RESUMO
A fusion complementary DNA in the T cell line HSB-2 elucidates a provocative mechanism for the disruption of the putative hematopoietic transcription factor SCL. The fusion cDNA results from an interstitial deletion between a previously unknown locus, SIL (SCL interrupting locus), and the 5' untranslated region of SCL. Similar to 1;14 translocations, this deletion disrupts the SCL 5' regulatory region. This event is probably mediated by V-(D)-J recombinase activity, although neither locus is an immunoglobulin or a T cell receptor. Two other T cell lines, CEM and RPMI 8402, have essentially identical deletions. Thus, in lymphocytes, growth-affecting genes other than immune receptors risk rearrangements.
Assuntos
DNA Nucleotidiltransferases/metabolismo , Rearranjo Gênico , Fatores de Transcrição/genética , Sequência de Bases , Fatores de Transcrição Hélice-Alça-Hélice Básicos , Linhagem Celular , Deleção Cromossômica , Proteínas de Ligação a DNA/genética , Éxons , Humanos , Dados de Sequência Molecular , Sondas de Oligonucleotídeos , Plasmídeos , Proteínas Proto-Oncogênicas/genética , Mapeamento por Restrição , Homologia de Sequência do Ácido Nucleico , Proteína 1 de Leucemia Linfocítica Aguda de Células T , Linfócitos T , VDJ RecombinasesRESUMO
The leukemic cells and derivative cell line from a 74-year-old male with T-cell acute lymphoblastic leukemia showed chromosomal abnormalities including a t(14;14)(q11.2;q32). This translocation is characteristic of a variety of T-cell malignancies, particularly T-cell prolymphocytic leukemia and the clonal proliferations of peripheral T cells in patients with ataxia-telangiectasia. Using DNA probes that spanned the T-cell receptor alpha chain (TCRA) joining (J) locus, the DNA rearrangement caused by the translocation was identified, cloned, and sequenced. The breakpoint shows site-specific juxtaposition of a TCRA joining segment and DNA from a region of 14q32 centromeric to the immunoglobulin heavy chain locus. Comparison of restriction map and nucleotide sequence from this translocation with other related chromosomal breakpoints suggests a dispersion of breakpoints throughout the 14q32 region.
Assuntos
Cromossomos Humanos Par 14 , Leucemia-Linfoma de Células T do Adulto/genética , Translocação Genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Southern Blotting , Bandeamento Cromossômico , Clonagem Molecular , Cricetinae , Sondas de DNA , Rearranjo Gênico da Cadeia alfa dos Receptores de Antígenos dos Linfócitos T/genética , Humanos , Células Híbridas , Dados de Sequência Molecular , Polimorfismo de Fragmento de Restrição , Mapeamento por Restrição , Células Tumorais CultivadasRESUMO
The Sil gene encodes a cytosolic protein required for mouse embryonic midline and left/right axial development. Based on the phenotype of Sil mutant embryos, we hypothesized that Sil may be required for the activity of Sonic Hedgehog (Shh), a secreted signaling molecule also critically important for the development of the embryonic axes and found mutated in multiple types of cancer. Here we tested the genetic interaction between Sil and the Shh pathway by generating and analyzing embryos carrying mutations in both Sil and Patched (Ptch), a Shh receptor that normally inhibits the signaling pathway in the absence of ligand and when mutated leads to constitutive activation of the pathway. We find that Sil(-/-) Ptch(-/-) embryos do not activate the Shh pathway and instead have a phenotype indistinguishable from Sil(-/-) embryos, in which there is a loss of activity of Shh. These results provide genetic evidence that Sil is an essential component of the Shh response, acting downstream to Ptch.
Assuntos
Embrião de Mamíferos/metabolismo , Proteínas de Membrana/genética , Proteínas de Fusão Oncogênica , Proteínas/genética , Proteínas/metabolismo , Transdução de Sinais , Transativadores/metabolismo , Animais , Morte Celular/genética , Cruzamentos Genéticos , Embrião de Mamíferos/embriologia , Epistasia Genética , Feminino , Deleção de Genes , Regulação da Expressão Gênica no Desenvolvimento , Genótipo , Cabeça/embriologia , Proteínas Hedgehog , Hibridização In Situ , Marcação In Situ das Extremidades Cortadas , Peptídeos e Proteínas de Sinalização Intracelular , Masculino , Proteínas de Membrana/deficiência , Camundongos , Camundongos Knockout , Receptores Patched , Receptor Patched-1 , RNA Mensageiro/análise , RNA Mensageiro/genética , Receptores de Superfície CelularRESUMO
The SIL gene was discovered at the site of a cancer-associated interstitial deletion in which its promoter assumed the regulation of a second gene, SCL. The human SIL gene encodes a 1287-amino acid cytosolic protein that has been found to be highly conserved in the mouse. SIL is expressed in proliferating cells and is down-regulated when cellular proliferation ceases because of serum starvation, contact inhibition, or induction of terminal differentiation. SIL is induced within 1 h of stimulation by 20% serum in growth-arrested 3T3 cells. This induction is independent of protein synthesis because "superinduction" is observed in the presence of the protein synthesis inhibitor cyclohexamide. Thus, SIL is an immediate-early gene. Upon release from serum starvation of 3T3 fibroblasts, SIL mRNA and protein levels display a biphasic pattern during the first cell cycle. In contrast, in exponentially growing EL4 lymphoblasts, SIL mRNA is stable throughout the cell cycle, whereas SIL protein accumulates into G2 phase and then falls precipitously at the completion of the cell cycle. This pattern of cell cycle expression suggests that SIL may play an important role in cellular growth and proliferation.
Assuntos
Proteínas de Fusão Oncogênica , Biossíntese de Proteínas , Animais , Células COS , Ciclo Celular , Diferenciação Celular , Divisão Celular , Regulação para Baixo , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Camundongos , RNA Mensageiro/metabolismoRESUMO
The establishment of the main body axis and the determination of left-right asymmetry are fundamental aspects of vertebrate embryonic development. A link between these processes has been revealed by the frequent finding of midline defects in humans with left-right anomalies. This association is also seen in a number of mutations in mouse and zebrafish, and in experimentally manipulated Xenopus embryos. However, the severity of laterality defects accompanying abnormal midline development varies, and the molecular basis for this variation is unknown. Here we show that mouse embryos lacking the early-response gene SIL have axial midline defects, a block in midline Sonic hedgehog (Shh) signalling and randomized cardiac looping. Comparison with Shh mutant embryos, which have axial defects but normal cardiac looping, indicates that the consequences of abnormal midline development for left-right patterning depend on the time of onset, duration and severity of disruption of the normal asymmetric patterns of expression of nodal, lefty-2 and Pitx2.