A Pathogenic NRAS c.38G>A (p.G13D) Mutation in RARA Translocation-negative Acute Promyelocytic-like Leukemia with Concomitant Myelodysplastic Syndrome.

An acute promyelocytic leukemia (APL) patient not demonstrating the retinoic acid receptor α (RARA) translocation is rare. A 76-year-old man was diagnosed with myelodysplastic syndrome (MDS). After a year, abnormal promyelocytes were detected with pancytopenia and disseminated intravascular coagulopathy. Morphologically, the patient was diagnosed with APL; however, a genetic examination failed to detect RARA translocation. Thereafter, whole-genome sequencing revealed an NRAS missense mutation [c.38G>A (p.G13D)]. This mutation was not detected in posttreatment bone marrow aspirate, despite residual MDS. Few reports are available on similar cases. Furthermore, the NRAS c.38G>A mutation may be a novel pathogenic variant exacerbating RARA translocation-negative acute promyelocytic-like leukemia.

Two-step regulation of centromere distribution by condensin II and the nuclear envelope proteins.

The arrangement of centromeres within the nucleus differs among species and cell types. However, neither the mechanisms determining centromere distribution nor its biological significance are currently well understood. In this study, we demonstrate the importance of centromere distribution for the maintenance of genome integrity through the cytogenic and molecular analysis of mutants defective in centromere distribution. We propose a two-step regulatory mechanism that shapes the non-Rabl-like centromere distribution in Arabidopsis thaliana through condensin II and the linker of the nucleoskeleton and cytoskeleton (LINC) complex. Condensin II is enriched at centromeres and, in cooperation with the LINC complex, induces the scattering of centromeres around the nuclear periphery during late anaphase/telophase. After entering interphase, the positions of the scattered centromeres are then stabilized by nuclear lamina proteins of the CROWDED NUCLEI (CRWN) family. We also found that, despite their strong impact on centromere distribution, condensin II and CRWN proteins have little effect on chromatin organization involved in the control of gene expression, indicating a robustness of chromatin organization regardless of the type of centromere distribution.

Plant condensin II is required for the correct spatial relationship between centromeres and rDNA arrays.

Plants possess the structural maintenance of chromosome (SMC) protein complexes cohesin, condensin, and SMC5/6, which function in fundamental biological processes such as sister chromatid cohesion, chromosome condensation and segregation, and damaged DNA repair. Recently, increasing evidence in several organisms has suggested that condensin is involved in chromatin organizations during interphase. In Arabidopsis thaliana, condensin II is localized in the nucleus throughout interphase and is suggested to be required for keeping centromeres apart and the assembly of euchromatic chromosome arms. However, it remains unclear how condensin II organizes chromatin associations. Here, we first showed the high possibility that the function of condensin II as a complex is required for the disassociation of centromeres. Analysis of the rDNA array distribution revealed that condensin II is also indispensable for the association of centromeres with rDNA arrays. Reduced axial compaction of chromosomes and impaired genome integrity in condensin II mutants are not related to the disruption of chromatin organization. In contrast, the axial compaction of chromosomes by condensin II produces the force leading to the disassociation of heterologous centromeres in Drosophila melanogaster. Taken together, our data imply that the condensin II function in chromatin organization differs among eukaryotes.

Auxin decreases chromatin accessibility through the TIR1/AFBs auxin signaling pathway in proliferative cells.

Chromatin accessibility is closely associated with chromatin functions such as gene expression, DNA replication, and maintenance of DNA integrity. However, the relationship between chromatin accessibility and plant hormone signaling has remained elusive. Here, based on the correlation between chromatin accessibility and DNA damage, we used the sensitivity to DNA double strand breaks (DSBs) as an indicator of chromatin accessibility and demonstrated that auxin regulates chromatin accessibility through the TIR1/AFBs signaling pathway in proliferative cells. Treatment of proliferating plant cells with an inhibitor of the TIR1/AFBs auxin signaling pathway, PEO-IAA, caused chromatin loosening, indicating that auxin signaling functions to decrease chromatin accessibility. In addition, a transcriptome analysis revealed that several histone H4 genes and a histone chaperone gene, FAS1, are positively regulated through the TIR1/AFBs signaling pathway, suggesting that auxin plays a role in promoting nucleosome assembly. Analysis of the fas1 mutant of Arabidopsis thaliana confirmed that FAS1 is required for the auxin-dependent decrease in chromatin accessibility. These results suggest that the positive regulation of chromatin-related genes mediated by the TIR1/AFBs auxin signaling pathway enhances nucleosome assembly, resulting in decreased chromatin accessibility in proliferative cells.

Mixed Phenotype Acute Leukemia with t(12;17)(p13;q21)/TAF15-ZNF384 and Other Chromosome Abnormalities.

The t(12;17)(p13;q11∼21) translocation is a very rare but recurrent cytogenetic aberration observed predominantly in early pre-B acute lymphoblastic leukemia (ALL) with CD19+CD10-CD33+ phenotype. This translocation was shown to form a fusion gene between TAF15 at 17q12 and ZNF384 at 12p13. On the other hand, der(1;18)(q10;q10) has been detected as a rare unbalanced whole-arm translocation leading to trisomy 1q in myeloid malignancies. We describe here the first case of mixed phenotype acute leukemia (MPAL) with a t(12;17)(p13;q21)/TAF15-ZNF384, which also had der(1;18)(q10;q10) as an additional abnormality. A 74-year-old woman was diagnosed with MPAL, B/myeloid, because bone marrow blasts were positive for myeloperoxidase, CD19, and CD22. Chromosome analysis showed 46,XX, +1,der(1;18)(q10;q10),t(2;16)(q13;q13),t(12;17)(p13;q21). Expression of the TAF15-ZNF384 fusion transcript was confirmed: TAF15 exon 6 was fused in-frame to ZNF384 exon 3. This type of fusion gene has been reported in 1 acute myeloid leukemia case and 3 ALL cases. Thus, at present, it is difficult to find a specific association between the structure of the TAF15-ZNF384 fusion gene and the leukemia phenotype. The TAF15-ZNF384 fusion may occur in early common progenitor cells that could differentiate into both the myeloid and lymphoid lineages. Furthermore, der(1;18)(q10;q10) might play some role in the appearance of an additional myeloid phenotype.

Identification and analysis of prophet of Pit-1-binding sites in human Pit-1 gene.

Prophet of Pit-1 (Prop1) is a transcription factor that regulates Pit-1 gene expression. Because Pit-1 regulates the differentiation of pituitary cells and the expressions of GH, prolactin and TSHbeta genes, Prop1 mutation results in combined pituitary hormone deficiency in humans. However, Prop1-binding sites in human Pit-1 gene and the mechanism leading to combined pituitary hormone deficiency have remained unclear. In this study, we identified and analyzed Prop1-binding elements of the human Pit-1 gene. Prop1 stimulated the expression of the reporter plasmid containing Pit-1 gene from translation start site to -1340 dose dependently in GH3 cells. The activation by Prop1 was observed in GH3 and TtT/GF cells but not COS7, HeLa, JEG3, and HuH7 cells. Deletion analysis of Pit-1 gene showed that the Prop1-responsive elements were present within the -257-bp region. Within the -257-bp region, there are four elements similar to consensus sequence of paired-like transcription factors. Because Prop1 is a member of paired-like transcription factors, we assessed the elements. EMSA and transient transfection assay using the mutation of the elements revealed that the element from -63 to -53 (the proximal Prop1 binding element) was essential to Prop1-binding and Prop1-induced activation of Pit-1 reporter plasmid. A region at -8kb of human Pit-1 gene is similar to the distal region containing Prop1-binding elements in mouse Pit-1 gene. We showed the region functioned as an enhancer. Furthermore, chromatin immunoprecipitation assay showed that the proximal element could bind Prop1 in vivo cultured cells. Taken together, these findings indicated the novel functioning binding elements of Prop1 in human Pit-1 gene.