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Single intraperitoneal injections of dimethylnitrosamine (DMN) in concentrations of up to 16 mg/g body weight, failed to have any lethal effect in newts. This treatment also failed to induce tumours in newts maintained for one year after injection.Six or 7 injections of 16 mg/g body weight of DMN, administered over a period of 3-4 weeks, gave rise to a short-term lethal effect due to liver necrosis and in the long term to liver tumours. The tumours induced were of similar type to nitrosamineinduced tumours in rats, one being an anaplastic liver tumour and the other nodular hepatic cell tumours.Attempts to maintain the tumours by grafting failed, probably due to homograft rejection.
Restriction enzyme analysis of mitochondrial (mt) DNA isolated from oocytes of 185 individuals of the T. cristatus complex collected from 10 European countries has demonstrated that large length variation (greater than 40 bp) is a common feature of the group. Insertion polymorphism was found both within and among populations, and in all cases maps to the control region of the molecule. In addition, 2 individuals from Pisa, (Italy) were each found to be heteroplasmic for 2 large insertions comprising tandem repeats of 1100 bp of the control region. Large-scale length variation has been described in a few other lower vertebrates, but some of the insertion variants within populations described here are of unprecedented size (up to 8500 bp). This is in dramatic contrast to mammalian mtDNA in which size variation is largely restricted to small (less than 15 bp) insertions and deletions.
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Absorption measurements in violet light (lambda 4047 A) of thin sections of mature newt erythrocytes have indicated the presence of a haem compound, probably haemoglobin, within the chromosomal regions of the nucleus. The amount is about 45 per cent of that in the cytoplasm. The possible significance of this nuclear haemoglobin in determining nuclear structure is discussed in terms of the electrostatic interaction of haemoglobin and nucleohistone.
The unique reticulum in the basal membrane of the adult newt's skin consists of a series of nodular swellings from which there radiate fibers. Electron micrographic studies showed that the nodules consist of layers of fibrillae arranged approximately and irregularly at right angles to one another. Some are packed to form a capsule; still others extend into the internodular zone to form the radiating fibers. The fibrils are banded and are revealed best after fixation with potassium permanganate. The reticulum is compared with that of the larval newt and the frog tadpole. The epidermal side of the reticulum is bounded by a membrane separated from the plasma wall of the epidermal cell by a clear space. These we have termed adepidermal membrane and space, and have compared them with similar structures in larvae.
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