Natural variation in population densities and vertical transmission rates of a Spiroplasma endosymbiont in Drosophila hydei

A bacterium belonging to the genus Spiroplasma, an endosymbiont of the fly Drosophila hydei, is vertically transmitted through host egg cytoplasm. To infer vertical transmission rates of Spiroplasma in natural populations of D. hydei, the infection status of Spiroplasma was examined for offspring produced by Spiroplasma-positive females that were collected in two geographical populations. In both populations, nearly half of the broods consisted of only infected offspring. Infection frequencies of the rest of the broods ranged from 0.364 to 0.975. Quantitative PCR demonstrated that the Spiroplasma titers in the whole body of wild-caught females were highly variable (1.81?×?10⁶–5.60?×?10⁸ cells per insect). Contrary to our expectations, however, the Spiroplasma titers did not account for the variation in infection frequencies among offspring (i.e., vertical transmission rates). These results suggest that the spatial distribution of Spiroplasma, particularly in somatic tissues and germ tissues, is highly variable among host individuals, which may be caused by environmental stochasticity or some unknown effects.     

Intracochlear Bleeding Enhances Cochlear Fibrosis and Ossification: An Animal Study

The aim of this study was to investigate the effects of intracochlear bleeding during cochleostomy on cochlear inflammatory response and residual hearing in a guinea pig animal model. Auditory brainstem response threshold shifts were greater in blood injected ears (p<0.05). Interleukin-1β, interleukin-10, tumor necrosis factor-α and nitric oxide synthase 2, cytokines that are related to early stage inflammation, were significantly increased in blood injected ears compared to normal and cochleostomy only ears at 1 day after surgery; with the increased IL-1β being sustained until 3 days after the surgery (p<0.05). Hair cells were more severely damaged in blood injected ears than in cochleostomy only ears. Histopathologic examination revealed more extensive fibrosis and ossification in blood injected ears than cochleostomy only ears. These results show that intracochlear bleeding enhanced cochlear inflammation resulting in increased fibrosis and ossification in an experimental animal model.     

Generation of motor neurons requires spatiotemporal coordination between retinoic acid and Mib-mediated Notch signaling

Mind bomb (Mib) is an E3 ubiquitin ligase that activates the Notch signaling pathway. A previous study demonstrated that the generation of late-born GABAergic neurons may be regulated by the interplay between Mib and retinoic acid (RA). However, the relationship between Mib function and the retinoid pathway during the generation of late-born motor neurons remains unclear. We investigated the differentiation of neural progenitors into motor neurons by inhibition of Notch signaling and administration of RA to Tg[hsp70-Mib:EGFP] embryos. The number of motor neurons in the ventral spinal cord increased or decreased depending on the temporal inhibition of Mib-mediated Notch signaling. Inhibition of the retinoid pathway by citral treatment had a synergistic effect with overexpression of Mib:EGFP on the generation of ectopic motor neurons. Additionally, the proteolytic fragment of Mib was detected in differentiated P19 cells following treatment with RA. Our observations imply that the function of Mib may be attenuated by the retinoid pathway, and that Mib-mediated Notch signaling and the retinoid pathway play critical roles in the spatiotemporal differentiation of motor neurons.     

Comparison of Virulence between Seoul Virus Strain SR-11 and Hantaan Virus Strain 76–118 of Hantaviruses in Newborn Mice

Virulence of hantavirus strain of SR-11 Seoul virus and Hantaan 76–118 (HTN) of Hantaan virus were compared. Infections of both strains were lethal in newborn mice. However, inoculum required to cause lethal infection was about 4,000 times higher for strain HTN (1.65 × 10³ PFU/mouse/LD₅₀) than for strain SR-11 (0.36 PFU). Thus, both strains were considered pathogenic to newborn mice but they possessed different levels of virulence. The assay system used for these strains in newborn mice proved to be useful in the study of hantavirus vilurence. Growth curves of the two strains in CV-7 cell cultures were compared. Strain SR-11 was shown to have higher activity of virus replication and virus release into the culture fluids than strain HTN. The possibility of a relationship between replication activity and high levels of virulence in mice was suggested.     

Enhancement effect of water activity on enzymatic synthesis of cephalexin

The effect of water activity (a(w)) of the reaction medium on the enzymatic synthesis of cephalexin (CEX) from 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and D-alpha-phenylglycine methyl ester (PGM) was investigated using the alpha-amino acid ester hydrolase enzyme from Xanthomonas citri. It was found that the synthetic activity of the enzyme and the conversion yield were markedly improved when the a(w) of the reaction medium was lowered to about 0.97. The water activity depressing agents evaluated were glycerol, sucrose, and sorbitol, and the conversion yields were improved up to 170% with 15% glycerol, 230% with 30% sucrose, and 270% with 20% sorbitol, respectively. The extent of favorable effect of a(w) on the conversion yield was not the same among the a(w) depressors, probably due to other unknown interactions between the enzyme and depressors. However, optimal a(w) values corresponding to the maximum conversion yield coincided for all a(w) depressors used. The conversion yield of CEX showed an increasing trend with increasing a(w) up to the optimal a(w) value (0.96-0.97) which corresponds to the maximum conversion yield and a decreasing trend beyond the optimal a(w). There appears to be a delicate balance between the hydrolytic reaction of PGM and synthetic reaction of CEX. The increasing a(w)-[E . PGM] complex and the branched reaction pathway fluxes from [E . PGM] to PG (D-alpha-phenyl glycine) and CEX are balanced in such a way that the maximum CEX conversion yield is obtained at a(w) value of 0.96-0.97. The a(w) depressors stabilized the enzyme somewhat, but this positive effect was considered to be only a minor contribution to the substantial yield enhancement. The a(w) depressor effect on viscosity and in turn the mass transfer rate limitation was ruled out since the change in conversion due to the viscosity change was found to be insignificant. (c) 1993 John Wiley & Sons, Inc.     

Enhancement effect of polyethylene glycol on enzymatic synthesis of cephalexin

In an enzymatic synthesis of cephalexin (CEX) using an acylase from Xanthomonas citri, the effect of polyethylene glycol (PEG) on the synthetic reaction of 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and D-alpha-phenyl-glycine methyl ester (PGM) to CEX was investigated. The addition of PEG (MW 300-20,000) increased the yield significantly. This yield enhancement effect tended to increase with the increasing molecular weight of PEG. Addition of PEG to the reaction system did not affect both the CEX and PGM hydrolytic reactions. The PEG added to the reaction medium used in these experiments did not depress the water activity significantly, and the product yield improvement could not be explained by the activity alone. The PEG stabilized the enzyme activity to some extent, but this stabilizing effect was only partially attributable to the yield enhancement of CEX. The enhancing effect of PEG on the synthetic yield increased with the increasing PEG molecular weight or the length of the poly(oxy-1,2-ethanediyl) chain, which increases the hydrophobicity of PEG. This finding consequently has led to the conclusion that the PEG structure renders the affinity between enzyme and 7-ADCA, which is a hydrophobic substrate. The microenvironmental hydrophobicity of PEG and its interaction with the hydrophobic substrate was found to be the main reason for the improvement of the CEX yield. In fact, the Michaelis-Menten kinetic constant for 7-ADCA, K(7-ADCA) in the presence of PEG was smaller than that in the control system (without PEG addition). (c) 1993 John Wiley & Sons, Inc.