RAG蛋白在V（D）J重组中的作用

V（D）J重组分为两步,第一步是对特定DNA序列的识别和切割,第二步是断理解末端的解离和重接。V（D）J重组过程中的切割是由RAG蛋白介导的,RAG蛋白在第二阶段起什么样的作用还是一个模糊的问题,但目前已有实验显示RAG蛋白在末端重接反应中亦起着重要的结构性（或许还有催化性）作用。RAG蛋白激活V（D）J重组的活性还受其它一些因素的调节。所有这些都揭示RAG蛋白在其他因素辅助下参与了V（D）J重组的全过程。     

RAG1-mediated ubiquitylation of histone H3 is required for chromosomal V(D)J recombination

RAG1 and RAG2 proteins are key components in V(D)J recombination. The core region of RAG1 is capable of catalyzing the recombination reaction; however, the biological function of non-core RAG1 remains largely unknown. Here, we show that in a murine-model carrying the RAG1 ring-finger conserved cysteine residue mutation (C325Y), V(D)J recombination was abrogated at the cleavage step, and this effect was accompanied by decreased mono-ubiquitylation of histone H3. Further analyses suggest that un-ubiquitylated histone H3 restrains RAG1 to the chromatin by interacting with the N-terminal 218 amino acids of RAG1. Our data provide evidence for a model in which ubiquitylation of histone H3 mediated by the ring-finger domain of RAG1 triggers the release of RAG1, thus allowing its transition into the cleavage phase. Collectively, our findings reveal that the non-core region of RAG1 facilitates chromosomal V(D)J recombination in a ubiquitylation-dependent pathway.     

Paternal reciprocal translocation t(11;16)(p13;q24.3) in a Silver-Russel syndrome patient

We describe a 7-month-old male child with Silver-Russel syndrome (SRS) phenotype, presented with two major clinical features: low birth weight, short stature, and minor features, such as macrocephaly, clinodactyly, essential for the diagnosis of SRS. Routine cytogenetic studies with GTG-banding showed 46,XY,t(11;16)(p13;q24.3). Fluorescence in situ hybridisation (FISH) with single copy probes BAC (11p13) and PAC (16q24.3), showed a reciprocal translocation. Chromosomal analysis of the mother was normal and the phenotypically normal father had apparently identical translocation t(11;16)(p13;q24.3). The disruption of growth factor genes at 11p and 16q breakpoint regions due to reciprocal translocation in the father might have caused SRS phenotype in the child.     

Complex translocation t(9;21)(9;22)(q12p13)(q12q11) in the family of a child with 9p trisomy syndrome

Summary Leukocyte peroxidase activity was estimated in 5 patients with the juvenile form of neuronal ceroid lipofuscinosis (Spielmeyer-Vogt's disease) and in 15 healthy controls. In contradiction to recent reports normal activity of p-phenylene diamine mediated peroxidase was found in the patients. The possible role of contamination of the white cell preparation with hemoglobin is discussed.     

A novel translocation,t(9;21)(q13;q22) rearranging the RUNX1 gene in acute myelomonocytic leukemia

A novel translocation t(9;21)(q13;q22) associated with trisomy 4 has been detected in a patient with acute myelomonocytic leukemia (AML,M4) in relapse. The chromosomal translocation results in rearrangement of the RUNX1 gene at 21q22. The DNA sequence rearranged on chromosome 9 remains unidentified. The diversity of the partners involved in translocations implicating RUNX1 suggests that the functional consequences of the abnormality are more due to the truncation of RUNX1 than to the identity of its partner in the rearrangement.     

Modulation of RAG/DNA complex by HSP70 in V(D)J recombination

V(D)J recombination, a site-specific gene rearrangement process, requires two RAG1 and RAG2 proteins specifically recognizing recombination signal sequences and forming DNA double-strand breaks. The broken DNA ends tightly bound to RAG proteins are joined by repair proteins. Here, we found that heat shock protein 70 was associated with RAG2 following two-step affinity chromatography purification. It was also co-immunoprecipitated with RAG2 in pro-B cells. Purified HSP70 protein disrupted RAG/DNA complexes assembled in vitro and also inhibited the V(D)J cleavage (both nick and hairpin formation) in a dose-dependent manner. This HSP70 action required ATP energy. These data suggest that HSP70 might play a crucial role in disassembling RAG/DNA complexes stably formed during V(D)J recombination.     

De novo balanced translocation (2;10)(q24;q22) associated with mental retardation

We report a case of a reciprocal translocation between the long arms of the 2 and 10 chromosomes observed in a 14-year-old male with mild mental impairment, compulsive and obsessive behavior. The apparently balanced translocation was characterized by fluorescence in situ hybridization and the karyotype was 46, XY, t(2;10)(q24;q22). The way by balanced chromosomal translocations can lead to a disease phenotype are reviewed and discussed.     

Interchange trisomy 21 by t(1;21)(p22;q22)mat

Interchange trisomy 21 by t(1:21)(p22:q22)mat: Interchange trisomy 21 by t(1;21)(p22;q22)mat was identified in a sporadic patient with Down syndrome. With a 21q22 specific probe, we observed signals on both normal 21 chromosomes and on the der. We reviewed the 23 published reports of families with reciprocal translocations leading to viable offspring with interchange trisomy 21. The breakpoints in chromosome 21 were mainly located in 21q (19/24 instances, including the present report) and in 19/23 cases the other chromosome involved in the translocation was (pairs 1-12). The underlying 3:1 segregation occurred mainly in carrier mothers; only one patient presented a de novo imbalance and in another case the father was the carrier. In addition, there were 4 instances of concurrence with another unbalanced segregation (adjacent-1 or tertiary trisomy) and 3 families with recurrence of interchange trisomy 21. The mean age of 14 female carriers at birth of interchange trisomy 21 offspring (24.8 yr) was lower that the mean (28.3 yr) found in a larger sample of mothers of unbalanced offspring due to 3:1 segregation (mostly tertiary trisomics) and was not increased with respect to the general population average. Overall, these data agree with previous estimates regarding recurrence risk (9-15%) and abortion rate (about 28%) in female carriers ascertained through an interchange trisomic 21 child.     

VprBP binds full-length RAG1 and is required for B-cell development and V(D)J recombination fidelity

The N-terminus of full-length RAG1, though dispensable for RAG1/2 cleavage activity, is required for efficient V(D)J recombination. This region supports RING E3 ubiquitin ligase activity in vitro, but whether full-length RAG1 functions as a single subunit or a multi-subunit E3 ligase in vivo is unclear. We show the multi-subunit cullin RING E3 ligase complex VprBP/DDB1/Cul4A/Roc1 associates with full-length RAG1 through VprBP. This complex is assembled into RAG protein-DNA complexes, and supports in-vitro ubiquitylation activity that is insensitive to RAG1 RING domain mutations. Conditional B lineage-specific VprBP disruption arrests B-cell development at the pro-B-to-pre-B cell transition, but this block is bypassed by expressing rearranged immunoglobulin transgenes. Mice with a conditional VprBP disruption show modest reduction of D-J(H) rearrangement, whereas V(H)-DJ(H) and V(κ)-J(κ) rearrangements are severely impaired. D-J(H) coding joints from VprBP-insufficent mice show longer junctional nucleotide insertions and a higher mutation frequency in D and J segments than normal. These data suggest full-length RAG1 recruits a cullin RING E3 ligase complex to ubiquitylate an unknown protein(s) to limit error-prone repair during V(D)J recombination.     

Familial (11;21)(p13;q22)pat balanced reciprocal translocation in a female child with regression of milestones

The role of balanced translocations in the human morphogenesis is difficult to interpret. A balanced reciprocal translocation (BRT) was observed in a female child referred with a history of regression of milestones. The cytogenetic findings by GTG-banding and fluorescence in situ hybridization revealed a BRT involving chromosomes 11p and 21q, i.e. 46,XX, t(11;21)(p13;q22). The father was found to be a carrier of the same BRT. This is the first report of reciprocal translocation involving 11p and 21q. The possible reasons for the manifestation of clinical features in the proband due to inherited BRT are discussed.     

Familial aniridia and translocation t(4;11)(q22;p13) without Wilms' tumor

A family with dominantly inherited aniridia in three generations is presented. All three patients had an apparently balanced chromosome translocation t(4;11)(q22;p13). The patients were otherwise clinically normal and without signs of Wilms' tumor; their erythrocyte catalase activities were within the normal range. We suggest that in this family aniridia is caused either by a submicroscopic deletion at the translocation breakpoint 11p13 or by a position effect on the same chromosome segment. Furthermore, the loci for aniridia and Wilms' tumor susceptibility are separate. It follows that the WAGR complex is caused by a mutation of more than one gene located at 11p13. The theoretical implications of a presumably defective allele causing a mendelian dominant phenotype are discussed.     

Sperm chromosome analysis of two males heterozygous for a t(2;17)(q35;p13) and t(3;8)(p13;p21) reciprocal translocation

Summary Sperm chromosome complements from two males, one heterozygous for the reciprocal translocation t(2;17)(q35;p13) (n = 18) and one for t(3;8) (p13;p21) (n = 73), were analyzed. Only 2:2 segregations were observed with t(2;17): alternate, 56%; adjacent-I, 33%; adjacent-II, 11%. Both 2:2 and 3:1 meiotic segregations occurred in t(3;8): alternate, 34.2%; adjacent-I, 43.8%; adjacent-II, 20.5% and 3:1, 1.4%. A significant excess of chromosomally normal versus balanced sperm complements was observed with both translocation heterozygotes. The frequencies of other chromosome aberrations unrelated to the translocations were 16.7% for t(2;17) and 8.2% for t(3;8). The ratio of X-bearing to Y-bearing sperm was not different from the theoretically expected ratio of 1:1.     

A case of chronic myeloid leukemia with a translocation (12;22)(p13;q11)

Summary Chromosomal studies of the bone marrow and cultured peripheral blood cells in a 42-year-old female with the clinical and laboratory features typical for CML revealed a previously undescribed variant translocation involving chromosomes 12 and 22.     

Congenital hyperthyroidism with reciprocal translocation t(1;17)(q25;q21)

Summary The authors report a case of 1;17 translocation and request contact with colleagues who have observed similar cases.     

Systemic mastocytosis associated with t(8;21)(q22;q22) acute myeloid leukemia

Although KIT mutations are present in 20–25% of cases of t(8;21)(q22;q22) acute myeloid leukemia (AML), concurrent development of systemic mastocytosis (SM) is exceedingly rare. We examined the clinicopathologic features of SM associated with t(8;21)(q22;q22) AML in ten patients (six from our institutions and four from published literature) with t(8;21) AML and SM. In the majority of these cases, a definitive diagnosis of SM was made after chemotherapy, when the mast cell infiltrates were prominent. Deletion 9q was an additional cytogenetic abnormality in four cases. Four of the ten patients failed to achieve remission after standard chemotherapy and seven of the ten patients have died of AML. In the two patients who achieved durable remission after allogeneic hematopoietic stem cell transplant, recipient-derived neoplastic bone marrow mast cells persisted despite leukemic remission. SM associated with t(8;21) AML carries a dismal prognosis; therefore, detection of concurrent SM at diagnosis of t(8;21) AML has important prognostic implications.