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Variant estrogen receptor transcripts (lacking exon 5 of the hormone binding domain) investigated by Reverse transcription/Polymerase chain reaction in a series of patients with chronic active hepatitis, cirrhosis, cirrhosis with dysplasia and with hepatocellular carcinoma, increased progressively from CAH to HCC. Patients with liver cell dysplasia showed the same alterations as patients with HCC. As the variant ER transcripts when translated could give rise to truncated receptors still able to constitutively activate transcription, overexpression of these ER transcripts could be a key factor in liver carcinogenesis.

The wide variety of genetic alterations that can be induced in human populations when exposed to chemical genotoxic substances present in our environment may be predictable using laboratory organisms such as yeasts. In the present paper methodologies are described for analysing the genetic effects induced by a well known chemical mutagen, ethyl methanesulfonate (EMS). Haploid or diploid yeast cells have been treated in vitro , in buffer or in the presence of mouse liver microsomes, and in vivo , in the peritoneum of the mouse (host-mediated assay). With these different methods of assaying the genetic activity of a compound, its metabolic activation occuring in the mammalian body is taken into account: this might lead to a more reliable extrapolation of data from laboratory experiments to man. The relationships between doses and frequencies of the induced genetic effects are described by equations obtained after regression analysis of the data, thus allowing a quantitative comparison among different methodologies and different genetic systems. One genetic system analyzed is represented by forward-mutations scored phenotypically on a non selective medium. Mutations induced in five loci with different sensitivity and average data of mutation-induction per locus have been derived. The second genetic system was provided by scoring on a selective medium mitotic gene-conversions induced in two loci with different kinetics. Haploid cells of Schizosaccharomyces pombe and diploid cells of Saccharomyces cerevisiae were submitted to analysis for the evaluation of gene-mutations and gene-conversions respectively.

As part of a programme of investigations on the biological effects of the industrial compound vinyl chloride monomer (VCM), the raw material for the production of polyvinyl chloride (PVC), analyses on the genetic effects by this compound have been done by experiments (in vitro) which have taken mammalian metabolism into account. Vinyl chloride in the presence of purified microsomes (sedimented at 105,000 g) obtained from mouse liver was converted into an active metabolite(s) which produced gene mutations in the yeast Schizosaccharomyces pombe (forward mutation) and gene conversions in two loci of a diploid Saccharomyces cerevisiae. Moreover, the compound was active in the host-mediated assay, when mice were treated with an oral dose of 700 mg/kg. The role is discussed of mutagenicity tests for the prediction of both genetic and carcinogenic risks of chemical compounds in industrial use.

Let me begin with an apology. My original intention was to present a synthesis of what is known about mutation and repair in the yeast and try to define a conclusive theory or single hypothesis consistent with the available data. When, however, I was confronted with the task of writing down on paper such coherent ideas, I realized my complete inadequacy to formulate any general theory. Consequently, I shall just tell you now my little story, containing some of the many possible approaches to the problem under discussion, in the hope that the theory, or the organic vision that is needed today by everybody, will result from the critical inspection and discussion of all available data, which is exactly the aim of meetings like the one we are attending.

Styrene and its presumed metabolite, styrene oxide, were tested for their mutagenic effect on a forward mutation system of yeast and of Chinese hamster cells, and on a gene-conversion system of yeast. Experiments with liver microsomal preparations and host-mediated assay with yeast were also carried out. Styrene oxide was mutagenic in all test systems. Styrene was mutagenic only in the host-mediated assay.

Experiments on strains of yeast with different genetic backgrounds were done to evaluate the kinetics of inactivation and mutation induction by X-radiations. A system of forward mutation induction in five loci was used as a specific mutation rate of 0.14-10-minus 8 times locus times rad was evaluated for the wild type. From a comparison of observations with wild type and radiation-sensitive strains, it may be assumed that, in this yeast, mutations are mainly the result of a repair-active process. The range of genotypic and phenotypic influence upon the specific locus mutation rate was evaluated with appropriate biological material and experiments.