The role of the microtubular cytoskeleton in determining nuclear chromatin structure and passage of maize root cells through the cell cycle

Depolymerization of microtubules in metabolically inactive quiescent center (QC) cells of maize root apices by means of three different antimicrotubular treatments (colchicine, oryzalin and low temperature) elicited very similar responses in their nuclei. Conspicuous nuclear enlargement was closely associated with chromatin decondensation and accelerated traverse of their cell cycle. This latter finding was inferred not only from cytophotometry which showed an increased proportion of S and G2 nuclei in this group of cells, but also from autoradiography which confirmed the greater proportion of nuclei engaged in the S phase of the cell cycle. Activation of the QC cells with various antimicrotubular agents may be a reflection of a dependency of nuclear cell cycle events on the turnover of cytoplasmic microtubules during interphase. The nuclear size, nuclear chromatin structure, as well as cell cycle progression, seem to be regulated by the dynamic nature of the microtubular cytoskeleton.     

Treatment of mild hyperhomocysteinemia in vascular disease patients

Mild hyperhomocysteinemia is recognized as a risk factor for premature arteriosclerotic disease. A few vitamins and other substances have been reported to reduce blood homocysteine levels, but normalization of elevated blood homocysteine concentrations with any of these substances has not been reported. Therefore, we screened 421 patients suffering from premature peripheral or cerebral occlusive arterial disease by oral methionine loading tests for the presence of mild hyperhomocysteinemia. Thirty-three percent of patients with peripheral and 20% of patients with cerebral occlusive arterial disease were identified with mild hyperhomocysteinemia (14% of the men, 34% of the premenopausal women, and 26% of the postmenopausal women). Mildly hyperhomocysteinemic patients were administered vitamin B6 250 mg daily. After 6 weeks methionine loading tests were again assessed to evaluate the effect of treatment. Patients with nonnormalized homocysteine concentrations were further treated with vitamin B6 250 mg daily and/or folic acid 5 mg daily and/or betaine 6 g daily, solely or in any combination. Vitamin B6 treatment normalized the afterload homocysteine concentration in 56% of the treated patients (71% of the men, 45% of the premenopausal women, and 88% of the postmenopausal women). Further treatment resulted in a normalization of homocysteine levels in 95% of the remaining cases. Thus, mild hyperhomocysteinemia, which is frequently encountered in patients with premature arteriosclerotic disease, can be reduced to normal in virtually all cases by safe and simple treatment with vitamin B6, folic acid, and betaine, each of which is involved in methionine metabolism.     

Archetypal organization of the amphioxus Hox gene cluster

Organization into gene clusters is an essential and diagnostic feature of Hox genes. Insect and nematode genomes possess single Hox gene clusters (split in Drosophila); in mammals, there are 38 Hox genes in four clusters on different chromosomes. A collinear relationship between chromosomal position, activation time and anterior expression limit of vertebrate Hox genes suggests that clustering may be important for precise spatiotemporal gene regulation and hence embryonic patterning. Hox genes have a wide phylogenetic distribution within the metazoa, and are implicated in the control of regionalization along the anteroposterior body axis. It has been suggested that changes in Hox gene number and genomic organization played a role in metazoan body-plan evolution, but identifying significant changes is difficult because Hox gene organization is known from only very few and widely divergent taxa (principally insects, nematodes and vertebrates). Here we analyse the complexity and organization of Hox genes in a cephalochordate, amphioxus, the taxon thought to be the sister group of the vertebrates. We find that the amphioxus genome has only one Hox gene cluster. It has similar genomic organization to the four mammalian Hox clusters, and contains homologues of at least the first ten paralogous groups of vertebrate Hox genes in a collinear array. Remarkably, this organization is compatible with that inferred for a direct ancestor of the vertebrates; we conclude that amphioxus is a living representative of a critical intermediate stage in Hox cluster evolution.     

An unknown genetic defect increases venous thrombosis risk, through interaction with protein C deficiency

OBJECTIVES: Nitric oxide (NO), a highly reactive species produced by the activity of NO synthases (NOS), is normally present in the exhaled air of humans and animals. Exhaled NO concentration increases significantly in humans with sepsis and animals, but neither the source nor NOS isoforms responsible for this rise in pulmonary NO production are known. The main objective of this study is to determine the sites and the mechanisms of enhanced NO production in the exhaled air of endotoxemic pigs. DESIGN: Randomized, controlled, animal study. SETTING: University-based animal research facility. SUBJECTS: Thirteen pathogen-free adult female pigs (22 to 27 kg). INTERVENTIONS: Anesthetized pigs were divided into two groups: control and lipopolysaccharides (LPS) (septic) groups. In both groups, extrathoracic (upper airways, nasal, and paranasal) and intrathoracic (bronchi, bronchioles, and alveoli) compartments were ventilated equally with two separate ventilators connected to two tracheal tubes. The LPS group received slow infusion (over 2 h) of Escherichia coli endotoxin (10 microg/kg/h), whereas saline solution was infused into the control group. Expired air of the two compartments was collected throughout the 2-h observation period. The animals were then killed and the lungs were quickly excised and frozen. MEASUREMENTS: Hemodynamic variables were measured in both groups. NO concentration in the exhaled air of both compartments was measured with a chemiluminescence analyser. Pulmonary NOS activity was evaluated by measuring the conversion of L-[2,3H]-arginine to L-[2,3H]-citrulline, and pulmonary expression of NOS was evaluated by immunoblotting. RESULTS: Baseline NO concentration in both groups was significantly higher in the extrathoracic vs intrathoracic compartment (average of 5.2 vs 3.4 parts per billion). Endotoxin infusion elicited a significant and early (after 45 min) rise in exhaled NO concentration in the extrathoracic compartment. Exhaled NO in the intrathoracic compartment also rose significantly but after 90 min of endotoxin infusion. Measurement of lung NOS activity showed a substantial rise in Ca++/calmodulin-dependent activity in the LPS group with no rise in Ca++/calmodulin-independent activity. Immunoblotting of lung tissue samples indicated the absence of the inducible isoform in both groups of animals. Moreover, LPS injection elicited no significant alterations in the pulmonary expression of the endothelial and the neuronal isoforms. CONCLUSIONS: Both extrathoracic and intrathoracic compartments contribute to the rise in exhaled NO production in experimental septic shock. The rise in exhaled NO production is due to increased activity of constitutive NOS isoforms as a result of increased cofactor availability and/or downregulation of the endogenous inhibitors of NOS.     

Multiplex sequencing of 1.5 Mb of the Mycobacterium leprae genome

The nucleotide sequence of 1.5 Mb of genomic DNA from Mycobacterium leprae was determined using computer-assisted multiplex sequencing technology. This brings the 2.8-Mb M. leprae genome sequence to approximately 66% completion. The sequences, derived from 43 recombinant cosmids, contain 1046 putative protein-coding genes, 44 repetitive regions, 3 tRNAs, and 15 tRNAs. The gene density of one per 1.4 kb is slightly lower than that of Mycoplasma (1.2 kb). Of the protein coding genes, 44% have significant matches to genes with well-defined functions. Comparison of 1157 M. leprae and 1564 Mycobacterium tuberculosis proteins shows a complex mosaic of homologous genomic blocks with up to 22 adjacent proteins in conserved map order. Matches to known enzymatic, antigenic, membrane, cell wall, cell division, multidrug resistance, and virulence proteins suggest therapeutic and vaccine targets. Unusual features of the M. leprae genome include large polyketide synthase (pks) operons, inteins, and highly fragmented pseudogenes.     

A novel phosphatidylinositol-3,4,5-trisphosphate 5-phosphatase associates with the interleukin-3 receptor

To gain insight into the intracellular signaling cascades that are activated by the binding of interleukin-3 (IL-3) to its target cells, we have embarked on the identification of proteins that are associated with the IL-3 receptor (IL-3R). In a previous study we reported that a 110-kDa serine/threonine protein kinase is constitutively associated with the IL-3R and activated following IL-3 stimulation. We now report that a phosphatidylinositol-3,4, 5-trisphosphate (PtdIns-3,4,5-P3) 5-phosphatase (5-ptase) is also constitutively associated with the IL-3R. This 5-ptase is magnesium-dependent and removes the 5-position phosphate from PtdIns-3,4,5-P3 but does not metabolize PtdIns-4,5-P2, inositol (Ins)-1,3,4,5-P4, or Ins-1,4,5-P3. This substrate specificity distinguishes it from any previously characterized 5-ptase. Interestingly, it may be bound indirectly via phosphatidylinositol 3-kinase (PI 3-kinase), another enzyme that is constitutively bound to the IL-3R. However, unlike PI 3-kinase which becomes activated following IL-3 stimulation, this receptor-associated 5-ptase activity does not increase following IL-3 stimulation, and its primary function may be to keep the principal in vivo product of PI 3-kinase, PtdIns-3,4,5-P3, at low levels in unstimulated cells, to terminate the PI 3-kinase signal following IL-3 stimulation or to metabolize PtdIns-3,4,5-P3 to a metabolically active second messenger, i.e. PtdIns-3,4-P2.     

Adolescent female craniofacial morphology associated with advanced bilateral TMJ disc displacement

The aim of this study was to determine if cephalometric measurement differences occurred between two groups of similarly aged female adolescents which differed with respect to their diagnoses of temporomandibular joint disc position on magnetic resonance images (MRI). One group consisted of 17 female adolescents exhibiting complete bilateral disc displacement affecting the temporomandibular joints (TMJ), while the second group of 17 female adolescents was diagnosed as having bilateral normal disc position on MRI. Independent sample t-tests identified statistically significant differences in cephalometric measurements between the two groups, but no age difference between the two groups was evident. The group with bilateral total disc displacement exhibited the following significant angular differences from the group with normal disc position: an increased mandibular and palatal plane relative to sella-nasion; posterior rotation of the mandible as illustrated by an increased angle between the posterior border of the mandibular ramus and sella-nasion; and a decrease in Rickett's facial axis. Significant differences in linear cephalometric variables were also evident between the two groups. Total posterior facial height and ramus height were reduced in the totally disc displaced group. Furthermore, a slight increase in the middle anterior facial height was noted, with a decrease in the posterior cranial base vertical height in the totally disc displaced group.