A major difference between the divergence patterns within the lines-1 families in mice and voles

L1 retroposons are represented in mice by subfamilies of interspersed sequences of varied abundance. Previous analyses have indicated that subfamilies are generated by duplicative transposition of a small number of members of the L1 family, the progeny of which then become a major component of the murine L1 population, and are not due to any active processes generating homology within preexisting groups of elements in a particular species. In mice, more than a third of the L1 elements belong to a clade that became active approximately 5 Mya and whose elements are > or = 95% identical. We have collected sequence information from 13 L1 elements isolated from two species of voles (Rodentia: Microtinae: Microtus and Arvicola) and have found that divergence within the vole L1 population is quite different from that in mice, in that there is no abundant subfamily of homologous elements. Individual L1 elements from voles are very divergent from one another and belong to a clade that began a period of elevated duplicative transposition approximately 13 Mya. Sequence analyses of portions of these divergent L1 elements (approximately 250 bp each) gave no evidence for concerted evolution having acted on the vole L1 elements since the split of the two vole lineages approximately 3.5 Mya; that is, the observed interspecific divergence (6.7%-24.7%) is not larger than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses showed no clustering into Arvicola and Microtus clades.      

Molecular phylogeny and divergence times of drosophilid species

The phylogenetic relationships and divergence times of 39 drosophilid species were studied by using the coding region of the Adh gene. Four genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and Sophophora--were included. After conducting statistical analyses of the nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila as the outgroup. The phylogenetic tree obtained showed that the first major division of drosophilid species occurs between subgenus Sophophora (genus Drosophila) and the group including subgenera Drosophila and Engiscaptomyza plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then divided into D. willistoni and the clade of D. obscura and D. melanogaster species groups. In the other major drosophilid group, Zaprionus first separates from the other species, and then D. immigrans leaves the remaining group of species. This remaining group then splits into the D. repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila, Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups is monophyletic. The splitting of subgenera Drosophila and Sophophora apparently occurred about 40 Mya, whereas the D. repleta group and the Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya, suggesting that Scaptomyza experienced a rapid morphological evolution. The D. obscura and D. melanogaster groups apparently diverged about 25 Mya. Many of the D. repleta group species studied here have two functional Adh genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two duplication events.      

Submillisecond rotational dynamics of spin-labeled myosin heads in myofibrils.

The rotational motion of crossbridges, formed when myosin heads bind to actin, is an essential element of most molecular models of muscle contraction. To obtain direct information about this molecular motion, we have performed saturation transfer EPR experiments in which spin labels were selectively and rigidly attached to myosin heads in purified myosin and in glycerinated myofibrils. In synthetic myosin filaments, in the absence of actin, the spectra indicated rapid rotational motion of heads characterized by an effective correlation time of 10 microseconds. By contrast, little or no submillisecond rotational motion was observed when isolated myosin heads (subfragment-1) were attached to glass beads or to F-actin, indicating that the bond between the myosin head and actin is quite rigid on this time scale. A similar immobilization of heads was observed in spin-labeled myofibrils in rigor. Therefore, we conclude that virtually all of the myosin heads in a rigor myofibril are immobilized, apparently owing to attachment of heads to actin. Addition of ATP to myofibrils, either in the presence or absence of 0.1 mM Ca2+, produced spectra similar to those observed for myosin filaments in the absence of actin, indicating rapid submillisecond rotational motion. These results indicate that either (a) most of the myosin heads are detached at any instant in relaxed or activated myofibrils or (b) attached heads bearing the products of ATP hydrolysis rotate as rapidly as detached heads.     

Stem cells and immunological parameters in mice during the latency period and after the development of chemically induced leukemia

T-cell leukemias have been induced in adult BDF1 mice by 12 or 15 weeks of exposure to butylnitrosourea (BNU) in the drinking water. This led to a depression of CFU-S numbers and reduced T- and B-cell responses to mitogens. These parameters were then studied during the BNU-free preleukemic latency period in individual mice. At the same time, leukemic cells were traced in the thymus, the spleen, and the bone marrow by transplantation. In mice without leukemia and mice with leukemic cells in only one organ, there was a general tendency to normal CFU-S numbers and T- and B-cell responses with time after BNU, although control levels were reached in only a few of the mice. The reaction of mixed lymphocyte cultures (MLC) remained low during the latency period. In the thymus an imbalance of the Con A, PHA, and MLC responses was observed. Out of 25 mice with induced leukemia, 8 had leukemic cells in the thymus only and 2 in the marrow only. In mice with leukemic cells in all 3 hemopoietic organs and an enlargement of the spleen, a shift of CFU-S from the marrow to the spleen was observed.     

Relationship between mutagenicity and DNA adduct formation in mammalian cells for fjord- and bay-region diol-epoxides of polycyclic aromatic hydrocarbons

Chinese hamster V79 cells were treated with the anti- and syn-diastereomers of the bay- or fjord-region diol-epoxides of four polycyclic aromatic hydrocarbons, namely benzo[a]pyrene (BP), benzo[c]chrysene (BcC), benzo[g]chrysene (BgC) and benzo[c]phenanthrene (BcPh). The frequency of induction of 6-thioguanine-resistant mutations was determined, and the extent of formation of DNA adducts was measured by 32P-postlabelling. When expressed as mutation frequency per nanomoles compound per millilitre incubation medium, this group of chemicals expressed a 160-fold range in potency. In agreement with previous experimental studies, the anti-diol-epoxide of BcC was highly mutagenic, inducing in excess of 3 x 10(4) mutations/10(6) cells per nmol compound/ml. The mutagenic activities of the anti- and syn-diol-epoxides of BP were 10- and 100-fold lower, respectively. Both diol-epoxides of BgC, the syn-BcC and the anti-BcPh derivatives were also highly mutagenic, and only the syn-BcPh diol-epoxide was less mutagenic than the anti-diol-epoxide of BP. Determination of the levels of DNA adducts formed by the diol-epoxides indicated that the most mutagenic compounds were the most DNA reactive, although the fjord-region diol-epoxides gave rise to more complex patterns of adducts than those of the BP diol-epoxides. When the mutagenicity results were expressed as mutations per femtomoles total adducts formed, all compounds showed similar activities. Thus the potent mutagenicity of the fjord region diol-epoxides appears to be due to the high frequency with which they form DNA adducts in V79 cells, rather than to formation of adducts with greater mutagenic potential.     

Superovulation of cattle with equine pituitary extract and porcine ESH

Superovulation has been practiced in cattle for more than 50 years but the results have been highly variable. Scientists at six locations compared a horse pituitary extract (HAP) with a single batch of porcine FSH (pFSH) to determine the efficacy of these hormones to induce superovulation and to test for variability in the superovulatory response. Acetone-dried equine pituitaries were suspended in 40% ethanol containing 6% ammonium acetate, and the supernatant was mixed with 2.5 volumes of cold ethanol. The resulting precipitate was washed with cold ether and dried. Total doses of 18 mg of HAP and 36 mg of pFSH were injected intramuscularly (i.m.) over 4 days, two injections per day, and prostaglandin (PGF(2)alpha; 25 mg, i.m.) was administered on Day 3. Injections were begun on Days 6 to 13 of the estrous cycle. The overall ovulation rates (mean +/- SEM) for HAP and FSH were 8.8 +/- 0.7 and 15.1 +/- 1.0, respectively (n=231; P<0.01). Location interacted (P<0.01) with the type of gonadotropin for the ovulation rate. When expressed as a proportion of the number of corpora lutea, the total number of embryos recovered was greater (P=0.03) for pFSH than for HAP, but there was no difference in the number of Quality 1 and 2 embryos. The results show that HAP can induce a satisfactory superovulatory response, but there was no evidence of reduced variability of response to HAP compared with pFSH.