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Biomedical subjects

J W Lash

Publications and source records attributed to J W Lash.

At least 37 records · Page 2Linked to original sources
PubMed1986

Precardiac cell migration: fibronectin localization at mesoderm-endoderm interface during directional movement.

The pathway of directional movement of chick precardiac mesoderm cells was studied by indirect immunofluorescence and by scanning electron microscopy. Directional movement of the precardiac cells begins at stage 6 from the lateral sides of the embryo at the level of Hensen's node. The cells move anteriorly in an arc to the embryo's midline. By stage 8 the cells arrive at the lateral sides of the anterior intestinal portal and movement ceases. The interval of this directional movement is approximately 10 hr. During migration the precardiac cells are in close association with the underlying endoderm. As migration proceeds, the cells encounter increasing amounts of fibrils in the substratum at the mesoderm-endoderm interface. Concomitant with increasing fibril formation there is an increase in fibronectin (FN) in the heart-forming region. During stage 5 FN first appears in the lateral heart-forming regions and increases in amount during the period of cell migration. By stage 7 a concentration difference of FN is apparent in the lateral regions with more FN cephalad and decreasing amounts caudad. At stages 7 and 8 large amounts of extracellular FN-associated fibrils are observed at the lateral sides of the anterior intestinal portal where the cells stop moving. The precardiac cells moving into this region are oriented perpendicular to the anterior intestinal portal and in close association with these fibrils. There is no evidence that the fibrillar meshwork forming the substratum of the precardiac mesoderm cells is physically oriented as a guide for directional movement. The correlations between FN distribution at the mesoderm-endoderm interface and directional cell movement suggest that the precardiac cells may migrate by haptotaxis, i.e., by moving along the substratum toward areas of greater adhesiveness.

Animals↗
PubMed1985

Alpha actinin distribution and extracellular matrix products during somitogenesis and neurulation in the chick embryo.

A discrete stage in two different morphogenetic processes has been examined employing fluorescently labelled alpha-actinin as a probe to localize native alpha-actinin and antibodies to localize fibronectin and collagen type I. The stage of somitogenesis examined is the transition from the compact mesenchymal somitic mass to the epithelial somitic vesicle (ie, epithelialization of the somite). The stage of neurulation examined is the transition from the relatively flat neuroepithelium to the approximation of the neural folds. Before these morphogenetic movements begin, the neuroepithelium is sitting upon a basal lamina and interstitial collagen, and the somite is surrounded by a meshwork of interstitial collagen. During both of these processes, the cells become narrowed at their apices in the region of the tissue that is becoming concave, and alpha-actinin is localized in the apices. The localization of intracellular alpha-actinin and extracellular fibronectin, and the distribution of collagen, suggest that there is a coordinated appearance and distribution of these molecules that is temporally associated with these discrete morphogenetic events.

Actinin↗
PubMed1984

On the role of fibronectin during the compaction stage of somitogenesis in the chick embryo.

During the early stages of somitogenesis in the chick embryo the presomitic cells in the segmental plate undergo compaction. The aggregation of segmental plate cells is stimulated by fibronectin. The stimulation of segmental plate cells to aggregate and undergo compaction can be effected in isolated segmental plate cells, in isolated segmental plates, and in intact embryos removed from the yolk. The fact that the segmental plate cells react with greater vigor to cellular fibronectin than to plasma fibronectin suggests a specific molecular mechanism in the initiation of somitogenesis.

Animals↗
PubMed1984

An increase in cell-cell adhesion in the chick segmental plate results in a meristic pattern.

Cell-cell adhesion in the anterior portion of the segmental plate plays an important role in the initiation of somitogenesis. Dissociated somites show a marked tendency to reassociate into somite-size clumps within a few hours after dissociation. Segmental plate cells show very little tendency to reassociate, even after 24 h in culture. The cells from the anterior portion of the segmental plate do show a tendency to reassociate. This supports the hypothesis that cell-cell adhesion between the cells in the anterior portion of the segmental plate plays a major role in the initiation of somitogenesis.

Animals↗
PubMed1983

Inhibition of precartilaginous chick somites by oncogenic virus.

Infection of embryonic chicken notochord-somite explants with Rous sarcoma virus inhibited the in vitro differentiation of somites into cartilage. Visual inspection of the explants revealed that viral infection reduced the size of cartilage nodule formation. Formation of the complex of sulfated proteoglycans with hyaluronic acid was inhibited by RSV infection, and sedimentation analysis of the sulfated proteoglycans showed that very little fast sedimenting proteoglycans were synthesized by RSV-infected explants. The infected explants primarily synthesize a slowly sedimenting sulfated proteoglycan which was chondroitinase resistant. These slow-sedimenting sulfated proteoglycans lack the ability to associate with hyaluronic acid and appear to be noncartilaginous. These effects of RSV are apparently due to the src gene of this virus since the mutant td108, which lacks part of the src gene, has no detectable influence on the chondrogenic differentiation of somite explants. Similarly, infection with RAV-2 as well as with uv-irradiated virus had no detectable effect. The inhibition of synthesis of fast sedimenting proteoglycans was observed at 41 degrees C with explants infected with tsNY68, suggesting that residual activity of transforming gene of this virus at the non-permissive temperature is sufficient for this inhibition in the explants.

Animals↗
PubMed1983

Biosynthesis of proteoglycans in organ cultures of developing kidney mesenchyme.

The biosynthesis of proteoglycans was studied in organ cultures of differentiating metanephric mesenchymes. When triggered by a contact-mediated inductive interaction, this tissue undergoes transition from a mesenchyme to an epithelium. In the present study, proteoglycans were extracted by guanidinium hydrochloride in the presence of protease inhibitors. We found that, as a response to induction, the differentiating mesenchyme begins to synthesize large size proteoglycans with an apparent molecular weight (MW) of 1 X 10(6) D. The major glycosaminoglycans detected were chondroitin sulfates. Heparan sulfate proteoglycans were also detected, constituting 20% of the proteoglycans. An inhibitor of glucosamine synthesis, 6-diazo-5-oxo-norleucine (DON) was found to inhibit glycosaminoglycan synthesis by approx. 60%, and the size of the proteoglycans was also diminished. Our studies suggest that the transition of the mesenchyme to epithelium is associated with initiation of synthesis of large size proteoglycans.

Animals↗
PubMed1983

Fibronectin distribution during somitogenesis in the chick embryo.

Somite formation in vertebrates is a multi-stage process. From a relatively homogeneous rod of mesenchyme, the segmental plate, somites are formed in a repeating sequence. Cell-cell adhesion has been proposed as a causal factor in somitogenesis. This led to an analysis of fibronectin in the segmental plate with respect to the initiation of somitogenesis. The pattern of fibronectin distribution can be correlated with the initiation of somitogenesis in the anterior portion of the segmental plate. Fibronectin distribution was determined using a high resolution antibody localization technique. Differences in fibronectin distribution were verified with computer-assisted image analysis. The evidence presented supports the hypothesis that an increase in cell-cell adhesion is a significant factor in the initiation of somitogenesis.

Animals↗
PubMed1983

Light microscope observations on actin distribution during morphogenetic movements in the chick embryo.

The cellular distribution of actin during two morphogenetic processes in the chick embryo has been observed, using a high-resolution fluorescent technique, with heavy meromyosin as a probe. These cytoskeletal elements have been implicated in all cell and tissue movements in the embryo. It is now commonly accepted that microfilaments are necessary to provide the motive force for morphogenesis. Two morphogenetic movements in the early embryo have been studied at the light microscope level. During somitogenesis, the mesenchymal segmental plate becomes transformed into a meristic series of transient epithelial vesicles. Again, actin distribution is diffuse and random before the morphogenetic event. During epithelialization, actin becomes prominent in the apical regions of the epithelial cells. Cells in the somitic epithelial vesicles, the core cells, appear to be passive participants in this process, and consequently show no distinct cellular localization of actin.

Actins↗
PubMed1980

Extracellular matrix synthesis in the chick embryo lateral plate prior to and during limb outgrowth.

Little is known at the present time about the molecular basis and mechanisms of morphogenesis. The present study is an attempt to determine what influence the extracellular matrix has on the initial outgrowth of the limb bud. Stage -12 to -18 chick embryo lateral plates were examined in relation to proline and sulfate incorporation into collagen and proteoglycan. The flank and limbs incorporated the same amount of labeled proline and sulfate before stage 16. At stage 16 the flank began to incorporate more of both isotopes until at stage 18 there was twice as much incorporation into the flank as into the limbs. The flank and limbs contained the same type of collagen during the period examined. The limbs contained both large and small proteoglycans but the flank contained only small proteoglycans. These data suggest that the extracellular matrix in the flank and limb regions may play a role in limb outgrowth and that the limb buds at these stages may be more inclined toward cartilage development.

Age Factors↗
PubMed1980

Changing patterns of proteoglycan synthesis during chondrogenic differentiation.

The pattern of proteoglycan synthesis was examined in the cartilages of the anterior and the posterior limbs, the vertebra and the sterna of the developing chick embryo, during chondrogenic differentiation. At stage 18, the limb primordia synthesize small monomeric proteoglycans. In all nine cartilages examined, there was a shift during differentiation from small to larger intermediate forms followed by a transition toward the aggregate forms. As development proceeds, the proportion of aggregates increases and the small proteoglycans almost disappear. Chondrogenic differentiation is thus marked by a increase in the size of the proteoglycan molecules, and an increase in the proportion of the large proteoglycan aggregates.

Animals↗
PubMed1979

Monomeric and aggregate proteoglycans in the chondrogenic differentiation of embryonic chick limb buds.

Proteoglycan heterogeneity was studied during the in vivo differentiation of embryonic chick limb cartilage. Recently, it has been shown that during the differentation of limb cartilage the proportion of the aggregated form of proteoglycans increases whereas the unassociated monomeric forms decrease, and this has been related to the synthesis of two link proteins at a specific stage of differentation. In this study it is suggested that the appearance of the aggregate formation is also due to synthesis of a stable hyaluronic acid binding region of the core protein. Thus, it can be concluded that differential gene expression for these proteins takes place as a differentiation phenomenon.

Animals↗