Cancer chemotherapy and somatic cell mutation

The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm.     

Morphological mutation of Lentinula edodes mycelium, particularly detectable in the dikaryotic state

A morphological mutation particularly detectable in the dikaryotic state was found in Lentinula edodes. The mutant dikaryon was readily distinguishable from the normal dikaryon by the irregularly branched short hyphae, very slow hyphal growth, and sparse aerial hyphae. Genetic analysis revealed that expression of this mutation was controlled by a single recessive gene, mor-13. Linkage analysis showed that the mor-13 was not linked to either the incompatibility factors (A and B) or the five kinds of mor genes that were segregated independently of each other in a previous study. Contribution no. 380 from the Tottori Mycological Institute     

Development of sporeless/low sporing strains of Pleurotus through mutation

Summary The sporophores of Pleurotus are gymnocarpous and continuously release spores in the atmosphere causing respiratory allergies like hay fever and farmer’s lung disease among workers. The allergy is caused by the antigens present on the walls of the spores. Apart from this, during commercial production, these spores settle on the fruit bodies, germinate and form a velvety film which gives an unpleasant appearance to the mushrooms. The spores emitted may include new genotypes likely to attack wood or trees. Spore allergy is one of the most important limiting factors for the large scale cultivation of this species. Different approaches are being adopted at IIHR for the production of commercial sporeless/low-sporing strains of Pleurotus to alleviate the spore allergy problem. Attempts were made during the present investigation to produce sporeless or low-sporing mutants through u.v. mutation. Mutation of the mycelium did not yield the desired results. Mutation of the spores of Pleurotus sajor-caju yielded an extremely low-sporing mutant after 75 min exposure. The character has been found to be stable for more than 10 generations of subculturing.     

Within-tree spatial variation in the leaf monoterpenes of Sequoia sempervirens

Location within a tree was analyzed as a source of variation in Sequoia sempervirens leaf monoterpenes. No differences were found for quantitative composition or total yield/dry wt among lower, middle and upper canopy positions. The awlshaped, spirally arranged leaves of vigorous upper shoots showed small quantitative compositional differences, but not differences in total yield. The intermediate leaf form of young sprouts had the most different monoterpene quantitative composition and about three times the total yield of the above two leaf forms. Analysis of a clonal ring of 17 adult trees resulted in coefficients of variation similar to those for samples collected from different canopy levels of the same shoot. Results revealed the sources and magnitudes of experimental error in comparative studies of this species' leaf monoterpenes, and did not support the concept that somatic mutation provides an important source of variation in a large, long-lived organism such as coast redwood.     

Chitin biosynthesis during pupal development of Drosophila melanogaster and the effect of the lethalcryptocephal mutation

Estimation of chitin deposition in the pupal and adult cuticles of adult Drosophila melanogaster during the pupal period is described. The timing of the periods of chitin deposition is compared with that deduced by previous workers using electron microscopy. The hypothesis that lethalcryptocephal mutant homozygotes are unable to evert their cephalic complexes at pupation because of excess chitin deposition is examined. The data obtained show no evidence that the mutation has any effect on chitin deposition.     

The congenital cataract-causing mutations P20R and A171T are associated with important changes in the amyloidogenic feature,structure and chaperone-like activity of human αB-crystallin

Cataract is the major reason for human blindness worldwide. α-Crystallin, as a key chaperone of eye lenses, keeps the lenticular tissues in its transparent state over time. In this study, cataract-causing familial mutations, P20R and A171T, were introduced in CRYАB gene. After successful expression in Escherichia coli and subsequent purification, the recombinant proteins were subjected to extensive structural and functional analyses using various spectroscopic techniques, gel electrophoresis, and electron microscopy. The results of fluorescence and Raman assessments suggest important but discreet conformational changes in human αB-Cry upon these cataractogenic mutations. Furthermore, the mutant proteins exhibited significant secondary structural alteration as revealed by FTIR and Raman spectroscopy. An increase in conformational stability was seen in the human αB-Cry bearing these congenital cataractogenic mutations. The oligomeric size distribution and chaperone-like activity of human αB-Cry were significantly altered by these mutations. The P20R mutant protein was observed to loose most of the chaperone-like activity. Finally, these cataractogenic mutant proteins exhibited an increased propensity to form the amyloid fibrils when incubated under environmental stress. Overall, the structural and functional changes in mutated human αB-Cry proteins can shed light on the pathogenic development of congenital cataracts.     

EVOLUTION AND EXTINCTION IN A CHANGING ENVIRONMENT: A QUANTITATIVE-GENETIC ANALYSIS

Because of the ubiquity of genetic variation for quantitative traits, virtually all populations have some capacity to respond evolutionarily to selective challenges. However, natural selection imposes demographic costs on a population, and if these costs are sufficiently large, the likelihood of extinction will be high. We consider how the mean time to extinction depends on selective pressures (rate and stochasticity of environmental change, and strength of selection), population parameters (carrying capacity, and reproductive capacity), and genetics (rate of polygenic mutation). We assume that in a randomly mating, finite population subject to density-dependent population growth, individual fitness is determined by a single quantitative-genetic character under Gaussian stabilizing selection with the optimum phenotype exhibiting directional change, or random fluctuations, or both. The quantitative trait is determined by a finite number of freely recombining, mutationally equivalent, additive loci. The dynamics of evolution and extinction are investigated, assuming that the population is initially under mutation-selection-drift balance. Under this model, in a directionally changing environment, the mean phenotype lags behind the optimum, but on the average evolves parallel to it. The magnitude of the lag determines the vulnerability to extinction. In finite populations, stochastic variation in the genetic variance can be quite pronounced, and bottlenecks in the genetic variance temporarily can impair the population's adaptive capacity enough to cause extinction when it would otherwise be unlikely in an effectively infinite population. We find that maximum sustainable rates of evolution or, equivalently, critical rates of environmental change, may be considerably less than 10% of a phenotypic standard deviation per generation.     

Regressive evolution: ontogeny and genetics of cavefish eye rudimentation

Two hypotheses exist to explain ontogenetic eye reduction in Astyanax cave fish: first, after lens induction by the primordial eye cup, the lens plays the role of a central regulator of eye and retina regression or, second, the retina itself is an independent unit of eye development. A comparative study of five blind cave fish populations and their surface sister form was performed to investigate the differences of ontogenetic eye regression between the cave populations during different stages of development. The study revealed that, in addition to the initial formation of smaller primordia, eye regression is also caused during later ontogeny by different relative growth and specific histological characteristics. Whereas the cave fish lens never properly differentiates, the regressive process of the retina is transitorily interrupted by ongoing differentiation. In the newly-discovered Molino cave population, even visual cells with well-organized outer segments develop, which are secondarily reduced at a later ontogenetic stage. This result shows that the retina and lens are independent developmental units within the eye ball. Presumably, the genetic systems responsible for both show independent inheritance, which is also corroborated by hybrids of F ₂-crosses between the cave and surface fish, in which lens and retina development do not correlate. During ontogeny, the eye size differs between the cave populations. In Pachón cave fish, the relatively large eye size correlates with an ancient introgression from a surface population, which may have delayed eye regression.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 287–296.     

A new gene controlling the frequency of cell division per round of DNA replication in Escherichia coli

Summary A novel mutant of Escherichia coli, named cfcA1, was isolated from a temperature-sensitive dnaB42 strain, and found to have the following characteristics. Division arrest and lethality induced by inhibition of DNA replication was reduced and delayed in the cfcA1 dnaB42 strain, as compared with the parental dnaB42 strain. Two types of inhibition of division induced by the addition of nalidixic acid or hydroxyurea were suppressed by the cfcA1 mutation. Under permissive conditions for DNA replication, the colony forming ability of cfcA1 cells was significantly reduced as compared with that of cfc ⁺ cells; conversely the division rate of cfcA1 cells was higher than that of cfc ⁺ cells. The cfcA1 mutation partially restored division arrest induced in the thermosensitive ftsZ84 mutant at the restrictive temperature and suppresed the UV sensitivity of the lon mutation. The mutation was mapped at 79.2 min on the E. coli chromosome. Taking these properties into account, it is hypothesized that the cfcA gene is involved in determining the frequency of cell division per round of DNA replication by interacting with the FtsZ protein which is essential for cell division.