G1 phase A8 Xenopus laevis (toad) and V79B Cricetulus griseus (hamster) tissue cultures were used to observe the frequency of ultraviolet-induced chromosomal aberrations as a function of dose. When cultures are irradiated with ultraviolet light, visible aberrations are virtually absent until a threshold of approximately 80 ergs mm⁻¹ is reached. Aberrations then occur as a nonlinear function of dose. Chromatid aberrations are by far the most prevalent until doses in excess of 200 ergs mm⁻¹ are administered, at which point chromosome aberrations become common

Griggs, H. Gaston

Orr, Troy V.

English

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 30 Article 24 1976 Study of Ultraviolet-Induces Chromatid and Chromosome Aberrations as a Function of Dose in G1 Phase Vertebrate Tissue Cultures Troy V. Orr John Brown University H. Gaston Griggs John Brown University Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Genetics Commons Recommended Citation Orr, Troy V. and Griggs, H. Gaston (1976) "Study of Ultraviolet-Induces Chromatid and Chromosome Aberrations as a Function of Dose in G1 Phase Vertebrate Tissue Cultures," Journal of the Arkansas Academy of Science: Vol. 30 , Article 24. Available at: https://scholarworks.uark.edu/jaas/vol30/iss1/24 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. Arkansas Academy of Science Proceedings, Vol. XXX,197664The Study ofUltraviolet-Induced Chromatid and ChromosomeAberrations as a Function ofDose inGiPhase Vertebrate Tissue Cultures*TROY V.ORR and H. GASTON GRIGGSDepartment of Biology, John Brown University,Siloam Springs, Arkansas 72761ABSTRACTGi phase A8 Xenopus laevis (toad) and V79B Cricetulus griseus (hamster) tissue cultureswere used to observe the frequency of ultraviolet-induced chromosomal aberrations as afunction of dose. When cultures are irradiated with ultraviolet light,visible aberrations arevirtually absent until a threshold of approximately 80 ergs mm-1is reached. Aberrationsthen occur as a nonlinear function of dose. Chromatid aberrations are by far the mostprevalent until doses inexcess of 200 ergs mm'are administered, at which point chromo-some aberrations become common.INTRODUCTIONThe study of ultraviolet light (UV)-induced chromosomal aberra-tions in eukaryotic cells has been limited in comparison with that ofthe induction of chromosomal aberrations by ionizing radiation. Thefrequency ofchromosomal aberrations inGi vertebrate cells inducedby ionizingradiation has been observed tobe a logarithmic functionof the dose administered. These aberrations are basically of thechromosome type, which can be subdivided into deletions, resultingfrom single breaks, and exchanges, resulting from multiple breaksand rejoining (Evans 1967). Humphrey et al. (1963) studied aberra-tion production inhamster cells by a single dose of UV (100 ergsmm-1, 254 nm) in the DNA-sensitive absorption range. Log phasecells in monolayers were irradiated and samples were collected forchromosome analysis when they reached the first mitosis afterexposure. To determine whether the cells in a given collectionsample were in the Gi, S, or G> phase of the cell cycle duringexposure, the monolayers were flash labelled withtritiated thymidinebefore UV was administered. Somewhat surprisingly, Humphrey'sgroup found that a high frequency of chromatid aberrations wasproduced in the Gi cells, but the frequency of chromosome aberra-tions observed inthese same Gi cells was not significantly above thecontrol level. Chu (1965) carried out a detailed study of aberrationproduction in hamster cells, using 265 nm in the DNA absorptionrange and 280 nmin the protein absorption range. These studies with265 nm were carried out inessentially the same manner as the workby Humphrey et al. (1963). Chu found, however, that doses such as50, 100, and 200 ergs mm~]produced a significant frequency of bothchromatid and chromosome aberrations inGi cells. He also con-cluded that UV-induced aberration frequencies increased withincreasing dose, as was the case with ionizing radiations. Both ofthese studies were complicated by the complex "mixing"of cellsafter UV exposure of logphase cultures, because of the fact that cellsin different phases of the cell cycle during a given exposure aredelayed by different time intervals in their progression towardmitosis. Griggs and Bender (1973), working with synchronouscultures ofA8 Xenopus and V79B hamster cells, observed that a doseof 120 ergs mm'' (254 nra) induced damage inGi cells which wasexpressed as chromatid aberrations inexposed cells that reached thefirst mitosis after exposure. A significant frequency of chromosomeaberrations was not observed. By a rather detailed study ofaberration frequencies as a function of UV dose (254 nm) over anextended dose range, using synchronous cultures of cells to circum-vent the problem of cell mixing, the writers hoped to elucidate themechanism of aberration production byUV inGi cells and to aid inthe resolution of the apparent conflict mentioned above.'Research supported inpart by National Cancer Institute Grant CA-18809-01.MATERIALSANDMETHODSThe A8amphibian cell line is maintained in monolayer cultures atapproximately 24C in glass tissue culture bottles and plastic tissueculture flasks inF12A medium. F12A medium consists of powderedF-12 medium (Grand Islands Biological Company) supplementedwith fetal calf serum. Penicillin and streptomycin are added to aid incontrolling contamination, and the pH is controlled with N-2-hydroxy ethylpiperazine-N'2' ethane sulfonic acid (HEPES) andsodium bicarbonate (Griggs and Bender 1972).The V79B Chinese hamster cell line is maintained inmonolayercultures at 37C in F10 medium. This medium consists of F-10powdered medium (Grand Islands Biological Company) supple-mented withfetal calf serum. Penicillin and streptomycin are addedtohelp control contamination, and the pH is controlled withsodiumbicarbonate and carbon dioxide after titration with sodium hydrox-ide.Both types ofmedia are sterilized by filtration.Routine cultivation is achieved in the A8 cell line by vigorousshaking of the culture to produce a suspension of cells. The V79Bcells, however, being more firmlyattached to the surface of thecontainer, are treated witha trypsin-versene solution toproduce cellsuspensions.The UVsource consisted of a single 15W germicidal lamp (Sylvan-nia G15 T8). The lamp was suspended 60 cm above the floor of theradiation chamber, a glass enclosure with a plastic front containingentry ports (to permit the use of hands and forplacing items withinthe chamber). Thin sheets of plastic were placed between the lampand the radiation area to decrease the UV dose rate to the point atwhich relatively accurate dosages could be obtained by varying theexposure time. The exposure time was controlled by manuallyexposing the cells while recording the elapsed time. The modifieddose rate, approximately 4 ergs mm-1sec-', was checked periodicallywitha Westinghouse WL 755 phototube designed to read intensity at254 nm.Each culture for irradiation was prepared and irradiated as follows.The stock culture bottle was shaken lightlyand the medium changedto remove dead cells and start the synchronization of the culture forGi cells. Cells were collected from the stock culture by similar"shake-offs" every 30 minutes, to remove only those cells that hadjust come through mitosis. Then 2 ml of each resulting cell suspen-sion was deposited carefullyin the center of a 10-cm petri plate so asto form a large drop. Within approximately two hours at roomtemperature the cells had settled to the bottom and attached to thesurface, withno cells more than 2 cm from the center of the plate andwith essentially no touching or overlap; thus exposure was uniformwithout interference from the shadow cast by the sides of the petriplate. Once the cells had attached to the plate, the medium wasremoved, the cells were irradiated for a specific length of timeaccording to the desired dose, and fresh medium was gentlyreapplied.64Journal of the Arkansas Academy of Science, Vol. 30 [1976], Art. 24Published by Arkansas Academy of Science, 1976Arkansas Academy of Science Proceedings, Vol. XXX,1976 65Troy V.Orrand H. Gaston GriggsAllA8 irradiations were done under red light to avoid photoreac-tivation, and the irradiated cultures were transferred immediately toa light-proof container. Irradiated cultures were incubated at 24C inthese covered glass containers, which kept the humiditynear 100%,until the cultures were ready for fixing.Colcemid, to a final concen-tration of 10~*M, was added after the appropriate incubation period,and 24 hours later the cells were fixed on glass slides with 3:1methanol-acetic acid and stained with crystal violet. Chromosomespreads were scored by conventional methods (Wolff 1961). Spreadscontaining anormal complement of chromosome (36 forA8 cells and22 for V79B cells) were examined forchromatid terminal deletions,isochromatid breaks, chromatid exchanges, chromosome terminaldeletions, interstitial deletions, and chromosome exchanges (ringsand tlit•entries).The monolayers of V79B Gi cells were treated throughout theexperiments inessentially the same manner as the A8 cells withthefollowing exception. Allcultures were maintained at 37C in glasscontainers and irradiated cultures were fixed approximately 15 hoursafter treatment withcolcemid to a final concentration of4 x 10~'M.RESULTS ANDDISCUSSIONExtensive mitotic index determinations notonly provided a guide-line for appropriate incubation periods, but also yielded informativedata for doses between 0 and 120 ergs mm"* (Fig. 1). A markedincrease in the time required for the cells toreach mitosis after irrad-iation was observed through the 60 erg point, beyond which therequired time became more consistent. Asimilar pattern was notedinthe effect of the radiation dose on the optimum mitotic index (Fig.2); there was a relatively sudden decrease in the fraction of cellsreaching mitosis, again through the 60 erg point. Thesedeterminations have an important bearing on the validity of dataconcerning chromatid aberrations at doses below 200 ergs mm"1(Griggs and Bender 1973). Figures 1,2, and 4and Table Ishow onlydata for the A8 cell line to maintain clarity, but similar data wereobserved for the V79B mammalian line. Griggs and Bender (1972)reported that the surviving fraction for A8cells varied logarithmical-ly with dose, which also seems true of the writers' mitotic index databetween 0and 60 ergs mm"1.When aberration frequencies are plotted as a function of dose, noclear increase inaberration frequency is observed untildoses exceed60 ergs mm"1,beyond which the curves sharply rise (Fig. 3). This riseis first noticed in the V79B cells at the 75 erg point, and appears inthe A8 cells at about the 90 erg point (Fig. 3, and Table I).This eventoccurs after the aforementioned observed effect of UVradiation onmitotic index. These data suggest that some threshold radiation valuemust be exceeded before aberrations appear, and thus imply that an"accumulation of UV-induced events" leads to aberrations. Thiseffect is not observed in aberration production with ionizingradiation, and has not been observed before in studies reported onUV-induced aberration production, probably because no one hasstudied doses below 50 ergs mm"1for damage induced by wave-lengths in the DNA-sensitive absorption range.Separate compilation of the chromatid and chromosomeaberration frequencies showed that chromosome aberrations becamenoticeably more prevalent at 200 ergs mm"1than at any lower doseadministered (Fig. 4). The fact that relatively low frequency ofchromosome aberrations was noticed in the controls and at lowradiation levels suggests a threshold radiation value forchromosomeaberrations at a higher dose level than the threshold for chromatidThe data are somewhat similar to Chu's (1965) findings at higherdoses, but are more in accord with the data presented by Humphreyet al. (1963) for doses of about 100 ergs mm" 1. Consideration of thelong and complicated division delays (more than 70 hours in somecases) reported by Chu suggests that he may have scored many cellsat the second mitosis after exposure instead of the first. For example,irradiation of a given Gi cell might result in damage which wouldappear in a cell scored at the first division as a chromatid terminaldeletion. However, if this cell were capable of moving through asecond cell cycle, the damage would appear at the second mitosis asa terminal chromosome deletion. Such an effect could significantlybias results in such a manner as to overestimate chromosomeFigure 1. Time interval of the A8 cell line from irradiation to themaximum mitotic index as a function of dose.DOSE (ergs mm"2)Figure 2. Maximum fraction of A8cells reaching mitosis as a functionofdose.Figure 3. Total aberration frequencies (both chromatid andchromosome types) of the A8 and V79B cells lines as a function ofdose between 0 and 120 ergs mm"1. Average number of cells scoredwas 365 for the A8and 780 for the V79B.65Journal of the Arkansas Academy of Science, Vol. 30 [1976], Art. 24https://scholarworks.uark.edu/jaas/vol30/iss1/24The Study of Ultraviolet-Induced Chromatid and Chromosome Aberrationsaberration frequencies and underestimate chromatid aberration A3_ABERRATION FREQUENCIESfrequencies. Use of synchronous cultures minimized this problem inthe writers' study.I0LITERATURECITEDCHU, E.H.Y. 1965. Effects of ultraviolet radiation on mammaliancells. I.Induction of chromosome aberrations. Mutation Res. 42:75-94.EVANS, H.J. 1967. Actions of radiations on chromosomes. Scien-tificBasis ofMedicine Annual Reviews 13:321-339.LjJGRIGGS, H.G. and M.A.BENDER. 1972. Ultraviolet and gamma-° °'Aray induced reproductive death and photoreactivation in a CCXenopus tissue culture cell line. Photochem. and Photobiol. A15:517-526.toGRIGGS, H.G. and M.A. BENDER. 1973. Photoreactivation of qultraviolet induced chromosomal aberrations. Science 179:86- |_orUJ aHUMPHREY, R.M., W.C. DEWEY and A. CORK. 1963. Relative 3°°" *ultraviolet sensitivity of different phases in the cell cycle of AAAChinese hamster cells grown invitro.Radiation Res. 19:247-260.AA &-CHROMATIDWOLFF, S. 1961. Radiation genetics. Mechanisms inRadiobiology. . A cmromosomcAcademic Press, New York. 1:419-475.A A A AA(0)100 200 300DOSE (ergs mm"2)Figure 4. Aberration frequencies of the A8 cell line over an extendeddose range, with aberrations separated into chromatid andchromosome types. Average number ofcells scored was 425.Table I.Aberration Distribution forA8Cells at LowDosesNumber Chromatid aberrations Chromosome aberrationsDose cells Terminal Isochromatid Terminal Interstitialergs mm"1 scored deletions breaks Exchanges deletions breaks Exchanges0 200 2 0 0 10 010 400 1 0 0 020300 2 0 00030 310 2 0 0 1140 500 3 0 1 3 0 050400 4 0 00060 400 1 0 0 2 0 075 400 6 0 0 10 090 400 M 2_ 1 0 0 166 Arkansas Academy of Science Proceedings, Vol. XXX,197666Journal of the Arkansas Academy of Science, Vol. 30 [1976], Art. 24Published by Arkansas Academy of Science, 1976

Study of Ultraviolet-Induces Chromatid and Chromosome Aberrations as a Function of Dose in G1 Phase Vertebrate Tissue Cultures

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 30 Article 241976Study of Ultraviolet-Induces Chromatid andChromosome Aberrations as a Function of Dose inG1 Phase Vertebrate Tissue CulturesTroy V. OrrJohn Brown UniversityH. Gaston GriggsJohn Brown UniversityFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Genetics CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationOrr, Troy V. and Griggs, H. Gaston (1976) "Study of Ultraviolet-Induces Chromatid and Chromosome Aberrations as a Function ofDose in G1 Phase Vertebrate Tissue Cultures," Journal of the Arkansas Academy of Science: Vol. 30 , Article 24.Available at: http://scholarworks.uark.edu/jaas/vol30/iss1/24Arkansas Academy of Science Proceedings, Vol. XXX,197664The Study ofUltraviolet-Induced Chromatid and ChromosomeAberrations as a Function ofDose inGiPhase Vertebrate Tissue Cultures*TROY V.ORR and H. GASTON GRIGGSDepartment of Biology, John Brown University,Siloam Springs, Arkansas 72761ABSTRACTGi phase A8 Xenopus laevis (toad) and V79B Cricetulus griseus (hamster) tissue cultureswere used to observe the frequency of ultraviolet-induced chromosomal aberrations as afunction of dose. When cultures are irradiated with ultraviolet light,visible aberrations arevirtually absent until a threshold of approximately 80 ergs mm-1is reached. Aberrationsthen occur as a nonlinear function of dose. Chromatid aberrations are by far the mostprevalent until doses inexcess of 200 ergs mm'are administered, at which point chromo-some aberrations become common.INTRODUCTIONThe study of ultraviolet light (UV)-induced chromosomal aberra-tions in eukaryotic cells has been limited in comparison with that ofthe induction of chromosomal aberrations by ionizing radiation. Thefrequency ofchromosomal aberrations inGi vertebrate cells inducedby ionizingradiation has been observed tobe a logarithmic functionof the dose administered. These aberrations are basically of thechromosome type, which can be subdivided into deletions, resultingfrom single breaks, and exchanges, resulting from multiple breaksand rejoining (Evans 1967). Humphrey et al. (1963) studied aberra-tion production inhamster cells by a single dose of UV (100 ergsmm-1, 254 nm) in the DNA-sensitive absorption range. Log phasecells in monolayers were irradiated and samples were collected forchromosome analysis when they reached the first mitosis afterexposure. To determine whether the cells in a given collectionsample were in the Gi, S, or G> phase of the cell cycle duringexposure, the monolayers were flash labelled withtritiated thymidinebefore UV was administered. Somewhat surprisingly, Humphrey'sgroup found that a high frequency of chromatid aberrations wasproduced in the Gi cells, but the frequency of chromosome aberra-tions observed inthese same Gi cells was not significantly above thecontrol level. Chu (1965) carried out a detailed study of aberrationproduction in hamster cells, using 265 nm in the DNA absorptionrange and 280 nmin the protein absorption range. These studies with265 nm were carried out inessentially the same manner as the workby Humphrey et al. (1963). Chu found, however, that doses such as50, 100, and 200 ergs mm~]produced a significant frequency of bothchromatid and chromosome aberrations inGi cells. He also con-cluded that UV-induced aberration frequencies increased withincreasing dose, as was the case with ionizing radiations. Both ofthese studies were complicated by the complex "mixing"of cellsafter UV exposure of logphase cultures, because of the fact that cellsin different phases of the cell cycle during a given exposure aredelayed by different time intervals in their progression towardmitosis. Griggs and Bender (1973), working with synchronouscultures ofA8 Xenopus and V79B hamster cells, observed that a doseof 120 ergs mm'' (254 nra) induced damage inGi cells which wasexpressed as chromatid aberrations inexposed cells that reached thefirst mitosis after exposure. A significant frequency of chromosomeaberrations was not observed. By a rather detailed study ofaberration frequencies as a function of UV dose (254 nm) over anextended dose range, using synchronous cultures of cells to circum-vent the problem of cell mixing, the writers hoped to elucidate themechanism of aberration production byUV inGi cells and to aid inthe resolution of the apparent conflict mentioned above.'Research supported inpart by National Cancer Institute Grant CA-18809-01.MATERIALSANDMETHODSThe A8amphibian cell line is maintained in monolayer cultures atapproximately 24C in glass tissue culture bottles and plastic tissueculture flasks inF12A medium. F12A medium consists of powderedF-12 medium (Grand Islands Biological Company) supplementedwith fetal calf serum. Penicillin and streptomycin are added to aid incontrolling contamination, and the pH is controlled with N-2-hydroxy ethylpiperazine-N'2' ethane sulfonic acid (HEPES) andsodium bicarbonate (Griggs and Bender 1972).The V79B Chinese hamster cell line is maintained inmonolayercultures at 37C in F10 medium. This medium consists of F-10powdered medium (Grand Islands Biological Company) supple-mented withfetal calf serum. Penicillin and streptomycin are addedtohelp control contamination, and the pH is controlled withsodiumbicarbonate and carbon dioxide after titration with sodium hydrox-ide.Both types ofmedia are sterilized by filtration.Routine cultivation is achieved in the A8 cell line by vigorousshaking of the culture to produce a suspension of cells. The V79Bcells, however, being more firmlyattached to the surface of thecontainer, are treated witha trypsin-versene solution toproduce cellsuspensions.The UVsource consisted of a single 15W germicidal lamp (Sylvan-nia G15 T8). The lamp was suspended 60 cm above the floor of theradiation chamber, a glass enclosure with a plastic front containingentry ports (to permit the use of hands and forplacing items withinthe chamber). Thin sheets of plastic were placed between the lampand the radiation area to decrease the UV dose rate to the point atwhich relatively accurate dosages could be obtained by varying theexposure time. The exposure time was controlled by manuallyexposing the cells while recording the elapsed time. The modifieddose rate, approximately 4 ergs mm-1sec-', was checked periodicallywitha Westinghouse WL 755 phototube designed to read intensity at254 nm.Each culture for irradiation was prepared and irradiated as follows.The stock culture bottle was shaken lightlyand the medium changedto remove dead cells and start the synchronization of the culture forGi cells. Cells were collected from the stock culture by similar"shake-offs" every 30 minutes, to remove only those cells that hadjust come through mitosis. Then 2 ml of each resulting cell suspen-sion was deposited carefullyin the center of a 10-cm petri plate so asto form a large drop. Within approximately two hours at roomtemperature the cells had settled to the bottom and attached to thesurface, withno cells more than 2 cm from the center of the plate andwith essentially no touching or overlap; thus exposure was uniformwithout interference from the shadow cast by the sides of the petriplate. Once the cells had attached to the plate, the medium wasremoved, the cells were irradiated for a specific length of timeaccording to the desired dose, and fresh medium was gentlyreapplied.64Journal of the Arkansas Academy of Science, Vol. 30 [1976], Art. 24Published by Arkansas Academy of Science, 1976Arkansas Academy of Science Proceedings, Vol. XXX,1976 65Troy V.Orrand H. Gaston GriggsAllA8 irradiations were done under red light to avoid photoreac-tivation, and the irradiated cultures were transferred immediately toa light-proof container. Irradiated cultures were incubated at 24C inthese covered glass containers, which kept the humiditynear 100%,until the cultures were ready for fixing.Colcemid, to a final concen-tration of 10~*M, was added after the appropriate incubation period,and 24 hours later the cells were fixed on glass slides with 3:1methanol-acetic acid and stained with crystal violet. Chromosomespreads were scored by conventional methods (Wolff 1961). Spreadscontaining anormal complement of chromosome (36 forA8 cells and22 for V79B cells) were examined forchromatid terminal deletions,isochromatid breaks, chromatid exchanges, chromosome terminaldeletions, interstitial deletions, and chromosome exchanges (ringsand tlit•entries).The monolayers of V79B Gi cells were treated throughout theexperiments inessentially the same manner as the A8 cells withthefollowing exception. Allcultures were maintained at 37C in glasscontainers and irradiated cultures were fixed approximately 15 hoursafter treatment withcolcemid to a final concentration of4 x 10~'M.RESULTS ANDDISCUSSIONExtensive mitotic index determinations notonly provided a guide-line for appropriate incubation periods, but also yielded informativedata for doses between 0 and 120 ergs mm"* (Fig. 1). A markedincrease in the time required for the cells toreach mitosis after irrad-iation was observed through the 60 erg point, beyond which therequired time became more consistent. Asimilar pattern was notedinthe effect of the radiation dose on the optimum mitotic index (Fig.2); there was a relatively sudden decrease in the fraction of cellsreaching mitosis, again through the 60 erg point. Thesedeterminations have an important bearing on the validity of dataconcerning chromatid aberrations at doses below 200 ergs mm"1(Griggs and Bender 1973). Figures 1,2, and 4and Table Ishow onlydata for the A8 cell line to maintain clarity, but similar data wereobserved for the V79B mammalian line. Griggs and Bender (1972)reported that the surviving fraction for A8cells varied logarithmical-ly with dose, which also seems true of the writers' mitotic index databetween 0and 60 ergs mm"1.When aberration frequencies are plotted as a function of dose, noclear increase inaberration frequency is observed untildoses exceed60 ergs mm"1,beyond which the curves sharply rise (Fig. 3). This riseis first noticed in the V79B cells at the 75 erg point, and appears inthe A8 cells at about the 90 erg point (Fig. 3, and Table I).This eventoccurs after the aforementioned observed effect of UVradiation onmitotic index. These data suggest that some threshold radiation valuemust be exceeded before aberrations appear, and thus imply that an"accumulation of UV-induced events" leads to aberrations. Thiseffect is not observed in aberration production with ionizingradiation, and has not been observed before in studies reported onUV-induced aberration production, probably because no one hasstudied doses below 50 ergs mm"1for damage induced by wave-lengths in the DNA-sensitive absorption range.Separate compilation of the chromatid and chromosomeaberration frequencies showed that chromosome aberrations becamenoticeably more prevalent at 200 ergs mm"1than at any lower doseadministered (Fig. 4). The fact that relatively low frequency ofchromosome aberrations was noticed in the controls and at lowradiation levels suggests a threshold radiation value forchromosomeaberrations at a higher dose level than the threshold for chromatidThe data are somewhat similar to Chu's (1965) findings at higherdoses, but are more in accord with the data presented by Humphreyet al. (1963) for doses of about 100 ergs mm" 1. Consideration of thelong and complicated division delays (more than 70 hours in somecases) reported by Chu suggests that he may have scored many cellsat the second mitosis after exposure instead of the first. For example,irradiation of a given Gi cell might result in damage which wouldappear in a cell scored at the first division as a chromatid terminaldeletion. However, if this cell were capable of moving through asecond cell cycle, the damage would appear at the second mitosis asa terminal chromosome deletion. Such an effect could significantlybias results in such a manner as to overestimate chromosomeFigure 1. Time interval of the A8 cell line from irradiation to themaximum mitotic index as a function of dose.DOSE (ergs mm"2)Figure 2. Maximum fraction of A8cells reaching mitosis as a functionofdose.Figure 3. Total aberration frequencies (both chromatid andchromosome types) of the A8 and V79B cells lines as a function ofdose between 0 and 120 ergs mm"1. Average number of cells scoredwas 365 for the A8and 780 for the V79B.65Journal of the Arkansas Academy of Science, Vol. 30 [1976], Art. 24http://scholarworks.uark.edu/jaas/vol30/iss1/24The Study of Ultraviolet-Induced Chromatid and Chromosome Aberrationsaberration frequencies and underestimate chromatid aberration A3 _ ABERRATION FREQUENCIESfrequencies. Use of synchronous cultures minimized this problem inthe writers' study.I0LITERATURECITEDCHU, E.H.Y. 1965. Effects of ultraviolet radiation on mammaliancells. I.Induction of chromosome aberrations. Mutation Res. 42:75-94.EVANS, H.J. 1967. Actions of radiations on chromosomes. Scien-tificBasis ofMedicine Annual Reviews 13:321-339.LjJGRIGGS, H.G. and M.A.BENDER. 1972. Ultraviolet and gamma-° °'Aray induced reproductive death and photoreactivation in a CCXenopus tissue culture cell line. Photochem. and Photobiol. A15:517-526.toGRIGGS, H.G. and M.A. BENDER. 1973. Photoreactivation of qultraviolet induced chromosomal aberrations. Science 179:86- |_orUJ aHUMPHREY, R.M., W.C. DEWEY and A. CORK. 1963. Relative 3°°" *ultraviolet sensitivity of different phases in the cell cycle of AAAChinese hamster cells grown invitro.Radiation Res. 19:247-260.AA &-CHROMATIDWOLFF, S. 1961. Radiation genetics. Mechanisms inRadiobiology. . A cmromosomcAcademic Press, New York. 1:419-475.A A A AA(0)100 200 300DOSE (ergs mm"2)Figure 4. Aberration frequencies of the A8 cell line over an extendeddose range, with aberrations separated into chromatid andchromosome types. Average number ofcells scored was 425.Table I.Aberration Distribution forA8Cells at LowDosesNumber Chromatid aberrations Chromosome aberrationsDose cells Terminal Isochromatid Terminal Interstitialergs mm"1 scored deletions breaks Exchanges deletions breaks Exchanges0 200 2 0 0 10 010 400 1 0 0 020300 2 0 00030 310 2 0 0 1140 500 3 0 1 3 0 050400 4 0 00060 400 1 0 0 2 0 075 400 6 0 0 10 090 400 M 2_ 1 0 0 166 Arkansas Academy of Science Proceedings, Vol. XXX,197666Journal of the Arkansas Academy of Science, Vol. 30 [1976], Art. 24Published by Arkansas Academy of Science, 1976

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Study of Ultraviolet-Induces Chromatid and Chromosome Aberrations as a Function of Dose in G1 Phase Vertebrate Tissue Cultures

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