Humans with inherited mutations in BRCA2 are at increased risk for developing breast and ovarian cancer; however, the relationship between BRCA2 mutation and these cancers is not understood. Studies of Brca2 mutation by gene targeting in mice are limited, given that homozygous Brca2 mutation typically leads to early embryonic lethality. We established a zebrafish line with a nonsense mutation in brca2 exon 11 ( brca2 Q658X ), a mutation similar in location and type to BRCA2 mutations found in humans with hereditary breast and ovarian cancer. brca2 Q658X homozygous zebrafish are viable and survive to adulthood; however, juvenile homozygotes fail to develop ovaries during sexual differentiation. Instead, brca2 Q658X homozygotes develop as infertile males with meiotic arrest in spermatocytes. Germ cell migration to the embryonic gonadal ridge is unimpaired in brca2 Q658X homozygotes; thus, failure of ovarian development is not due to defects in early establishment of the embryonic gonad. Homozygous tp53 mutation rescues ovarian development in brca2 Q658X homozygous zebrafish, reflecting the importance of germ cell apoptosis in gonad morphogenesis. Adult brca2 Q658X homozygous zebrafish are predisposed to testicular neoplasias. In addition, tumorigenesis in multiple tissues is significantly accelerated in combination with homozygous tp53 mutation in both brca2 Q658X homozygous and brca2 Q658X heterozygous zebrafish. These studies reveal critical roles for brca2 in ovarian development and tumorigenesis in reproductive tissues.

Acute lymphoblastic leukemia (ALL) is a clonal disease that evolves through the accrual of genetic rearrangements and͞or mutations within the dominant clone. The TEL-AML1 (ETV6-RUNX1) fusion in precursor-B (pre-B) ALL is the most common genetic rearrangement in childhood cancer; however, the cellular origin and the molecular pathogenesis of TEL-AML1-induced leukemia have not been identified. To study the origin of TEL-AML1-induced ALL, we generated transgenic zebrafish expressing TEL-AML1 either ubiquitously or in lymphoid progenitors. TEL-AML1 expression in all lineages, but not lymphoid-restricted expression, led to progenitor cell expansion that evolved into oligoclonal B-lineage ALL in 3% of the transgenic zebrafish. This leukemia was transplantable to conditioned wildtype recipients. We demonstrate that TEL-AML1 induces a B cell differentiation arrest, and that leukemia development is associated with loss of TEL expression and elevated Bcl2͞Bax ratio. The TEL-AML1 transgenic zebrafish models human pre-B ALL, identifies the molecular pathways associated with leukemia development, and serves as the foundation for subsequent genetic screens to identify modifiers and leukemia therapeutic targets.stem cell ͉ translocation ͉ childhood cancer ͉ genetics T he TEL-AML1 fusion generated by the t(12, 21)(p13;q22) chromosomal translocation is present in 25% of childhood pre-B acute lymphoblastic leukemia (ALL), making it the most common genetic rearrangement in childhood cancer (1-3). The translocation fuses the first five exons of the Ets transcription factor TEL (also known as ETV6) in-frame to nearly the entire AML1 gene (also known as RUNX1). Retrospective studies in twins with pre-B ALL, as well as Guthrie cards studies from 567 normal newborns (4), reveal that the TEL-AML1 fusion occurs in utero, with a protracted time course for leukemia development (5, 6).Murine studies involving TEL-AML1 suggest that this fusion protein confers a low transforming ability. Transgenic mice expressing TEL-AML1 from the Ig heavy chain promoter (E) did not develop any hematological disorder (7). Mice transplanted with bone marrow cells transduced with retroviral vectors expressing TEL-AML1 developed a preleukemic state without occult leukemia (8-10). The incidence of leukemia in such mice increased only in the presence of cooperating mutations (11).The cell initially transformed by TEL-AML1 remains to be elucidated; however, in ALL patients, the TEL-AML1 fusion event precedes differentiation of lymphoid progenitors to pre-B cells (12). This finding confines the origin of pre-B ALL to a B-lineage restricted progenitor(s) (4) or a multipotent hematopoietic stem cell (HSC) with preferential B-lymphoid clonal expansion (13).We used the zebrafish to study TEL-AML1 leukemogenesis for several reasons. First, the zebrafish has well conserved genetic processes controlling hematopoesis (14, 15). Second, zebrafish develop tumors that are histologically similar to human tumors (16)(17)(18)(19)(20). The lymphoid expression of mouse c-Myc led to...

SUMMARYBackground: There are no management criteria for optimum out-patient care in mild-to-moderate acute colonic diverticulitis. Aim: To enable such patients to be managed in an outpatient setting, by establishing criteria and treatment protocols. Methods:We conducted an open trial and follow-up study from 1997 to 2002. On the basis of ultrasonography, we defined and categorized mild-to-moderate acute colonic diverticulitis ranging from limited inflammation within diverticulum to an abscess < 2 cm in diameter. Subjects were treated as out-patients and

Zebrafish is a powerful vertebrate model system for using forward genetics to elucidate mechanisms of early development. We have used chemical mutagenesis to screen for mutants that show defects in the CNS. Here we describe the isolation of the bap28 mutation that leads to abnormalities in the brain starting at midsomitogenesis stages. Mutant embryos display excess apoptosis primarily in the central nervous system (CNS) and die by days 6 -7 after fertilization. The mutation was positionally cloned and shown to affect a gene that encodes a large protein with high similarity to the uncharacterized human protein BAP28 and lower similarity to yeast Utp10. Utp10 is a component of a nucleolar U3 small nucleolar RNA-containing RNP complex that is required for transcription of ribosomal DNA and for processing of 18 S rRNA. We show that zebrafish Bap28 likewise is required for rRNA transcription and processing, with a major effect on 18 S rRNA maturation. We suggest that bap28 is required for cell survival in the CNS through its role in rRNA synthesis and processing. Inhibition of p53 protein expression in bap28 mutants led to embryos with morphologically normal appearance, suggesting that p53 is involved in triggering apoptosis in the bap28 mutant CNS. The bap28 mutation provides a genetic approach to study the role of ribosome biogenesis in the development of a vertebrate embryo.Cell growth and proliferation in vertebrates must be synchronized with differentiation because cells usually withdraw from the cell cycle before terminal differentiation. Deregulation of these processes can lead to hypertrophy, apoptosis, or cancer. Such coordinate control requires the production of proteins in proportion to the rate of proliferation and increases in cell size. Thus, ribosome biogenesis is a tightly regulated process that involves many events including rRNA transcription, processing, modification, and folding, the coordinated synthesis of ribosomal proteins, and the assembly and export of the ribosomal particles. This process has been studied most extensively in yeast because of the powerful genetic and biochemical tools available in this organism.The steps for rRNA synthesis and maturation are complicated processes that are regulated by protein complexes at different levels. RNA polymerase I and cofactors transcribe the multicopy rRNA genes to produce a large rRNA precursor that contains the 18 S, 5.8 S, and 28 S rRNA sequences as well as spacer regions. External transcribed spacers (ETS) 3 are located at both the 5Ј and 3Ј ends of the pre-rRNAs, and two internal transcribed spacers (ITS) lie between the 18, 5.8, and 28 S sequences. The pre-rRNA undergoes multiple modifications and cleavages to generate the mature forms. This overall pattern of rRNA synthesis and processing is well conserved among eukaryotes, but the specific order of processing steps and the length of spacers and to a lesser extent of mature rRNAs varies considerably. In Saccharomyces cerevisiae, cleavage in the ETS followed by cleavages in the ITS1 generat...