Comparison of Genomes of Brucella melitensis M28 and the B. melitensis M5-90 Derivative Vaccine Strain Highlights the Translation Elongation Factor Tu Gene tuf2 as an Attenuation-Related Gene

Brucella melitensis causes brucellosis, a disease affecting sheep, cattle, and sometimes humans. Attenuated B. melitensis strain M5-90, derived from virulent strain M28, is widely used as a live vaccine in ruminants in China. Genetic differences between the strains may cast light on the mechanism of attenuation. We recently reported the complete genomic sequences of M28 and M5-90. Genome organization is highly conserved between these isolates, and also with virulent strains 16 M and ATCC 23457. Analysis revealed 23 open reading frames (ORFs) with consistent differences between M5-90 and the virulent strains. Notably, the tuf2 gene encoding translation elongation factor EF-Tu from M5-90 contained 50 single nucleotide polymorphisms (SNPs) and 9 gaps (indels) compared to tuf2 of M28 or of the other virulent strains. There were no changes in tuf1. To evaluate the potential role of EF-Tu in pathogenesis, tuf1 and tuf2 mutants of M28 and an M5-90 strain harboring wild-type tuf2 were constructed, and their virulence/attenuation was evaluated in vivo. We report that the tuf2 gene plays an important role in the attenuation of M5-90 virulence.     

Systemic mastocytosis with associated clonal hematological non-mast-cell lineage disease: analysis of clinicopathologic features and activating c-kit mutations

The majority of patients with systemic mastocytosis with associated clonal, hematological non-mast cell lineage disease (SM-AHNMD) have a myeloid stem cell malignancy including myelodysplastic syndromes (MDS), myelodysplastic/myeloproliferative disorders, acute myeloid leukemia (AML), or chronic myeloproliferative disease. The clinicopathologic features of SM-AHNMD have not been fully characterized. We describe seven cases of this entity: 3 with MDS, 3 with AML, and 1 with chronic myelomonocytic leukemia. In the majority of cases, SM was diagnosed concurrently with the myeloid malignancy and aberrant mast cell morphology was observed. The commonly described c-kit enzymatic site mutation Asp816Val was detected only in 2 cases, while 3 patients carried the Asp816His mutation. Among the 3 cases with AML, 2 patients carried the translocation t(8;21). On the basis of our results and other reported cases, there appears to be a specific association between SM and AML with t(8;21). Concurrent occurrence of SM may define a subset of patients with de novo AML and other myeloid malignancies who have an adverse prognosis. As clinically effective tyrosine kinase inhibitors that inhibit enzymatic-type c-kit mutations are being developed, detection of mast cell proliferation associated with myeloid malignancy may have important therapeutic implications.     

LRP1-Dependent Endocytic Mechanism Governs the Signaling Output of the Bmp System in Endothelial Cells and in Angiogenesis

Rationale: Among the extracellular modulators of Bmp (bone morphogenetic protein) signaling, Bmper (Bmp endothelial cell precursor-derived regulator) both enhances and inhibits Bmp signaling. Recently we found that Bmper modulates Bmp4 activity via a concentration-dependent, endocytic trap-and-sink mechanism. Objective: To investigate the molecular mechanisms required for endocytosis of the Bmper/Bmp4 and signaling complex and determine the mechanism of Bmper's differential effects on Bmp4 signaling. Methods and Results: Using an array of biochemical and cell biology techniques, we report that LRP1 (LDL receptor-related protein 1), a member of the LDL receptor family, acts as an endocytic receptor for Bmper and a coreceptor of Bmp4 to mediate the endocytosis of the Bmper/Bmp4 signaling complex. Furthermore, we demonstrate that LRP1-dependent Bmper/Bmp4 endocytosis is essential for Bmp4 signaling, as evidenced by the phenotype of lrp1-deficient zebrafish, which have abnormal cardiovascular development and decreased Smad1/5/8 activity in key vasculogenic structures. Conclusions: Together, these data reveal a novel role for LRP1 in the regulation of Bmp4 signaling by regulating receptor complex endocytosis. In addition, these data introduce LRP1 as a critical regulator of vascular development. These observations demonstrate Bmper's ability to fine-tune Bmp4 signaling at the single-cell level, unlike the spatial regulatory mechanisms applied by other Bmp modulators.