Giorgio Morpurgo

STARVATION IN YEAST INCREASES NON-ADAPTIVE MUTATION

Abstract The frequency of reversion in a histidine-requiring mutant of Saccharomyces cerevisiae increases about ten-fold in stationary cells during histidine starvation. Histidine starvation enhances a similar frequency of reversion in a tryptophan-requiring mutant. Starvation, therefore, enhances mutation frequencies in a non-adaptive manner. The base analogue 6-N-hydroxylaminopurine (HAP) added prior to plating on medium with limited histidine strongly increases reversion of the histidine mutant. HAP-induced reversion increases further in stationary starving cells with the same kinetics as that which increases spontaneous reversion. Adding HAP to the stationary starving cells does not produce any effect.

The increased incidence of malignant melanoma in obese individuals is due to impaired melanogenesis and melanocyte DNA repair

Obese individuals have a higher incidence of malignant melanoma (MM). We here suggest that the higher incidence is caused by a reduction of melanogenesis and a decreased capacity of melanocytes DNA repair. These effects are caused by an increase in the haematic levels of melanocyte stimulating hormone (MSH) antagonists, namely of the protein attractin, the melanocyte concentrating hormone (MCH), the agouti related protein (ASRP) and perhaps also agouti protein (ASIP), determining a lower activity of circulating MSH and of melanocortotropin receptors (MCRs) 1 and 4. MCR1 is fundamental in melanocyte DNA repair and melanogenesis, and a reduction of its activity could well account for the increased incidence of MM. All these changes are ultimately caused by the leptin resistance normally present on obese individuals, that is a low effectiveness of leptin in spite of its high circulating level.

The exceptionally high rate of spontaneous mutations in the polymerase delta proofreading exonuclease-deficient Saccharomyces cerevisiae strain starved for adenine

BackgroundMutagenesis induced in the yeast Saccharomyces cerevisiae by starvation for nutrilites is a well-documented phenomenon of an unknown mechanism. We have previously shown that the polymerase delta proofreading activity controls spontaneous mutagenesis in cells starved for histidine. To obtain further information, we compared the effect of adenine starvation on mutagenesis in wild-type cells and, in cells lacking the proofreading activity of polymerase delta (phenotype Exo-, mutation pol3-01).ResultsAde+ revertants accumulated at a very high rate on adenine-free plates so that their frequency on day 16 after plating was 1.5 × 10-4 for wild-type and 1.0 × 10-2 for the Exo- strain. In the Exo- strain, all revertants arising under adenine starvation are suppressors of the original mutation, most possessed additional nutritional requirements, and 50% of them were temperature sensitive.ConclusionsAdenine starvation is highly mutagenic in yeast. The deficiency in the polymerase delta proofreading activity in strains with the pol3-01 mutation leads to a further 66-fold increase of the rate of mutations. Our data suggest that adenine starvation induces genome-wide hyper-mutagenesis in the Exo- strain.

The influence of colonial organization on thermotolerance and thermoresistance in Saccharomyces cerevisiae.

In this study we show that thermotolerance and thermoresistance of the yeast Saccharomyces cerevisae is enhanced when cells are in colonial condition. We also describe a method to select stable thermoresistant mutants which produce colonies from single plated cells at a temperature 2.5 °C higher than the maximum growth temperature of their parental strain.

Research inAspergillus nidulans genetics

One of the major goals ofAspergillus nidulans genetical research in Italy has been to set up a series of tests for the evaluation of the genetical risk derived from environmental pollution.The induced frequency of mutation and recombination (mitotic crossing-over and non-disjunction) has been studied for many chemicals and important results have been obtained from a practical and theoretical point of view.Because of the great versatility of Aspergillus as a model organism in genetical research, major basic genetical problems have also been investigated in Italy. Among them it is worth to remember the research on the mitotic intra- and inter-genic recombination.Aspergillus is still used mostly to test non-disjunctional properties of chemicals; in fact it is the only organism where non-disjunction can be properly estimated.Moreover the population genetics and the DNA repair in Aspergillus are currently investigated in our laboratory.

Are tyrosinase inhibitors in sunscreens and cosmetics enhancing UV carcinogenicity

Skin metabolism is becoming a major consideration in the development of new cosmetic ingredients, skin being the first organ exposed to them. In order to replace limited samples of Excised human skin (EHS), in vitro engineered human skins (a) (b)

Synthetic aromatic compounds interfering with melanogenesis are responsible of the rising trend of malignant melanoma incidence.

The hypotheses is forwarded that the introduction in the environment of high concentrations of phenols and other aromatic compounds (AC) is one, perhaps the main cause of the continuously rising trend of malignant melanoma (MM) incidence. Two, non-mutually exclusive, possibilities could explain how AC may induce MM: (1) AC may act as inhibitors or alternative substrates of tyrosinase, the enzyme synthesizing melanin, thus impairing the melanocyte photoprotection. (2) AC may impair, directly or indirectly, the activity or synthesis of the melanocorticotropin receptor (MC1R), which photoprotects melanocytes from the UV rays (UVR) by stimulating the DNA repair system. Particularly suspected are sunscreens, as they contain high concentrations of a large variety of AC, three of which are known to be tyrosinase inhibitors. AC that may interfere with tyrosinase are also present in a large variety of medicines used orally or as creams, and in many industrial products with which man is frequently in contact.

Colony Density Influences Invasive and Filamentous Growth in Saccharomyces cerevisiae

The effect of colony density on the dimorphic switch was determined in natural strains ofSaccharomyces cerevisiae. In some strains invasiveness and pseudohyphal (PH) growth were highly sensitive to colony density; moreover, strains constitutively able to invade the substrate with PH formation positively influenced the invasiveness but not the PH growth of a different strain less prone to the dimorphic switch.

6-N-hydroxylaminopurine (HAP)-induced accumulation of variability in haploid and diploid strains of Aspergillus nidulans.

Abstract Haploid and diploid strains of Aspergillus nidulans have been repeatedly treated with the strong mutagen 6-N-hydroxylaminopurine (HAP) which causes only base substitutions. An enormous amount of variability may be rapidly accumulated in haploid or diploid strains of A. nidulans. In particular, in the diploids the analysis of the results shows that after 12 cycles of treatment the conidia differ from each other for about ten recessive lethals and therefore probably for several hundreds of mutations. The viability of the heterozygous multiply mutant diploids is not appreciably different from that of untreated controls. In the diploid strains the accumulated variability was very high. The treatment of a haploid strain during vegetative growth also caused a strong accumulation of mutations, even though deleterious, because they can be maintained in the heterokaryotic condition.

Haplodiploidy and evolution of eusociality in insects

Hymenoptera is the order of insects where eusociality has arisen more frequently. The propensity of this order to evolve complex eusocial traits has been linked to their haplodiploidy (i.e. diploid females and haploid males). In this paper we propose a new theory explaining why eusocial traits evolve more frequently in haplodiploid than in diploid species. The probability to fix an allele(s) in haplodiploid systems may be orders of magnitude higher than in diploid species and the ratio of the two probabilities is inversely correlated with allele frequencies and with the number of genes involved. This property of the haplodiploid system should greatly facilitate the evolution of complex multigenic altruistic traits as those present in the eusocial systems. This theory is not incompatible with that proposed by Hamilton (1964), but foresees much higher advantages in the evolution of sociality both by kin and group selection.RiassuntoL’ordine degli Imenotteri è quello in cui l’eusocialità è sorta più frequentemente. La tendenza di questo ordine ad evolvere caratteri eusociali complessi è stata correlata con l’aploidiploidia (cioè femmine diploidi e maschi aploidi). In questo lavoro proponiamo una nuova teoria la quale spiega perché i caratteri eusociali si evolvono più frequentemente nelle specie aplodiploidi rispetto a quelle diploidi. La probabilità che si fissi un allele (alleli) in sistemi aplodiploidi può essere ordini di grandezza maggiore rispetto alle specie diploidi ed il rapporto delle due probabilità è inversamente correlato con le frequenze alleliche e con il numero di geni coinvolti. Questa proprietà del sistema aplodiploide dovrebbe grandemente facilitare l’evoluzione di caratteri multigenici complessi come sono quelli che operano nei sistemi eusociali. Questa teoria non è incompatibile con quella proposta da Hamilton (1964) ma prevede vantaggi molto maggiori nell’evoluzione dell’eusocialità sia attraverso la «kin selection» che la selezione di gruppo.