PubMed Health⌕ Search

Biomedical subjects

D C Beebe

Publications and source records attributed to D C Beebe.

54 records · Page 3Linked to original sources
PubMed1986

Localized vascular regression during limb morphogenesis in the chicken embryo: II. Morphological changes in the vasculature.

The regression of blood vessels in the distal wing bud of chicken embryos from stages 19 to 31 was examined by light and electron microscopy. The vessels were double-labelled by an injection of Monastral blue B (MB) to label the regressing endothelial cells, followed 6-48 hours later with an injection of India ink which marked the lumens of patent vessels. Prior to stage 26 the vessels contained only India ink since the endothelial cells were not phagocytic at this stage. Vessels at stage 26 or later were often double-labelled, with MB sequestered in the endothelial cell cytoplasm and India ink in the vessel lumens. After stage 27 cells not associated with lumens, but labelled with MB, were observed in areas undergoing vascular regression. Ultrastructural changes in the endothelial cells as the vessels regressed included formation of luminal and abluminal processes, long complex junctions, and vacuoles containing MB. In many involuting vessels the endothelial cells appeared normal even though the lumens were collapsed. Occasionally, isolated pyknotic cells were observed in regions that had been previously vascularized. At stage 31 cells in the developing cartilage had vacuoles containing MB. Our study suggests that blood vessels may disappear from the prechondrogenic zone of the distal wing bud by several mechanisms. These could include a type of cell death that does not elicit a cellular infiltrate, migration of the endothelial cells away from vascularized regions, and/or transdifferentiation into cells that resembled chondrocytes.

Animals↗
PubMed1986

Transport and steady-state concentration of plasma proteins in the vitreous humor of the chicken embryo: implications for the mechanism of eye growth during early development.

The nature and origin of the proteins of the vitreous humor were examined in chickens during embryonic and early posthatching stages. The major proteins of the vitreous humor were similar in electrophoretic mobility to plasma proteins at all ages examined. Earlier studies from our laboratory and experiments described below showed that plasma proteins continuously entered and left the eye throughout its development. From these data it was concluded that the majority of vitreous-humor proteins were derived from the blood. The protein concentration of the vitreous humor was 13% of that of the plasma from embryonic Days 6 through 15 (E6 through E15). After E15, the relative protein concentration in the vitreous humor declined with respect to the plasma and reached 4% of the plasma protein concentration at hatching. Several possibilities were considered to account for how proteins can rapidly enter and leave the eye, yet maintain a steady-state concentration in the vitreous humor that is less than one-seventh of that in the blood.

Animals↗
PubMed1986

Morphological and cell volume changes in the rat lens during the formation of radiation cataracts.

Earlier studies in our laboratory showed that 24 hr after X-irradiation, epithelial cells of early postnatal rat lenses increased in volume. Three days after X-irradiation, the underlying lens fibers increased in volume. This finding suggested a correlation between damage to epithelial cell volume regulation and subsequent fiber cell swelling. To test this hypothesis 4-week-old rat lenses were three-dimensionally reconstructed to determine average cell volumes of specific lens regions and wet weights of whole lenses were measured during radiation cataract formation. In addition, the differentiation of epithelial cells into lens fibers was monitored by autoradiography. Four-week-old Sprague-Dawley rats were injected with [3H]-thymidine and, 24 hr later, their eyes were irradiated with either 400 or 1200 rad. Lenses were examined with a slit lamp and cataracts were graded on a scale of 1+ to 4+. Animals were killed 24 hr and 3, 5, 15 and 30 weeks after exposure. Lenses were serially sectioned at 0.75 micron and epithelial, equatorial and cortical fiber cell volumes were determined. Rats exposed to 400 or 1200 rad developed 0.5-1.5+ or 2.5-3.0+ cataracts, respectively, 10-16 weeks after X-irradiation. Epithelial and equatorial cells of both groups did not significantly increase in volume during this period. Three weeks after irradiation with 1200 rad cortical fibers were disorganized and had increased volume. By 5 and 15 weeks, cortical fibers had more normal cell volumes, although their morphology remained grossly altered. Cortical fiber volume of lenses irradiated with 400 rad were not significantly different from control lenses throughout the experimental period. By 15 weeks lenses irradiated with 400 rad showed subtle changes in morphology. Wet weight determinations indicated that the localized increase in cortical fiber volume did not result in an increase in the wet weight of the entire lens. Autoradiography showed that affected fibers had been epithelial cells at the time of X-irradiation. These results provide additional evidence that disturbances in fiber differentiation are involved with cataract formation, but do not support the initial hypothesis that a disturbance in epithelial cell volume regulation leads to fiber cell swelling. Earlier results suggesting defects in lens epithelial volume regulation in radiation cataract formation may have been complicated by ocular inflammation.

Animals↗
PubMed1986

Development of the ciliary body: a brief review.

The ciliary body is an important component in the tissue interactions that occur during the normal development of the eye. The ciliary epithelium is induced by the lens from the rim of the optic cup and probably reciprocates by determining the position of the germinative zone of the lens. The ciliary epithelium is also likely to induce the differentiation of the ciliary muscle and stroma from the surrounding neural crest-derived mesenchyme. Intraocular pressure plays a major role in co-ordinating the growth and morphogenesis of many ocular tissues, including the ciliary body. A central question addressed in this review is whether this pressure is generated by the early activity of the ciliary epithelium or by the growth and osmotic activity of the vitreous body.

Animals↗
PubMed1985

delta- and beta-Crystallin mRNA levels in the embryonic and posthatched chicken lens: temporal and spatial changes during development.

The levels of delta- and beta-crystallin mRNAs were examined by cDNA hybridization in the embryonic and posthatched chicken eye lens. Four different cloned beta-crystallin cDNAs were used, allowing discrimination among different members of the beta-crystallin family. Each crystallin mRNA displayed a characteristic temporal and spatial pattern in the developing lens. delta-Crystallin mRNA accumulated rapidly during early embryonic development; by contrast, the beta-crystallin mRNAs began to accumulate rapidly near the end of embryogenesis. Both delta- and beta-crystallin mRNAs increased in the lens for the first month after hatching and began to decrease 3 months after hatching. The levels of the delta- and the different beta-crystallin mRNAs were also differentially regulated in cultured embryonic lens epithelia. The most fiber cell specific crystallin gene product in the differentiating lens was the beta 35 mRNA. These experiments provide a quantitative basis for exploring the differential expression of the delta- and beta-crystallin gene families in the chicken lens.

Animals↗
PubMed1984

Developmental changes in the blood-ocular barriers in chicken embryos.

Changes in the permeability characteristics of the developing chicken eye were studied using light and electron microscopy. Chicken embryos from 6-19 days of gestation (E9-E19) and within 1 day of hatching (P1) were injected intravascularly with horseradish peroxidase (HRP) and examined 1 and 5 min after injection. Within 1 min of injection there was focal accumulation of horseradish peroxidase reaction product (HRP-RP) at the angle of the anterior chamber in embryos up to E15. By 5 min post-injection the HRP diffused into the anterior and posterior chambers and vitreous body; and extended posteriorly into the developing uveal tract. No leakage was detected in the E19 or older animals. In the posterior segment of the eye prior to E12, HRP from the adjacent connective tissues diffused into zone III of the optic nerve. After E12 the developing meninges prevented the influx of the HRP. At the level of the lamina cribosa HRP permeated zone II up to E19 after which only 25% of the animals examined showed HRP-RP in this area. In zone I in all ages examined no HRP-RP was detected 5 min after injection. Developing blood vessels in the deep iris stroma, optic nerve and pecten remained impermeable even as they grew, while the choroidal vessels were consistently leaky. This study suggests: (1) that proteins from the vascular system reach the intraocular chambers before E19; (2) that the leakage occurs from vessels located in the uveal tract adjacent to the angle; (3) that the permeability of the optic nerve depends on the development of the meninges and the border tissues associated with the lamina cribosa; and (4) that the growing blood vessels in the developing eye have permeability characteristics similar to those found in mature vessels.

Animals↗
PubMed1984

Growth, synthesis and regional specialization of the embryonic chicken lens capsule.

The growth, synthesis and regional specialization of the lens capsule has been studied in chicken embryos and compared to adult chickens and mammals. During the final 15 days of embryonic development the surface area of the capsule increased 11-fold. This represents the minimum estimate of capsule growth, since it also increased in thickness during this period. Autoradiographic examination of [3H]proline- or 35SO4-labeled, detergent-cleaned, flat-mounted capsules suggested that all lens cells participated in capsule synthesis. This was supported by the observation that both lens epithelial and fiber cells incorporated [35S]-methionine into collagenase-sensitive proteins with molecular weights similar to type IV collagen. Histochemical staining of detergent-cleaned capsule explants (DCCEs) revealed regional differences in the carbohydrate composition of the capsule. Differences in collagenous proteins were also seen between the anterior and posterior regions of the capsule of the embryonic lenses. Following SDS-PAGE and silver staining a total of six collagenase-sensitive proteins were seen with molecular weights between 150 and 180 K. Three of these polypeptides were common to both anterior and posterior capsules, one was found only in the anterior capsule and the other two were found predominantly in the posterior capsule. No regional differences were seen in the collagenous proteins of capsules from adult chickens, rats or hamsters. The possibility is discussed that the unique pattern of collagenous polypeptides seen in embryonic capsules is related to the rapid growth of the embryonic lens.

Animals↗
PubMed1983

Hyaluronate in vasculogenesis.

Limb buds of chicken embryos contain within the peripheral mesoderm an avascular zone that is rich in hyaluronic acid. Epithelial tissues that synthesize large amounts of hyaluronic acid relative to other glycosaminoglycans caused avascularity when implanted into normally vascular wing mesoderm. Epithelia that synthesize little hyaluronic acid did not cause avascularity. Elvax implants containing hyaluronic acid caused the formation of avascular zones, whereas similar implants containing other glycosaminoglycans did not give rise to avascular zones. Hyaluronic acid may thus play a role in determining the location of blood vessels in the embryo.

Animals↗
PubMed1982

Transmethylation of phosphatidylethanolamine: an initial event in embryonic chicken lens fiber cell differentiation.

Agents that induce differentiation of lens epithelial cells into lens fiber cells in vitro transiently stimulate the transmethylation of phosphatidylethanolamine. Inhibition of transmethylation by 3-deazaadenosine results in a corresponding inhibition of the cell elongation that characterizes lens fiber formation, suggesting that phospholipid methylation plays an essential role in the differentiation of these cells.

Animals↗
PubMed1980

Lentropin: a factor in vitreous humor which promotes lens fiber cell differentiation.

An activity has been identified in chicken vitreous humor which stimulates embryonic chicken lens epithelial cells to elongate and specialize for lens crystallin synthesis. The activity is heat-labile and is destroyed by treatment with trypsin or agents that reduce disulfides. Gel filtration and ultrafiltration analyses indicate that it has an apparent molecular weight of approximately 60,000. Its properties differ from those of an activity present in serum which also can promote lens fiber cell formation in vitro. We call this material "lentropin" and suggest that it is responsible for stimulating lens fiber cell formation in vivo and, consequently, plays an important role in determining the shape and polarity of the lens.

Animals↗
PubMed1979

Lens epithelial cell elongation in the absence of microtubules: evidence for a new effect of colchicine.

Embryonic chick lens epithelial cells cultured in serum-supplemented medium elongated in the absence of microtubules after treatment with the antimicrotubule drug nocodazole. Colchicine, at concentrations lower than those that dissociate microtubules, blocks cell elongation and the associated increase in cell volume. These results indicate that an increase in cell volume, not microtubules, is responsible for lens cell elongation and suggest a previously undescribed effect of colchicine on cell volume regulation.

Animals↗