Strain C3H-A-vy-fB mice: ninety percent incidence of mammary tumors transmitted by either parent

Primary Tumors and Adenomatosis Of The Lung In Untreated and In Irradiated Guineá Pigs

The morphology of alveologenic tumor, hemangiosarcoma, lymphangioma, intrabronchial papilloma and adenomatosis observed in the lung of guinea pigs is described. Electron micrographs revealed alveologenic tumor to consist of Type II pneumocytes and the lesion of adenomatosis to consist of distended alveoli lined with ciliated bronchial type epithelial cells.

A relationship between the dose of gamma or X-ray irradiation received and the frequency of guinea pigs with lung tumors could not be established. In guinea pigs, which survived over 20 months, the frequency of alveologenic tumors in the inbred strains was 23/107 in irradiated and 11/79 in untreated guinea pigs; this difference was statistically not significant. The frequency of tumor bearing inbred males (11/60) was significantly lower than of tumor bearing noninbred males (23/65). In the irradiated guinea pigs alveologenic tumors occurred earlier and tumor nodules in the lung were more numerous than in the untreated guinea pigs.

Primary hemangiosarcoma involved the lung of one untreated and one irradiated strain 2 guinea pig. A single lymphangioma was found in an untreated inbred guinea pig. Intrabronchial papillomas were observed twice in irradiated and once in untreated guinea pigs.

Adenomatosis was present in the lung of 2 untreated inbred and 5 irradiated noninbred guinea pigs.

Precursor Lesions and Pathogenesis of Spontaneous Mammary Tumors in Mice

A histologic study was done on the spontaneously occuring precursor and neoplastic lesions of mammary gland in inbred and hybrid female mice.

Hyperplastic alveolar nodules (HAN) are small groups of non-encapsulated mammary acini lined by a single layer of low cubodial epithelial cells. The stroma of HAN often contain macrophages laden with ceroid pigment, which imparts to them a yellow color. Microfoci of carcinoma may be found within HAN, and adenoacanthomas may arise within acini in which there is chronic inflammation. Plaques are pregnancy-dependent lesions which occur in three albino mouse strains: DD, GRS, and RIII. These plaques are disc-shaped, are circumscribed or unencapsulated, have a central myxomatous core, and have acini which exhibit radial symmetry. Plaques can give rise to adenocarcinomas type P, type B (papillary and cystic) and also to the unusual and distinctive pale cell carcinoma. The spontaneous tumors described in this paper are mammary gland adenocarcinomas with sebaceous cell nests, tumors which are papillomas and contain basal epithelial elements and acini derived from mammary, sebaceous glands, or hair follicles.

MMTV mouse models and the diagnostic values of MMTV-like sequences in human breast cancer

Mouse mammary tumor virus (MMTV) long terminal repeat (LTR)-driven transgenic mice are excellent models for breast cancer as they allow for the targeted expression of various oncogenes and growth factors in neoplastic transformation of mammary glands. Numerous MMTV-LTR-driven transgenic mouse models of breast cancer have been created in the past three decades, including MMTV-neu/ErbB2, cyclin D1, cyclin E, Ras, Myc, int-1 and c-rel. These transgenic mice develop mammary tumors with different latency, histology and invasiveness, reflecting the oncogenic pathways activated by the transgene. Recently, homologous sequences of the env gene of MMTV have been identified in approximately 40% of human breast cancers, but not in normal breast or other types of cancers, suggesting possible involvement of mammary tumor virus in human breast carcinogenesis. Accumulating evidence demonstrates the association of MMTV provirus with progesterone receptor, p53 mutations and advanced-stage breast cancer. Thus, the detection of MMTV-like sequences may have diagnostic value to predict the clinical outcome of breast cancer patients.

Liver-specific expression of the agouti gene in transgenic mice promotes liver carcinogenesis in the absence of obesity and diabetes

Background

The agouti protein is a paracrine factor that is normally present in the skin of many species of mammals. Agouti regulates the switch between black and yellow hair pigmentation by signalling through the melanocortin 1 receptor (Mc1r) on melanocytes. Lethal yellow (A^y) and viable yellow (A^vy) are dominant regulatory mutations in the mouse agouti gene that cause the wild-type protein to be produced at abnormally high levels throughout the body. Mice harboring these mutations exhibit a pleiotropic syndrome characterized by yellow coat color, obesity, hyperglycemia, hyperinsulinemia, and increased susceptibility to hyperplasia and carcinogenesis in numerous tissues, including the liver. The goal of this research was to determine if ectopic expression of the agouti gene in the liver alone is sufficient to recapitulate any aspect of this syndrome. For this purpose, we generated lines of transgenic mice expressing high levels of agouti in the liver under the regulatory control of the albumin promoter. Expression levels of the agouti transgene in the liver were quantified by Northern blot analysis. Functional agouti protein in the liver of transgenic mice was assayed by its ability to inhibit binding of the α-melanocyte stimulating hormone (αMSH) to the Mc1r. Body weight, plasma insulin and blood glucose levels were analyzed in control and transgenic mice. Control and transgenic male mice were given a single intraperitoneal injection (10 mg/kg) of the hepatocellular carcinogen, diethylnitrosamine (DEN), at 15 days of age. Mice were euthanized at 36 or 40 weeks after DEN injection and the number of tumors per liver and total liver weights were recorded.

Results

The albumin-agouti transgene was expressed at high levels in the livers of mice and produced a functional agouti protein. Albumin-agouti transgenic mice had normal body weights and normal levels of blood glucose and plasma insulin, but responded to chemical initiation of the liver with an increased number of liver tumors compared to non-transgenic control mice.

Conclusions

The data demonstrate that liver-specific expression of the agouti gene is not sufficient to induce obesity or diabetes, but, in the absence of these factors, agouti continues to promote hepatocellular carcinogenesis.

MMTV-induced mammary tumorigenesis: gene discovery, progression to malignancy and cellular pathways

The study of the mouse mammary tumor virus (MMTV) has provided important insights into the mechanisms of gene transcription regulation by steroid hormones, the mode of action of heritable super antigens and the progressive nature of neoplastic transformation in the mammary gland. Here we describe the current situation with respect to the latter aspect of MMTV biology and the prospects for further advance in our understanding of breast cancer in humans that may be expected from a continued study of MMTV-induced mammary neoplasia. MMTV is a heritable somatic mutagen whose target range is limited. Commonly, the tumorigenic capacity of MMTV is restricted to mammary gland, whereas infection is found in a variety of cell types. In order to replicate, proviral DNA must be inserted into the cell DNA and cell division is required to fix the mutation. Yet only in the mammary epithelium does this lead to neoplastic transformation. This suggests a unique relationship between MMTV and mammary epithelium. In evaluating this relationship, we and others have discovered genes and potential gene pathways that are pertinent in mammary differentiation and neoplasia. In addition, the clonal nature of these progressive events from normal to malignant phenotype has become increasingly clear. The weight of these observations compel us to conclude that mammary neoplasms arise from multipotent mammary epithelial cells through a process of acquired mutations that are reflected in the increasingly malignant nature of the population of progeny produced by these damaged stem cells.

Investigations of the mechanisms of metastatic spread of naturally occurring neoplasms

Much of the effort of this laboratory in recent years has been directed towards developing a reliable protocol for the experimental analysis of factors affecting metastatic spread from naturally occurring (i.e. not transplanted) neoplasms. The objective of this has been to develop a data base on the variations in metastatic behaviour between spontaneously arising neoplasms and to examine the tumour-specific and host-specific mechanisms accounting for this. This paper details the experimental technique and underlying conceptual basis which have been developed for reproducible investigations of this subject. It also reviews our conclusions from such work on the role in metastatic spread of tumour cell surface properties, collagenase secretion, microenvironmental effects on tumour cell growth in various organs, tumour macrophage content, and degree of cell shedding into the bloodstream.

Genetic transmission of mammary tumour virus in the DBAf mouse strain

MTV antigens were demonstrable by radioimmunoassay in milk samples from individual DBAf mice, and in samples from (male BALB/c X female DBAf) F1 mice. Although some samples collected during the first lactation periods of these mice were virus-negative, all samples of later lactation periods were virus-positive. From 75 mice of the [ male BALB/c X female (male BALB/c X female DBAf)]Bc I population, milk samples were collected during one or more lactation periods and tested for the presence of viral antigens; the samples of 42 mice were virus-positive. In the ([BALB/c X (BALB/c X DBAf)] X BALB/c)Bc II population two groups were distinguished. In the first group, the progeny of virus-positive Bc I mothers, 37 out of 62 mice had detectable levels of viral antigen in the milk. None of the 43 samples from mice of the second group, derived from MTV-negative Bc I females, were virus-positive. These data suggest that the presence of viral antigens in the milk of DBAf mice is controlled by a single dominant gene; evidence for linkage of this gene and the albino locus was obtained (recombination percentage: 20).

Studies of genetic transmission of mammary tumour virus by C3Hf mice

By radioimmunoassay (RIA) mammary tumour virus (MTV) antigens were detected in individual milk samples of C3Hf mice, (female BALB/c X male C3Hf)F1 mice and (female C3Hf X male BALB/c)F1 mice; milk samples of BALB/c mice were negative. In the segregating backcross I population, female BALB/c X male (female BALB/c X male C3Hf) viral antigens were found in the milk of 93 out of 169 mice (55%). In the Bc II population (daughters of Bc I mothers and BALB/c fathers) two groups were distinguished. In the first group, derived from positive Bc I mothers, 55 out of 110 mice (50%) had detectable levels of viral antigens in the milk. In the second group, progeny of negative Bc I mothers, 1 mouse out of 47 was positive. These data are consistent with the assumption that one dominant gene is responsible for the presence of viral antigens in the milk of C3Hf mice. This gene (Mtv-1) seems to be linked with the albino locus situated on chromosome 7; the recombination percentage was about 29. In the first experiment with Bc I mice a significant difference was found between the tumour ages of the mice with virus-positive milk and of the mice with virus-negative milk: all mice (18) with viral antigens in the milk developed mammary tumours at an age ranging from 7 to 18 months, whereas in only 7 out of 16 mice with virus-negative milk were mammary tumours found before the age of 21 months. Viral antigens were detectable (by RIA) in the tumours of mice of both subgroups; however, the amounts (mU/mg tumour) were significantly lower in the tumours derived from mice with virus-negative milk. Although MTV-L of C3Hf mothers could be transmitted to BALB/c mice by foster-nursing, viral antigens could not be detected in milk samples collected prior to the third lactation period; thus an influence on the data of extrachromosomally transmitted MTV-L is unlikely.

Mammary tumor virus and host genome in the transmission and causation of mammary tumors in mice

A review of the genetics of mammary tumor virus is presented in which the discoveries and hypotheses are given as they have historically developed.