Chromosomal localization of the gene for AA-type platelet-derived growth factor receptor (PDGFRA) in humans and mice

An update on molecular genetics of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GISTs) are the most common primary mesenchymal tumours of the gastrointestinal tract. Most of them show activating mutations of the genes coding for KIT or platelet-derived growth factor receptor alpha (PDGFRalpha), two receptor tyrosine kinases (RTKs). The RTK inhibitor Imatinib (Gleevec, Novartis, Switzerland), induces regression of the tumour. The level of response to treatment, together with other clinicopathological parameters is related to the type and site of the activating mutation, thus suggesting that these tumours should be classified according to the molecular context. This is confirmed also by the phenomenon of the resistance to treatment, which arises because of different mechanisms (second mutation, amplification, activation of other RTKs) and can be fought only by specific RTK inhibitors, that are at present under development. RTK activation involves an homogeneous transduction pathway whose components (MAPK, AKT, PI3K, mTOR and RAS) are possible targets of new molecular treatment. A new paradigm of classification integrating the classic pathological criteria with the molecular changes will permit personalised prognosis and treatment.

Foxn4--a new member of the forkhead gene family is expressed in the retina

We report the cloning and expression of a novel murine forkhead/winged helix family member--Foxn4--that is expressed during neural development in the retina, the ventral hindbrain and spinal cord and dorsal midbrain. Retinal Foxn4 expression is associated with the zone of proliferating progenitor cells. In the mouse mutant ocular retardation (or(J)), Foxn4 expression in the retina is significantly reduced and terminates prematurely.

Platelet-derived growth factor in human brain tumors

This paper initially reviews ligand and receptor systems for the PDGF family and the signalling systems they use as well as their role in neural developments. It then describes the putative role of this family in astrocytoma, meningioma, and pituitary adenoma pathogenesis. Potential therapies with receptor antagonists or dominant negative mutants are discussed in the final sections.

Use of fluorescence in situ hybridization and comparative genomic hybridization in the cytogenetic analysis of testicular germ cell tumors and uveal melanomas

Fluorescence in situ hybridization (FISH) with specific DNA probes and comparative genomic hybridization (CGH) are molecular cytogenetic methods that provide powerful supplementations of classical cancer cytogenetics. We present two examples of successful application of these new techniques in solid tumors in which basic information about specific cytogenetic aberrations had been gained previously by conventional karyotyping. In the first, testicular germ cell tumors (TGCT), FISH analysis allowed further characterization of the i(12p) marker chromosome. By CGH, chromosomal subregions that may harbor genes important for tumorigenesis or progression could be identified. In the second, uveal melanoma, CGH enabled a retrospective study in which monosomy 3 was statistically proved to be a relevant marker for poor prognosis.

Detection of chromosomal DNA gains and losses in testicular germ cell tumors by comparative genomic hybridization

To extend the results of conventional cytogenetic analysis of testicular germ cell tumors (TGCTs), we applied the new molecular cytogenetic method of comparative genomic hybridization (CGH), which enables the detection of chromosomal imbalances without the need for dividing cells. DNA from II TGCTs was studied by CGH. In all tumors examined, gain of 12p, mostly of the whole p arm, could be demonstrated. However, in three tumors, an amplification of 12p material restricted to the chromosomal bands 12p11.2-p12.1 was found. Further fluorescence in situ hybridization (FISH) analysis using a yeast artificial chromosome (YAC) that was previously mapped to that region revealed multiple copies of that chromosomal segment in interphase nuclei of these tumors. This finding is an important clue to the localization of candidate protooncogenes at 12p involved in TGCTs. Gains of small chromosomal regions at 2p, 4q, 6p, and 19p were also detected recurrently. Furthermore, gains of chromosomes 8, 14, 21, and X as well as loss of chromosome 13 were frequent findings. In conclusion, CGH provides new insights into genetic alterations of TGCTs. By using CGH, chromosomal subregions could be identified that may harbor genes involved in the pathogenesis of this malignancy.

Structural analysis of chromosomal rearrangements associated with the developmental mutations Ph, W19H, and Rw on mouse chromosome 5

We are studying the chromosomal structure of three developmental mutations, dominant spotting (W), patch (Ph), and rump white (Rw) on mouse chromosome 5. These mutations are clustered in a region containing three genes encoding tyrosine kinase receptors (Kit, Pdgfra, and Flk1). Using probes for these genes and for a closely linked locus, D5Mn125, we established a high-resolution physical map covering approximately 2.8 Mb. The entire chromosomal segment mapped in this study is deleted in the W19H mutation. The map indicates the position of the Ph deletion, which encompasses not more than 400 kb around and including the Pdgfra gene. The map also places the distal breakpoint of the Rw inversion to a limited chromosomal segment between Kit and Pdgfra. In light of the structure of the Ph-W-Rw region, we interpret the previously published complementation analyses as indicating that the pigmentation defect in Rw/+ heterozygotes could be due to the disruption of Kit and/or Pdgfra regulatory sequences, whereas the gene(s) responsible for the recessive lethality of Rw/Rw embryos is not closely linked to the Ph and W loci and maps proximally to the W19H deletion. The structural analysis of chromosomal rearrangements associated with W19H, Ph, and Rw combined with the high-resolution physical mapping points the way toward the definition of these mutations in molecular terms and isolation of homologous genes on human chromosome 4.

The gamma phosphorylase kinase gene, Phkg, maps to mouse chromosome 5 near Gus

Phosphorylase kinase is a multimeric regulatory enzyme in the glycogenolytic pathway. Interest in various types of phosphorylase kinase enzyme deficiency has focused attention on cloning and mapping the enzyme subunits. We report the mapping of the catalytic gamma subunit gene, Phkg, to mouse Chromosome (Chr) 5 near beta-glucuronidase (Gus), between alpha fetoprotein (Afp) and erythropoietin (Epo). In addition, PCR-based polymorphism assays have been developed for the human (EPO) and mouse erythropoietin genes, and a unique recombinant inbred strain distribution pattern has been defined for Epo, a distal anchor marker on mouse Chr 5.

The c-kit proto-oncogene in normal and malignant human hematopoiesis

The c-kit proto-oncogene encodes a tyrosine kinase receptor (KIT) which is expressed on many types of human cells. Numerous studies attest to the importance of the c-kit receptor and its ligand, known variously as stem cell factor (SCF), mast cell growth factor (MGF), Steel factor (SF), or kit ligand (KL) (the nomenclature we prefer), in the development of human hematopoietic cells. KL, which is produced in membrane-bound and soluble forms by bone marrow stromal cells, acts on pre-colony forming units (pre-CFU) and CFU cells. In synergistic combination with other cytokines, KL enhances the growth of myeloid progenitor cells. However, using an antisense oligodeoxynucleotide strategy to disrupt c-kit function, we have demonstrated that the KL-KIT complex is of greatest importance for generation and/or proliferation of normal human erythropoietic progenitor cells. In malignant hematopoietic cells, the complex also appears to be important for growth of granulocyte/macrophage (GM) CFU as well.

Human cyclin B1 gene (CCNB1) assigned to chromosome 5 (q13-qter)

Cyclins play an important role in cell cycle regulation. At least five classes of cyclins have been identified--A, B, C, D, and E. B cyclins are generally of two types in most organisms--B1 and B2. We have mapped the gene for human cyclin B1 (CCNB1) to human chromosome 5 (region q13-qter) by Southern blot analysis of human x Chinese hamster somatic cell hybrid panels. Many more cyclin B-related sequences have been identified in the mouse (Cycb-1 to Cycb-10) and have been mapped to chromosomes 4, 5, 7, 8, 13, 14, 15, and 17. Based on our mapping of human CCNB1 and known evolutionary conservation of chromosomal regions, we propose that the homologous cyclin B1 locus, Cycb-4, on mouse chromosome 13 is a functional gene.