The long-term goal of these studies is to identify tumor suppressor genes which are lost on inactivated in medulloblastomas. Cytogenetic and restriction fragment length polymorphism (RFLP) analyses have demonstrated loss of chromosomal region 17p in a subset of medulloblastomas which suggests that a suppressor gene normally located in this region may be important in these tumors. Although the TP53 gene is located within this deleted region point mutations of this gene are uncommon in medulloblastomas which suggests that either a different type of TP53 alteration is involved in these tumors or that the loss of 17p is targeting a previously undescribed tumor suppressor gene in this location. The following aims have been generated to answer this question.
AIM 1). Specific chromosomes and chromosomal regions that are deleted in medulloblastoma will be identified by allelotyping, using both minisatellite probes and analysis of microsatellite sequences by polymerase chain reaction (PCR), and karyotyping. These studies will establish the incidence and specificity of 17p loss as compared to other chromosomes and will identify additional chromosomal regions, the loss of which is important in medulloblastomas.
AIM 2). The TP53 will be analyzed in medulloblastomas to exclude the possibility that it is the target of 17p loss in these tumors. Specifically, gross rearrangements and deletions will be analyzed by Southern blotting, expression of the gene will be determined by Northern analysis, immunohistochemical studies will be performed to evaluate expression of the TP53 protein, and mutations will be sought by sequencing.
AIM 3). This aim will be focused on the isolation of the region harboring the 17p suppressor gene in medulloblastoma. Polymorphic probes will be isolated from a human chromosome 17 genomic library, and dinucleotide repeats on 17p will be defined. These probes will be regionally mapped on chromosome 17p, and used to define a small region of consistent loss in medulloblastomas by RFLP analysis. The definition of the regional 17p loss will provide the basis for eventual identification of the suppressor gene in that location. These comprehensive studies will determine whether the loss, mutation, or inactivation of known tumor suppressor gene TP53 is critical to the pathogenesis of medulloblastomas. In additionl regions of chromosomal loss will be narrowly defined on 17p and other chromosomes which are lost in these tumors will be determined forming the basis for the isolation and characterization of tumor suppressor genes. Characterization of such genes and their products will help to elucidate the mechanisms of growth control which are operative in normal and neoplastic cells and which are important in development, differentiation,a nd in regulation of cells in repair and regeneration. Gene probes emerging from these studies can be used to detect specific genetic alterations in medulloblastomas as well as in the tumors and the products of these genes can be used for the preparation of specific antibodies which are potentially useful in clinical diagnosis and therapy.
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