Knock-down of DMY initiates female pathway in the genetic male medaka, Oryzias latipes

DMY is the second vertebrate sex-determining gene identified from the fish, Oryzias latipes. In this study, we used two different ways of sex reversal, DMY knock-down and estradiol-17beta (E2) treatment, to determine the possible function of DMY during early gonadal sex differentiation in XY medaka. Our findings revealed that the mitotic and meiotic activities of the germ cells in the 0 day after hatching (dah) DMY knock-down XY larvae were identical to those of the normal XX larvae, suggesting the microenvironment of these XY gonads to be similar to that of the normal XX gonad, where DMY is naturally absent. Conversely, E2 treatment failed to initiate mitosis in the XY gonad, possibly due to an active DMY, even though it could initiate meiosis. Present study is the first to prove that the germ cells in the XY gonad can resume the mitotic activity, if DMY was knocked down.     

Effect of disulfide-bond introduction on the activity and stability of the extended-spectrum class A beta-lactamase Toho-1

The production of class A beta-lactamases is a major cause of clinical resistance to beta-lactam antibiotics. Some of class A beta-lactamases are known to have a disulfide bridge. Both narrow spectrum and extended spectrum beta-lactamases of TEM and the SHV enzymes possess a disulfide bond between Cys77 and Cys123, and the enzymes with carbapenem-hydrolyzing activity have a well-conserved disulfide bridge between Cys69 and Cys238. We produced A77C/G123C mutant of the extended-spectrum beta-lactamase Toho-1 in order to introduce a disulfide bond between the cysteine residues at positions 77 and 123. The result of 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) titrations confirmed formation of a new disulfide bridge in the mutant. The results of irreversible heat inactivation and circular dichroism (CD) melting experiments indicated that the disulfide bridge stabilized the enzyme significantly. Though kinetic analysis indicated that the catalytic properties of the mutant were quite similar to those of the wild-type enzyme, E. coli producing this mutant showed drug resistance significantly higher than E. coli producing the wild-type enzyme. We speculate that the stability of the enzymes provided by the disulfide bond may explain the wide distribution of TEM and SHV derivatives and explain how various mutations can cause broadened substrate specificity without loss of stability.     

Potential role for astroglial D-amino acid oxidase in extracellular D-serine metabolism and cytotoxicity

D-amino acid oxidase (DAO) is a flavoenzyme that catalyzes the oxidation of D-amino acids. In the brain, gene expression of DAO is detected in astrocytes. Among the possible substrates of DAO in vivo, D-serine is proposed to be a neuromodulator of the N-methyl-D-aspartate (NMDA) receptor. In a search for the physiological role of DAO in the brain, we investigated the metabolism of extracellular D-serine in glial cells. Here we show that after D-serine treatment, rat primary type-1 astrocytes exhibited increased cell death. In order to enhance the enzyme activity of DAO in cells, we established stable rat C6 glial cells overexpressing mouse DAO designated as C6/DAO. Treatment with a high dose of D-serine led to the production of hydrogen peroxide (H(2)O(2)) followed by apoptosis in C6/DAO cells. Among the amino acids tested, D-serine specifically exhibited a significant cell death-inducing effect. DAO inhibitors, i.e., sodium benzoate and chlorpromazine, partially prevented the death of C6/DAO cells treated with D-serine, indicating the involvement of DAO activity in d-serine metabolism. Overall, we consider that extracellular D-serine can gain access to intracellular DAO, being metabolized to produce H(2)O(2). These results support the proposal that astroglial DAO plays an important role in metabolizing a neuromodulator, D-serine.     

Structures of the carbohydrate recognition domain of Ca2+-independent cargo receptors Emp46p and Emp47p

Emp46p and Emp47p are type I membrane proteins, which cycle between the endoplasmic reticulum (ER) and the Golgi apparatus by vesicles coated with coat protein complexes I and II (COPI and COPII). They are considered to function as cargo receptors for exporting N-linked glycoproteins from the ER. We have determined crystal structures of the carbohydrate recognition domains (CRDs) of Emp46p and Emp47p of Saccharomyces cerevisiae, in the absence and presence of metal ions. Both proteins fold as a beta-sandwich, and resemble that of the mammalian ortholog, p58/ERGIC-53. However, the nature of metal binding is distinct from that of Ca(2+)-dependent p58/ERGIC-53. Interestingly, the CRD of Emp46p does not bind Ca(2+) ion but instead binds K(+) ion at the edge of a concave beta-sheet whose position is distinct from the corresponding site of the Ca(2+) ion in p58/ERGIC-53. Binding of K(+) ion to Emp46p appears essential for transport of a subset of glycoproteins because the Y131F mutant of Emp46p, which cannot bind K(+) ion fails to rescue the transport in disruptants of EMP46 and EMP47 genes. In contrast the CRD of Emp47p binds no metal ions at all. Furthermore, the CRD of Emp46p binds to glycoproteins carrying high mannosetype glycans and the is promoted by binding not the addition of Ca(2+) or K(+) ion in These results suggest that Emp46p can be regarded as a Ca(2+)-independent intracellular lectin at the ER exit sites.     

Immunological effects of recombinant feline interferon-omega (KT-80) administration in the dog

The immunological effects of recombinant feline interferon-omega (rFeIFN-omega ; KT-80, Toray) were examined on administration to healthy dogs. The activities of whole blood cells, macrophages, and natural killer cells were enhanced. Moreover, the whole blood activity was examined when KT-80 was administered to dogs which had been diagnosed as having natural canine parvovirus (CPV) infection. Only some cases in which the activity increased until 3 hr post-administration survived. These results suggest that rFeIFN-omega (KT-80) treatment enhanced the cellular immunity of normal dogs, and could exert significant therapeutic effects on only natural CPV infected dogs with induced continuous immunoenhancement.     

Deletion polymorphisms in the promoter region of Fcgamma receptor IIB is not associated with antigen-specific IgG2a and IgG2b antibody responses in NC/Nga mice

Fcgamma receptor (R) IIB, a low-affinity FcR for IgG, inhibits B cell Ag R (BCR)-mediated activation when these two receptors are cross-linked by Ag and IgG-containing immune complexs (ICs). We found deletion polymorphisms in the promoter region of fcgr2b in NC/Nga mice, a model for human atopic dermatitis. NC/Nga mice produced significantly higher levels of ovalbumin (OVA)-specific IgG, IgG2a and IgG2b than did BALB/c mice. Analysis of (BALB/c x NC/Nga)F1 x BALB/c or (BALB/c x NC/Nga) F1 x NC/Nga backcross mice revealed that deletion polymorphisms of fcgr2b in NC/Nga mice does not directly regulate hyper OVA-specific IgG2a and IgG2b Ab responses.