Genetic predisposition to tumors in the rabbit

Neoplastic transformation of rabbit cells by murine sarcoma viruses

Neoplastic transformation of rabbit cells by Kirsten murine sarcoma virus (Ki-MSV), the Ki-MSV pseudotype of baboon endogenous virus (Ki-MSV[BaEV]) and the Moloney-MSV pseudotype of feline leukemia virus (M-MSV[FeLV]) is reported. Rabbit cells can be readily transformed by Ki-MSV, Ki-MSV(BaEV) and M-MSV(FeLV). Rabbit cells transformed by Ki-MSV and M-MSV(FeLV) were found to be virus producers, whereas those transformed by Ki-MSV(BaEV) were nonproducers (NP). The NP cells were obtained by simply infection rabbit cells with Ki-MSV(BaEV) and subculturing the infected cells. Although the morphologically altered NP cells did not produce infectious virus or murine leukemia virus antigen, they did contain a rescuable MSV genome. All of the transformed cells formed colonies in soft agar, grew to high saturation densities and produced tumors when transplanted into nude mice. The Ki-MSV and M-MSV(FeLV)-transformed cells produced tumors in newborn WH/J rabbits, thus providing an important tool for studying tumor immunity in the rabbit.

Frequency of congenital abnormalities and of anatomical variations among JAX rabbits

The frequency of congenital abnormalities and anatomical variations as observed among JAX rabbits is reported. Data were drawn from 32,082 inbred and partially inbred rabbits and 3,208 hybrids from the colony of the Jackson Laboratory over an eight-year period. Data reported here include stillbirths, rabbits dying from natural causes, and those killed for specific experimental regimens. Frequency data are based on the number of abnormalities observed in each category as a function of the total number of animals necropsied. This is approximately 95% of the animals born during the eight-year period and gives the frequency of abnormalities within each category rather than the number of individuals with one or more abnormalities. Anatomical variations have been found in almost all organ systems of JAX rabbits. Their presence adds to our knowledge of the characteristics of these strains, a knowledge that is critical to the understanding of the results of experimental manipulation or for determination of the presence of new mutations. There is considerable between-strain variation. Where frequencies are relatively high, the conditions are either known or suspected to be of genetic origin. Most of the anomalies are not deleterious, or their frequency is so low as to cause no problems within the colony. Hybrid populations have substantially fewer anomalies than do the parental strains. Where frequency is relatively high, it tends to be intermediate between the parental strains.

Carcinogenic mechanisms: a critical review and a suggestion that oncogenesis may be adaptive ontogenesis

The precise mechanism(s) whereby normal cells become malignant are not known with any degree of certainty. However, many mechanisms have been proposed on the basis of available experimental evidence as interpreted by the proposer. These fall into two main groups and are based upon changes in genetic structure (somatic mutation hypotheses) or in genetic expression (epigenetic hypotheses). Yet a third group embodies elements of the first two. The more important of all these proposals are critically reviewed and yet another hypothesis is ventured. In this hypothesis, the induction of neoplasia is envisaged as embodying (a) initiation of preferentially partly-differentiated and resting stem cells and (b) promotion of the initiated cells, through mitosis and further differentiation and by adaptations of normal ontogenic mechanisms, into a variety of novel phenotypes which are malignant or potentially so. Cancer-specifying genes, altered chromosomes, de-differentiations and interrupted re-differentiations are not considered to be causally involved, although the last three of these can be present as epiphenomena. Evidence cited in support of this proposal appears to show a general absence from cancer cells of any single property, including an abnormality in genetic constitution or in cellular expression, which is specific to malignancy. Malignancy is thus envisaged as abnormal expressions of the genetic potential of the zygote. Some practical and theoretical implications of this concept are discussed.