Intrinsic resistance to the lethal effects of x-irradiation in insect and arachnid cells

Abstract

Twelve cell lines representing 10 genera of three orders (Diptera, Lepidoptera, and Orthoptera) of the class Insecta and one cell line (Acarina) from the class Arachnida were examined to discern their sensitivity to the lethal effects of x-irradiation. Radiosensitivity was measured by a combination of colony formation and population growth curve techniques. Each of these arthropod cell lines is significantly more radioresistant than mammalian cells, though the degree of resistance varies greatly with order. Dipteran cells are 3 to 9 times and lepidopteran cells 52 to 104 times more radioresistant than mammalian cells. Orthopteran and acarine cells are intermediate in radiosensitivity between dipteran and lepidopteran cells. These cells, especially the lepidopteran, should be valuable in determining the molecular nature of repair mechanisms that result in resistance to ionizing radiation.The pronounced radioresistance of adult insects has been well documented (1, 2). This resistance has been attributed primarily to the lack of cell division in adult insects, in that the sensitivity of cells to irradiation is directly proportional to their reproductive activity (1-3), and because insects have minimal or no cell division in the adult state, they are extremely resistant to radiation (1, 2).. Recent evidence has suggested that cells of insects have an intrinsic radioresistance (4). This cellular basis of resistance derives largely from studies with the TN-368 lepidopteran cell line. These mitotically active cells are approximately two orders of magnitude more radioresistant than mammalian cells (4-6). The unique nature and the ubiquity of radioresistance in insect cells have important implications concerning the innate ability of cells to tolerate large doses of radiation. Therefore, the present experiments examined 13 cell lines representing three orders of the class Insecta, along with 1 arachnid cell line ( Population Doubling Times. Doubling times were derived from the logarithmic portion of growth curves obtained by seeding 106 cells in replicate 25-cm2 flasks and counting at 24-hr intervals until the populations were well into stationary phase (each point on these growth curves represents at least two separate experiments having two duplicate flasks per experiment and four hemocytometer cell counts per flask).X-Irradiations. A Picker Vanguard x-ray machine operated at 260 kV and 15 mA was used for all irradiations. X-rays passed through approximately 5 mm of glass but were otherwise unfiltered. Dosimetry, utilizing the same geometry as for experiments, was performed according to the method of Fricke and Hart (7).Growth Curves. Exponentially growing cells were diluted in fresh growth medium to a concentration of 2 x 0L cells per ml. They were irradiated at room temperature in 2.0-ml aliquots as an aerated, stirred suspension at a dose rate of just under 0.83 Gy (83 cGy)/sec. Cells irradiated with a given dose were pooled and 1 x 106 cells were seeded into Costar 25-cm2 flasks. Pooling was done to insure...

A New Generation of X Ray Irradiators for Insect Sterilization

“…But huge differences exist between mammalian and arthropod cells that must be taken into account before any comparison of biological effectiveness of different energy radiations among such studies. Dipteran cells are 3 to 9 times and lepidopteran cells 52Ð104 times more radioresistant than mammalian cells to X radiation (Koval et al 1978(Koval et al , 1979Koval 1983) and radiosensitivity also decreases with age in insects.…”

The Mdm2 and p53 genes are conserved in the Arachnids

“…Furthermore, the discovery of Mdm2-p53, a key regulator of cell cycle control, may shed light on the mechanisms of increased resistance to radiation in arachnids. 20 of one of the Deer Tick proteins to the recently identified p53 delta isoforms. The common position for the start of translation of the Tick, Human and Zebrafish proteins strongly support the concept that such an N-terminally deleted p53 protein can have a distinct biological activity.…”

Gamma radiation tolerance of a tropical species of midge,Chironomus ramosusChaudhuri (Diptera: Chironomidae)

“…However, the comparative studies revealed that the degree of radioresistance varies greatly from one insect group to the other. Among the different taxonomic groups of insects, lepidopterans (butterflies and moths), orthopterans (cockroaches and grasshoppers) and hemipterans (true bugs) are noteworthy as radiation-resistant insect orders (O'Brien and Wolfe 1964, Koval 1983a, 1983b, Chandna et al 2004. Within these insect orders, radiation threshold doses vary widely, ranging from 1000-2000 Gy.…”