A model for spontaneous B-lineage lymphomas in IgHμ-HOX11 transgenic mice

HOX11, a divergent homeodomain-containing transcription factor, was isolated from the breakpoint of the nonrandom t(10;14)(q24;q11) chromosome translocation found in human T cell acute lymphoblastic leukemias. The translocation places the HOX11 coding sequence under the transcriptional control of TCR α/δ regulatory elements, resulting in ectopic expression of a normal HOX11 protein in thymocytes. To investigate the oncogenic potential of HOX11, we targeted its expression in lymphocytes of transgenic mice by placing the human cellular DNA under the transcriptional control of Ig heavy chain or LCK regulatory sequences. Only IgHμ-HOX11 mice expressing low levels of HOX11 were viable. During their second year of life, all HOX11 transgenic mice became terminally ill with more than 75% developing large cell lymphomas in the spleen, which frequently disseminated to thymus, lymph nodes, and other nonhematopoietic tissues. Lymphoma cells were predominantly clonal IgM+IgD+ mature B cells. Repopulation of severe combined immunodeficient mice with cells from hyperplastic spleens indicated that the HOX11 tumor phenotype was transplantable. Before tumor development, expression of the transgene did not result in perturbations in lymphopoiesis; however, lymphoid hyperplasia involving the splenic marginal zones was present in 20% of spleens. Our studies provide direct evidence that expression of HOX11 in lymphocytes leads to malignant transformation. These mice are a useful model system to study mechanisms involved in transformation from B-lineage hyperplasia to malignant lymphoma and for testing novel approaches to therapy. They represent a novel animal model for non-Hodgkin’s lymphoma of peripheral mature B cell origin.

Distinct leukemia phenotypes in transgenic mice and different corepressor interactions generated by promyelocytic leukemia variant fusion genes PLZF–RARα and NPM–RARα

Acute promyelocytic leukemia (APL) is characterized by a specific chromosome translocation involving RARα and one of four fusion partners: PML, PLZF, NPM, and NuMA genes. To study the leukemogenic potential of the fusion genes in vivo, we generated transgenic mice with PLZF–RARα and NPM–RARα. PLZF–RARα transgenic animals developed chronic myeloid leukemia-like phenotypes at an early stage of life (within 3 months in five of six mice), whereas three NPM–RARα transgenic mice showed a spectrum of phenotypes from typical APL to chronic myeloid leukemia relatively late in life (from 12 to 15 months). In contrast to bone marrow cells from PLZF–RARα transgenic mice, those from NPM–RARα transgenic mice could be induced to differentiate by all-trans-retinoic acid (ATRA). We also studied RARE binding properties and interactions between nuclear corepressor SMRT and various fusion proteins in response to ATRA. Dissociation of SMRT from different receptors was observed at ATRA concentrations of 0.01 μM, 0.1 μM, and 1.0 μM for RARα–RXRα, NPM–RARα, and PML–RARα, respectively, but not observed for PLZF–RARα even in the presence of 10 μM ATRA. We also determined the expression of the tissue factor gene in transgenic mice, which was detected only in bone marrow cells of mice expressing the fusion genes. These data clearly establish the leukemogenic role of PLZF–RARα and NPM–RARα and the importance of fusion receptor/corepressor interactions in the pathogenesis as well as in determining different clinical phenotypes of APL.

Unveiling the molecular mechanism of BRCA2-RAD51 interaction to tackle cancer onset

Different kinds of lesions can occur to DNA, and among them, one of the most dangerous is the double strand breaks (DSBs). Actually, DSBs can result in mutations, chromosome translocation or deletion. For this kind of lesions, depending on cell cycle phase as well as DNA-end resection, cells have developed specific repair pathways. Among these the error-free homologous recombination (HR) plays a crucial role. HR takes place during S/G2 phases, since the sister chromatids can be used as homologous templates. In this process, hRAD51 and BRCA2 are key players. hRAD51 is a recombinase of 339 amino-acids highly conserved through evolution which displays an intrinsic tendency to form oligomeric structures. BRCA2 is a very large protein of 3418 amino-acids, essential for the recruitment and accumulation of hRAD51 in the nucleus repairing-foci. BRCA2 interacts with hRAD51 through eight, so-called, BRC repeats, composed of 35-40 amino-acids. Mutations within this region have been linked to an increased risk of ovarian cancer development. In particular, several reports highlighted that missense mutations within one BRC repeat can hamper BRCA2 activity. Considering the close homology between the BRC repeats, it is striking how these mutations cannot be counterbalanced by the other non-mutated repeats preserving the function and the interactions of BRCA2 with hRAD51. To date the only interaction that has been structurally elucidated, is the one taking place amid the fourth BRC repeat and hRAD51. Only very little biophysical information is available on the interaction of the other BRC repeats with hRAD51. This thesis aims at elucidating the mechanism of hRAD51-BRCA2 interaction, by means of biophysical and structural approaches.

Centric fusion in goats (Capra hircus): Identification of a 6/15 translocation by high resolution chromosome banding

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

X monosomy and balanced Robertsonian translocation in a girl with Turner Syndrome

We describe a case of X monosomy associated with a maternally inherited t(13;14) Robertsonian translocation in a girl with Turner syndrome. The girl's X chromosome was demonstrated to be maternally inherited, ruling out the hypothesis that the translocation exerted an interchromosomal effect on the origin of the monosomy. Chromosomes 13 and 14 showed biparental inheritance.

SYNAPTONEMAL COMPLEX-ANALYSIS IN GOATS CARRYING THE 5/15 ROBERTSONIAN TRANSLOCATION

Synaptonemal complexes were analysed by electron microscopy in 2 bucks heterozygous for the 5/15 Robertsonian translocation. The cis configuration (free homologous 5 and 15 chromosomes on the same side of the 5/15 translocated chromosome) was found in all 50 cells examined. This feature is considered a prerequisite for the development of balanced gametes. No association between the sex bivalent and trivalent was observed.

A rare non-Robertsonian translocation involving chromosomes 15 and 21

CONTEXTO:Translocações robertsonianas (TR) estão entre os rearranjos estruturais balanceados mais comuns em humanos e compreendem a fusão da cromatina completa do braço longo de dois cromossomos acrocêntricos. No entanto, são raras as translocações não Robertsonianas envolvendo esses cromossomos.RELATO DE CASO:Nós descrevemos uma translocação não balanceada de novo envolvendo os cromossomos 15 e 21. A recém-nascida era filha de uma mãe de 29 anos e de um pai de 42 anos, casal não consanguíneo. Os achados clínicos levaram ao diagnóstico de síndrome de Down (SD) com defeitos cardíacos congênitos graves (persistência do canal arterial e defeito do septo atrioventricular completo), além de baixos comprimento e peso ao nascimento (< 5o e < 10o percentil em curvas de medidas específicas para SD, respectivamente). A análise citogenética convencional revelou o cariótipo 46,XX,der(15)(15pter→15q26.2

Meiotic drive favors Robertsonian metacentric chromosomes in the common shrew (Sorex araneus, Insectivora, mammalia).

Meiotic drive has attracted much interest because it concerns the robustness of Mendelian segregation and its genetic and evolutionary stability. We studied chromosomal meiotic drive in the common shrew (Sorex araneus, Insectivora, Mammalia), which exhibits one of the most remarkable chromosomal polymorphisms within mammalian species. The open question of the evolutionary success of metacentric chromosomes (Robertsonian fusions) versus acrocentrics in the common shrew prompted us to test whether a segregation distortion in favor of metacentrics is present in female and/or male meiosis. Performing crosses under controlled laboratory conditions with animals from natural populations, we found a clear trend toward a segregation distortion in favor of metacentrics during male meiosis, two chromosome combinations (gm and jl) being significantly preferred over their acrocentric homologs. Apart for one Robertsonian fusion (hi), this trend was absent in female meiosis. We propose a model based on recombination events between twin acrocentrics to explain the difference in transmission ratios of the same metacentric in different sexes and unequal drive of particular metacentrics in the same sex. Pooled data for female and male meiosis revealed a trend toward stronger segregation distortion for larger metacentrics. This is partially in agreement with the frequency of metacentrics occurring in natural populations of a chromosome race showing a high degree of chromosomal polymorphism.

Sex chromosome evolution in fish: the formation of the neo-Y chromosome in Eigenmannia (Gymnotiformes)

Chromosomes of a species of Eigenmannia presenting a X1X1X2X2:X1X2Y sex chromosome system, resulting from a Y-autosome Robertsonian translocation, were analyzed using the C-banding technique, chromomycin A(3) (CMA(3)) and mithramycin (MM) staining and in situ digestion by the restriction endonuclease AluI. A comparison of the metacentric Y chromosome of males with the corresponding acrocentrics in females indicated that a C-band-positive, CMA(3)/MM-fluorescent and AluI digestion-resistant region had been lost during the process of translocation, resulting in a diminution of heterochromatin in the males. It is hypothesized that the presence of a smaller amount of G+C-rich heterochromatin in the sex chromosomes of the heteromorphic sex when compared with the homomorphic sex may be associated with the sex determination mechanism in this species and may be a more widely occurring phenomenon in fish with differentiated sex chromosomes than was initially thought.

ULTRASTRUCTURE OF THE GERMINATIVE EPITHELIUM IN A GOAT WITH A 5/15-ROBERTSONIAN TRANSLOCATION

The spermatogenesis of two goats bearing a 5/15 Robertsonian translocation was investigated by electron microscopy. There was no dramatic change in the morphology of the cells of the spermatic line. All cells of the seminiferous epithelium seemed quite normal at the ultrastructural level. However a certain disturbance in the cell localization and some morphological abnormalities involving nuclear structure were seen. Spermatocytes and spermatids normal in appearance were observed, but a great number of cells presented two or more nuclei. These cells were frequently seen to become degenerated during spermatogenesis. We believe that unbalanced spermatocytes degenerate during the process and only some spermatocytes succeed in fertilizing gametes.

Trisomy X and 1 29 translocation in infertile heifers

In a group of 12 Pitangueiras breed heifers exhibiting a high return rate to service, three were noted to be carriers of the 1 29 translocation. One of the heifers exhibited trisomy for the X-chromosome in addition to the 1 29 translocation. The appearance and external genitalia of the 1 29 T; trisomy X heifer were not altered, although on rectal examination the internal genitalia, including the ovaries, appeared similar to that of a prepubertal heifer. © 1987.

Distribution of a Robertsonian translocation in goats

Two hundred and five animals were cytogenetically studied. They were related to a male goat called 'Harald', imported from Switzerland, who was a t 5 15 chromosomic translocation carrier. 29.27% of the analyzed animals were heterozygous and 4.88% were homozygous. All carrying animals were found in Botucatu, Limeira and São Manuel city in Brazil. Descendants of this buck were sold in several regions of Brazil, and may have spread this aberration. © 1992.

Meiotic pairing of B chromosomes, multiple sexual system, and Robertsonian fusion in the red brocket deer Mazama americana (Mammalia, Cervidae)

Deer species of the genus Mazama show significant inter and intraspecific chromosomal variation due to the occurrence of rearrangements and B chromosomes. Given that carriers of aneuploidies and structural rearrangements often show anomalous chromosome pairings, we here performed a synaptonemal complex analysis to study chromosome pairing behavior in a red brocket deer (Mazama americana) individual that is heterozygous for a Robertsonian translocation, is a B chromosome carrier, and has a multiple sex chromosome system (XY1Y2). The synaptonemal complex in spermatocytes showed normal chromosome pairings for all chromosomes, including the autosomal and sex trivalents. The electromicrographs showed homology among B chromosomes since they formed bivalents, but they also appeared as univalents, indicating their anomalous behavior and non-Mendelian segregation. Thus, synaptonemal complex analysis is a useful tool to evaluate the role of B chromosomes and rearrangements during meiosis on the intraspecific chromosomal variation that is observed in the majority of Mazama species. © FUNPEC-RP.