The glycosylation of human myelin basic protein at threonines 95 and 98 occurs sequentially

Human myelin basic protein (MBP) was glycosylated by the enzyme, UDP-GalNAc:polypeptide N-acetylgalactosaminyl transferase (EC 2.4.2.41). A maximum of 1.7 mol of GalNAc was transferred to basic protein on threonines 95 and 98 of the protein. Proton NMR studies of basic protein glycosylated with 0.48-1.7 mol of GalNAc/mol of MBP showed that the order of addition to the two threonine residues is not random but sequential. The Thr-95 resonances shifted downfield, followed by the downfield shift of the Thr-98 resonances with increasing glycosylation. Since this peptide segment of the molecule is highly structured, conformational factors are probably responsible for this directed addition.     

Differential behaviour of 25-hydroxyvitamin D3 24-hydroxylase and 1-hydroxylase in response to protein synthesis inhibitors and cytochrome P-450 inhibitors

To characterize 25-hydroxyvitamin D3 24-hydroxylase and 25-hydroxyvitamin D3 1-hydroxylase, the activities of the two enzymes were measured in the presence of two types of inhibitors. The effect of protein synthesis inhibitors on 25-hydroxyvitamin D3-stimulated 24-hydroxylase activity in 1-hydroxylating rat kidneys perfused in vitro was tested. Actinomycin D (4 microM) and cycloheximide (10 microM) each abolished 25-hydroxyvitamin D3 24-hydroxylase synthesis when added at the start of perfusion but not when added 4 h later; they did not affect 25-hydroxyvitamin D3 1-hydroxylase activity. The effects of cytochrome P-450 inhibitors on the two enzyme activities were then studied in vivo. Metyrapone and SKF-525A (50 mg/kg body weight) each inhibited 25-hydroxyvitamin D3 24-hydroxylase at 6 and 24 h; in contrast 1-hydroxylase increased and was 5 times the control value at 24 h. Finally, the in vitro effects of six cytochrome P-450 inhibitors at concentrations ranging from 10(-7) to 10(-3) M on enzyme activities in renal mitochondrial preparations were compared. Both enzymes were inhibited by all of the inhibitors, but inhibition of 25-hydroxyvitamin D3 24-hydroxylase was consistently greater than that of 25-hydroxyvitamin D3 1-hydroxylase. These studies demonstrate that 24-hydroxylation and 1-hydroxylation respond differently to protein synthesis inhibitors and to cytochrome P-450 inhibitors. The findings are consistent with the hypothesis that the two enzyme activities are associated with different cytochrome P-450 moieties.     

Mapping of neural crest pathways in Xenopus laevis using inter- and intra-specific cell markers

This study examines the pathways of migration followed by neural crest cells in Xenopus embryos using two recently described cell marking techniques. The first is an interspecific chimera created by grafting Xenopus borealis cells into Xenopus laevis hosts. The cells of these closely related species can be distinguished by their nuclear dimorphism. The second type of marker is created by microinjection of lysinated dextrans into fertilized eggs which can then be used for intraspecific grafting. These recently developed fluorescent dyes are fixable and identifiable in both living and fixed embryos. After grafting labeled donor neural tubes into unlabeled host embryos, the distribution of neural crest cells at various stages after grafting was used to define the pathways of neural crest migration. To control for possible grafting artifacts, fluorescent lysinated dextran was injected into a single blastomere which gives rise to a large number of neural crest cells, thereby labeling the neural crest without grafting. By all three techniques, Xenopus neural crest cells were observed along two predominant pathways in the trunk. The majority of neural crest cells were observed along a "ventral" route, between the neural tube and somite, the notochord and somite, and along the dorsal mesentery. A second group of neural crest cells was observed "dorsally" where they populated the dorsal fin. A third minor "lateral" pathway was observed primarily in borealis/laevis chimerae and in blastomere-injected embryos; some neural crest cells were observed underneath the ectoderm lateral to the neural tube. Along the rostrocaudal axis, neural crest cells were not continuously distributed but were primarily located across from the caudal two-thirds of the somite. Fewer than 3% of the neural crest cells were observed across from the rostral third of each somite. When grafted to ventral locations, neural crest cells were not able to migrate dorsally but migrated laterally along the dorsal mesentery. Labeled neural crest cells gave rise to cells of the spinal, sympathetic, and enteric ganglia as well as to adrenal chromaffin cells, Schwann cells, pigment cells, mesenchymal cells of the dorsal fin, and some cells in the integuments and in the region of the pronephros. These results show that the neural crest migratory pathways in Xenopus differ from those in the avian embryo. In avians NC cells migrate as a closely associated sheet of cells while in Xenopus they migrate as individual cells. Both species exhibit a metamerism in the neural crest cell distribution pattern along the rostrocaudal axis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Molecular evolution of the carbonic anhydrase genes: Calculation of divergence time for mouse carbonic anhydrase I and II

Summary A cDNA clone in pBR322 that cross-hybridizes with a mouse carbonic anhydrase form II (CAII) probe has been sequenced and identified as mouse carbonic anhydrase form I (CAI). The 1224-base-pair clone encodes the entire 260-amino-acid protein and appears to contain an Alu-like element in the 3 untranslated region. The deduced amino acid sequence exhibits 77% homology to human CAI and contains 17 of the 20 residues that are considered unique to and invariant for all mammalian CAI isozymes. The results of a detailed comparison of the nucleic acid sequences spanning the coding regions of mouse CAI and rabbit CAI have been used to calibrate an evolutionary clock for the carbonic anhydrases (CAs). These data have been applied to a comparison of the mouse CAI and CAII nucleic acid sequences to calculate the divergence time between the two genes. The divergence-time calculation provides the first estimation of the evolutionary relationship between CAs based entirely on nucleotide sequence comparison.     

Chromosomal organization of the herpes simplex virus genome during acute infection of the mouse central nervous system.

After corneal inoculation, herpes simplex virus type 1 replicates in the mouse eye, trigeminal ganglia, and brainstem, producing first an acute and then a latent infection. Previous work from this laboratory focused on the structure of the viral DNA in this system. We have now examined the structure of the viral genome at the chromosome level by using micrococcal nuclease digestion. Studies with disaggregated cell preparations made from the brainstems of acutely infected mice show that the majority of the viral DNA is in a nonnucleosomal form; however, a nucleosomelike fraction was also consistently detected. A similar result was obtained for viral DNA in herpes simplex virus type 1-infected C1300 (clone NA) neuroblastoma cells (a neuronal cell line).     

Albumin is required to support the acrosome reaction but not capacitation in mouse spermatozoa in vitro

Albumin was required specifically for penetration of the zona pellucida (less than 10% of eggs fertilized in the absence of albumin), but was not required for capacitation. A similar rate of capacitation was observed in the presence of albumin at concentrations ranging from 30 to 1 mg/ml, while a slightly slower rate was observed in the presence of 0.25 and 0.1 mg albumin/ml. In the absence of albumin, capacitation occurred at a rate which lagged behind that of the albumin-incubated counterparts by about 30 min; once capacitated, the addition of albumin promoted rapid sperm penetration. In albumin-free media (+/- the macromolecule PVA), sperm motility was frequently reduced, with fewer cells exhibiting hyperactivated motility, but improvements were observed after introduction of albumin. Acrosome loss was significantly lower in the absence of albumin, but within 5 min of its addition at concentrations ranging from 30 to 0.1 mg/ml to capacitated sperm suspensions, acrosome loss was stimulated and reached levels similar to those seen in control samples. Therefore, albumin can trigger the acrosome reaction in capacitated spermatozoa. It appears to act by assisting in the removal of a surface-associated inhibitory component, the presence of which stabilizes the sperm membranes and inhibits the acrosome reaction.     

Intermediate filament structure

In a previous communication (Biosci. Rep. 3, 517–525, 1993) we described quantitative X-ray diffraction studies of -keratin which were shown to be consistent with the presence of finite arrays of repeating units, successive arrays being set down at axial intervals of 470 Å. In addition the axial interval between repeating units in an array was shown to be 197.9 Å. It was suggested that this could most readily be explained by supposing that a surfacelattice was present which contained a dislocation along a helical path with unit heighth = 470 Å and unit twist |t| = 49.1° . The number of repeating units was shown to be in the range 7–9. With 7 repeats the mismatch of the lattice along the dislocation is small and this choice was used to develop a detailed model for the filament. Subsequent studies of molecular interactions have shown however that the coiled-coil rope segments in the rod domain of the molecule are most probably oriented parallel to the dislocation, and so minimization of lattice mismatch may be less important than originally supposed. In the present communication it is shown that the choice of 8, rather than 7, for the number of repeating units yields a model which is more compatible with estimates of the linear density and also provides the basis for a general model for polymorphism in intermediate filament lattices.     

Effect of upper airway carbon dioxide on ventilation and blood gases in the awake pony

Carbon dioxide concentrations were increased during expiration in the upper one-half of the trachea, pharynx, and nasal sinuses to determine if elevation of upper airway CO2 would alter breathing or arterial blood gases in the awake pony. Carbon dioxide (100%) was injected into the midcervical trachea via a chronically implanted transcutaneous cannula during the first part of the animal's expiration. This maneuver elevated upper airway expiratory CO2 concentrations but prevented any exogenous CO2 from entering the lung and being absorbed into the arterial blood. Twelve experiments were performed on six ponies in which upper airway CO2 was elevated 2, 4, and 6% above the normal expired CO2 concentrations. Tidal volume increased in a dose dependent manner during upper airway CO2 exposure, but total ventilation was unchanged from base-line measurements made while the animal breathed room air. Arterial Po2 also increased during upper airway CO2 administration, reaching a mean value 6 Torr (1 Torr = 133.322 Pa) greater than the base-line values at the +6% CO2 exposure. We conclude that upper airway CO2 exposure alters breathing pattern slightly (increases tidal volume) and increases arterial PO2 in the awake pony.