Inhibition of mucopolysaccharide synthesis by 5-bromodeoxyuridine in cultures of chick amnion cells

Cloning and sequencing of a developmentally regulated avian mRNA containing the LEA motif found in plant seed proteins

We report the cloning of a bromodeoxyuridine (BrdU)-sensitive transcript of 918 bp from an immortalized quail heart cell line containing an open reading frame (ORF) of 215 amino acids (aa) (approximately 23 kDa). Analysis of the secondary structure predicts two amphipathic alpha-helices with oppositely oriented amphipathic surfaces at the C-terminus of the protein. Each of the helices contains an LEA (late embryogenesis abundant) consensus sequence (A/TAEKAK/RETKD) which has been previously described only in a group of plant seed-specific proteins. Temporal and spatial distribution patterns of the transcript during chick embryo development were examined by whole-mount in situ hybridization and Northern blot analysis. At H&H (Hamburger and Hamilton, 1951) stages 11-14, the message was expressed strongly in blood islands in the area opaca. At day 5, strong signals were found in the liver primordia, mesonephrons, and nephric duct. Frozen sections of whole mount-stained embryonic liver demonstrated that the message was restricted to developing blood cells. The expression pattern of this transcript suggests that its protein product may be involved in hematopoiesis during avian development.

Effect of 5-bromodeoxyuridine on the appearance of the liver isoenzyme of pyruvate kinase

Hepatocyte cultures derived from 15-day foetal rats produce the liver form of pyruvate kinase (EC 2.7.1.40) only after 3 days of culture. The appearance of the liver form of the enzyme can be blocked by the addition of 5-bromodeoxyuridine on day 2 of culture, but not by addition on day 3 of culture. The reversibility of the action of 5-bromodeoxyuridine was shown when the inhibitor was added on day 2 and removed on day 4. By day 6 of culture the liver form of pyruvate kinase was detectable. The specificity of the action of 5-bromodeoxyuridine was monitored by following changes in the closely related embryonic form of the enzyme as a control. This was unaltered by the inhibitor.

Effect of low density lipoprotein on glycosaminoglycan secretion by cultured human smooth muscle cells and fibroblasts. Influence of serum concentration and cell proliferation rate

Glycosaminoglycan (GAG) secretion was studied in cultures of human fibroblasts and arterial smooth muscle cells. Supplementation of culture medium with whole human serum increased the secretion of GAG but this effect disappeared as cell density increased. Lipoprotein-free serum (LFS) supported cell growth but led to a decrease in GAG secretion and in cell cholesterol. Addition of human low density lipoprotein (LDL) to the medium containing 10% LFS produced increases in GAG secretion (200%) and cell cholesterol (300%) and a decrease (60%) in cell population. The effects of LDL were considerably smaller in medium containing 5% LFS; this was related to the lower rate of proliferation in this medium, since there was a close relationship between rate of proliferation and stimulation of GAG secretion by LDL independent of serum concentration. In addition, fetal smooth muscle cells showed a qualitatively different response to LDL in 5% LFS, with a biphasic dose-response of GAG secretion and cell number. It is concluded that: (1) whole human serum stimulates GAG secretion by sparse cell cultures, (2) LFS can support cell growth but not GAG secretion, (3) LDL stimulates GAG secretion but has a cytotoxic effect, (4) the degree of GAG stimulation by LDL is dependent on the proliferative state of cells, (5) at low serum concentrations fibroblasts and fetal smooth muscle cells show differences in response to LDL which are not evident at higher serum concentration.

Teratogenic and clastogenic effects of BUdR in mice

Pregnant mice (C57B1/6JFfm) were treated with BUdR on day 9 of gestation. For doses ranging from 300 to 1,200 mg/kg b.w. of BUdR the teratogenic effect in near-term fetuses was analyzed. The findings confirm the phase and dose dependency of the induced malformations found by other authors. They also demonstrate, however, a BUdR-specific induction of special malformations. For a dose of 1,200 mg/kg of BUdR the effect on mitotic rates and the induction of chromosomal aberrations were investigated. Mitotic rates were counted in single organs as well as in total homogenized embryos. The methods are equally useful. The embryos were analyzed 3, 6, 12, and 24 hours after BUdR treatment either after homogenization or in serial sections. Decrease of mitotic rates has been found to be most remarkable at 3 and 12 hours after treatment. At 24 hours only the neural tissue showed a slight decrease of the mitotic rate. Chromosomal aberrations are induced at all times, but the highest rates are seen at 3 and 12 hours after treatment. The aberrations are of the chromatid type.

Collagen type I trimer synthesis by cultured embryonic mouse molars

Embryonic mouse tooth germs were cultured in vitro and the collagens type I, type III and type I trimer were purified and biochemically characterized. Collagen type I trimer has been identified by means of CM-cellulose chromatography, CNBr peptide analysis, pepsin resistance and molecular sieve chromatography. Already before the odontoblasts were functional, this molecule was found to be a constituent of the dental extracellular matrix. However, the synthesis of collagen type I trimer was considerably increased when odontoblasts polarized and became functional. the incorporation of 5-bromodeoxyuridine into the dental cells inhibited the polarization of odontoblasts as well as the amplification of collagen type I and type I trimer synthesis.

Mitosis in beating cardiac myoblasts treated with cytochalasin-B

Time-lapse pictures of isolated chick cardiac myoblasts grown in a medium with cytochalasin-B reveal that normal mitotic chromosomal separation and muscle contraction can take place simultaneously. These observations indicate that the contractile stimulation for the cells' myogibrils does not affect the movement of the chromosomes and that the cell can regulate two different motile systems inside one cell.

Induction of placental alkaline phosphatase in choriocarcinoma cells by 5-bromo-2'-deoxyuridine

Growth of choriocarcinoma cells in the presence of 5-bromo-2'-deoxyuridine (BrdUrd) results in a 30- to 40-fold increase in alkaline phosphatase activity. The effects of BrdUrd is specific for phosphatase with an alkaline pH optimum. The induction by BrdUrd is probably not due to the production of an altered enzyme, since the induced enzyme resembles the basal enzyme in thermal denaturation and kinetic properties. Enzyme induction can be prevented by thymidine but not by deoxycytidine or deoxyuridine. The induction of alkaline phosphatase appears to require incorporation of the BrdUrd into cellular DNA. The presence of BrdUrd in the growth medium is not necessary for alkaline phosphatase induction in proliferating cells containing BrdUrd-substituted genomes. However, enzyme induction and maintenance of the induced levels of alkaline phosphatase in nonproliferating cells containing BrdUrd-substituted DNA requires the presence of the analogues in the medium. The induction of alkaline phosphatase by BrdUrd in probably an indirect process.

The effect of centrifugal force on glycosaminoglycan production by aortic smooth muscle cells in culture

Cultured smooth muscle cells from pig aorta subjected to centrifugation (48 h at 45 g over a 72-h period) increased their production of glycosaminoglycans by approximately 50%. The sulphated components, heparan sulphate, dermatan sulphate and chondroitin sulphate, showed a relatively greater increase than hyaluronic acid (66-34%). The results are consistent with the hypothesis that mechanical stress, such as hypertension, leads to increased accumulation of glycosaminoglycans in the aortic wall and that secondary trapping of lipoproteins by sulphated glycosaminoglycans produces atherosclerotic plaques.

Amplification of moderately repetitive DNA sequences during chick cartilage differentiation

A 5-bromo-2'-[3H]deoxyuridine (BrdUrd) probe was isolated to analyze DNAs obtained from various chick tissues and cell types. [3H]BrdUrd-substituted DNA, prepared from limb bud cultures, was sheared and freed from palindromic DNA. Nonradioactive DNA was prepared from embryonic liver, undifferentiated limb bud mesenchyme, sternal cartilage, differentiated limb bud cultures, and BrdUrd-blocked cultures, and was sheared. These DNAs were used in 100-fold excess to drive the reassociation of the [3H]-BrdUrd-DNA probe. Purified mature cartilage DNAs of embryonic sternae or differentiated limb bud cultures drove the reassociation of the probe approximately two times faster than did DNA from liver, undifferentiated limb bud, or BrdUrd-blocked cells. These data indicate that cartilage DNA contains a greater number of sequences complementary to the BrdUrd probe than do DNAs of noncartilage or undifferentiated precartilage cells. Calculations determined an average substitution of 10% of thymidine residues by BrdUrd in purified probe, whereas CsCl density gradients of unsheared probe revealed radioactive peaks of greater than 20% substitution. The BrdUrd appears to be clustered in the genome.

Distribution of 5-bromodeoxyuridine and thymidine in the DNA of developing chick cartilage

In order to study the mechanism of the irreversible effects of BrdUrd on the differentiation of limb bud mesenchyme to cartilage, the reannealing behavior of DNA obtained from such cells was examined. Cells incubated with [3H]thymidine ([3H]dThd) during days 1 and 2 of culture incorporated label into repetitive, moderately repetitive, and unique classes of DNA. In contrast, when 5-bromo-2'-[3H]deoxyuridine ([3H]Brd Urd) was added during the first 48 hr (in the presence of 32 muM BrdUrd), the label was preferentially incorporated into a late moderately repetitive region. Simultaneous incubation of unlabeled BrdUrd and [3H]dThd revealed a selective inhibition of [3H]dThd incorporation into moderately repetitive regions. Cultures incubated during days 3 and 4 with [3H]dThd incorporated label into all three classes of DNA; however, when [3H]dThd was present during days 3 and 4 in cultures previously incubated with BrdUrd during days 1 and 2, the [3H]dThd was incorporated preferentially in the late moderately repetitive region. The melting behavior of this reannealed DNA was identical with that of the reannealed 1-2 day [3H]BrdUrd-labeled, late moderately repetitive DNA. Turnover experiments revealed that whereas there was no loss of [3H]deoxycytidine or [3H]dThd, 37% of [3H]BrdUrd activity was lost from the DNA in 2 days after removal of the isotopes.

Suppression of melanoma cell tyrosinase activity and tumorigenicity after incorporation of bromouracil for one or two cell divisions

We have studied the kinetics of suppression of tyrosinase activity and tumorigenicity in unsynchronized B16 mouse melanoma cells (clone B559) exposed to 5-bromodeoxyuridine (BrdU, 3 mug/ml) for one or two cell divisions, then cultured in BrdU-free medium (RM) for five or six days. Bromouracil replaced about 23% of thymine residues after 24 hours (1 cell division) and almost 40% after 48 hours (2 cell divisions) in the presence of BrdU. Upon subsequent growth in RM the extent of replacement declined in a manner consistent with dilution by new DNA synthesis, reaching 5-10% substitution by day 7 of these experiments. Tyrosinase activity was significantly reduced after treatment with BrdU for 24 or 48 hours but continued to decline after the cultures were changed to RM, approaching undetectable levels on day 7. The time course of reduction was similar to that previously determined in cells grown continuously for seven days in the presence of BrdU. Therefore, suppression of tyrosinase activity can result from incorporation of BrdU during a single cell cycle, but requires about seven days for full manifestation of the effect. Tumorigenicity decreased to 55% after 24 hours and to 15% after 48 hours with BrdU but rapidly reversed to approach that of untreated melanoma cells when subsequently grown in RM for 5-6 days. The effects of BrdU on total RNA or protein synthesis, or on plating efficiency appeared insufficient to account for the degree of suppression observed. Our results indicate that substitution by bromouracil into either strand of DNA loci controlling tyrosinase activity or tumorigenic potential may be sufficient for suppression. In addition, they demonstrate that such brief treatment with BrdU may be used to probe the regulation of differentiated function and tumorigenicity in these melanoma cells.

Analysis of changes in collagen biosynthesis that occur when chick chondrocytes are grown in 5-bromo-2'-deoxyuridine

Chick embryo chondrocytes, in primary culture, initially synthesize only Type ii collagen (chain composition, [alpha1(II)13), as judged by two criteria: (i) carbosymethyl-cellulose chromatography of the denatured collagen, and (ii) carbosymethyl-cellulose chromatography of the cyanogen bromide peptides derived from the isolated chains. After a period of growth in 5-bromo-2'-deoxyuridine, however, synthesis of two different types of collagen could be detected after differential salt precipitation of the newly synthesized native collagens from neutral salt solutions at 2.2 M NaCl and subsequently at 0.01 M Na2hPO4. By criteria indicated above, the collagen precipitating at 2.2 M NaCl was identified as Type I collagen (chain composition, [alpha(I)]2alpha2), whereas the collagen subsequently precipitated at 0.01 M Na2HPO4 was found to be comprised entirely of alpha1(I) chains, indicating a chain composition, [alpha](I)]3. We propose to designate the latter type of molecule as the Type I trimer.

Changing patterns of actin localization during cell division

Changing patterns of actin localization have been studied on a light microscopic level by means of fluorescently labeled heavy meromyosin. The cellular distribution of actin is characterized by four major patterns, each of which corresponds to a particular phase of cell division. Long actin fibers are a prominent feature of the interphase cell. They disappear as the cell rounds up for mitosis and are replaced by a diffuse distribution of actin throughout the cytoplasm. During cytokinesis, the actin is localized predominantly in the cleavage furrow. The final shift of actin occurs after the completion of cytokinesis. At this time the actin becomes concentrated in the distal poles of the cell where pseudopods form to pull the daughter cells apart. When the daughter cells have separated, they flatten on the culture dish and the fibrous pattern of actin characteristic of interphase cells returns. All of these changes take place during the 1-hr period required for cell division.

Tissue-specific suppression of differentiation by 5-bromodeoxyuridine in vitro

Embryonic rat tooth germs were treated with 5-bromodeoxyuridine in vitro. Morphodifferentiation and histodifferentiation were arrested. Epithelial and mesenchymal deoxyribonucleic acid and protein synthesis were unaffected, whereas ribonucleic acid and collagen synthesis were retarded in the mesenchyme only. Inhibition of odontogenesis by this agent appears to be tissue-specific.

The phenotypic complexity of myogenic clones

A single cell isolated from cultured 8-day leg muscle may, when subcultured, yield a myogenic clone. A myogenic clone consists of myotubes and mononucleated cells. When such a myogenic clone is subcultured, large numbers of mononucleated cells are recovered. These mononucleated cells histologically and biochemically are indistinguishable from authentic fibroblasts cultured under the same conditions: they synthesize (alpha1)(2)alpha2 chains of collagen, large amounts of hyaluronic acid, and modest amounts of chondroitin sulfate. These mononucleated cells, however, will not chondrify when grown under culture conditions known to permit presumptive chondroblasts to differentiate terminally. These findings demonstrate that there is a population of single cells in 8-day muscle that is neither a myoblast nor a fibroblast, but is the common progenitor for cells in the myogenic and fibrogenic lineages: this progenitor, however, is beyond the point of readily yielding chondrogenic cells. These findings are discussed in terms of the limited number of phenotypic options open to differentiating cells in each of the successive compartments of their respective lineages.

Suppression of pigmentation in mouse melanoma cells by 5-bromodeoxyuridine: effects on tyrosinase activity and melanosome formation

Low concentrations (1-3 microg/ml) of 5-bromodeoxyuridine (BrdU) reversibly suppress pigmentation in a highly pigmented clone (B(5)59) of cultured B16 mouse melanoma cells. We have found that unpigmented cells (clone C(3)471), derived by long-term culture of B(5)59 cells in 1 microg of BrdU/ml, were completely amelanotic with no biochemically or cytochemically detectable tyrosinase activity or ultrastructural evidence of premelanosomes. The process by which pigmentation is suppressed was studied in B(5)59 cells during a 7-day period of growth with BrdU (3 microg/ml). Assays of tyrosinase activity showed that activity was reduced after 1 day and decreased progressively, approaching zero by 7 days. A quantitatively minor part of this reduction was directly attributable to the appearance of a dialyzable inhibitor of tyrosinase activity. Acrylamide gel electrophoresis revealed two bands of activity corresponding in Rx values to the T(1) and T(2) forms of soluble tyrosinase. Both were progressively reduced during growth with BrdU but one form (T(1)) was consistently affected earlier than the other (T(2)). Ultrastructural-cytochemical studies also showed an early effect on the localization of tyrosinase reaction product. At day 3, reaction product was no longer present in Golgi saccules and Golgi-associated smooth surfaced tubules, but was still seen within premelanosomes, compound melanosomes, and occasional Golgi-associated vesicles. By 7 days tyrosinase reaction product was usually not demonstrable. The number of premelanosomes was progressively decreased during growth with BrdU. Premelanosomes became concentrated in the juxtanuclear region and at day 3 many were contained within abnormally large and numerous compound melanosomes. Premelanosomes and compound melanosomes were rarely seen at 7 days, by which time the cultures were nearly amelanotic. The coordinated suppression of melanogenesis by BrdU may provide a useful model in which to study the normal regulation of this process.

Somite chondrogenesis. A structural analysis

Light and electron microscopy are used in this study to compare chondrogenesis in cultured somites with vertebral chondrogenesis These studies have also characterized some of the effects of inducer tissues (notochord and spinal cord), and different nutrient media, on chondrogenesis in cultured somites Somites from stage 17 (54-60 h) chick embryos were cultured, with or without inducer tissues, and were fed nutrient medium containing either horse serum (HS) and embryo extract (EE), or fetal calf serum (FCS) and F12X Amino acid analyses were also utilized to determine the collagen content of vertebral body cartilage in which the fibrils are homogeneously thin (ca. 150 A) and unbanded. These analyses provide strong evidence that the thin unbanded fibrils in embryonic cartilage matrix are collagen. These thin unbanded collagen fibrils, and prominent 200-800 A protein polysaccharide granules, constitute the structured matrix components of both developing vertebral cartilage and the cartilage formed in cultured somites Similar matrix components accumulate around the inducer tissues notochord and spinal cord. These matrix components are structurally distinct from those in embryonic fibrous tissue The synthesis of matrix by the inducer tissues is associated with the inductive interaction of these tissues with somitic mesenchyme. Due to the deleterious effects of tissue isolation and culture procedures many cells die in somitic mesenchyme during the first 24 h in culture. In spite of this cell death, chondrogenic areas are recognized after 12 h in induced cultures, and through the first 2 days in all cultures there are larger accumulations of structured matrix than are present in equivalently aged somitic mesenchyme in vivo. Surviving chondrogenic areas develop into nodules of hyaline cartilage in all induced cultures, and in most non-induced cultures fed medium containing FCS and F12X There is more cell death, less matrix accumulation, and less cartilage formed in cultures fed medium containing HS and EE. The inducer tissues, as well as nutrient medium containing FCS and F12X, facilitate cell survival, the synthesis and accumulation of cartilage matrix, and the formation of cartilage nodules in cultured somites.

Lac operator analogues: bromodeoxyuridine substitution in the lac operator affects the rate of dissociation of the lac repressor

As measured by a decreased rate of dissociation, lac repressor binds 10-times tighter to 5-bromodeoxyuridine-substituted lac operator than it does to normal lac operator. This result is obtained both in the absence and in the presence of isopropylthiogalactoside, an inducing ligand. These data are significant with regard to the mechanism of sequence-specific protein-DNA interaction, and also suggest a possible explanation for the effects of bromodeoxyuridine on the expression of differentiated functions in eukaryotic cells.

Cytochalasin B: effects on cell morphology, cell adhesion, and mucopolysaccharide synthesis (cultured cells-contractile microfilaments-glycoproteins-embryonic cells-sorting-out)

Cytochalasin B reversibly causes extensive branching of myoblasts, fibroblasts, and nonencapsulated chondroblasts; it does not induce the formation of similar processes in myotubes, erythrocytes, amnion cells, encapsulated chondroblasts, or HeLa cells. The drug has no effect on the spontaneous contractions of isolated skeletal, cardiac, or smooth-muscle cells. Within 60 min, it depresses the incorporation of [(14)C]glucosamine into total mucopolysaccharide and glycoproteins by over 50%. The drug interferes with adhesion and sorting-out of dissociated embryonic cells. Cytochalasin B is likely to produce changes in components of the cell surface whose function is not readily or solely related to a system of "primitive contractile microfilaments."