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Biomedical subjects

H J Jacob

Publications and source records attributed to H J Jacob.

At least 145 records · Page 8Linked to original sources
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.

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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.

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PubMed1977

Experimental analysis of the origin of the wing musculature in avian embryos.

Interspecific grafts of somites, as well as parts of the somatic plate mesoderm, have been made between quail and chick embryos (stages 12--14 H. H.) at the level of the prospective wing bud in order to examine the relationship between somites and wing bud myogenesis. The stability of the natural quail nuclear labelling makes it possible to follow the developmental fate of grafted mesodermal cells in the host embryo. Embryos examined after subsequent incubation periods of 3--7 days show the following distribution of somatic and somitic cells within the wing bud: as soon as the three zones of different cell density within the mesoderm can be distinguished, cells of somitic origin are limited to the prospective myogenic area which is made up of mixed population of somatic and somitic cells, whereas the prospective chondrogenic area as well as the subectodermal zone only consists of cells originated from the somatic plate mesoderm. After further incubation, single muscle blastema are present which were also seen to be a mixture of somatic and somitic cells. The cells of muscular bundles are of somitic origin, while the muscle connective tissue cells are derived from the somatic plate mesoderm. After grafting into the coelomic cavity or on the chorio-allantoic membrane, fragments of the somatic plate mesoderm previously isolated from quail embryos (stage 14 H.H.) at the level of the prospective wing bud exhibit well developed skeletal elements, but fail to differentiate any musculature. These experimental investigations support previous evidence for a somitic origin of wing bud myogenic cells. Histological and scanning electron microscopic studies of the brachial somites and the adjacent somatic plate mesoderm of chick embryo (stages 13--15 H.H.) reveal that migration of still undifferentiated somitic cells into the brachial somatic plate mesoderm begins to take place in embryos at stage 14.

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PubMed1976

[Differention of the neural tube. Experimental study in chick and quail embryos].

In order to study the possible influence of adjacent structures upon differentiation and proliferation of the chick spinal cord, a piece of neural tube of chick embryos incubated for 2 days (stages 12-14 of HAMBURGER and HAMILTON) was extirpated and replaced by an equal graft from a donor embryo of the same age. The grafts were rotated 90 or 180 degrees around their longitudinal axis. The examination of the serial histological sections and the analysis of the distribution of mitotic density in the rotated spinal cord of embryos fixed 2-8 days after the operation led to the following results: the differences in morphogenesis and histogenesis between dorsal and ventral sectors of the spinal cord are already determined in 2-day-old chick embryos. The reversal of the neural tube at this time has no effect either upon the typical differentiation or the characteristic distribution of the mitotic cells in the spinal cord.

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