A comparative study of the tapetum, retina and skull of the ferret, dog and cat

Results of this investigation indicate that the ferret (Mustela putorius) closely resembles the dog (Canis familiaris) and should be a useful research animal alternative. The tapetum lucidum is a common structure present in the eyes of dogs, cats (Felis catus) and other nocturnal animals. Our study showed that this structure was present in ferret eyes. The color or reflection of the ferret and dog tapetum was remarkably reduced by the general fixation with glutaraldehyde. However, this color fading phenomenon was not observed in the cat tapetum. These observations led to this comparative study on several morphological, histochemical and biochemical parameters on mature ferrets, dogs and cats including: (1) the number of center tapetum cell layers, (2) thickness of center tapetum, (3) presence of a microtubule-like structure in each tapetal rod, (4) presence of electron-dense cores in tapetal rods after prolonged fixation in glutaraldehyde, (5) retention of reflection or color of tapetum after prolonged glutaraldehyde fixation, (6) zygomatic bones of eye orbits, (7) zinc content in tapetum, (8) cysteine in the tapetum, (9) cysteine sulfinic acid decarboxylase in liver, (10) thickness of retina from center tapetum, (11) anterior view of skull configuration, and (12) lateral view of skull configuration (jaw and teeth). Among these 12 parameters, ferret and dog were similar in the first nine points; ferret and cat were similar to each other only in the last two points. There was no difference in retinal thickness among these three animals.     

Proteolytic cleavage of the E2 glycoprotein of murine coronavirus: activation of cell-fusing activity of virions by trypsin and separation of two different 90K cleavage fragments.

In the murine coronavirus mouse hepatitis virus, a single glycoprotein, E2, is required both for attachment to cells and for cell fusion. Cell fusion induced by infection with mouse hepatitis virus strain A59 was inhibited by the addition of monospecific anti-E2 antibody after virus adsorption and penetration. Adsorption of concentrated coronavirions to uninfected cells did not cause cell fusion in the presence of cycloheximide. Thus, cell fusion was induced by E2 on the plasma membrane of infected 17 Cl 1 cells but not by E2 on virions grown in these cells. Trypsin treatment of virions purified from 17 Cl 1 cells quantitatively cleaved 180K E2 to 90K E2 and activated cell-fusing activity of the virions. This proteolytic cleavage yielded two different 90K species which were separable by sodium dodecyl sulfate-hydroxyapatite chromatography. One of the trypsin cleavage products, 90A, was acylated and may be associated with the lipid bilayer. The other, 90B, was not acylated and yielded different peptides than did 90A upon limited digestion with thermolysin or staphylococcal V8 protease. Thus, the cell-fusing activity of a coronavirus required proteolytic cleavage of the E2 glycoprotein, either by the addition of a protease to virions or by cellular proteases acting on E2, which was transported to the plasma membrane during virus maturation. There is a striking functional similarity between the E2 glycoprotein of coronavirus, which is a positive-strand RNA virus, and the hemagglutinin glycoprotein of negative-strand orthomyxoviruses, in that a single glycoprotein has both attachment and protease-activated cell-fusing activities.     

Effects of Motility and Adsorption Rate Coefficient on Transport of Bacteria through Saturated Porous Media

Three strains of Pseudomonas fluorescens with different motility rates and adsorption rate coefficients were injected into porous-medium reactors packed with l-mm-diameter glass spheres. Cell breakthrough, time to peak concentration, tailing, and cell recovery were measured at three interstitial pore velocities (higher than, lower than, and much lower than the maximal bacterial motility rate). All experiments were done with distilled water to reduce the effects of growth and chemotaxis. Contrary to expectations, motility did not result in either early breakthrough or early time to peak concentration at flow velocities below the motility rate. Bacterial size exclusion effects were shown to affect breakthrough curve shape at the very low flow velocity, but no such effect was seen at the higher flow velocity. The tendency of bacteria to adsorb to porous-medium surfaces, as measured by adsorption rate coefficients, profoundly influenced transport characteristics. Cell recoveries were shown to be correlated with the ratio of advective to adsorptive transport in the reactors. Adsorption rate coefficients were found to be better predictors of microbial transport phenomena than individual characteristics, such as size, motility, or porous-medium hydrodynamics.     

Histochemical localization of zinc in the feline tapetum

Summary High resolution electron microscopy of ultrathin sections confirms the presence of a membrane surrounding the tapetal rods in the cat. Cats depleted of taurine exhibit disruption and disorganization of this membrane, probably the first stage of more severe tapetal degeneration. Histochemical localization of zinc shows it to be present on the periphery of the tapetal rods. The amount of zinc present on the periphery of the tapetal rods of taurine depleted cats was greatly reduced. Taurine in feline tapetum, confirmed by autoradiography and direct measurement, was also greatly reduced in taurine-depleted cats. We conclude that both taurine and zinc are localized on the periphery of the tapetal rods and that they contribute to the stability of the membrane. We have also confirmed earlier reports that the cat tapetal rods contain riboflavin and no detectable cysteine.Presented in part at the International Symposium Taurine-Questions and Answers Mexico City, November 16–19, 1980     

Cell wall assembly in Bacillus subtilis: location of wall material incorporated during pulsed release of phosphate limitation, its accessibility to bacteriophages and concanavalin A, and its susceptibility to turnover.

Addition of a pulse of phosphate to a phosphate-limited chemostat culture of Bacillus subtilis W23 led to the synthesis of teichoic acid and the consequent development by the bacteria of the ability to bind phage SP50. In cultures growing at different rates, phage-binding properties became maximal approximately one generation time after addition of the pulse. Removal of the incorporated teichoic acid by turnover also reached its maximum rate after a similar interval. After pulsed release of phosphate limitation in B. subtilis NCTC 3610, the alpha-glucosyl residues of the incorporated teichoic acid, detected by their interaction with concanavalin A, became maximally exposed at the same time that phage binding was maximum. At that time the bacteria bound phage all over the cylindrical part of the surface and at about one-third of the polar caps. That fraction of the receptor material that is exposed soon after its incorporation was distributed along the cylindrical length of most of the bacteria, but few phages bound to the polar caps, except in the case of short bacteria; these bound phages in a markedly asymmetric manner at one pole and along their length. The significance of these results is discussed in relation to the mode of assembly of the cell wall.     

TAURINE IN THE BRAIN AND LIVER OF THE DEVELOPING HUMAN AND MONKEY

—The concentrations of taurine in brain and liver from human fetuses (2nd trimester) and adults and from Rhesus monkeys from mid-gestation, through birth and neonatal life to maturity have been measured. The concentration of taurine in human and monkey fetal brain was 4-5-fold higher than that in adult monkey brain. In human fetal brain the concentration of taurine decreased linearly with increasing crown-rump length (r=−0·75; P < 0·001). In fetal monkey brain, no correlation with gestational age was found. After birth, the concentration of taurine in monkey brain decreased linearly with increasing age (r=−0·96; P < 0·001) until values comparable to those found in the adult were reached 8-9 months after birth, approximately the end of weaning. The concentration of taurine in liver both from fetal humans and from fetal monkeys was approximately twice that in mature liver. Concentrations of taurine similar to those found in adult liver were reached within a few days of birth, compared to several months for brain. These results suggest that taurine may be associated with brain development in addition to any functional role it may play in the mature brain.     

Subcellular distribution of S-adenosylmethionine decarboxylase in rat liver. Evidence of decarboxylation of S-adenosylmethionine separate from synthesis of spermidine.

The activity of S-adenosylmethionine decarboxylase in rat liver homogenates is localized chiefly in the crude nuclear fraction, probably associated with membrane fragments, with the remainder in the supernatant fraction. This distribution is not paralleled by the activity of the cytoplasmic enzyme, lactate dehydrogenase. The spermidine-synthesizing activity of whole homogenate is recovered entirely in the supermidine-synthesizing activity of whole homogenate is recovered entirely in the supernatant fraction. Measurement of various kinetic parameters in crude fractions provided not positive evidence for isozymes of S-adenosylmethionine decarboxylase. Some species do not possess a sedimentable fraction of S-adenosylmethionine decarboxylase activity in liver. In those species all activity present in the whole homogenate of liver is released into the supernatant fraction.     

Structure of the full‐length insecticidal protein Cry1Ac reveals intriguing details of toxin packaging into in vivo formed crystals

For almost half a century, the structure of the full‐length Bacillus thuringiensis (Bt) insecticidal protein Cry1Ac has eluded researchers, since Bt‐derived crystals were first characterized in 1965. Having finally solved this structure we report intriguing details of the lattice‐based interactions between the toxic core of the protein and the protoxin domains. The structure provides concrete evidence for the function of the protoxin as an enhancer of native crystal packing and stability.     

Taurine in toad brain and blood under different conditions of osmolality: An immunohistochemical study

The concentrations of taurine in blood and brain regions of the toadBufo boreas have been measured. Most of these values are considerably lower than those found in mammals. Using an antibody prepared against conjugated taurine, the distribution of taurine in three brain regions of the toad has been visualized. The possible osmoregulatory functions of taurine have been investigated by making toads hyper- or hypo-osmotic in vivo. Induction of hypoosmolality is accompanied by a massive taurine tide in blood plasma, but has no immediate effects upon the taurine concentrations in the brain areas studied. However, histochemical visualization indicates a marked redistribution of taurine between cellular components and extracellular space of brain tissues. This may indicate that taurine has an osmoregulatory function in brain tissue under hypo-osmotic conditions. Hyperosmolality results in no elevation of the taurine concentration in blood plasma of toads, but rather in a very gradual decline of total plasma taurine content over a prolonged time period. Histochemical studies reveal little change in frontal cortex after 1 hour but deeper staining of many neurons in optic lobe accompanied by greater staining in the extracellular fluid. By 3 hours there is a depletion of taurine from all compartments of cerebral cortex tissues. No evidence of any prolonged direct osmoregulatory role for taurine is indicated under hyperosmotic conditions. A possible indirect osmoregulatory function of taurine is discussed.Special issue dedicated to Dr. Claude Baxter.     

Poliovirus Adsorption by 34 Minerals and Soils

The adsorption of radiolabeled infectious poliovirus type 2 by 34 well-defined soils and mineral substrates was analyzed in a synthetic freshwater medium containing 1 mM CaCl₂ and 1.25 mM NaHCO₃ at pH 7. In a model system, adsorption of poliovirus by Ottawa sand was rapid and reached equilibrium within 1 h at 4°C. Near saturation, the adsorption could be described by the Langmuir equation; the apparent surface saturation was 2.5 × 10⁶ plaque-forming units of poliovirus per mg of Ottawa sand. At low surface coverage, adsorption was described by the Freundlich equation. The soils and minerals used ranged from acidic to basic and from high in organic content to organic free. The available negative surface charge on each substrate was measured by the adsorption of a cationic polyelectrolyte, polydiallyldimethylammonium chloride. Most of the substrates adsorbed more than 95% of the virus. In general, soils, in comparison with minerals, were weak adsorbents. Among the soils, muck and Genesee silt loam were the poorest adsorbents; among the minerals, montmorillonite, glauconite, and bituminous shale were the least effective. The most effective adsorbents were magnetite sand and hematite, which are predominantly oxides of iron. Correlation coefficients for substrate properties and virus adsorption revealed that the elemental composition of the adsorbents had little effect on poliovirus uptake. Substrate surface area and pH, by themselves, were not significantly correlated with poliovirus uptake. A strong negative correlation was found between poliovirus adsorption and both the contents of organic matter and the available negative surface charge on the substrates as determined by their capacities for adsorbing the cationic polyelectrolyte, polydiallyldimethylammonium chloride.