Selective breeding of miniature pigs bearing cutaneous tumours resulted in the establishment of the MeLiM strain with hereditary malignant melanoma. The inheritance of melanoma was tested in a two-generation kindred comprising 456 progeny from 78 li�ers. Melanomas were recognisable visually as black-pigmented lesions on the skin. Their size, shape, number, progression and metastatic spreading varied widely. All possible melanoma forms known in human melanoma, i.e. pigmented naevi, dysplastic naevi, superficial spreading melanoma and nodular malignant melanoma, were found in the MeLiM pigs. Because the occurrence of nodular malignant melanoma segregated in all recorded li�ers we have included only this form in the genetic analysis. The tumours were nodular with exophytic growth over the skin surface. All showed similar histopathological features, vertical growth to muscle fascia and high metastatic activity. We hypothesize, on the basis of segregation ratios obtained from various mating types, that the mode of inheritance of nodular melanoma in the MeLiM strain is probably controlled by three genes.
Tyrosine, a key enzyme of melanin biosynthesis, is widely used as a specific marker for the detection of dissemination or metastatic melanoma cells in peripheral blood and other tissues like lymph node or bone marrow, which are normally tyrosinase negative. The amplification of tyrosinase-specific mRNA by means of RT-PCR is a sensitive technique capable of detecting a single tumour cell in 5–10 ml of whole blood. We have utilised this method to analyse the peripheral blood of laboratory miniature pigs with advanced cutaneous melanoma for the presence of tumor cells. This highly invasive hereditary malignancy can serve as an experimental model for the study of melanoma development and dissemination. For amplification of porcine gene, oligonucleotide primers derived from the sequence of human tyrosinase were used. These primers amplified fragment of the predicted length and restriction enzyme digestion confirmed their homology with the sequences of human tyrosinase gene. After the second round of amplification, tyrosinase could be detected up to the amount of 1 × 10<sup>–5</sup> µg of total RNA isolated from porcine melanoma per 1 µg of control RNA. Blood samples from eight animals with advanced melanoma and from five non-melanoma control animals were examined for tyrosinase expression. Tyrosinase mRNA was detected in five samples from animals with malignant melanoma. Non-melanoma control animals gave negative results.
Suspensions of highly viable (< 95 To) granulocytes minimally contaminated by other cell types were isolated from the peripheral blood of pigs by a single centrifugation with low molecular weight dextran and after preferential lysis of erythrocytes by hypotonic shock. A complement-dependent cytotoxic test showed the presence of antigens of the SLA major histocompatibility complex, the SLB leucocyte system and the A and E blood group systems on the granulocytes. Some SLA typing reagents against class I (SD) antigens did not react with granulocytes, however, or yielded dubious reactions. The findings showed that the reactivity of SLA sera resembles the reactivity of human HLA sera. The results also show that compatibility in the SLA, SLB, A and E systems will have to be taken into account when preparing alloirnrnune sera for the determination of granulocyte-specific antigens of pigs.
SummaryLinkage studies of three‐point crosses (triple backcross matings) showed that the linear sequence of three of the pig's immunogenetic traits — the SLA major histocompatibility complex and the J and C blood group loci — is SLA‐J‐C. Andresen & Baker (1964) and Rasmusen (1965) described close linkage between the J and C blood group loci and respectively found their recombination frequency to be 5.29 ± 1.1 % and 7.00 ± 3.4 %; by combining the data the exact frequency was determined at 5.75 ± 0.79 % (Muir & Rasmusen, 1974). Later, linkage of the SLA major histocompatibility complex with both J (Hruban et al., 1976) and C (Hruban et al., 1977) erythrocytic loci was found. The maximum tabular lod score values were found in the recombination fraction Θ= 0.10 in comparison of SLA and J and in the fraction Θ= 0.20 in comparison of SLA and C (Hruban et al., 1977).
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