels, the neural crest cells differentiating into melanocytes and Schwann cells, and the blood-derived cells like chrondro- or osteoclasts. The differentiation of somatopleural cells into cartilage, connective tissue or smooth muscle depends on their position within the hand anlage. Possible mechanisms leading to the specific pattern are discussed.

Animals↗
PubMed1984

Isoelectrically focused carboxyesterases as a biological marker in chimeras.

Species-specific multiple forms of carboxyesterases (CE) were determined in zymograms obtained by isoelectric focusing (IEF) using homogenized wing zeugopodal tissues of chick, quail and quail-chick chimeras. The validity of the CE pattern of chimeric tissues was verified by the nuclear marker technique. Analytical IEF of CE was found to be useful for investigation of the origin of tissues in chimeras.

Animals↗
PubMed1984

Ontogeny of avian extrinsic ocular muscles. I. A light- and electron-microscopic study.

Light- and electron-microscopic studies were performed on those tissues that are supposed to deliver the anlagen of the extrinsic ocular muscles. Since the blastemata of the ocular muscles can be traced back into the prechordal mesoderm, it can be concluded that this tissue is the source of these muscles. In embryos from stage 8-10 according to Hamburger and Hamilton (HH) cells are found to detach from the lateral border of the prechordal mesoderm. These cells are assumed to give rise to the trochlearis and abducens musculature. In stage-14 embryos the paired premandibular cavity arises within the lateral wings of the prechordal mesenchyme. In 4-day embryos the lateral wall of each premandibular cavity becomes denser forming a premuscular mass, which is subdivided into the anlagen of the oculomotorius muscles in 5-day embryos. The head cavities are not homologous to somites because their structures, origins and sites are very different.

Animals↗
PubMed1983

On the origin and development of the ventrolateral abdominal muscles in the avian embryo. An experimental and ultrastructural study.

In avian embryos the formation of ventrolateral abdominal muscles was studied by (1) heterospecific grafting experiments between chick and quail embryos and (2) ultrastructural examinations of cells having part in this process. The results demonstrate that the muscle cells are of somitic origin while the connective tissue derives from the somatopleure. Somatopleural cells do not differentiate into myocytes, and somite cells which have entered the ventrolateral abdominal wall, do not contribute to the connective tissue. It is concluded that both dermatome and myotome cells undergo muscular differentiation. The formation of muscles is found to take place in four characteristic steps. During the 4th day of development, epithelially structured ventral somite buds enter the somatopleure. The light cells of the inner myotome layer are elongated in a cranio-caudal direction and contain randomly distributed microfilaments. On the 5th day, the buds lose their epithelial arrangement and change into compact processes in which cells intermingle. The myotome cells show short bundles of thin and thick microfilaments. The third step can be characterized by the appearance of intercellular spaces and the disaggregation of processes becoming invaded by somatopleural cells. Thus, subdivision in single muscle blastemata begins to occur. In 7-day embryos, the muscle anlagen are distinctly separated and the first myotubes containing regularly arranged myofibrils are found. Coincidentally, signs of cell death are observed. Up to the 10th day, the tendons being of somatopleural origin become plainly outlined and the muscle anlagen move to their definitive positions. It is assumed that the formation of muscle pattern is controlled by the somatopleure.

Abdominal Muscles↗
PubMed1982

Grafting experiments on determination and migratory behaviour of presomitic, somitic and somatopleural cells in avian embryos.

The state of determination of somites, parts of somites, unsegmented paraxial mesoderm and of somatopleure was investigated by grafting these tissues from quail embryos to the wing buds of chicken embryos. It was found that muscular and chondrogenic determination occur before the formation of somites. Muscular determination takes place earlier than previously assumed and ahead of chondrogenic determination. Somatopleure yields cartilage, but no skeletal muscle. Prospective sclerotomes are primarily capable of differentiating into muscle and loose this potency in the course of development. Myogenic cells extensively migrate within the wing bud in a proximo-distal direction, whereas chondrogenic cells both of somitic and somatopleural origin show no overt migratory tendency.

Animals↗
PubMed1981

On the determination of mesodermal tissues in the avian embryonic wing bud.

The quail-chick-marker technique has been employed to elucidate the determination of embryonic tissues in the avian wing bud. It was found that myogenic cells of somitic origin are determinated to give rise only to muscular tissue from HH-stage 19 on. Mesenchyme in the cartilage forming regions is determinated to form cartilage from HH-stage 20 on. Tissue from non-cartilage forming regions retains the option to form cartilage at least up to HH-stage 26. Whereas cells of somatopleural lineage do not migrate within the limb bud, cells of somitic origin do so up to at least HH-stage 28.

Animals↗
PubMed1981

[Experimental contribution to the formation of digital flexion creases].

Flexion creases on the toes of birds show remarkable similarities to human digital flexion creases, concerning both morphology and development. Muscle-free avian limbs were raised in the coelomic cavity or on the chorioallantoic membrane of chick embryos. Flexion creases were found to be formed after both procedures. From these experiments it may be concluded that regional differences, rather than mechanical factors, concerning the involved tissues are responsible for the formation of digital flexion creases. This may hold true also for human digital flexion creases.

Animals↗
PubMed1979

Differentiating abilities of avian somatopleural mesoderm.

Quail-to-chick grafting experiments were performed on 2-day embryos in order to test the differentiating abilities of the somatopleure. After orthotopic and heterotopic transplatations of different parts of quail somatopleural mesoderm into chick embryos it is demonstrated that avian somatopleural cells differentiate into skeletal elements, smooth muscles, tendons and connective tissues. However, skeletal muscle fibres do not originate from somatopleural cells.

Animals↗
PubMed1979

The migration of myogenic cells from the somites into the leg region of avian embryos. An ultrastructural study.

The migration of myogenic stem cells into the leg anlagen of chick embryos between stages 16--20 of Hamburger and Hamilton was examined. SEM and TEM studies reveal that cell migration starts at stage 16 from the just-formed somites 26-28. The migrating myogenic cells are elongated and oriented in a medio-lateral direction. The leading ends branch into filopodia which contact a fibrillar network. At first, single cells migrate; later on the cells leaving the ventro-lateral edge of the dermatome migrate in strands and have specialized contacts between them. After reaction with ruthenium red and concanavalin A the migrating cells show a thick surface coat to which ruthenium red-positive particles are attached. The surface coat may be important in the interactions among the migrating cells as well as between the cells and the substrate. The migration of myogenic stem cells was found to take place in a matrix of collagenous fibrils and ruthenium red-positive particles, probably containing glycosaminoglycans. At the onset of migration the fibrillar network exhibits a preferred medio-lateral orientation. Therefore, it may be concluded that this alignment of the fibrils influences the direction of cell migration.

Animals↗
PubMed1978

On the migration of myogenic stem cells into the prospective wing region of chick embryos. A scanning and transmission electron microscope study.

In chick embryos undifferentiated myogenic stem cells migrate from the ventrolateral somite respectively dermatome edge into the prospective wing region after the second day of incubation. At first, single cells that are elongated in mediolateral direction, later also small groups of cells, are found in the space between somites and somatopleura at the wing bud level. The leading ends of the migrating cells are formed like finger-shaped lobopodia as well as flattened lamellipodia from which thin filopodia arise. The main structural features of the cell processes are microtubules and microfilaments predominantly oriented parallel to the long axis of the cells. The filopodia are found to be in close connection with the surrounding network of collagen fibrils. Since the main strands of the fibrils show a mediolateral orientation, it may be assumed that the direction of cell migration depends on the arrangement of the collagen fibrils.

Animals↗