Use of the specific-locus test to measure the frequency of transmitted gene mutations induced in mouse spermatogonia has shown ethylnitrosourea to be by far the most potent mutagen yet discovered in the mouse. The dose used, 250 mg/kg, gave a mutation rate 5 times as high as had been obtained with 600 R, the most effective acute dose of x-rays. Compared to procarbazine, heretofore the most mutagenic chemical known in the mouse, ethylnitrosourea proved to be 15 times more mutagenic than the peak effect obtained with the most effective dose of procarbazine. Because of its high mutagenicity, ethylnitrosourea can serve as a model compound in exploring the effect of such factors as dose response, dose fractionation, sex, and cell stage on the mutagenic action of a chemical. Ethylnitrosourea is clearly the mutagen of choice for the production of any kind of desired new gene mutations in the mouse. More than a score of chemicals, most of them well-known mutagens in other organisms, have been tested by the mouse specific-locus method. Only three, however, have shown a clear-cut positive mutagenic effect in treated mouse spermatogonial stages (1), and the most effective dose of the most potent of these three-namely, procarbazine (2)-produced only approximately one-third as many mutations as had been obtained with 600 R (1 R = 2.6 X 10-4 coulombs/kg) of acute x-irradiation. The impression was developing that perhaps the mammalian testis was efficiently protected against damage by chemicals. The possibility also existed that the spermatogonia might be effective at repairing mutational damage. It began to appear possible that perhaps no chemical could break through the mammalian body's defense barriers to produce more than a moderate mutagenic effect in spermatogonia.Although repair and other defense mechanisms may still prove to operate against many substances, the present results show that N-ethyl-N-nitrosourea (ENU) provides a dramatic exception.MATERIALS AND METHODS ENU (purchased from Bio-Clinical Laboratories, Bohemia, NY) was dissolved in phosphate buffer (3) adjusted to pH 6. The dose injected intraperitoneally was matched to the body weight of each animal by adjusting the volume of the injected solution, which never exceeded 1 ml. Wild-type (101XC3H)Fl male mice 9-19 weeks old were injected with a single dose (250 mg/kg) of ENU. All animals given this dose survive, whereas a 300-mg/kg dose kills about 40%. All injections were completed within less than 1 hr after the chemical was dissolved. The injected males were mated to females of our standard specific-locus test strain (T) which is homozygous for seven marker genes (4). Each male was mated to a group of either two or four females and moved to a new group of females each week. After each 7-week period the males were rotated back to the original group of females to start the cycle over again. The offspring were scored for mutations at the seven loci. RESULTS AND DISCUSSIONThe 250-mg/kg dose induced a long period of sterility. The males were fertile for a...

As serially homologous structures, mammalian fore-and hindlimbs ancestrally share a common developmental and genetic architecture. As a result, mammalian fore-and hindlimbs are predicted to be highly integrated in the absence of selective pressures to form divergent limb morphologies. Marsupials experience such a divergent selective pressure to form a robust forelimb to power a post-natal crawl to the teat. In this study, phenotypic covariation in marsupials was assessed to determine if specialization for the crawl did indeed reduce integration between their fore-and hindlimbs. To explore the evolution of mammalian limb integration, phenotypic covariation in representative eutherians and monotremes was also examined. Phenotypic covariation in limbs was quantified morphometrically, and analysed with correlational and phylogenetic methods. Results indicate that marsupials generally have relatively high levels of within-limb phenotypic covariation, and low levels between limbs, in contrast to the pattern reconstructed for the mammalian ancestor. Our findings support the hypothesis that pressure to specialize in one limb (either the fore-or the hindlimb) can reduce phenotypic covariation between limbs, and that reduced limb phenotypic covariation is derived in marsupials. Further research is needed to test the effect that these differences in limb phenotypic covariation had on the evolution of the major mammalian groups.

Abstract. In this paper we report on massive computer experiments aimed at finding spherical point configurations that minimize potential energy. We present experimental evidence for two new universal optima (consisting of 40 points in 10 dimensions and 64 points in 14 dimensions), as well as evidence that there are no others with at most 64 points. We also describe several other new polytopes, and we present new geometrical descriptions of some of the known universal optima.

Plastic bronchitis (PB) is a poorly understood disease that can complicate any underlying pulmonary disease. However, it appears to most often occur in patients with surgically palliated congenital heart disease, particularly after the Fontan procedure. Few data exist about the prevalence and etiology of PB in this population. In an effort to establish data about prevalence, we conducted a retrospective study of an existing Fontan surgery database (n = 654) comprised of data, including sex, age at date of surgery, alive/dead status, New York Heart Association classification at last follow-up, right-ventricular end-diastolic pressure and pulmonary artery pressure before Fontan surgery, and the presence of a Fontan fenestration. An initial medical record review of 173 patients in the database who were followed at the University of Michigan identified seven patients with PB resulting in an estimated prevalence of 4 %. Subsequently, 14 % of 211 surveyed patients reported that they presently expectorate mucus or fibrin plugs (casts). Demographic and clinical variables did not differ between patients with or without possible PB. Collectively, these findings suggest that Fontan patients presently with PB may range from 4 to 14 %, indicating potential under-diagnosis of the disease. There were no remarkable physical or hemodynamic indicators that differentiated patients with or without possible PB. These data also highlight the need for more elaborate, prospective studies to improve our understanding of PB pathogenesis so that more definitive diagnostic criteria for this devastating disease can be established and its prevalence more accurately determined.

Estimation of the genetic hazards of ionizing radiation in men is based largely on the frequency of transmitted specific-locus mutations induced in mouse spermatogonial stem cells at low radiation dose rates. The publication of new data on this subject has permitted a fresh review of all the information available. The data continue to show no discrepancy from the interpretation that, although mutation frequency decreases markedly as dose rate is decreased from 90 to 0.8 R/min (1 R = 2.6x 10' coulombs/kg) there seems to be no further change below 0.8 R/min over the range from that dose rate to 0.0007 R/min. Simple mathematical models are used to compute: (a) a maximum likelihood estimate of the induced mutation frequency at the low dose rates, and (b) a maximum likelihood estimate of the ratio of this to the mutation frequency at high dose rates in the range of 72 to 90 R/min. In the application ofthese results to the estimation of genetic hazards of radiation in man, the former value can be used to calculate a doubling dose-i.e., the dose of radiation that induces a mutation frequency equal to the spontaneous frequency. The doubling dose based on the low-dose-rate data compiled here is 110 R. The ratio of the mutation frequency at low dose rate to that at high dose rate is useful when it becomes necessary to extrapolate from experimental determinations, or from human data, at high dose rates to the expected risk at low dose rates. The ratio derived from the present analysis is 0.33. An earlier publication (1) dealt with mutation frequencies in female mice and the estimation of genetic hazards of radiation in women. The present paper provides a similar analysis for males.One of the most important pieces of experimental information for the estimation of genetic hazards of radiation in men is the mutational response of mouse spermatogonial stem cells at low radiation dose rates. The publication of new data on this subject (2), including some at the lowest dose rate so far tested, and the inclusion of additional results in this report provide an opportunity for a fresh review of all the information now available. The data are used to compute a maximum likelihood value for induced mutation frequency at low dose rates and also to compare this with the mutation frequency at high dose rates. The results are in close agreement with earlier analyses by Russell (3) and Searle (4).All of the data reported here were obtained by the mouse specific-locus method which uses seven visible markers and permits the detection of mutations involving any of the seven gene loci in the first-generation offspring of the irradiated parent (5).. Only the results from treated and control adult males are presented here, and all the offspring came from germ cells which, at the time of irradiation, were in spermatogonial stemcell, As, stage. The .radiation was y-rays (from a 13 Cs or 60Co source) or x-rays. The new data considered in this analysis consist of(a) results from exposures to 300 R of 137Cs y radiation at 0.005 R/min (1 R = ...