We have investigated the role of the p53 gene in oncogenesis in vivo by generating transgenic mice carrying murine p53 genomic fragments isolated from a mouse Friend erythroleukemia cell line or BALB/c mouse liver DNA. Elevated levels of p53 mRNA were detected in several tissues of two transgenic lines tested. Increased levels of p53 protein were also detected in most of the tissues analyzed by Western blotting (immunoblotting). Because both transgenes encoded p53 proteins that were antigenically distinct from wild-type p53, it was possible to demonstrate that overexpression of the p53 protein was mostly, if not entirely, due to the expression of the transgenes. Neoplasms developed in 20% of the transgenic mice, with a high incidence of lung adenocarcinomas, osteosarcomas, and lymphomas. Tissues such as ovaries that expressed the transgene at high levels were not at higher risk of malignant transformation than tissues expressing p53 protein at much lower levels. The long latent period and low penetrance suggest that overexpression of p53 alone is not sufficient to induce malignancies and that additional events are required. These observations provide direct evidence that mutant alleles of the p53 oncogene have oncogenic potential in vivo and that different cell types show intrinsic differences in susceptibility to malignant transformation by p53. Since recent data suggest that p53 may be a recessive oncogene, it is possible that the elevated tumor incidence results from functional inactivation of endogenous p53 by overexpression of the mutant transgene. The high incidence of lung and bone tumors suggests that p53 transgenic mice may provide a useful model to investigate the molecular events that underlie these malignancies in humans.

1. The effect of manipulating egg incubation temperature for short periods on turkey muscle development was determined using the M. semitendinosus, a thigh muscle, as the model. 2. Experiment 1. Eggs were incubated at a control temperature of 37.5 degrees C. For a 4-d period of 0 to 4, 5 to 8, 9 to 12, 13 to 16, 17 to 20 or 21 to 24 embryonic days (ED) eggs were transferred to either 38.5 or 35.5 degrees C. A regime of 38.5 degrees C at 5 to 8 and 9 to 12 ED caused an increased myonuclei number and muscle fibre number, respectively. 3. Experiment 2. Eggs were incubated at a control temperature of 37.5 degrees C. At 5 to 8 ED eggs were transferred to 38.5 or 35.5 degrees C. Temperature-manipulated embryos showed a delay in differentiation (myogenin expression) of the semitendinosus muscle compared to controls. 4. Manipulating the incubation temperature for 4 d in early incubation alters muscle development in the turkey with no observation of deformities or reduction in hatchability. We speculate that this increase in temperature may result in an improved muscle growth in the post-hatch bird.

The mammalian c-fps/fes proto-oncogene encodes a 92-kilodalton cytoplasmic protein-tyrosine kinase (p92c-fes), which is expressed in immature and differentiated hematopoietic cells of the myeloid lineage. To determine the limits of the c-fps/fes locus and to investigate the cis-acting sequences required to direct appropriate tissue-specific expression, a 13-kilobase-pair fragment of human genomic DNA containing the entire c-fps/fes coding sequence was introduced into the mouse germ line. Transcription of the human c-fps/fes transgene was highest in bone marrow and showed a tissue distribution identical to that of the endogenous mouse gene. Macrophages cultured from transgenic mouse bone marrow contained particularly high levels of human and murine c-fps/fes RNA. Furthermore, expression of human c-fps/fes RNA induced a proportionate increase in the level of the p92c-fes protein-tyrosine kinase in bone marrow, bone marrow-derived macrophages, and spleen. Elevated levels of normal human p92c-fes had no obvious effect on mouse development or hematopoiesis. Remarkably, given the short 5'- and 3'-flanking sequences, expression of the human proto-oncogene in bone marrow was independent of integration site, was proportional to the transgene copy number, and was of comparable efficiency to that of the endogenous mouse c-fps/fes gene. The 13-kilobase-pair fragment therefore defines a genetic locus sufficient for the appropriate tissue-specific expression of the fps/fes protein-tyrosine kinase and includes a dominant cis-acting element that directs integration-independent myeloid expression in transgenic mice.

Transgenic mice that widely express the v-frs protein-tyrosine kinase develop several independent pathological conditions, in addition to a high tumor incidence. v-frs expression and protein-tyrosine kinase activity in the heart were directly correlated with cardiac enlargement. This cardiomegaly was accompanied by severe myocardial and endocardial damage, which was concentrated in the left ventricular wall, and characterized by a progressive atrophy and necrosis of cardiac muscle fibers with concomitant fibrosis. This pathology was associated with congestive heart failure. Mice from five lines developed a marked trembling, correlated with expression of the v-fs transgene in the brain, and two lines showed a striking bilateral enlargement of the trigeminal nerves. Unlike tumor formation, these cardiac and neurological phenotypes were evident shortly after birth and showed 100% penetrance. The pleiotropic effects of the v-fps transgene suggest the involvement of protein-tyrosine kinases in mammalian neural development and cardiac function.

src, abl, and fps/fes are prototypes for a family of genes encoding nonreceptor protein-tyrosine kinases. The oncogenic potential of the v-fps protein-tyrosine kinase was investigated by introduction of the gag-fps coding sequence of Fujinami sarcoma virus into the mouse germ line. Transgenic mice with v-fps under the transcriptional control of a 5' human beta-globin promoter (GF) or with both 5' and 3' beta-globin regulatory sequences (GEF) were viable. Unexpectedly, both GF and GEF transgenes were expressed in a wide variety of tissues and induced a spectrum of benign and malignant tumors. These tumors, which included lymphomas, thymomas, fibrosarcomas, angiosarcomas, hemangiomas, and neurofibrosarcomas, developed with various frequencies after latent periods of 2 to 12 months. The majority of lymphoid neoplasms appeared to be of T-cell origin and were monoclonal, as judged by rearrangements of the T-cell receptor beta or immunoglobulin genes. Some tissues that expressed the v-fps oncogene, such as heart, brain, lung, and testes, developed no malignant tumors. The v-fps protein-tyrosine kinase therefore has a broad but not unrestricted range of oncogenic activity in cells of lymphoid and mesenchymal origin. The incomplete penetrance of the neoplastic phenotype and the monoclonality of lymphoid tumors suggest that tumor formation in v-fps mice requires genetic or epigenetic events in addition to expression of the P130gag-fps protein-tyrosine kinase.