Leo E. Lachance

Cytogenetic investigations on radiation and chemically induced dominant lethal mutations in oocytes and sperm of the screw-worm fly

Abstract Adult females containing oocytes in early prophase or early anaphase of the first meiotic division, and day-old males containing mature sperm were exposed to γ-radiation or the alkylating agent, 2,4,6-tris (1-aziridinyl)-s.-triazine (= tretamine). The doses used induced nearly 100% dominant lethals in the reproductive cells. Treated insects were crossed with untreated ones. Eggs were collected and fixed after different periods of development at room temperature. Stained whole-mounts of the embryos were studied to determine: (1) The kind of chromosome aberrations associated with dominant lethal mutations, (2) the stage of development at which the chromosome aberrations appeared, (3) the stage at which development ceased in embryos containing dominant lethal mutations of either maternal or paternal origin, (4) whether damage induced by tretamine was cytologically similar to that induced by ionizing radiations. Dominant lethal mutations are characterized by the presence of chromosome bridges and fragments between dividing nuclei in the embryo, but the stage of development at which these first appear differs with the type of mutagen used. The damage produced by irradiation of meiotic oocytes is evident during the first and second meiotic divisions (which are completed after oviposition) and continues into the early cleavage divisions, at which time development ceases. After treatment of meiotic oocytes with tretamine, the majority of the subsequent meiotic divisions appear normal and the detection of most of the chromosomal damage is first possible in cleavage divisions, or after the treated nucleus undergoes one replication of chromatin material. Treatment of mature sperm with either γ-rays or tretamine does not prevent syngamy. Chromosome aberrations become evident at the first cleavage division. It is obvious that chromosome-breakage phenomena formed the basis of dominant lethality in these cells. Each of these treatments stops embryonic development generally after only a few cleavage divisions. Various types of abnormalities were observed in the embryos. The relevance of these observations to the mode of action of the mutagens, the chromosomal basis of dominant lethality, and the differential sensitivity of the three types of germ cells to these mutagens are discussed.

Chromosomal Fragments Transmitted through Three Generations in Oncopeltus (Hemiptera)

Chromosomal fragments and translocations induced by x-rays in the sperm of adult milkweed bugs, Oncopeltus fasciatus (Dallas), were detected in the meiotic cells of F1, F2, and F3, males and caused high levels of sterility in lintreated progeny. The persistence of these fragments through numerous generations of cells confirmed the holokinetic nature of the milkweed bug chromosomes.

Comparative Mutagenicity of Two Chemosterilants, Tepa and Hempa, in Sperm of Bracon hebetor

In an assessment of the mutagenic efficiency of the alkylating agent, tepa, and its nonalkylating analog, hempa, both chemicals induced a high frequency of recessive lethal mutations in the sperm of the parasitic wasp, Bracon hebetor Say (Habrobracon), although tepa was the more efficient mutagen.

Comparative effects of chemosterilants on spermatogenic stages in the house fly. I. Induction of dominant lethal mutations in mature sperm and gonial cell death.

Abstract Adult house flies, Musca domestica L., were treated with 12 chemosterilants: 6 aziridines (apholate, tepa, tretamine, 2 bifunctional carboxamines—ENT-50838 and ENT-50172—and the bifunctional compound ENT-51909); 3 ethanesulfonates (2 bifunctional compounds and the monofunctional compound, EMS); hempa, nitrogen mustard, and diepoxybutane. Dominant lethal mutations in the mature sperm were measured and gonial cell killing was studied cytologically. At the minimum doses that induced dominant lethal mutations in all the sperm, some compounds, usually the aziridines and hempa, killed all the gonial cells and no sign of any spermatogenic activity was found in testes 14 days post-treatment. With the sulfonates, there was no destruction of gonial cells and a completely normal level of spermatogenic activity was found even though dominant lethals were induced in the sperm. In fact, with methanediol dimethanesulfonate (ENT-51799), doses that were 4 times higher than the sterilizing dose for mature sperm failed to kill gonial cells. Configuration of the carrier molecule also played an important role in determining the effects on gonial cells. Since recovery of fertility is associated with survival of gonial cells and continued spermatogenic activity, all 12 compounds could be classified as those that would: (1) permit no recovery, (2) permit complete recovery, or (3) those in which recovery of fertility was most likely.