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3.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
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4.
Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells 总被引:4,自引:2,他引:2
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Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction. 相似文献
5.
David A. Loebel Roderick K. Nurthen Richard Frankham David A. Briscoe Duncan Craven 《Zoo biology》1992,11(5):319-332
Equalizing founder representation is a recommended practice for maintaining captive populations. However, this procedure has not been subject to controlled experimental evaluation. The effects on inbreeding, genetic variation, and reproductive fitness of maintaining small captive populations by equalizing founder representation (EFR) versus randomly choosing parents (RC) were compared. Ten replicate lines were created with unequal founder representations, split into EFR and RC lines, and maintained for a further eight generations. Founder representations computed from pedigrees were closer to equality in the EFR lines than in the RC lines or the base population, most of the changes being evident after one generation. Significant benefits of EFR were found in lowered inbreeding (mean inbreeding coefficients of 0.35 and 0.41, respectively, for EFR and RC lines) and average heterozygosity (0.141 for EFR, 0.084 for RC, compared with 0.216 in the base population). However, EFR was not significantly better than RC in moving allele frequencies towards equalized founder representation. No significant difference was found in reproductive fitness between EFR and RC (relative fitnesses compared to the base population were 0.179 for EFR and 0.182 for RC). The use of equalization of founder representation for a few generations can be recommended in the genetic management of captive populations derived from a small number of founders that contribute unequally. © 1992 Wiley-Liss, Inc. 相似文献
6.
DNA sequence has an effect on the extent and kinds of alkylation of DNA by a potent carcinogen 总被引:4,自引:0,他引:4
A system has been developed to study the effects of base sequence (neighboring bases) upon the alkylation of guanine (G) and adenine (A) bases in DNA. The study was performed on the synthetic polydeoxyribonucleotides, poly(dG).poly(dC), poly(dG-dC).poly(dG-dC), poly(dA).poly(dT), poly(dA-dT).poly(dA-dT), poly(dA-dC).poly(dG-dT), poly(dA-dG).poly(dC-dT), as well as calf thymus DNA. Each polynucleotide was treated with N-[3H]methyl-N-nitrosourea (MNU), depurinated, and the freed alkylpurines separated by HPLC and quantitated by liquid scintillation counting. The amounts of 3-methylguanine (3-MG), 7-MG, and O6-MG relative to guanine, and 3-methyladenine (3-MA) and 1-MA plus 7-MA relative to adenine, and also the O6-MG/7-MG ratios were highly reproducible for a given polynucleotide. Significant differences were found in the amounts of each of the methylpurines formed when compared among the six synthetic polynucleotides and DNA. This evidence is interpreted as an effect upon alkylation which is ultimately dependent upon the base sequence. These findings may have significance in defining the specificity of chemical carcinogens in terms of the susceptability to modification of nucleotide sequences such as those found in certain oncogenes. 相似文献
7.
8.
Diabetes and host resistance. I. Effect of alloxan diabetes upon the phagocytic and bactericidal efficiency of rat leukocytes for Pneumococcus 总被引:1,自引:0,他引:1
Briscoe, H. Frances (University Medical Center, Jackson, Miss.), and Fred Allison, Jr. Diabetes and host resistance. I. Effect of alloxan diabetes upon the phagocytic and bactericidal efficiency of rat leukocytes for pneumococcus. J. Bacteriol. 90:1537-1541. 1965.-Chronic diabetes mellitus was induced in rats with alloxan monohydrate. Glycosuria persisted for the 6 weeks of study, but ketonuria was never encountered. The cellular composition of peritoneal exudate recovered from diabetic rats after starch aleuronat administration was the same as that obtained from normal rats. The quantity of exudate recovered from the diabetic rats was thought to be less than that obtained from normal rats subjected to the same irritant. Phagocytosis was found to be essentially the same for both diabetic and normal cells when suspended in normal saline. The killing efficiency of harvested peritoneal phagocytes suspended in saline from both diabetic and normal rats for type 1 pneumococcus was compared and no difference between the groups was found. 相似文献
9.
Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans 总被引:13,自引:3,他引:10
Recent studies of mitochondrial DNA (mtDNA) variation in mammals and
Drosophila have shown an excess of amino acid variation within species
(replacement polymorphism) relative to the number of silent and replacement
differences fixed between species. To examine further this pattern of
nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5
genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans.
Of interest are the frequency spectra of silent and replacement
polymorphisms, and potential variation among genes and taxa in the
departures from neutral expectations. The Drosophila ND3 and ND5 data show
no significant excess of replacement polymorphism using the
McDonald-Kreitman test. These data are in contrast to significant
departures from neutrality for the ND3 gene in mammals and other genes in
Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however,
both Drosophila and human mtDNA show very significant excesses of amino
acid polymorphism. Silent polymorphisms at ND5 show a significantly higher
variance in frequency than replacement polymorphisms, and the latter show a
significant skew toward low frequencies (Tajima's D = -1.954). These
patterns are interpreted in light of the nearly neutral theory where mildly
deleterious amino acid haplotypes are observed as ephemeral variants within
species but do not contribute to divergence. The patterns of polymorphism
and divergence at charge-altering amino acid sites are presented for the
Drosophila ND5 gene to examine the evolution of functionally distinct
mutations. Excess charge-altering polymorphism is observed at the carboxyl
terminal and excess charge-altering divergence is detected at the amino
terminal. While the mildly deleterious model fits as a net effect in the
evolution of nonrecombining mitochondrial genomes, these data suggest that
opposing evolutionary pressures may act on different regions of
mitochondrial genes and genomes.
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10.