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Dose protraction and induced compound autosome non-disjunction in immature oocytes of Drosophila melanogaster
Mutation Research, 25 (I974) I4I-I 42 ~:) Elsevier Scientific Publishing Company, Amsterdanl - Printed in The Netherlands
141
Dose protraction and induced compound autosome non-disjunction in immature oocytes of Drosophila melanogaster TRAUT5 reported a dose rate effect on the i n d u c t i o n of n o n - d i s j u n c t i o n a n d loss of X-chromosomes when i m m a t u r e oocytes are irradiated. Slightly different effects were found with dose fractionation a n d dose protraction. The effects of dose fractionation on the i n d u c t i o n of c o m p o u n d second chromosome, C(2), n o n - d i s j u n c t i o n has been reported b y SOBELS4. The effects of dose protraction will be reported here. I;or acute exposure a dose rate of 2800 R per rain was used a n d the comparative p r o t r a c t e d exposures were given at IO R per rain. An E N R A F X - r a y m a c h i n e was used for all t r e a t m e n t s . For each set of irradiations, y o u n g virgin C ( 2 L ) , j ; C ( 2 R ) , p x females were collected a n d split into three groups. The first group were given an exposure at high dose rate (Acute I), the second group a protracted exposure (Protracted), a n d the t h i r d group were t h e n given a high dose rate exposure (Acute 2). After irradiation the females were mass m a t e d to C ( 2 L ) , b pr; C ( 2 R ) , v g males. They were kept in vials for 2 days (brood A), then in bottles for i day (brood B), and s u b s e q u e n t l y fresh bottles for a further 2 days (brood C). Five sets of irradiations were given using an exposure of IOOO R a n d three sets using an exposure of 15oo R. No significant differences were found between the repeats at each dose level a n d the pooled data are given in Table I. TABLE I THE FREQUENCIES OF DISOMIC AND NULLOSOMIC GAMETES INDUCED BY IRRADIATION OF C ( 2 L ) , j ; C ( 2 R ) , p x FEMALES, ABOUT 4 h AFTER HATCHING FROM THE PUPAE
The treated females were mated to C(2L),b pr; C(2R),vg males. Brood
A
B
C
Acute i Protracted Acute 2
2.00 (47/2339) 1.39 (35/2524) 1.71 (42/245 o)
1.17 (54/4613) 1.44 (55/3825) 1.55 (65/4200)
0.72 (61/8496) 0.69 ( 4 8 / 6 9 6 I ) 0.96 (85/8871)
r5oo R Acute 1 Protracted Acute 2
o.9 (3/346) o.8 (3/377) o. 7 (3/43o)
1.8 (27/I472) 2.2 (3o/1393) 2.4 (32/1339)
o. 7 (45/6o56) o.9 (5o/5633) 1.2 (67/5751)
i.i 5 (27/2339) 1.35 (34/2524) 1.o2 (25/245o)
i.oo (46/4613) 1.o7 (41/3825) o.98 (41/42oo)
o.64 (54/8496) o.34 124/696I) o.57 (51/8871)
0.6 i.I 0. 7
1. 4 1.5 1.3
0,6 0.6 0.7
Disomics zooo R
Nullosomics Iooo R Acute i Protracted Acute 2 ±500 R Acute I Protracted Acute2
(2/346) (4/377) (3/43 o)
(2i/i472) (21/1393) (18/1339)
(38/6o56) (32/5633) (43/5751)
The frequencies of i n d u c e d chromosome loss (nullosomics) are lower t h a n the corresponding frequencies of chromosome gain (disomics). This is unusuM a, b u t consistent with the observations of CLARK AND SOBELS1 when t h e y used the same genetic system. It has since been found t h a t this results from a deficit of nullosomic males (LEITH, m a n u s c r i p t in preparation). Therefore, a detailed statistical analysis was made of only the d a t a on disomics.
142
SHORT COMMUNICATIONS
There were no significant dose rate effects in a n y of t h e t h r e e broods a t either dose level. This is i n t e r e s t i n g because SOBELS4 found a f r a c t i o n a t i o n effect, a l t h o u g h only at 3000 R a n d n o t at lower doses. Technically, it would be v e r y difficult to give such a dose at IO R p e r min. C(2) non disjunction, like X chromosome n o n - d i s j u n c t i o n 3, is often accomp a n i e d b y a b n o r m a l segregation of o t h e r chromosomes *. This indicates t h a t similar m u l t i - h i t mechanisms m a y be involved a n d a d o s e - p r o t r a c t i o n effect would be expected. CLARK AND SOBELS1 found a linear d o s e - f r e q u e n c y relationship for the induction of disomics in their first brood. This, however, covered the first three d a y s of egg laying. I n Table I it can be seen t h a t there is significant h e t e r o g e n e i t y within this period. In b r o o d A, d a y s I a n d 2, the frequencies of disomics recovered after an exposure of IOOO R are significantly higher t h a n after 15oo R (P < 0.05). I n b r o o d B, d a y 3, the higher dose induces higher frequencies (P < o.oi). The mechanism, which causes t h e inverse dose relationship in brood A, is n o t clear. The observation, however, provides an i n d i c a t i o n t h a t t h e l i n e a r i t y r e p o r t e d b y CLARK AND SOBELS 1 p r o b a b l y has a complex origin a n d does n o t s i m p l y reflect 1-hit kinetics. In b r o o d B a n d C there is an a p p a r e n t t e n d e n c y for the frequencies of disomics to be higher after A c u t e 2 t h a n after A c u t e I. This indication of a s e n s i t i v i t y change in a r e l a t i v e l y short period of t i m e was not found in later e x p e r i m e n t s (SOBELS, unpublished).
Department of Radiation Genetics and Chemical Mutagenesis, University of Leiden; J. A. Cohen Institute for Radiopathology and Radiation Protection, Leiden (The Netherlands)
B. LEIGH
A. M., AND F. H. SOBELS, Studies on non-disjunction of the major autosomes in Drosophila melanogaster, I. Methodology and rate of induction by X-rays for the compound second chromosome, Mutation Res., 18 (1973) 47-61.
I CLARK,
2 LEIGH, B., Disjunction and induced non-disjunction of X-chromosomes and compound autosomes in Drosophila melanogaster (Abstr.), Genetics, 74 suppl. (1973) 1543 PARKER, D. R., AND J. H. WILLIAMSON, Aberration induction and segregation in oocytes, in M. ASHBURNER AND E. NOVlTSKI (Eds.), The Genetics and Biology of Drosophila, Academic Press, New York, 1974, in press. 4 SOBELS, V. H., An unexpected effect of fractionation of radiation dose on the induction of nondisjunction in Drosophila (Abstr.), Genetics, 74 suppl. (1973) 260. 5 TRAUT, H., The influence of the temporal distribution of the X-ray dose on the induction of Xchromosomal non-disjunction and X-chromosome loss in oocytes of Drosophila melanogaster, Mutation Res., 12 (1971) 321-327. Received M a y and, 1974
141
Dose protraction and induced compound autosome non-disjunction in immature oocytes of Drosophila melanogaster TRAUT5 reported a dose rate effect on the i n d u c t i o n of n o n - d i s j u n c t i o n a n d loss of X-chromosomes when i m m a t u r e oocytes are irradiated. Slightly different effects were found with dose fractionation a n d dose protraction. The effects of dose fractionation on the i n d u c t i o n of c o m p o u n d second chromosome, C(2), n o n - d i s j u n c t i o n has been reported b y SOBELS4. The effects of dose protraction will be reported here. I;or acute exposure a dose rate of 2800 R per rain was used a n d the comparative p r o t r a c t e d exposures were given at IO R per rain. An E N R A F X - r a y m a c h i n e was used for all t r e a t m e n t s . For each set of irradiations, y o u n g virgin C ( 2 L ) , j ; C ( 2 R ) , p x females were collected a n d split into three groups. The first group were given an exposure at high dose rate (Acute I), the second group a protracted exposure (Protracted), a n d the t h i r d group were t h e n given a high dose rate exposure (Acute 2). After irradiation the females were mass m a t e d to C ( 2 L ) , b pr; C ( 2 R ) , v g males. They were kept in vials for 2 days (brood A), then in bottles for i day (brood B), and s u b s e q u e n t l y fresh bottles for a further 2 days (brood C). Five sets of irradiations were given using an exposure of IOOO R a n d three sets using an exposure of 15oo R. No significant differences were found between the repeats at each dose level a n d the pooled data are given in Table I. TABLE I THE FREQUENCIES OF DISOMIC AND NULLOSOMIC GAMETES INDUCED BY IRRADIATION OF C ( 2 L ) , j ; C ( 2 R ) , p x FEMALES, ABOUT 4 h AFTER HATCHING FROM THE PUPAE
The treated females were mated to C(2L),b pr; C(2R),vg males. Brood
A
B
C
Acute i Protracted Acute 2
2.00 (47/2339) 1.39 (35/2524) 1.71 (42/245 o)
1.17 (54/4613) 1.44 (55/3825) 1.55 (65/4200)
0.72 (61/8496) 0.69 ( 4 8 / 6 9 6 I ) 0.96 (85/8871)
r5oo R Acute 1 Protracted Acute 2
o.9 (3/346) o.8 (3/377) o. 7 (3/43o)
1.8 (27/I472) 2.2 (3o/1393) 2.4 (32/1339)
o. 7 (45/6o56) o.9 (5o/5633) 1.2 (67/5751)
i.i 5 (27/2339) 1.35 (34/2524) 1.o2 (25/245o)
i.oo (46/4613) 1.o7 (41/3825) o.98 (41/42oo)
o.64 (54/8496) o.34 124/696I) o.57 (51/8871)
0.6 i.I 0. 7
1. 4 1.5 1.3
0,6 0.6 0.7
Disomics zooo R
Nullosomics Iooo R Acute i Protracted Acute 2 ±500 R Acute I Protracted Acute2
(2/346) (4/377) (3/43 o)
(2i/i472) (21/1393) (18/1339)
(38/6o56) (32/5633) (43/5751)
The frequencies of i n d u c e d chromosome loss (nullosomics) are lower t h a n the corresponding frequencies of chromosome gain (disomics). This is unusuM a, b u t consistent with the observations of CLARK AND SOBELS1 when t h e y used the same genetic system. It has since been found t h a t this results from a deficit of nullosomic males (LEITH, m a n u s c r i p t in preparation). Therefore, a detailed statistical analysis was made of only the d a t a on disomics.
142
SHORT COMMUNICATIONS
There were no significant dose rate effects in a n y of t h e t h r e e broods a t either dose level. This is i n t e r e s t i n g because SOBELS4 found a f r a c t i o n a t i o n effect, a l t h o u g h only at 3000 R a n d n o t at lower doses. Technically, it would be v e r y difficult to give such a dose at IO R p e r min. C(2) non disjunction, like X chromosome n o n - d i s j u n c t i o n 3, is often accomp a n i e d b y a b n o r m a l segregation of o t h e r chromosomes *. This indicates t h a t similar m u l t i - h i t mechanisms m a y be involved a n d a d o s e - p r o t r a c t i o n effect would be expected. CLARK AND SOBELS1 found a linear d o s e - f r e q u e n c y relationship for the induction of disomics in their first brood. This, however, covered the first three d a y s of egg laying. I n Table I it can be seen t h a t there is significant h e t e r o g e n e i t y within this period. In b r o o d A, d a y s I a n d 2, the frequencies of disomics recovered after an exposure of IOOO R are significantly higher t h a n after 15oo R (P < 0.05). I n b r o o d B, d a y 3, the higher dose induces higher frequencies (P < o.oi). The mechanism, which causes t h e inverse dose relationship in brood A, is n o t clear. The observation, however, provides an i n d i c a t i o n t h a t t h e l i n e a r i t y r e p o r t e d b y CLARK AND SOBELS 1 p r o b a b l y has a complex origin a n d does n o t s i m p l y reflect 1-hit kinetics. In b r o o d B a n d C there is an a p p a r e n t t e n d e n c y for the frequencies of disomics to be higher after A c u t e 2 t h a n after A c u t e I. This indication of a s e n s i t i v i t y change in a r e l a t i v e l y short period of t i m e was not found in later e x p e r i m e n t s (SOBELS, unpublished).
Department of Radiation Genetics and Chemical Mutagenesis, University of Leiden; J. A. Cohen Institute for Radiopathology and Radiation Protection, Leiden (The Netherlands)
B. LEIGH
A. M., AND F. H. SOBELS, Studies on non-disjunction of the major autosomes in Drosophila melanogaster, I. Methodology and rate of induction by X-rays for the compound second chromosome, Mutation Res., 18 (1973) 47-61.
I CLARK,
2 LEIGH, B., Disjunction and induced non-disjunction of X-chromosomes and compound autosomes in Drosophila melanogaster (Abstr.), Genetics, 74 suppl. (1973) 1543 PARKER, D. R., AND J. H. WILLIAMSON, Aberration induction and segregation in oocytes, in M. ASHBURNER AND E. NOVlTSKI (Eds.), The Genetics and Biology of Drosophila, Academic Press, New York, 1974, in press. 4 SOBELS, V. H., An unexpected effect of fractionation of radiation dose on the induction of nondisjunction in Drosophila (Abstr.), Genetics, 74 suppl. (1973) 260. 5 TRAUT, H., The influence of the temporal distribution of the X-ray dose on the induction of Xchromosomal non-disjunction and X-chromosome loss in oocytes of Drosophila melanogaster, Mutation Res., 12 (1971) 321-327. Received M a y and, 1974