Theoretical aspects of extinction by inbreeding depression

Populational extinction due to inbreeding depression is analyzed with simple population genetic and population ecological models. Two alternative genetic mechanisms of inbreeding depression, i.e. recessive deleterious genes and overdominant genes, are assumed in separate analyses in order to examine their relative importance. With both mechanisms the population size and the coefficient of inbreeding are maintained at stable equilibria if there is no non-genetic demographic disturbance or stress. With a certain amount of demographic disturbance the population declines rapidly due to interaction between the decrease of population size and the increase of inbreeding coefficient. Such rapid extinction occurs with both genetic mechanisms. However, in the case of overdominant genes extinction happens only if the equilibrium population size is small and the selection coefficient is large such that segregation load is large. In nature, extinction due to overdominant genes is considered to be much less likely than extinction due to recessive deleterious genes.     

Action of metal ions directly involved in the cleavage reaction of hammerhead ribozymes.

Recently, hammerhead ribozyme-mediated cleavage was analyzed as a function of the concentration of La3+ ions in the presence of a fixed concentration of Mg2+ ions so that the role could be monitored of metal ions that are directly involved in the cleavage reaction. The resultant bell-shaped curve for activation of cleavage was used to support the proposed double-metal-ion mechanism of catalysis. However, other studies demonstrated that binding of a metal ion to the pro-Rp oxygen (P9 oxygen) of the phosphate moiety of nucleotide A9 and N7 of nucleotide G10.1 is critical for efficient catalysis. In order to clarify the effect of this metal ion, we chemically synthesized hammerhead ribozyme (7-deaza-R34) that included a minimal modification, namely, an N7-deazaguanine residue in place of G10.1.     

Introgressive hybridization as the breakdown of postzygotic isolation: a theoretical perspective

In this paper, both the empirical and theoretical genetic aspects of human-mediated introgressive hybridization are reviewed in terms of their association with the breakdown of postzygotic isolating mechanisms. I also compare several simulation models with an ecological or genetic focus that are relevant to the prediction and risk assessment of genetic extinction due to hybridization. One barrier to devising comprehensive risk assessment frameworks is a lack of sufficient population genetic studies that associate introgressive hybridization with specific isolating mechanisms. A gametic model based on multilocus underdominant fitness is one of the best genetic models for introgressive hybridization because it explicitly incorporates the postzygotic isolating mechanism known as Dobzhansky–Muller genetic incompatibility.     

Involvement of AP-2rep in morphogenesis of the axial mesoderm in <Emphasis Type="Italic">Xenopus</Emphasis> embryo

We have previously isolated a cDNA clone coding for Xenopus AP-2rep (activator protein-2 repressor), a member of the Krüppel-like factor family, and reported its expression pattern in developing Xenopus embryos. In the present study, the physiological function of AP-2rep in the morphogenetic movements of the dorsal mesoderm and ectoderm was investigated. Embryos injected with either AP-2rep or VP16repC (a dominant-negative mutant) into the dorsal marginal zone at the 4-cell stage exhibited abnormal morphology in dorsal structures. Both AP-2rep and VP16repC also inhibited the elongation of animal cap explants treated with activin without affecting the expression of differentiation markers. Whole-mount in situ hybridization analysis revealed that expression of brachyury and Wnt11 was greatly suppressed by injection of VP16repC or AP-2rep morpholino, but expression was restored by the simultaneous injection of wild-type AP-2rep RNA. Furthermore, the morphogenetic abnormality induced by injection of VP16repC or AP-2rep morpholino was restored by simultaneous injection of brachyury or Wnt11 mRNA. These results show that AP-2rep is involved in the morphogenesis of the mesoderm at the gastrula stage, via the brachyury and/or Wnt pathways. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This work was partly supported by a grant-in-aid from The Ministry of Education, Science, and Culture of Japan.     

Cloning of a 1.1-kb Fragment Including srnB+ Gene in the F Plasmid and Isolation of an srnB Mutant

The srnB⁺ gene, promoting stable RNA degradation at 42 C in the presence of rifampin, was cloned by using pBR322 as a vector; it was located on a 1.1-kilobase (kb) EcoRI/BamHI fragment between 1.4 and 2.5 kb of the F plasmid. The region between 93.3 and 4.0 kb of the F plasmid was physically mapped by using restriction endonucleases EcoRI, HindIII, BamHI, PstI, and SmaI, with reference to a standard HindIII site in IS3. An srnB1 mutant was isolated from a chimeric plasmid, pOY54, after treatment of its DNA with hydroxylamine. The srnB1 allele on the F fragment of the mutant plasmid was recessive to the wild-type allele. Thermal elevation of cell cultures to 39 C was high enough to promote RNA degradation in strain YS12 carrying plasmid pOY54.     

Realized heritability of behavioral responsiveness to an oviposition deterring pheromone in the azuki bean weevil Callosobruchus chinensis

Artificial selection was conducted to reduce the behavioral responsiveness of female bruchid beetles, Callosobruchus chinensis, to the oviposition deterring pheromone excreted by conspecific females. Significant responses to selection were observed after two generations of selection. Realized heritability was estimated as 0.052 ± 0.017 from cumulative responses regressed on cumulative selection differentials. These results indicate that this pheromone communication system has significant additive genetic variance needed for its evolution.     

Probing of the secondary structure of maxizymes.

The protein encoded by chimeric BCR-ABL mRNA causes chronic myelogenous leukemia (CML). We showed previously that a novel allosterically controllable ribozyme, of the type known as a maxizyme, can cleave this mRNA, with high specificity and high-level activity in vivo. In order to probe the putative conformational changes, we used a weakly alkaline solution to hydrolyze differentially phosphodiester bonds that were located in different environments. As indicated by earlier data obtained in vivo, our results demonstrated that the active conformation was achieved only in the presence of the junction within the chimeric BCR-ABL mRNA.