Genetic X-radiation Damage to Drosophila Germ Cells under Different Conditions

Drosophila melanogaster (Oregon-R, Oak Ridge strain) males, 19 to 21 hours old, were X-rayed with a total dose of 1000r. or 3000 r. given in two equal fractions of 500 r. or 1500 r. at a dose rate of 500r. per minute, except for Experiment #2 in which they were given a single dose of 1000 r. at 24 +/- 1 degree C in several gas environments, with a time interval of 40 minutes between the two doses. At each Change of gas(es),the system was evacuated to remove all gases, then Hushed with helium for 1 minute. Tests using CO were carried out in the dark and the others m the light, both at 1 atmosphere of the gas or gas mixture. In order to study the genetic radiation damage and its modification by several gases the frequencies of dominant lethals and translocations induced in cells which were in different stages of spermatogenesis were scored using seven sequential 2-day mating over a two-week test period. Data are prtsented which indicate that: 1) The frequency of dominant lethals increased from sperm to spermatids and meiotic cells, then decreased in spermatogonial cells which were the least susceptible to X-rays. 2) The cycle of damage for dominant lethals is similar to that for translocations, but does not coincide with it completely, and the peaks of damage for both are located in the early postmeiotic stages, and the cycle of frequencies of translocations coincides with that of percentages of sterility of F1 the coincidence frequencies between translocations and the sterility demonstrates that the mechanisms of damage for both are related, at least in part. 3) The NO effect on sperm and late spermatids is more drastic than the oxygen effect, but a major fraction of the effect is to cause the death of the sperm. 4) The carbon monoxide (CO) during radiation increase genetic damage above the other gases tested, and it is possible to conclude that the duration(s) of 4 minutes of gases in post-treatments is too short to modify the damage. 5) There are few (or no) translocations recovered from premeiotic cells. 6) The Y-chromosome was involved in 10.8% of total breaks, or about 1/4 as frequently as the two autosomes tested, and chromosomes 2 and 3 equally participated in an interchange.

An Electron Microscopic Study on the Junctional Complex in Frog Epithelia

Electron microscopy on the skin of young frogs, Rana temporaria, has been carried out with particular reference to cellular attachment sites. For the first time now several technical developments allow a more detailed visualization of the fine structure within the cellular attachment sites as well as making it possible to show the ultrastructural morphology of the junctional complexes, and to demonstrate that the desmosomes are regularly distributed around each skin cell, especially in the S. granulosum. The relations of these findings to those of previous investigations concerning the functional organization of the junctional complexes and to the findings in skin cancer from a cellular adhesion view point have been briefly discussed.

A Study of High Mutability Involving Two Loci in Drosophi1a Melanogaster

Data are presented which strongly indicate that the locus occupied by the mutant wz lies to the left of, or on the same locus of apricot (wa). The fact that wz shows a non-suppressor effect in combination with zeste as a typical phenomenon in mutants of sites 1, 2, and 3 of the white locus, also supports that wz is a mutant at or left of apricot (site 3). A "model" for the genetic fine structure of the mutants (wzm, wzl, and wz) is proposed and discussed to account for the mutability among those three mutants. Analysis of wz leads to the hypothesis that it is the result of an inversion (sites 3 and 4) at the white locus, by two mechanisms which are discussed briefly here.