The effect of 5-bromodeoxyuridine on the differentiation of chick embryo pigment cells

Embryonic and postnatal injections of bromodeoxyuridine produce age-dependent morphological and behavioral abnormalities

The mitotic marker 5-bromodeoxyuridine (BrdU) was injected twice daily (60 mg/kg) into pregnant hooded rats on one of embryonic days (E) 11, 12, 13, 15, 17, or 21, or into rat pups on postnatal day (P) 10. The principal findings were the following: (1) BrdU exposure on E11 produces profound effects on body morphology, and animals must be fed a special diet because of chronic tooth abnormalities; (2) BrdU exposure at E17 or earlier produces a change in coat spotting pattern, the precise pattern varying with age; (3) BrdU exposure on E15 or earlier produces a reduction in both brain and body weight; (4) BrdU exposure on E17 or earlier reduces cortical thickness; (5) BrdU exposure on E11-E13 and at P10 reduces cerebellar size relative to cerebral size; (6) spatial learning is significantly affected after injections of BrdU at E11-E17, but the largest effect is on E17; (7) the deficit in spatial learning may be related in part to a reduction in visual acuity; and (8) skilled forelimb ability is most disrupted after BrdU exposure at E15 but is also impaired after injections on E13 or earlier. BrdU thus has teratological effects on body, brain, and behavior that vary with the developmental age of the fetus or infant.

Detection of melanogenic proteins in cultured chick-embryo melanocytes

The phorbol ester, 12-0-tetradecanoylphorbol-13-acetate (TPA), was used as a reversible inhibitor of melanogenesis. Chick-melanocyte cultures of the black genotype, E/E, were grown in conditioned medium plus TPA. After growth in TPA and after its removal, the cells were pulse labeled with 3H-leucine. The membrane fraction, which included all tyrosinase activity as well as both mature and immature melanosomes, was solubilized with Triton X-100. The proteins were separated using two-dimensional electrophoresis and visualized by fluorography. One defined melanogenic protein, tyrosinase, was isolated, and its location was determined in the two-dimensional protein pattern. The protein patterns for both the TPA-inhibited cells and the cells in which the TPA effects were reversed after removal were compared. In addition to tyrosinase, at least nine TPA-sensitive proteins were found. These were designated as being putative melanogenic proteins which, along with tyrosinase, may be responsible for melanin-granule synthesis.

A simple method for the establishment of tissue culture melanocytes from regenerating fowl feathers

A quick and simple method for the establishment of tissue cultures of nonembryonic domestic fowl melanocytes was desired. The selected source of these cells was the 14-d-old regenerating feather. Three procedures were compared on the basis of the yield and purity of melanocytes. For the first method, 2 mm of the proximal end of the feather was cut off under sterile conditions and placed immediately in Hanks' balanced salt solution (BSS) containing antibiotics. The feather was split longitudinally and the pulp removed. The tissue was placed pulp side down in several drops of Ham's F12 medium containing 2.5 micrograms/ml Fungizone, 50 micrograms/ml gentamicin, 100 micrograms/ml streptomycin, 100 micrograms/ml penicillin, and 10% fetal bovine serum. After 2 h at 37 degrees C, the tissue was attached to the dish and new medium was added and changed every 3 d thereafter. Cells migrated from the tissue starting on Day 2 and the tissue was removed on Day 5. Large dendritic peripheral cells and small round central cells were seen. Approximately 6.5 X 10(4) cells were present on Day 10 and 8 X 10(4) cells were counted on Day 20. By Day 30, the pigmented melanocytes were large, flat, dendritic cells. Electron microscopy and the use of the dopa reaction indicated that the population of cells was almost entirely melanocytes. The second method used was similar to the first, the only difference being that the feather sheath was also removed and thus only the collar of cells remained. The third method tried was similar to the second with the difference that the collar of cells was gently agitated with 0.25% trypsin for 5, 10, and 20-min intervals at 37 degrees C. The trypsin supernatant fluid was removed by gentle centrifugation and medium plus fetal bovine serum was added to stop tryptic action. The second method showed no advantage over the first. The purity and yield of melanocytes in the third method were lower than in either of the previous two methods. The number of cells desired can be controlled by varying the number of the feather pieces used per culture.

A method for culturing chick melanocytes: the effect of BRL-3A cell conditioning and related additives

A method for growing chick embryo melanocytes is described that utilizes medium conditioned by Buffalo Rat liver (BRL-3A) cells. The dissected trunk region of each 72 h (Stages 14 to 19) embryo produces approximately 200,000 melanocytes (purity, 80%) when processed and cultured for 8 d. Thus, a typical experiment involving 20 embryos would produce a total of 4 x 10(6) melanocytes. Choice of serum, serum concentration, and cell density were determined experimentally. Partially purified multiplication stimulating activity (MSA) from BRL-3A cells and insulin were also tested as medium additives. MSA was not stimulatory, whereas insulin gave a positive response in 2% but not 10 or 0% serum. The final protocol used a modified F12 medium with 10% bovine calf serum conditioned by BRL-3A cells. Cultures were fed every other day. Small colonies of cells became evident by culture Day 3 and increased rapidly to Day 5 when pigmentation became obvious. Colony size continued to increase but more slowly from Days 5 to 8, whereas pigmentation increased rapidly and maximized on Day 8. There is a factor, or factors, present in BRL-3A conditioned medium that stimulates embryonic chick melanocytes to divide preferentially over contaminating cell types. This results in cultures that can provide adequate numbers and purity for biochemical studies.

Effect of 5-bromo-2'-deoxyuridine on growth and differentiation of cultured embryonic retinal pigment cells

Chicken embryo retinal pigment cells cultured for 2 weeks in 1 or 10 microns BrdU accumulate only 25% of the amount of melanin found in controls. Growth is inhibited by 10 microns BrdU but not by 1 micron BrdU. Cells cultured with BrdU had decreased tyrosinase activity and lost the typical epithelial appearance of controls. Equimolar concentrations of deoxythymidine did not prevent the inhibition of melanogenesis due to BrdU but did prevent the growth inhibition of the higher concentration of BrdU (10 microns). Tenfold higher concentrations of deoxythymidine prevented inhibition of epithelial differentiation and melanogenesis. Ultrastructurally, BrdU produced an absence of melanosomes and disruption of the lamellar array of rough endoplasmic reticulum. The perinuclear arrangement of microfilaments became irregular. The cell surface was radically affected as membranes were no longer ruffled and cell junctions disappeared. Melanogenesis is a complex form of differentiated function, involving synthesis of tyrosinase and control of its activity, macromolecular synthesis of the melanosome, and the subsequent synthesis of melanin within the melanosome. BrdU appears to inhibit melanogenesis through a coordinated and simultaneous interference with these processes, suggesting that there may be a "program" of gene activity for melanogenesis that is regulated as a unit.

Malformation of embryonic neural retina elicited by BrdU

Exposure of neural retina tissue from early chick embryos (5 and 6-days) to 5-bromo-2'-deoxyuridine (BrdU) for 24 h irreversibly prevented normal histogenesis and resulted in the formation of chaotically disorganized tissue. The sensitivity of the retina to this effect decreased with embryonic age and declined sharply after the commencement of cell stratification. Examination by electron microscopy revealed the following progressive morphologic changes resulting from BrdU treatment: complete breakdown of the outer limiting membrane due to disappearance of its constituent tight junctions which normally anchor cells at the outer retinal surface; collapse and endocytosis of cilia, resulting in the absence of photoreceptor processes; increasing disorganization of the cells which commenced at the outer surface of the retina and progressed inward, resulting in chaotic distortion of the histologic architecture of the retina. Ultrastructural differences were noted between cells in the malformed retina, indicating the presence of several cell types. Possible mechanisms of this BrdU-elicited malformation are considered in the Discussion.

The requirement of DNA synthesis for the induction of alkaline phosphatase by bromodeoxyuridine in a derivative of the HeLa cell line

Non-lethal concentrations of bromodeoxyuridine induce a 2- to 5-fold increase in the specific activity of alkaline phosphatase in a HeLa subclone, S3G. Experiments employing 10-hour pulses of BRdU showed that 48 hours were required before induction commenced, and that maximal induction was attained by 96 hours. Under conditions in which DNA synthesis was prevented with hydroxyurea induction did not occur. Upon removal of hydroxyurea both DNA synthesis and induction were rapidly reestablished. Furthermore, experiments employing radiolabelled BRdU demonstrated that the kinetics of the induction process paralleled the incorporation of the analogue into cellular DNA. These results indicate that DNA synthesis, or some process intimately linked to DNA synthesis, is required for the induction of alkaline phosphatase, and suggest that the mode of the induction may be through the incorporation of the analogue into cellular DNA.

Transformation of chicken embryo retinal melanoblasts by a temperature-sensitive mutant of Rous sarcoma virus

Retinal melanoblasts were transformed by a temperature-sensitive mutant of Rous sarcoma virus (ts-RSV). At the permissive temperature for transformation, the cells cease melanin synthesis, degrade their melanosomes and release much of their accumulated melanin into the medium. At the nonpermissive temperature, the cells assume an epithelioid morphology, actively synthesize melanin and become difficult to distinguish from normal uninfected control cultures. Both the transformed phenotype and the differentiated cell phenotype are temperature-dependent. Infected retinal melanoblasts which are incubated at the nonpermissive temperature and which accumulate a large amount of melanin are unable to transform in response to a temperature shift; instead, the cells degenerate and die. Retinal melanoblasts can be infected by subgroups A, B, C and D of RSV; however, their level of susceptibility to infection is about 1/40 compared to fibroblasts. Cultures infected by ts-RSV produce virus at both temperatures, suggesting that cell phenotype does not regulate virus synthesis.

A 5-bromodeoxyuridine-sensitive interval during drosophila myogenesis

Drosophila myogenesis was monitored in vitro and the cells were treated with 5-bromodeoxyuridine (BrdU) or with thymidine at certain intervals. Muscle cells were scored for survival, contractility, and the uptake of thymidine and BrdU. Results indicated that the final S period for myoblasts takes place in vitro between 1.3 and 3.3 h following the initiation of gastrulation in the donor embryos. Treatment with 10(-4) M BrdU during this internal inhibited myogenesis, but later treatment did not. Thymidine reversed or prevented the BrdU effect if given before the final myoblast division, but not if given after wards. All results support the hypothesis that BrdU inhibits Drosophila myogenesis through its incorporation into DNA.

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.