Investigations on radiosensitive and radioresistant populations of Drosophila melanogaster. VIII. The system of relative radioresistance in immature oocytes of the irradiated population ROI4

Prophase I oocytes of the irradiated population ROI4 of Drosophila melanogaster are radioresistant relative to those of a control population (+K). The system of relative radioresistance is apparently dose-modifying and can be described by Dose-Reduction Factors (DRFs). At least 3 constituent components of the system can be distinguished, as follows. The genetic factor rar-1 contributes to the system with respect to the induction of dominant (DRF = 1.31) and sex-linked recessive lethals (DRF = 1.31) in a way that is inhibited by caffeine. The factor rar-2, independently reduces both types of lethal to the same amount as does rar-1, but also affects the production of X-chromosome loss (DFR = 1.72). The results of several different approaches allow, as a working hypothesis, the interpretation that rar-2 reduces the association of heterologous, chiasmatic chromosomes in the chromocentre in time and/or space and thus minimizes the preconditions for the production of certain types of interchange and of non-disjunction. A third factor, rar-3, is postulated to contribute, independently from the others, to the system of relative radioresistance with respect to dominant lethals (DRF = 1.58), interchanges and non-disjunction (DRFs = 1.58), and sex-linked recessive lethals (DRF = 1.87).     

Regulation of drosophila folylpolyglutamates during development

The polyglutamate status of reduced folates during the larval, pupal and adult stages of Drosophila melanogaster development was investigated. The chain length distribution is very similar and is predominantly pentaglutamate. Half-life estimates of the hydrolytic degradation to the monoglutamate showed larva < pupa < adult. This raises the possibility that polyglutamate hydrolase may have a role in regulating the total intracellular reduced folate content of the different developmental stages.     

Investigations on radiosensitive and radioresistant populations of Drosophila melanogaster. IV. The genetics of the relative radioresistance in stage-7 oocytes of the irradiated population RO I

The genetic system that controls the relative radioresistance in an irradiated laboratory population of Drosophila melanogaster (RÖ I) was studied. Comparisons were made between an unirradiated control population (+60, +K), the population RÖ I (after 227–333 generations of irradiation at 2100 R per generation), the sub-population RÖ I₀ (derived from RÖ I after 260 generations of irradiation and kept without irradiation for up to 74 generations), the F₁ hybrids +60/RÖ I, various homo- and heterozygous carriers of the 3 major chromosomes of RÖ I and +60, respectively, in combination with suitable balancers, and several chromosome substitution stocks of +K and RÖ I. The criteria used to assess the magnitude of radiosensitivity were dominant lethals, X-chromosome loss, and sex-linked recessive lethals induced in stage-7 oocytes at various exposure levels of X-irradiation.The data show that the radioresistance in RÖ I is controlled by a stable and homozygous genetic system. The system is semidominant. With respect to the induction of dominant lethals and sex-linked recessive lethals, the relative resistance is mainly contributed by chromosomes I and II. The effects of the two chromosomes are additive, each contributing about half the relative resistance. Resistance to the X-ray induction of X-chromosome loss is solely contributed by chromosome II.The findings suggest that at least 2 different and independent mechanisms are involved in determining the resistance of the RÖ I population.     

Acquired radioresistance of progeny of irradiated cells is accompanied by rearrangements in chromatin organization

gamma-Irradiation action within a dose range of 0-20 Gy on parental djungarian hamster fiborblasts, DH-TK- cell line, and the progenies of these irradiated cells, surviving acute exposure to 20 Gy irradiation, PIC-20 cell line, was examined. The PICs were 3 times more radioresistant than the parental cells as calculated from D0. Using a method of anomalous viscosity time dependence (AVTD) it was revealed that starting (initial) level (in untreated cells) of chromatin compactness in radioresistant progenies was more than 1.4 times as high as for parental cells. The analysis of dose dependence has shown that irradiation with a dose of 5 Gy resulted in complete chromatin loop relaxation in radiosensitive DH-TK- cells and partial one in radioresistant PIC-20 cells. Besides, the beginning of DNA-membrane complexes degradation following the irradiation with doses over 15 Gy in DH-TK- cells was observed. It was shown that the increased state of relative chromatin relaxation in PIC-20 cells determines an increasing in reparation effectiveness that resulted in lower percent of residual damages in these cells. Using the Nosern hybridization method the expression level of mts 1, tag 7 and vseap 1 genes was studied. It is revealed that tag 7 and vseap 1 gene expression in radioresistant cells were correspondingly 6 and 10 times higher than in radiosensitive parental cells and the level of mts 1 gene expression was not changed. So, based on the results obtained we suggest that acquired radioresistance in progenies of irradiated cells is determined by rearrangements in chromatin structure and accompanied constitutive changes of gene expression.     

A search for radioresistance in experimental populations of Drosophila with radiation histories

Human lymphocytes in the G₀ stage were irradiated with UV light and X-rays. A 2-fold increase in the yield of dicentrics was observed in comparison with the yield for X-rays alone. This synergistic effect was constant irrespective of the variation in the UV dose between 50 and 100 erg/mm².The individual chromosomes participated in interchange aberrations as expected from a random distribution per mitotic chromosome length unit. This observation is in contrast with the recent finding that X-ray-induced chromosome-type breakage is preferentially located on chromosomes with relatively large amounts of R-bands. Thus, the present data indicate that the additional breakage points, due to the synergism, had a different distribution between chromosomes from those induced by X-irradiation alone. Mechanisms that could account for the synergistic reaction are discussed.     

Investigations on radiosensitive and radioresistant populations of Drosophila melanogaster. V. Relations between the relative radioresistance and some recombination properties in the irradiated population ROI

Experiments were conducted to inquire whether the radioressitance observed in an irradiated laboratory population (RÖI) of Drosophila melanogaster might be associated in some way with recombinational processes. Simultaneously, data were collected on the stage distribution of radioresistance in RÖI by studying the induction of dominant lethals and X-chromosome losses in mature females at various exposure levels of X-irradiation (in eggs sampled from subsequent 12-h broods).The data show that (1) the radiation response of both populations (RÖI and its control + K) is equal in the highly sensitive mature stages, (2) RÖI is resistant relative to +K in the medium-sensitive stage-7 and younger oocytes collected on days 1.0 to 5.5 after exposure, and (3) the difference between the populations disappears again when the sensitivity steeply decreases on days 5.5 to 6.5. Similar brood-pattern experiments indicate that exchanges between homologous chromosomes are induced (by temperature shock or X-irradiation) in eggs sampled after day 5.5. Thus it is evident that the relative radioresistance in RÖI is due to mechanisms which operate in the developing oocyte in the stages of a medium radiosensitivity between that phase in which recombination is inducible and stage-14.The observed temporal sequence of recombination and relative radioresistance in RÖI supports the speculation that the latter might be associated with recombination repair. However, the natural recombination frequencies were equal in +K and RÖI. Likewise, no clear evidence was obtained on differences between the two populations with respect to X-ray-induced modifications of homologous exchanges in various para- and pericentric parts of the genome.     

Larval development of theterebellid polychaete Eupolymnia nebulosa (Montagu) in the Mediterranean Sea

The morphology of young stages of Eupolymnia nebulosa (Montagu, 1818) is observed using SEM. Significant changes occur at several times after egg laying. The transition from endotrophy to exotrophy takes place when the larvae are about 13–15 days old. At the same time, the primary tentacle appears as a hemispherical bud; the first setae to emerge are transitory and club-shaped. They are shed when the larvae are about 50 days old. Observations on the development of the uncinigerous torus of the 11th segment (the first one bearing uncini with the main fang in an alternated direction) indicate that the uncini appear at the dorsal extremity of the torus and then move toward the medio-ventral axis as they increase in size. The uncini are shed when they reach the ventral extremity of the torus. These changes may result in taxonomic confusions unless the complete sequence of development is known.     

Chromosomal structure of populations of drosophila flavopilosa studied in larvae collected in their natural breeding sites

Summary D. flavopilosa Frey, is a neotropical species of Drosophila living in Chile that, together with 13 other species, has been included by Wheeler, Takada und Brncic (1962) in the flavopilosa species group. Despite the fact that it has not been possible to breed this species in the laboratory, the circumstance that its habitat is well known, has allowed the study of the chromosomal structure of some natural populations of this species, analyzing larvae directly taken to the laboratory from their natural breeding sites: the flowers of the solanacean Cestrum parqui L'Héritier.The present paper describes the mitetic and salivary gland chromosomes of D. flavopilosa, and gives a composite map of the Standard gene arrangement. In central Chile, natural populations of this species are polymorphic with respect to the gene orders in their chromosomes, due to the presence of four independent inversions, all located in one of the six chromosomes (the right arm of the V-chromosome). Quantitative data on the distribution of the inversions shows that there is an altitudinal gradient in the frequencies of two of the four inversions. Heterozygotes for Inversion A, are more frequent at high altitudes than at sea level. On the contrary, heterozygotes for inversion B, are abundant at sea level, but practically disappear at high altitudes. These altitudinal clines have been observed in two valleys near Santiago, Chile, which run from the Andes mountains to the Pacific coast.The work reported in this article has been carried out under Contract AT (30-1) 2465 US Atomic Energy Commission, and partially supported by Grants from the University of Chile, Faculty of Medicine and the Rockefeller Foundation under a joint program.