No abstract

Bacterial flagellar motors obtain energy for rotation from the membrane gradient of protons or, in some species, sodium ions. The molecular mechanism of flagellar rotation is not understood. MotA and MotB are integral membrane proteins that function in proton conduction and are believed to form the stator of the motor. Previous mutational studies identified two conserved proline residues in MotA (Pro 173 and Pro 222 in the protein from Escherichia coli) and a conserved aspartic acid residue in MotB (Asp 32) that are important for function. Asp 32 of MotB probably forms part of the proton path through the motor. To learn more about the roles of the conserved proline residues of MotA, we examined motor function in Pro 173 and Pro 222 mutants, making measurements of torque at high load, speed at low and intermediate loads, and solvent-isotope effects (D2O versus H2O). Proton conduction by wild-type and mutant MotA-MotB channels was also assayed, by a growth defect that occurs upon overexpression. Several different mutations of Pro 173 reduced the torque of the motor under high load, and a few prevented motor rotation but still allowed proton flow through the MotA-MotB channels. These and other properties of the mutants suggest that Pro 173 has a pivotal role in coupling proton flow to motor rotation and is positioned in the channel near Asp 32 of MotB. Replacements of Pro 222 abolished function in all assays and were strongly dominant. Certain Pro 222 mutant proteins prevented swimming almost completely when expressed at moderate levels in wild-type cells. This dominance might be caused by rotor-stator jamming, because it was weaker when FliG carried a mutation believed to increase rotor-stator clearance. We propose a mechanism for torque generation, in which specific functions are suggested for the proline residues of MotA and Asp32 of MotB.

Myxoid glioneuronal tumor, PDGFRA p.K385-mutant" is a recently described tumor entity of the central nervous system with a predilection for origin in the septum pellucidum and a defining dinucleotide mutation at codon 385 of the PDGFRA oncogene replacing lysine with either leucine or isoleucine (p.K385L/I). Clinical outcomes and optimal treatment for this new tumor entity have yet to be defined. Here, we report a comprehensive clinical, radiologic, and histopathologic assessment of eight cases. In addition to its stereotypic location in the septum pellucidum, we identify that this tumor can also occur in the corpus callosum and periventricular white matter of the lateral ventricle. Tumors centered in the septum pellucidum uniformly were associated with obstructive hydrocephalus, whereas tumors centered in the corpus callosum and periventricular white matter did not demonstrate hydrocephalus. While multiple patients were found to have ventricular dissemination or local recurrence/progression, all patients in this series remain alive at last clinical follow-up despite only biopsy or subtotal resection without adjuvant therapy in most cases. Our study further supports "myxoid glioneuronal tumor, PDGFRA p.K385mutant" as a distinct CNS tumor entity and expands the spectrum of clinicopathologic and radiologic features of this neoplasm.

Lipoblastoma (LPB) is a benign neoplasm that occurs predominantly in early childhood. We investigated clinicopathologic features, associated conditions, immunohistochemistry, and outcome in 59 LPB identified from surgical pathology and consultation files. Pathology materials, cytogenetics reports, and medical records were reviewed. Immunohistochemistry for S100 protein, CD34, and Mib-1 was performed on formalin-fixed, paraffin-embedded tissue using standard techniques. Fifty-nine patients had 74 samples, including 14 patients with one or more with local recurrences among the 30 patients who had available follow-up information. There were 37 males and 22 females (ratio 1.7). Age at diagnosis ranged from 3 months to 16 years with 22% in the first year, 68% at 1 to 9 years, and 10% at 10 to 16 years. Sixty-four percent arose on the trunk, 27% on the extremities, and 8% in the head/neck. Forty-six percent had one or more recurrences. Tumor diameter ranged from 1.2 to 15.5 cm. The white to yellow cut surface showed variable lobulation and myxoid change. Histologically, nodules of adipose and myxoid tissue were demarcated by bands of fibrous tissue. The cells displayed a range of differentiation from multivacuolated lipoblasts to mature adipocytes. Mitoses were nonexistent to rare. Histologic variations included a subtle zonal architecture of fat maturation, abundant myxoid material, primitive mesenchymal cells, a focal plexiform vascular pattern, and multinucleated cells. All cases tested were immunoreactive for S100 and CD34; Mib-1 reactivity was absent to low. Cytogenetic aberrations included chromosome 8 abnormalities in 8 cases, nonspecific numerical abnormalities in 1 case, and a normal karyotype in 1 case. Ten patients had other medical conditions including macrocephaly, seizures, developmental delay, autism, congenital anomalies, Sturge-Weber syndrome, or a family history of multiple lipomas. In summary, this large series of LPB demonstrates its occurrence in older children and adolescents, documents a recurrence rate of 46% and confirms that the degree of adipocytic differentiation does not predict biologic behavior. An unexpected finding was the presence in 17% of patients of central nervous system disorders such as seizures, autism, and developmental delay, congenital anomalies, Sturge-Weber syndrome, or a family history of lipomas. These observations raise the question of whether predisposing genetic or other constitutional factors contribute to the development of LPB or whether LPB is indicative of a syndrome.

In a study dedicated exclusively to "intermediate" nerve sheath tumors, no patients developed metastatic disease nor died of disease despite a high rate of microscopically positive surgical margins (78%). While positive margins did lead to increased rates of local recurrence, these data suggest that surgeons potentially can temper their zeal for negative surgical margins in the setting of low-grade MPNST and atypical neurofibroma, as surgical morbidity may be more important than a presumed survival benefit of wide resection.