Somatic Alleles Research Articles

Advances in the molecular characterization of Philadelphia-negative chronic myeloproliferative disorders

The identification and characterization of somatic disease alleles have greatly improved our understanding of the molecular pathogenesis of myeloproliferative disorders. This review focuses on recent studies investigating the role of activated tyrosine kinase signaling in the Philadelphia chromosome negative myeloproliferative disorders. Previously identified tyrosine kinase mutations in chronic myeloid leukemia and other myeloproliferative disorders suggested the possibility that polycythemia vera, essential thrombocythemia and primary myelofibrosis are also caused by activated tyrosine kinases. Recent studies identified an activating mutation in the JAK2 tyrosine kinase (JAK2V617F) in most patients with polycythemia vera and in approximately half of those with essential thrombocythemia and primary myelofibrosis. More recently, activating mutations in the thrombopoietin receptor and in JAK2 exon 12 have been identified in JAK2V617F negative myeloproliferative disorders. The discovery of activated tyrosine kinases in the majority of patients with polycythemia vera, essential thrombocythemia and primary myelofibrosis has diagnostic and pathogenetic implications. Subsequent studies are needed to elucidate the cause of myeloproliferative disorders without known disease alleles and to determine if inhibition of JAK2 signaling has therapeutic efficacy in the treatment of polycythemia vera, essential thrombocythemia and primary myelofibrosis.

Association of the bovine major histocompatibility complex (BoLA) BoLA-DRB3 gene with fat and protein production and somatic cell score in Brazilian Gyr dairy cattle (Bos indicus)

The effect of the bovine major histocompatibility complex (BoLA) locus on animal health may be due to a direct action of its alleles on immune functions, whereas its indirect effect on production traits might be explained by the better general health conditions of more productive animals. In the present study, the BoLA-DRB3 gene was investigated in 1058 cows belonging to seven Brazilian Gyr Dairy herds (Bos indicus, Zebu cattle). A total of 37 alleles were identified, 15 of them described for the first time in a Zebu breed. A highly significant association (p < 0.02) was observed between allele *54 and a decrease (-26.1 kg) in milk protein yield and there was a significant association (p < 0.05) between this allele and lower (-26.07 kg) milk fat yield. There was also a significant association (p < 0.05) between allele *6 and decreased (-12.47 kg) milk protein and allele *7 and increased (12.72 kg) milk protein. There were also indications of association (p < 0.10) between somatic cell score (SCS) and alleles *3 (SCS increased by 0.54 units) and *31 (SCS increased by 0.46 units). The highly significant association of allele *54 with lower protein yield suggests the possible use of this allele in marker-assisted selection programs.

Alfalfa (Medicago sativa) Somatic Embryogenesis: Genetic Control and Introduction of Favourable Alleles into Elite Argentinean Germplasm

The objectives of this work were to isolate regenerative genotypes from the alfalfa Canadian cultivar ‘Rambler’ to perform the genetic analysis of somatic embryogenesis in this species and to introgress regeneration favourable alleles into Argentinean alfalfa elite germplasm. For regeneration inheritance studies, greenhouse established plants from a cross between a ‘Rambler’ derived regenerative clone and a non-regenerative Argentinean clone as well as self-pollinated progenies of these clones were analyzed. The results showed that somatic embryogenesis is under the control of two complementary genes. The introgression of somatic embryogenesis favourable alleles was performed using two populations derived from crosses between regenerative clones, obtained in the first step of this work, and non-regenerative clones of Argentinean alfalfa elite populations. Twenty-seven plants obtained through this process showed somatic embryogenesis ability. Two of them, designated as INTA R1 and INTA R2, exhibited a high regeneration capacity as well as high regeneration multiplicity. Our results demonstrate that ‘Rambler’ derived somatic embryogenesis favourable alleles are successfully expressed in Argentinean elite alfalfa genetic background rendering it suitable for tissue culture-based breeding methodologies.

Genomic instability and endoreduplication triggered by RAD17 deletion.

Cell cycle checkpoints are critical for genomic stability. Rad17, a component of the checkpoint clamp loader complex (Rad17/Rfc2-5), is required for the response to DNA damage and replication stress. To explore the role of Rad17 in the maintenance of genomic integrity, we established somatic conditional alleles of RAD17 in human cells. We find that RAD17 is not only important for the Atr-mediated checkpoint but is also essential for cell viability. Cells lacking RAD17 exhibited acute chromosomal aberrations and underwent endoreduplication at a high rate. Therefore, RAD17 links the checkpoint to ploidy control and is essential for the maintenance of chromosomal stability.

Hereditary and sporadic ovarian cancer: genetic testing and clinical implications (review).

The two most common forms of hereditary ovarian cancer are: the breast ovarian cancer syndrome, and ovarian cancer associated with HNPCC (hereditary nonpolyposis colorectal cancer) syndrome. Studies have shown that these diseases may be associated with mutations in a number of tumor suppressor genes, mainly BRCA1 and BRCA2. Malfunction of the protein products of these genes have also been found to be involved in sporadic ovarian cancer, which makes up the majority of ovarian cancer cases. HNPCC-ovarian cancer associated families reveal frequent mutations in at least four genes (hMSH2, hMLH1, hPMS1, and hPMS2) involved in the repair of mismatched DNA. With ovarian cancer being such an important health issue, the push is on to design reliable screening tests to detect defective inherited or somatic alleles in individual carriers. So far, most progress has been demonstrated in those patients with family histories of the disease who are at increased risk. The ramifications of such research may impact a variety of scientific, clinical, legal, ethical, and psychosocial issues. In addition to current treatment modalities, positive results of these tests may indicate the need for increased clinical surveillance, prophylactic treatment, and genetic counseling of patients on an individual basis. It remains to be seen whether the technology can be made reliable enough to not only benefit high-risk individuals but also the general population.

A Tetranucleotide Repeat Mouse Minisatellite Displaying Substantial Somatic Instability during Early Preimplantation Development

The highly variable mouse minisatellite Hm-2 is located on chromosome 9 and consists of GGCA tetranucleotide repeats with alleles containing up to 5000 repeat units. This locus is unstable with a germline mutation rate to new length alleles of at least 3.6% per gamete. Hm-2 also shows substantial somatic instability, producing mutational mosaicism detectable in 20% of adult mice. Analysis of allele dosage in mice carrying somatic mutations, plus studies of mosaicism in mouse embryos and extraembryonic tissues, suggests that somatic mutant alleles preferentially arise during preimplantation development and particularly during the first two cell divisions after fertilization.

Molecular cloning and characterization of iojap (ij), a pattern striping gene of maize.

Iojap (ij) is a recessive striped mutant of maize affecting the development of plastids in a local and position-dependent manner on the leaves. The ij-affected plastids are transmitted to some of the progeny even when the function of the nuclear gene is restored. Developmental defects during embryogenesis and leaf proliferation are other phenotypic characteristics of ij. The extent of striping and the degree of developmental arrest in ij depend upon genetic background. To understand the diverse and unique phenotypic expression of ij, a transposon tagging experiment has been conducted using Robertson's Mutator (Mu). A new ij mutant was obtained from crosses of the reference allele of (ij-ref) to Mu lines. Subsequent genetic and molecular studies showed that the mutant carried a new ij allele (ij-mum1) from the Mu lines and contained a Mu1 element that cosegregated with the iojap phenotype. A 6.0 kb EcoRI genomic DNA fragment containing the Mu1 element was cloned. ij-ref is unstable, and revertants (Ij-Rev) have been obtained. Using the flanking DNA from the genomic clone as a probe, DNA polymorphisms were detected between ij-ref and these revertants. Further, transcripts were restored to the normal level in Ij-Rev seedlings. Comparison of genomic DNA clones from ij-ref, ij-mum1 and Ij indicated that the ij-ref allele contained 1.5 kb of additional DNA related to a transposable element, Ds. Germinal and somatic revertant alleles were derived by excision of this 1.5 kb element from ij-ref. The structure of the Ij gene and the DNA sequence of its transcribed region were determined. The Ij gene encodes a 24.8 kDa protein that showed no significant sequence similarity with proteins listed in databases.

The context of T cell receptor beta chain genes among wild and inbred mouse species.

The organization of the mouse T cell receptor (TCR) genes has been extensively reviewed (Hood 1985). The structure of the TCR alpha (α), beta (β) and gamma (γ) genes is analogous to the immunoglobulin (Ig) gene organization in the mouse. This homology probably reflects similar requirements for diversity in binding antigen. The major source of diversity for Ig genes comes from (1) multiple germline variable (VK, Vλ and VH) regions, diversity (DH) regions and joining (Jj(, JX and Jh) elements; (2) combinatorial joining of V, D and J; (3) somatic mutation and (4) multiple alleles present in inbred and wild mice (Tonegawa 1983). Preliminary findings among the TCRα and β chains of the mouse inbred strains indicate fewer germline variable (VTα, VTβ) genes are available (30–40 each) (Becker 1985; Barth 1985; Behlke 1985a) than VK and VH genes (100–300 each) (Valbuena 1978; Cory 1981; Brodeur and Riblet 1984). Furthermore, studies indicate that the frequency of somatic mutation in TCRα and TCRβ chain genes although present is as much as 10% or less than that of Ig genes (Augustin and Sim 1984; Ikuta 1985).