Assessing horizontal transfer of nifHDK genes in eubacteria: nucleotide sequence of nifK from Frankia strain HFPCcI3

The structural genes for nitrogenase, nifK, nifD, and nifH, are crucial for nitrogen fixation. Previous phylogenetic analysis of the amino acid sequence of nifH suggested that this gene had been horizontally transferred from a proteobacterium to the gram-positive/cyanobacterial clade, although the confounding effects of paralogous comparisons made interpretation of the data difficult. An additional test of nif gene horizontal transfer using nifD was made, but the NifD phylogeny lacked resolution. Here nif gene phylogeny is addressed with a phylogenetic analysis of a third and longer nif gene, nifK. As part of the study, the nifK gene of the key taxon Frankia was sequenced. Parsimony and some distance analyses of the nifK amino acid sequences provide support for vertical descent of nifK, but other distance trees provide support for the lateral transfer of the gene. Bootstrap support was found for both hypotheses in all trees; the nifK data do not definitively favor one or the other hypothesis. A parsimony analysis of NifH provides support for horizontal transfer in accord with previous reports, although bootstrap analysis also shows some support for vertical descent of the orthologous nifH genes. A wider sampling of taxa and more sophisticated methods of phylogenetic inference are needed to understand the evolution of nif genes. The nif genes may also be powerful phylogenetic tools. If nifK evolved by vertical descent, it provides strong evidence that the cyanobacteria and proteobacteria are sister groups to the exclusion of the firmicutes, whereas 16S rRNA sequences are unable to resolve the relationships of these three major eubacterial lineages.      

The relationship of glial fibrillary acidic protein to the shape,motility, and differentiation of human astrocytoma cells

Glial fibrillary acidic protein (GFAP), a protein largely limited to astrocytes, was studied in relation to the shape, motility, and differentiation and malignancy of astrocytoma cells in tissue culture by use of time-lapse photography and the immunoperoxidase method.A relationship was observed between the shape of astrocytes and the distribution of GFAP. Spindle-shaped cells showed abundant GFAP in the cell body and processes. In round or polyhedral cells without well developed processes the GFAP was largely perinuclear. As processes developed, GFAP extended out from the nucleus iri dense parallel arrays that radiated into the developing processes. Fully differentiated cells with stellate shape had abundant GFAP throughout.A relationship was also observed between the motility of astrocytes and GFAP. Stellate-shaped cells, showing paucity of locomotion and relatively rigid postures of processes, contained an abundance of GFAP which tended to form dense parallel arrays extending into the processes during their development. Spindle-shaped cells with extending and retracting processes and active migration also contained an abundance of GFAP but not organized into parallel arrays. Bulbous dilatations at the tips of processes (growth cones) contained abundant GFAP. There was also abundant GFAP in the intermittent dilatations along the processes of stellate cells. In contrast to these observations, a retraction of processes, a high degree of plasticity (undulating motion) and multidirectional locomotion were often associated with a paucity of GFAP in less differentiated cells. We hypothesize that GFAP filaments may be inhibitory to great plasticity of motion but not to extension-retraction movements.During mitosis GFAP was sparse at the spindle and in intercellular bridges. Colcemid caused GFAP to disappear from processes and peripheral parts of the cell and to become concentrated near the nucleus.In cultures derived from malignant tumors, undifferentiated and large multinucleated cells usually showed sparsity of GFAP, but occasional well differentiated stellate or spindle-shaped cells containing abundant GFAP were seen. Conversely, although cultures derived from benign tumors may have scattered less well differentiated cells, the differentiated cells with well developed processes were most densely stained and account for the high concentration of GFAP in tissue from these tumors.     

CEREBRAL ENERGY METABOLISM DURING TRANSIENT ISCHEMIA AND RECOVERY IN THE GERBIL1

Energy metabolism was studied in the cerebral cortex of gerbils during and following ischemia induced by 1 h of unilateral carotid artery occlusion. An aneurysm clip was applied to the right common carotid artery of 50-70 g gerbils under brief halothane anesthesia, and the clip was removed 1 h later. Clinical state (gait, responsiveness, seizures) was evaluated during carotid occlusion, and 40% of the animals showed clinical evidence of stroke. Cortical energy stores (2 ATP + ADP + P-creatine) were more than half depleted in the ipsilateral cortex of clinically-affected gerbils, and glucose fell by 75%; lactate rose over 7-fold in the same specimens. After release of the carotid clip, clinical state improved, and biochemical abnormalities partially resolved. However, even after 24 h, the concentration of ATP and the total pool of adenine nucleotides remained subnormal. Metabolic activity in the ischemic cortex, assessed as the utilization of high-energy phosphates following decapitation, was normal after 1 h of recovery and decreased (-50%) after 24 h but was increased by more than 50% after 4 h. Cerebral glucose utilization, evaluated from autoradiographs prepared after intravenous administration of 2-[1-¹⁴C]deoxyglucose, was also increased in the cortex, hippocampus, and thalamus after 4 h of recovery. This post-ischemic hypermetabolism in tissue damaged by ischemia may identify a critical period for cell repair, when therapy could be decisive.     

A comparison of the tryptic peptides of hemoglobin from two cricetine genera: Peromyscus and Calomys

The composition of tryptic peptides was determined for the major hemoglobin from two cricetine rodents. Peromyscus maniculatus bairdii and Calomys callosus. Amino acid sequences are proposed from homologous alignment with the respective sequences of white mouse and a microtine ‘stem’ developed from previous studies. These two hemoglobins differed at 11 - and 17 β-positions, showing only one common position beyond the cricetid stems (Hesperomyini, Cricetinae) and only three common positions with the microtinae beyond the muroid or myomorph stem (Cricetidae).     

The Biology of Gregarina fernandoi n. sp. in the Cockroach Pysnoscelus surinamensis with Observations on its Development and Cytochemical Nature

SYNOPSIS. Gregarina fernandoi n. sp. is a eugregarine. Its structure, development and life history in the gut of the cockroach Pycnoscelus surinamensis are described. It is named as a new species on the basis of its size, nuclear structure, structure and form of the gametocyst and oocyst. Observations were made on the different stages of the parasite and related to the pH of the gut. In the ceca, pH 4.5–5, the parasite was in its early stages of development, in the midgut, pH 6.5–7, it was in syzygy and in the rectum, pH 7.5–8, gametocysts were found.     

Improved survival after orthotopic liver grafting.

A total of 108 orthotopic liver transplants have been carried out in the Cambridge/King''s College Hospital series. Over 13 years, changes in patient selection, immunosuppression, and surgical and anaesthetic techniques have led to a steady improvement in results. Results obtained in the last 22 patients indicated that over half survive for one year. Although at considerable risk during the operation, patients with non-malignant cirrhotic diseases who survive one year have a good long-term chance of survival     

Sir William Osler revisited.

The basis of Sir William Osler''s fame is elusive to almost all and the appropriateness of such recognition is questioned by many. His many contributions as a practitioner, teacher, writer, and scientist in medicine do not adequately explain his prominence 60 years following his death. It was his participation in the covenant of medicine and the special components of that relationship that may account for his hold on his followers today.     

Individual mitochondrion characterization: a comparison of classical assays to capillary electrophoresis with laser-induced fluorescence detection.

A method has been developed that uses capillary electrophoresis (CE) with laser-induced fluorescence detection (LIF) for measuring protein abundance in individual mitochondria collected from a discontinuous density gradient and labeled with Mitotracker Green. From these measurements we determined the distribution of protein content per mitochondrion and the relative abundance of mitochondrial proteins in density gradient fractions. In addition, this method is useful for counting mitochondria and, as a consequence, determining the number of mitochondria per unit volume or estimate mitochondria copy number per cell. It was determined that mitochondria accumulate in two interfaces defined by consecutive layers of 35% Metrizamide, 17% Metrizamide, and 6% Percoll. The presence of mitochondria in these interfaces was also confirmed using a modified Lowry assay that prevents interference from Metrizamide and Percoll and determines total protein content, and a succinate dehydrogenase assay that uses dichloroindophenol as an electron acceptor and that specifically indicates abundance of mitochondria. The CE-LIF analysis of mitochondrial properties, based on the individual mitochondrial determinations, has a wider scope than the average values determined by enzymatic or bulk protein assays.