Reduced latency but no increased brain tumor penetrance in mice with astrocyte specific expression of a human p53 mutant.

p53-germline mutations located in the core DNA-binding domain have been associated with a more dominant tumor penetrance especially for breast cancer and brain tumors. We previously reported an unusual accumulation of CNS tumors associated with a unique p53 germline mutation, Y236delta (deletion of codon 236). To test whether this tissue-specific tumor predisposition reflects a gain-of-function activity of Y236delta, we generated transgenic mice expressing Y236delta in astrocytes using the regulatory elements of the glial fibrillary acidic protein (GFAP) gene. After transplacental exposure to N-ethyl-N-nitrosourea (25 mg/kg BW) brain tumors developed in 18% (7/39) of GFAP-Y236delta transgenic p53-/- mice, while in p53+/- mice the incidence was 28% (11/40) (P>0.3). However, the mean tumor latency for GFAP-Y236delta/p53+/- mice was significantly shorter than for p53+/- mice, with 19.9 weeks vs 31.6 weeks (P=0.039), respectively. Taken together, cell specific expression of Y236delta results in an acceleration of tumor progression but does not confer a higher tumor penetrance. Conceivably, the transdominant effect of Y236delta provided a growth advantage early in the progression of neoplastic cells, since the endogenous p53 wild-type allele was lost in all brain tumors independent of the genotype. This reflects well observations from human astrocytic neoplasms with p53 mutations.

p53 transdominance but no gain of function in mouse brain tumor model.

Although p53 mutations in tumors typically result in loss of transactivation of p53 target genes some mutants display gain-of-function activity. The latter has important implications for the design of rational cancer therapy. We previously described a germ-line p53 mutation (deletion of codon 236, Y236delta) associated with a familial brain tumor syndrome. To determine whether this tissue-specific tumor predisposition reflects a gain-of-function activity of Y236delta or an effect of genetic background we have developed a mouse brain tumor model. Primary neuroectodermal cells deficient for p53 (+/- or -/-) and transduced with Y236delta using a retroviral vector were transplanted into the brain of adult wild-type mice. This neurografting paradigm circumvents the problem of early lethal tumors at extracerebral sites associated with germ-line p53 deficiency. Brain tumors arising in this mouse model were highly invasive, reflecting an important feature of the human disease. Tumors arose from p53+/- cells only when transduced with Y236delta. In keeping with in vitro data showing that Y236delta has dominant-negative activity, these tumors retained the endogenous wild-type p53 allele but accumulated high levels of Y236delta. However, the presence of Y236delta in transplanted p53-/- cells had no effect on the tumor frequency, 15% versus 27% without the mutant. In conclusion, Y236delta is transdominant but exerts no gain-of-function activity mediating a more penetrant tumor phenotype.

Functional analyses of a unique p53 germline mutant (Y236delta) associated with a familial brain tumor syndrome.

We have evaluated the functional properties of the unique p53 mutant Y236delta (deletion of codon 236) that gave rise to apparent cell-type specific tumor development. Four family members carrying this mutation in the germline developed early onset brain tumors, as previously reported. Deletion of residue Y236, which is tightly packed in an evolutionary conserved hydrophobic pocket, results in a protein with a mutant conformation according to immunoprecipitation with the conformation-sensitive antibodies PAb240 and PAb1620. The Y236delta mutant lacks specific DNA binding to the p53-responsive element in the WAF1-promoter, and functional analysis in Saos-2 cells revealed inability to transactivate the p53-responsive elements in the WAF1-promoter and the RGC sequence. The mutant has retained a functional oligomerization domain, a key element mediating the dominant negative effect, and inhibits DNA binding of wild-type p53. In addition, transactivation of endogenous wild-type p53 in LoVo cells was inhibited upon transfection of the mutant in a dose-dependent manner. Thus, in vitro and in vivo data suggest the loss of important tumor-suppressing functions and demonstrate a dominant negative effect of this unique p53 mutant that is associated with an unusual clustering of familial brain tumors.

Hemizygous or homozygous deletion of the chromosomal region containing the p16INK4a gene is associated with amplification of the EGF receptor gene in glioblastomas.

The p16INK4a gene product acts as a negative regulator of the cell cycle by binding to cyclin-dependent kinases (CDKs) 4 and 6, thereby inhibiting the formation of an active CDK/cyclin D complex. Deletion of the p16 locus has been observed in tumor cell lines and, less frequently, in primary human neoplasms. We analyzed 31 glioblastomas and identified 6 cases with hemizygous and 6 with homozygous deletions of the p16 locus. Eight of these cases showed a concurrent amplification of the EGFR gene (epidermal growth factor receptor) while the overall frequency was 35%. This close correlation suggests that deletion of the p16 chromosomal region constitutes another genetic hallmark of the primary glioblastoma, which rapidly develops de novo, without a less malignant precursor lesion and for which EGFR amplification is a characteristic genetic change. The p16 protein was not detectable in 15 of 22 glioblastomas but only 4 of these showed homozygous deletion of the gene. The alternative transcript p16 beta, for which a growth-suppressing function has been suggested, was co-expressed with p16 alpha mRNA in most cases. Hypermethylation of CpG islands in the 5' region of the p16 gene was identified in only 1 case, suggesting that this alternative mechanism of gene silencing is rarely responsible for loss of p16 expression in glioblastomas. Likewise, only 1 glioblastoma carried a p16 mutation and in addition, unexpectedly, a homozygous deletion of p16 in approximately 80% of tumor cells. This mutation, Arg24Pro, has previously been identified in a melanoma kindred.

Determination of p53 mutations, EGFR overexpression, and loss of p16 expression in pediatric glioblastomas.

Glioblastoma multiforme is a rare neoplasm in children and is often located infratentorially, particularly in the brainstem: Pediatric glioblastomas arise frequently (here 60%) outside the cerebral hemispheres. We investigated 20 pediatric glioblastomas for mutational inactivation of the p53 tumor suppressor gene, loss of p16 protein expression and overexpression of the epidermal growth factor receptor (EGFR). Mutations in the p53 gene were identified in 5/20 (25%) glioblastomas, 4 of which occurred in primary glioblastomas with a clinical history of less than 4 months and neither clinical nor histologic evidence of a less malignant precursor lesion. Loss of p16 expression was detected in 11/18 (61%) glioblastomas. Overexpression of the EGFR was infrequent (2/19, 11%) and included 1 tumor with a p53 mutation. Of 4 secondary glioblastomas that progressed from histologically diagnosed lower grade tumors, one contained a p53 mutation. Our results are at variance with similar studies in adult patients in which primary and secondary glioblastomas are characterized by EGFR overexpression and p53 mutations, respectively, suggesting that the evolution of pediatric glioblastomas follows different genetic pathways.

Deregulated expression of PAX5 in medulloblastoma.

Medulloblatoma is a pediatric brain tumor originating in the human cerebellum. A collection of 23 medulloblastomas was analyzed for expression of the developmental control genes of the PAX and EN gene families by RNase protection and in situ hybridization. Of all nine PAX genes investigated, only PAX5 and PAX6 were consistently expressed in most medulloblastomas (70 and 78% of all cases, respectively), as were the genes EN1 (57%) and EN2 (78%). EN1, EN2, and PAX6 genes were also expressed in normal cerebellar tissue, and their expression in medulloblastoma is consistent with the hypothesis that this tumor originates in the external granular layer of the developing cerebellum. PAX5 transcripts were, however, not detected in the neonatal cerebellum, indicating that this gene is deregulated in medulloblastoma. In the desmoplastic variant of medulloblastoma, PAX5 expression was restricted to the reticulin-producing proliferating tumor areas containing undifferentiated cells; PAX5 was not expressed in the reticulin-free nonproliferating islands undergoing neuronal differentiation. These data suggest that deregulated expression of PAX5 correlates positively with cell proliferation and inversely with neuronal differentiation in desmoplastic medulloblastoma.

Transgenic and knock-out mice: models of neurological disease.

Besides providing useful model systems for basic science, studies based on modification of the mammalian germ line are changing our understanding of pathogenetic principles. In this article, we review the most popular techniques for generating specific germ line mutations in vivo and discuss the impact of various transgenic models on the study of neurodegenerative diseases. The "gain of function" approach, i.e., ectopic expression of exogenous genes in neural structures, has deepened our understanding of neurodegeneration resulting from infection with papova viruses, picorna viruses, and human retroviruses. Further, inappropriate expression of mutated cellular molecules in the nervous system of transgenic mice is proving very useful for studying conditions whose pathogenesis is controversial, such as Alzheimer's disease and motor neuron diseases. As a complementary approach, ablation of entire cell lineages by tissue-specific expression of toxins has been useful in defining the role of specific cellular compartments. Modeling of recessive genetic diseases, such as Lesch-Nyhan syndrome, was helped by the development of techniques for targeted gene deletion (colloquially termed "gene knock-out"). Introduction of subtle homozygous mutations in the mouse genome was made possible by the latter approach. Such "loss of function" mutants have been used for clarifying the role of molecules thought to be involved in development and structural maintenance of the nervous system, such as the receptors for nerve growth factor and the P0 protein of peripheral myelin. In addition, these models are showing their assets also in the study of enigmatic diseases such as spongiform encephalopathies.

[Treatments for elephants: a challenge fo the zoo veterinarian]. / Elefantenbehandlungen: Eine Herausforderung für den Zootierarzt.

The existence of the elephant is heavily threatened. It is of great importance--for saving our largest land mammal on earth--to research into biology of the elephant quickly and thoroughly. Keeping elephants in Zoos and circus should be improved, breeding efforts must be enhanced and veterinary treatment has to be intensified. This is imperative for all zoo veterinarians.

Spontaneous generalized Herpesvirus hominis infection of a lowland gorilla (Gorilla gorilla gorilla).

A 13-day-old lowland gorilla died from a generalized herpesvirus infection shortly after the onset of clinical signs. The pathologic-anatomical findings were compatible with those described for generalized herpes simplex infection in the human neonate. Electron microscopic examination of lung tissue revealed the presence of herpesvirus which was identified with the fluorescent antibody technique as Herpes simplex virus type I. Tests with related sera of the herpes group (varicella, herpesvirus-B) revealed no specific immunoflourescence.

[The karyotypes of Colobus vellersus and of C. palliatus: comparison with Cercopithecidae and man]. / Le caryotype de Colobus vellerosus et de C. palliatus: comparaison avec les Cercopithecidae et l'homme.

The karyotypes of two species of African Colobidae, Colobus vellerosus and C. palliatus, as well that of their hybrid, are described and compared. The two species differ by four pericentric inversions, indicating species divergence a relatively long time ago. Chromosome banding analogies with Papioninae, Cercopithecinae, and man are described. A common origin for Papioninae, Cercopithecinae, and Colobidae is indisputable; but, there are no arguments for considering that a close relationship exists between Colobidae and Hylobatidae as suggested by some authors.

The unusual karyotype of the lesser kudu, Tragelaphus imberbis.

The chromosome set of the lesser kudu, Tragelaphus imberbis, consists of 38 elements in both sexes. In contrast to most other members of the bovid subfamily Tragelaphinae, both the X and the Y chromosomes are compound, having fused with identical autosomes from ancestors presumed to have higher chromosome numbers. From a comparison of the unusual sex chromosomal rearrangements that have occurred in this family, a hypothetical lineage has been derived. This family tree and the details of various banding studies in the lesser kudu are described.