ABSTRACT
One obvious phenotype of tumor cells is the lack of terminal differentiation. We previously classified rhabdomyosarcoma cell lines as having either a recessive or a dominant nondifferentiating phenotype. To study the genetic basis of the dominant nondifferentiating phenotype, we utilized microcell fusion to transfer chromosomes from rhabdomyosarcoma cells into C2C12 myoblasts. Transfer of a derivative chromosome 14 inhibits differentiation. The derivative chromosome 14 contains a DNA amplification. MDM2 is amplified and overexpressed in these nondifferentiating hybrids and in the parental rhabdomyosarcoma. Forced expression of MDM2 inhibits MyoD-dependent transcription. Expression of antisense MDM2 restores MyoD-dependent transcriptional activity. We conclude that amplification and overexpression of MDM2 inhibit MyoD function, resulting in a dominant nondifferentiating phenotype.
Subject(s)
Gene Amplification , Hybrid Cells/pathology , Muscle Proteins/physiology , Muscles/cytology , MyoD Protein/antagonists & inhibitors , Neoplasm Proteins/physiology , Nuclear Proteins , Proto-Oncogene Proteins/physiology , Rhabdomyosarcoma/genetics , Animals , Cell Cycle , Cell Differentiation , Cell Fusion , Chromosomes, Human, Pair 14/genetics , Epistasis, Genetic , Gene Expression Regulation , Humans , Mice , Muscle Proteins/genetics , MyoD Protein/physiology , Neoplasm Proteins/genetics , Phenotype , Polymerase Chain Reaction , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins c-mdm2 , Rhabdomyosarcoma/pathology , Transcription, Genetic , Tumor Cells, CulturedABSTRACT
A genetic linkage map for loblolly pine (Pinus taeda L.) was constructed using segregation data from a three-generation outbred pedigree consisting of four grandparents, two parents, and 95 F2 progeny. The map was based predominantly on restriction fragment length polymorphism (RFLP) loci detected by cDNA probes. Sixty-five cDNA and three genomic DNA probes revealed 90 RFLP loci. Six polymorphic isozyme loci were also scored. One-fourth (24%) of the cDNA probes detected more than 1 segregating locus, an indication that multigene families are common in pines. As many as six alleles were observed at a single segregating locus among grandparents and it was not unusual for the progeny to segregate for three or four alleles per locus. Multipoint linkage analysis placed 73 RFLP and 2 isozyme loci into 20 linkage groups; the remaining 17 RFLP and 4 isozyme loci were unlinked. The mapped RFLP probes provide a new set of codominant markers for genetic analyses in loblolly pine.
