Dose-response modeling of life shortening in a retrospective analysis of the combined data from the JANUS program at Argonne National Laboratory

Life shortening was investigated in both sexes of the B6CF1 (C57BL/6 x BALB/c) mouse exposed to fission neutrons and 60Co gamma rays. Three basic exposure patterns for both neutrons and gamma rays were compared: single exposures, 24 equal once-weekly exposures, and 60 equal once-weekly exposures. Ten different dose-response models were fitted to the data for animals exposed to neutrons. The response variable used for all dose-response modeling was mean after-survival. A simple linear model adequately described the response to neutrons for females and males at doses less than or equal to 80 cGy. At higher neutron dose levels a linear-quadratic equation was required to describe the life-shortening response. An effect of exposure pattern was observed prior to the detection of curvature in the dose response for neutrons and emerged as a potentially significant factor at neutron doses in the range of 40-60 cGy. Augmentation of neutron injury with dose protraction was observed in both sexes and began at doses as low as 60 cGy. The life-shortening response for all animals exposed to gamma rays (22-1918 cGy) was linear and inversely dependent upon the protraction period (1 day, 24 weeks, 60 weeks). Depending on the exposure pattern used for the gamma-ray baseline, relative biological effectiveness (RBE) values ranged from 6 to 43. Augmentation, because it occurred only at higher levels of neutron exposure, had no influence on the estimation of RBEm.     

Interpretation of cytogenetic damage induced in the germ line of male mice exposed for over 1 year to 239Pu alpha particles, fission neutrons, or 60Co gamma rays

The relative biological effectiveness (RBE) of 239Pu alpha particles, fission neutrons (0.85 MeV), and 60Co gamma rays has been evaluated for the induction of reciprocal chromosome translocations in spermatogonia and of chromosome/chromatid fragments and chromatid rearrangements in the primary spermatocyte of adult male B6CF1 mice. Age concurrency was maintained for both internal and external radiations which were delivered at about 1 rad/week for 239Pu (single intravenous dose of 10 microCi/kg), 0.67, 1.67, and 2.67 rad/week for neutrons, and 6.95, 17.4, and 32 rad/week for gamma rays for at least 60 weeks. In terms of frequency of translocations, the response to the alpha emitter was nonlinear (concave downward) with little dose-response predictability; to cumulative neutron exposures the response was linear, without evidence of a dose-rate effect; and to gamma radiation the responses were linear, and a significant dose-rate effect was seen. RBE estimates are variable. For translocations, the n/gamma ratio is between 10 and 24, depending upon weekly dose level, and the ratio is 1 or less for the alpha particle relative to the neutron. For fragments, the n/gamma ratio is 18 to 22, depending upon age factors, and alpha/n is 1.5. For chromatid rearrangements, n/gamma is 7 and alpha/n is essentially indeterminate, but much below one. The overall response to the alpha emitter is interpreted to be a complex function of (a) microdosimetric heterogeneity, (b) a nearly invariant deposition pattern in the gonad, (c) the high sensitivity of differentiating spermatogonia to cell killing, and (d) the capacity of stem cells in relatively radiation-free areas to progressively assume the major spermatogenic role.     

Extinction of LINE-1 activity coincident with a major mammalian radiation in rodents

LINE-1 transposable elements (L1s) are ubiquitous in mammals and are thought to have remained active since before the mammalian radiation. Only one L1 extinction event, in South American rodents in the genus Oryzomys, has been convincingly demonstrated. Here we examine the phylogenetic limits and evolutionary tempo of that extinction event by characterizing L1s in related rodents. Fourteen genera from five tribes within the Sigmodontinae subfamily were examined. Only the Sigmodontini, the most basal tribe in this group, demonstrate recent L1 activity. The Oryzomyini, Akodontini, Phyllotini, and Thomasomyini contain only L1s that appear to have inserted long ago; their L1s lack open reading frames, have mutations at conserved amino acid residues, and show numerous private mutations. They also lack restriction site-defined L1 subfamilies specific to any species, genus or tribe examined, and fail to form monophyletic species, genus or tribal L1 clusters. We determine here that this L1 extinction event occurred roughly 8.8 million years ago, near the divergence of Sigmodon from the remaining Sigmodontinae species. These species appear to be ideal model organisms for studying the impact of L1 inactivity on mammalian genomes.     

Life shortening in mice exposed to fission neutrons and gamma rays. IV. Further studies with fractionated neutron exposures

When mice were exposed to a total dose of 240 rad of fission neutrons divided into two, four, or six fractions given at 1-week intervals, more life shortening was observed than was seen after a single exposure. Maximum life shortening was observed with four fractions, although the value for six fractions was not significantly lower. Much of the augmentation effect was attributable to an increase in early deaths during the first 200-300 days after exposure, although differences persisted throughout the lifetime of the animals. The changes in life shortening were associated with changes in the distribution of causes of death; however, decrementation of the populations for any given specific cause of death failed to eliminate completely the differences in mean aftersurvival time.     

O-linked N,N'-diacetyllactosamine (LacdiNAc)-modified glycans in extracellular matrix glycoproteins are specifically phosphorylated at subterminal N-acetylglucosamine

The terminal modification of glycans by β4 addition of N-acetylgalactosamine to N-acetylglucosamine with formation of the N,N-diacetyllactosediamine (LacdiNAc) moiety has been well documented for a number of N-linked glycoproteins and peptides, like neurohormones. Much less is known about O-glycoproteins in this regard because only human zona pellucida glycoprotein 3 (ZP3) and bovine proopiomelanocortin were reported to be LacdiNAc-modified. In searching for mammalian proteins modified with O-linked LacdiNAc we identified six positive species among nine endogenous and recombinant O-glycoproteins, which were extracellular matrix, or matrix-related proteins. These are ZP3 and the five novel LacdiNAc-positive species ECM1, AMACO, nidogen-1, α-dystroglycan, and neurofascin. The mass spectrometric analyses revealed a core 2-based tetrasaccharide as the common structural basis of O-linked LacdiNAc that could be further modified, similar to the type 2 LacNAc termini, with fucose, sialic acid, or sulfate. Here, we provide structural evidence for a novel type of mucin-type O-glycans that is strictly specific for LacdiNAc termini: sugar phosphorylation with formation of GalNAcβ1-4(phospho-)GlcNAc. The structural details of the phosphatase-labile compound were elucidated by MS(2) analysis of tetralysine complexes and by MS(n) measurements of the permethylated glycan alditols. Phospho-LacdiNAc was detected in human HEK-293 as well as in mouse myoblast cells and in bovine brain tissue.