Expression of inflammatory cytokines and beta-defensin 1 mRNAs in porcine epithelial rests of Malassez in vitro

In the present study, we investigated the mRNA expression of inflammatory cytokines, including interleukin (IL)-1 alpha, IL-6, IL-8, and granulocyte macrophage colony-stimulating factor (GM-CSF), and beta defensin 1 (BD-1), an antimicrobial peptide, in the epithelial rests of Malassez in vitro. A reverse transcription-polymerase chain reaction (RT-PCR) assay was performed in order to observe the expression of these mRNAs. The effect of lipopolysaccharide (LPS) on the mRNA expression was also studied by quantitative RT-PCR assay, with a LightCycler, using the double-stranded DNA dye SYBR Green I. The mRNAs of the four kinds of inflammatory cytokines and BD-1 were detected in the epithelial cells under normal culture conditions. Immunocytochemical staining showed the expression of CD14, a receptor for LPS, on the epithelial cells. The mRNA expressions of IL-1 alpha, IL-6, IL-8, and GM-CSF were upregulated by stimulation with LPS, in a dose- and time-dependent manner. Epithelial cells incubated with 1000 ng/ml of LPS for 6 h showed the most significant upregulation of the cytokine mRNAs. On the other hand, no obvious alteration of BD-1 expression by LPS stimulation was observed. The results indicated that the epithelial rests of Malassez may actively participate in the inflammatory response to bacterial infection, and that they play an important role in the defense mechanism of the radicular cyst.

[Current status and future of lung transplantation]

Lung transplantation has been performed successfully since 1983 in patients with various end-stage lung diseases including primary pulmonary hypertension. More than 10,000 lung transplants have been reported in The Registry of the International Society for Heart and Lung Transplantation. In contrast, a transplant law became effective in Japan only recently and 11 lung transplants have been performed with excellent results. We performed the first successful living-donor lobar lung transplantation for a 19-y-o-f with primary pulmonary hypertension on January 5, 2001 using her father's right lower lobe and her mother's left lower lobe. When the patients with primary pulmonary hypertension do not respond to prostacyclin therapy, lung transplantation is a workable option.

A vitamin D analog ameliorates glomerular injury on rat glomerulonephritis

OCT (22-oxa-calcitriol), a vitamin D analog, has been reported to show strong inhibitory effects on mesangial cell proliferation in vitro. In the present study, we report a study of the effect of OCT on anti-thy-1 glomerulonephritis. Both OCT and 1,25(OH)(2)D(3) significantly inhibited mesangial cell proliferation, the degree of glomerulosclerosis, and albuminuria at day 8 compared to the disease control group. The OCT-treated group showed normal calcium levels but the 1,25(OH)(2)D(3)-treated group showed higher levels. The disease control group showed a marked increase of type I and type IV collagens, and alpha-smooth muscle actin (alpha-SMA) compared to the normal group. The treatment of OCT or 1,25(OH)(2)D(3) significantly reduced the expression of these proteins. The mRNA of the glomeruli of anti-thy-1 model expressed significantly higher levels of type I and type IV collagens, and alpha-SMA at day 8 compared to normal rats. Treatment with OCT or 1,25(OH)(2)D(3) inhibited the mRNA expressions of type I and type IV collagens, as well as that of alpha-SMA. These data demonstrate that OCT inhibits mesangial cell proliferation and extracellular matrix expansion with a low calcemic activity. Disease control rats showed significantly increased levels of transforming growth factor-beta1 protein in the glomeruli, but treatment with OCT or 1,25(OH)(2)D(3) markedly reduced this expression. The levels of mRNA in glomeruli were also consistent with these protein levels. Therefore, the suppressive effect of OCT may be mediated by inhibition of transforming growth factor-beta1. The present results suggest that OCT has potential for use in therapeutic strategy for the treatment of glomerulonephritis without inducing hypercalcemia.

Sterility of Drosophila with mutations in the Bloom syndrome gene--complementation by Ku70

The Drosophila Dmblm locus is a homolog of the human Bloom syndrome gene, which encodes a helicase of the RECQ family. We show that Dmblm is identical to mus309, a locus originally identified in a mutagen-sensitivity screen. One mus309 allele, which carries a stop codon between two of the helicase motifs, causes partial male sterility and complete female sterility. Mutant males produce an excess of XY sperm and nullo sperm, consistent with a high frequency of nondisjunction and/or chromosome loss. These phenotypes of mus309 suggest that Dmblm functions in DNA double-strand break repair. The mutant Dmblm phenotypes were partially rescued by an extra copy of the DNA repair gene Ku70, indicating that the two genes functionally interact in vivo.

Microsomal p450s use specific proline-rich sequences for efficient folding, but not for maintenance of the folded structure

The amino-terminal region of microsomal P450s contains three distinct sequence motifs, the signal-anchor sequence (SA), the basic sequence (BS), and the proline-rich sequence (PR). Studies with two P450s of the CYP2C subfamily, P4502C11 (CYP2C11) and P4502C2 (CYP2C2), have indicated that upon expression in eukaryotic cells (yeast, COS cells, and insect cells), specific proline residues in PR are important for proper folding. In the present study, we have established that the PR region in a very different CYP gene family, P450c17 (CYP17), is also important for efficient folding. These studies have been carried out using expression in Escherichia coli. Using P4502C11, we have established that the folding requirements for P450s in bacteria are very similar to those in eukaryotic cells. Interestingly, when the PR from P450c17 is swapped for that of P4502C11 and visa versa, complete misfolding is observed. However, both the BS and SA can be swapped between these P450s without affecting folding. After proper folding of P450c17, removal of the PR by factor Xa protease has no effect on the maintenance of the P450 structure. Inspection of the sequences of many different CYP gene families indicates that the PR sequence is conserved within a gene family but varies considerably between families. We conclude that PR is important for directing the folding pathway leading to the functional P450, but not for maintaining the functional form.

Importance of a proline-rich sequence in the amino-terminal region for correct folding of mitochondrial and soluble microbial p450s

All microsomal P450s have a proline-rich sequence (PR) in the amino-terminal region that is needed for proper folding [Kusano, K., Sakaguchi, M., Kagawa, N., Waterman, M.R. and Omura, T. (2001) J. Biochem., 129, 259-269]. There are also multiple proline residues near the amino-termini of the mature forms of all mitochondrial P450s and the amino-termini of soluble microbial P450s. To examine the functional significance of the PR in mitochondrial P450s, we expressed human P450c27 (CYP27) and bovine P450scc (CYP11A1) in an Escherichia coli heterologous expression system, and found that in each one specific proline residue is important for correct folding. Deletions from the amino-terminus further indicated the importance of the PR for the expression of a spectrally normal P450c27. Essentially the same results were obtained with two soluble microbial P450s, P450cam (CYP101) and P450nor, in each of which a PR is important for proper folding. We conclude that in all P450s (mitochondrial, microbial and microsomal P450s), a proline-rich sequence located in the amino-terminal region is important for proper folding. Furthermore, we predict that the importance of the PR in P450 folding is to reduce the tendency of the polypeptide to misfold prior to heme binding.

Cellular responses to postsegregational killing by restriction-modification genes

Plasmids that carry one of several type II restriction modification gene complexes are known to show increased stability. The underlying mechanism was proposed to be the lethal attack by restriction enzyme at chromosomal recognition sites in cells that had lost the restriction modification gene complex. In order to examine bacterial responses to this postsegregational cell killing, we analyzed the cellular processes following loss of the EcoRI restriction modification gene complex carried by a temperature-sensitive plasmid in an Escherichia coli strain that is wild type with respect to DNA repair. A shift to the nonpermissive temperature blocked plasmid replication, reduced the increase in viable cell counts and resulted in loss of cell viability. Many cells formed long filaments, some of which were multinucleated and others anucleated. In a mutant defective in RecBCD exonuclease/recombinase, these cell death symptoms were more severe and cleaved chromosomes accumulated. Growth inhibition was also more severe in recA, ruvAB, ruvC, recG, and recN mutants. The cells induced the SOS response in a RecBC-dependent manner. These observations strongly suggest that bacterial cells die as a result of chromosome cleavage after loss of a restriction modification gene complex and that the bacterial RecBCD/RecA machinery helps the cells to survive, at least to some extent, by repairing the cleaved chromosomes. These and previous results have led us to hypothesize that the RecBCD/Chi/RecA system serves to destroy restricted "nonself" DNA and repair restricted "self" DNA.

Single cell reverse transcription-polymerase chain reaction analysis of rat supraoptic magnocellular neurons: neuropeptide phenotypes and high voltage-gated calcium channel subtypes

Magnocellular neurosecretory cells (MNCs) in the hypothalamo-neurohypophysial system that express and secrete the nonapeptides oxytocin (OT) and vasopressin (VP) were evaluated for the expression of multiple genes in single magnocellular neurons from the rat supraoptic nucleus using a single cell RT-PCR protocol. We found that all cells representing the two major phenotypes, the OT and VP MNCs, express a small, but significant, amount of the other nonapeptide's messenger RNA (mRNA). In situ hybridization histochemical analyses confirmed this observation. A third phenotype, containing equivalent amounts of OT and VP mRNA, was detected in about 19% of the MNCs from lactating female supraoptic nuclei. Analyses of these phenotypes for other coexisting peptide mRNAs (e.g. CRH, cholecystokinin, galanin, dynorphin, and the calcium-binding protein, calbindin) generally confirmed expectations from the literature, but revealed cell to cell variation in their coexpression. Our results also show that the high voltage-activated calcium channel subunit genes, alpha1A-D, alpha2, and beta1-4 are expressed in virtually all MNCs. However, the alpha1E subunit gene is not expressed at detectable levels in these cells. The expression of all of the beta-subunit genes in each MNC may account for the variations in physiological and pharmacological properties of the high voltage-activated channels found in these neurons. (Endocrinology 140: 5391-5401, 1999)

Quantitative analysis of oxytocin and vasopressin messenger ribonucleic acids in single magnocellular neurons isolated from supraoptic nucleus of rat hypothalamus

Oxytocin (OT) and vasopressin (VP) are peptide hormones that are derived from genes predominantly expressed in distinct magnocellular neurons in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Recent evidence suggests that some magnocellular neurons coexpress both peptides. Our qualitative RT-PCR experiments on single cells show that the majority of magnocellular neurons coexpress both peptide messenger RNAs (mRNAs) in varying amounts. Using a competitive RT-PCR method combined with a standard calibration curve, we quantitatively determined OT and VP mRNA in single magnocellular neurons from the normal female rat SON, with a detection sensitivity of less than 30 mRNA molecules/cell. We defined the phenotypes of the single magnocellular neurons according to their ratios of these two peptide mRNAs. Using this approach, we identified three major phenotypes: oxytocin neurons, where the average OT to VP mRNA ratio is about 256; vasopressin neurons, where the average VP to OT mRNA ratio is about 182; and one oxytocin/vasopressin coexisting neuron, where the OT/VP mRNA ratio is 2. Thus, there is some OT and VP mRNA coexpression in virtually all of the magnocellular neurons in supraoptic nuclei of hypothalamus. However, clear phenotypes are identifiable by considering quantitative as opposed to qualitative differences.

Protein synthesis inhibitors and ethanol selectively enhance heterologous expression of P450s and related proteins in Escherichia coli

The antibiotics chloramphenicol (Cm), tetracycline, and erythromycin, which inhibit bacterial protein synthesis and are known to induce the cold shock response, unexpectedly enhance the heterologous expression of P450s and related proteins in Escherichia coli. In contrast, antibiotics that mimic heat shock in E. coli such as puromycin, streptomycin, and kanamycin decrease the expression of the same proteins. A sublethal dose of Cm (1 microgram/ml) effectively enhances the expression of both membrane-bound proteins (microsomal and mitochondrial P450s) and a soluble mitochondrial protein (adrenodoxin) over the range of two- to eightfold. The expression level of N-terminal truncated P450c17 (1600 nmol/liter culture without Cm), for instance, reached 3500 nmol/liter culture by the addition of Cm, approximately 8.4% of the total cellular protein. Cm also enabled expression at useful levels of active P450s previously difficult to express in E. coli. In contrast, the expression of P450scc, a mitochondrial protein, is decreased by Cm but enhanced by ethanol, a powerful elicitor of heat shock response in E. coli. These results show that both the cold shock response induced by some antibiotics and the heat shock response induced by ethanol may lead to enhanced expression of certain heterologous proteins in E. coli. This study also indicates that protein synthesis inhibitors associated with the cold shock response may act as protein synthesis enhancers under certain conditions.

Evolution of the RECQ family of helicases: A drosophila homolog, Dmblm, is similar to the human bloom syndrome gene

Several eukaryotic homologs of the Escherichia coli RecQ DNA helicase have been found. These include the human BLM gene, whose mutation results in Bloom syndrome, and the human WRN gene, whose mutation leads to Werner syndrome resembling premature aging. We cloned a Drosophila melanogaster homolog of the RECQ helicase family, Dmblm (Drosophila melanogaster Bloom), which encodes a putative 1487-amino-acid protein. Phylogenetic and dot plot analyses for the RECQ family, including 10 eukaryotic and 3 prokaryotic genes, indicate Dmblm is most closely related to the Homo sapiens BLM gene, suggesting functional similarity. Also, we found that Dmblm cDNA partially rescued the sensitivity to methyl methanesulfonate of Saccharomyces cerevisiae sgs1 mutant, demonstrating the presence of a functional similarity between Dmblm and SGS1. Our analyses identify four possible subfamilies in the RECQ family: (1) the BLM subgroup (H. sapiens Bloom, D. melanogaster Dmblm, and Caenorhabditis elegans T04A11.6); (2) the yeast RECQ subgroup (S. cerevisiae SGS1 and Schizosaccharomyces pombe rqh1/rad12); (3) the RECQL/Q1 subgroup (H. sapiens RECQL/Q1 and C. elegans K02F3.1); and (4) the WRN subgroup (H. sapiens Werner and C. elegans F18C5.2). This result may indicate that metazoans hold at least three RECQ genes, each of which may have a different function, and that multiple RECQ genes diverged with the generation of multicellular organisms. We propose that invertebrates such as nematodes and insects are useful as model systems of human genetic diseases.

Effects of osmotic pressure and brain-derived neurotrophic factor on the survival of postnatal hypothalamic oxytocinergic and vasopressinergic neurons in dissociated cell culture

Neurons from hypothalamic paraventricular nuclei (PVN) and supraoptic nuclei (SON) from postnatal day 6-8 rats were enzymatically dissociated and separately maintained in monolayer cultures for 14 days. The osmotic pressure of the culture medium, based on Neurobasal medium (Life Technologies), was varied (255, 300 and 330 mOsm/l) by adjustment using mannitol. The survival of oxytocin (OT), vasopressin (VP) and oxytocin-vasopressin (OT/VP) coexpressing neurons were studied under these varied conditions, and the identification of the cell phenotypes in the cultures was carried out by using double-label immunofluorescence. Under control osmolar conditions (300 mOsm/l) equivalent numbers of OT and VP neurons were found in the SON (P = 0.8398) and PVN (P = 0.4721) cultures. The OT neurons' survival did not change in 255 or 330 mOsm media in the SON cultures, but the VP neurons in the SON cultures were significantly increased in 255 mOsm/l medium as compared to control (300 mOsm/l) medium (P = 0.0088). No significant changes were found in VP neuron survival in SON cultures between the 300-330 mOsm/l media (P = 0.2372). Similar data were obtained for the VP neurons in PVN-derived cultures, but the OT neurons in these cultures survived significantly better at 300 mOs/l than at 255 mOsm/l (P<0.0001), but were not significantly different at 330 mOsm/l (P = 0.1208). In general, the VP neurons were more vulnerable than OT neurons to increases of culture medium osmolarity with respect to their survival. The number of OT/VP coexpressing neurons was greater in SON-derived cell cultures as compared to PVN-derived cell cultures, and their numbers were higher in the lower osmolarity media. The effects of adding brain-derived neurotrophic factor (BDNF) to the culture medium on survival were determined. BDNF significantly increased the numbers of all three types of neurons in both PVN and SON cell cultures (P = 0.0001-0.0060). The phenotypically identified cells, cultured in the 300 mOsm/l medium, responded by depolarization or hyperpolarization when transferred to hypertonic or hypotonic perfusion salines, respectively.

Detection of a sequence involved in actin-binding and phosphoinositide-binding in the N-terminal side of cofilin

Cofilin is an actin-binding protein of low molecular weight which is widely distributed in eukaryotes and is deeply involved in the dynamics of actin assembly in the cytoplasm. The actin-binding ability of cofilin is inhibited by inositol phosphates (PIP2), and the PIP2- and actin-binding site(s) has been localized in residues W104-M115 of the cofilin primary sequence (Yonezawa et al. 1991 ). In the present study, in order to further clarify the functional domains in cofilin molecule, we constructed expression vectors containing cDNAs of different size with deletion at the 3'-region of the open reading frame. The truncated cofilin molecules produced in E. coli were purified and examined for their actin-binding and PIP2-binding ability. We found that the truncated cofilin molecule without C-terminal residues #100-#166 including the previously-described actin-binding site could be cross-linked with actin by EDC, a zero-length cross-linker. In addition, these truncated peptides as well as synthetic peptides corresponding to the N-terminal sequence of cofilin suppressed the inhibitory action of PIP2 on actin-cofilin interaction. These results strongly suggest that additional actin- and PIP2-binding sites exist in the N-terminal region of cofilin.

Stationary organotypic cultures of oxytocin and vasopressin magnocellular neurones from rat and mouse hypothalamus

Rat and mouse hypothalami from postnatal animals containing highly differentiated neurones survive very well in long-term (>15 days in vitro, DIV) stationary organotypic cultures. Magnocellular oxytocin (OT) and vasopressin (VP) neurones are present in identifiable paraventricular (PVN), supraoptic (SON) and accessory (ACC) nuclei in these cultures. After 15 DIV in standard medium immunocytochemistry revealed 427 +/- 63 OT cells and 217 +/- 27 VP cells per cultured rat hypothalamus, and 380 +/- 72 OT cells and 622 +/- 91 VP cells per cultured mouse hypothalamus. Following a 7-day adaptation period in standard culture medium containing serum, the rat slice-explants survived very well after subsequent transfer to defined, serum- free media (SFM) for an additional 8 days. The number of OT cells surviving in SFM was 612 +/- 147 OT cells per cultured rat hypothalamus. Only 0.5% of the magnocellular OT and VP neurones in the cultures appeared to express both peptides. Experiments on c-fos gene expression in these cultures showed that while only 12% of the magnocellular OT and VP neurones contained barely detectable Fos protein in their nuclei under control conditions, potassium depolarization of these cultures for 3 h produced intense c-fos expression in 87-91% of these cells. Thus, magnocellular neurones in these cultures are sufficiently stable and responsive to permit long-term physiological and gene expression studies to be done under defined media conditions.

Regulation of matrix metalloproteinases (MMP-2, -3, -9, and -13) by interleukin-1 and interleukin-6 in mouse calvaria: association of MMP induction with bone resorption

Interleukin-1 (IL-1) greatly induces osteoclast formation and stimulates bone resorption of mouse calvaria in culture. In the presence of soluble IL-6 receptor (sIL-6R), IL-6 similarly induces osteoclast formation, but the potency of IL-6 in inducing bone resorption in organ culture is weaker than that of IL-1. To study the differences in bone-resorbing activity between IL-1 and IL-6, we examined the effects of the two cytokines on the induction of matrix metalloproteinases (MMPs). In mouse calvarial cultures, IL-1 markedly enhanced the messenger RNA (mRNA) expression of MMP-13 (collagenase 3), MMP-2 (gelatinase A), MMP-9 (gelatinase B), and MMP-3 (stromelysin 1), which associated with increases in bone matrix degradation. A hydroxamate inhibitor of MMPs significantly suppressed bone-resorbing activity induced by IL-1. Gelatin zymography showed that both pro- and active-forms of MMP-2 and MMP-9 were detected in the conditioned medium collected from calvarial cultures, and IL-1 markedly stimulated both pro- and active-forms of the two gelatinases. IL-6 with sIL-6R also stimulated mRNA expression and biological activities of these MMPs, but the potency was much weaker than that of IL-1. Conditioned medium collected from IL-1-treated calvariae degraded native type I collagen, but 3/4- and 1/4-length collagen fragments were not detected, suggesting that both collagenases and gelatinases synergistically degraded type I collagen into smaller fragments. In mouse osteoblastic cells, the expression ofMMP-2, MMP-3, and MMP-13 mRNAs could be detected, and they were markedly enhanced by IL-1alpha on days 2 and 5. IL-6 with sIL-6R also induced expression of MMP-13 and MMP-2 mRNAs on day 2, but the expression was rather transient. These results demonstrate that the potency of induction of MMPs by IL-1 and IL-6 is closely linked to the respective bone-resorbing activity, suggesting that MMP-dependent degradation of bone matrix plays a key role in bone resorption induced by these cytokines.

Anthelmintic efficacy of milbemycin oxime against Trichuris vulpis in dogs

The anthelmintic efficacy of milbemycin oxime against dog whipworm, Trichuris vulpis, was evaluated. A total of 21 T. vulpis positive dogs were divided into 3 groups, one (5 dogs) for control and the other two (8 dogs each) for anthelmintic treatment with oral administration of milbemycin oxime.

Generalized LP(1m) Modes in an Optical Fiber with Constant Radius of Curvature

Accurate forms for the generalized LP(1m) mode in a uniform circular-core curved fiber are given. We show that each generalized LP(1m) mode is composed of four linearly polarized partial fields. We also show that, when the propagation constants of HE(2m), TM(0m), and TE(0m) modes are degenerate, there are four linearly polarized modes for each generalized LP(1m) mode.

A new type of illegitimate recombination is dependent on restriction and homologous interaction

Illegitimate (nonhomologous) recombination requires little or no sequence homology between recombining DNAs and has been regarded as being a process distinct from homologous recombination, which requires a long stretch of homology between recombining DNAs. Under special conditions in Escherichia coli, we have found a new type of illegitimate recombination that requires an interaction between homologous DNA sequences. It was detected when a plasmid that carried 2-kb-long inverted repeats was subjected to type II restriction in vitro and type I (EcoKI) restriction in vivo within a delta rac recBC recG ruvC strain. Removal of one of the repeats or its replacement with heterologous DNA resulted in a reduction in the level of recombination. The recombining sites themselves shared, at most, a few base pairs of homology. Many of the recombination events joined a site in one of the repeats with a site in another repeat. In two of the products, one of the recombining sites was at the end of one of the repeats. Removal of one of the EcoKI sites resulted in decreased recombination. We discuss the possibility that some structure made by homologous interaction between the long repeats is used by the EcoKI restriction enzyme to promote illegitimate recombination. The possible roles and consequences of this type of homologous interaction are discussed.

Chi-star, a chi-related 11-mer sequence partially active in an E. coli recC1004 strain

BACKGROUND

chi sequence (5'GCTGGTGG) of Escherichia coli was first identified as a site that increased the plaque size of bacteriophage lambda. Subsequent studies showed that this site is responsible for both the attenuation ofRecBCD exonuclease activity and the promotion of RecA, RecBCD-mediated recombination. It is known that bacteriophage lambda containing the chi site makes very small plaques on a recC* (recC1004) mutant because chi is not recognized by the RecBC*D mutant enzyme.

RESULTS

We cloned E. coli chromosomal fragments in lambda which allowed lambda to form larger plaques on this recC1004 mutant. The fragments were found to share a chi-like 11-mer sequence, 5'GCTGGTGCTCG. Substitution of these fragments with a synthetic 11-mer of this sequence and single-base-pair substitution analysis of its last four nucleotides demonstrated that this sequence is both necessary and sufficient for the observed activity. The sequence, designated X* (chi-star), protected rolling-circle DNA replication in the recC1004 mutant and in the recBCD+ strain, most likely because it attenuated the exonuclease activity of the RecBC*D and RecBCD+ enzyme. chi-star, did not significantly stimulate lambda recombination in two assays.

CONCLUSION

We have discovered that a mutant RecBCD enzyme responds, in vivo, to a longer chi variant.

Propionibacterium cyclohexanicum sp. nov., a new acid-tolerant omega-cyclohexyl fatty acid-containing propionibacterium isolated from spoiled orange juice

A non-spore-forming, coryneform bacterium, strain TA-12T, was isolated from spoiled off-flavor orange juice. Growth of this organism occurs at pH 3.2 to 7.5, and optimum growth occurs at pH values between 5.5 and 6.5. This organism produces lactic acid, propionic acid, and acetic acid from glucose. It is catalase negative. The cells are heat resistant and can withstand a temperature of 90 degrees C for 10 min. The DNA G + C content is 66.8 mol%. This strain has as MK-9(H4) respiratory quinone system and contains meso-diaminopimelic acid in its cell wall, and omega-cyclohexyl undecanoic acid is the major cellular fatty acid. The results of a phylogenetic analysis of the 168 rRNA gene of this organism indicated that its highest level of homology is its level of homology with the representative of the classical propionibacteria, Propionibacterium freudenreichii (97.1%). Strain TA-12T is phenotypically similar to P. freudenreichii, but it produces a large amount of lactic acid and has a distinct fatty acid composition, acid tolerance, and heat resistance, which differentiate it from P. freudenreichii and other propionic acid-producing bacteria. On the basis of these findings we propose the name Propionibacterium cyclohexanicum sp. nov. for this organism. The type strain is TA-12 (= IAM 14535 = NRIC 0247).

Genetic recombination through double-strand break repair: shift from two-progeny mode to one-progeny mode by heterologous inserts

Double-strand break repair models of genetic recombination propose that a double-strand break is introduced into an otherwise intact DNA and that the break is then repaired by copying a homologous DNA segment. Evidence for these models has been found among lambdoid phages and during yeast meiosis. In an earlier report, we demonstrated such repair of a preformed double-strand break by the Escherichia coli RecE pathway. Here, our experiments with plasmids demonstrate that such reciprocal or conservative recombination (two parental DNAs resulting in two progeny DNAs) is frequent at a double-strand break even when there exists the alternative route of nonreciprocal or nonconservative recombination (two parental DNAs resulting in only one progeny DNA). The presence of a long heterologous DNA at the double-strand break, however, resulted in a shift from the conservative (two-progeny) mode to the nonconservative (one-progeny) mode. The product is a DNA free from the heterologous insert containing recombinant flanking sequences. The potential ability of the homology-dependent double-strand break repair reaction to detect and eliminate heterologous inserts may have contributed to the evolution of homologous recombination, meiosis and sexual reproduction.

Primary structure of mouse actin-related protein 1 (Arp1) and its tissue expression

Different types of actin-related proteins which constitute an actin-superfamily together with conventional actin have recently been described (Mullins et al., 1996). Among them, Arp1 exhibits the highest homology with conventional actin. With the aim of clarifying the cellular function of Arp1 in mammalian cells, we cloned the cDNA encoding mouse alpha-Arp1, one of the variants of Arp1, from a mouse diaphragm cDNA library; two types of alpha-Arp1 cDNAs, which are probably generated by alternative RNA splicing from a single gene, were obtained and the entire sequences were determined. They differed only in the presence or absence of an insertion of 1.3 kb in the 3'-non-cooling region but shared a common open reading frame. The deduced amino acid sequence was identical with that of human alpha-Arp1. Northern blot analysis showed that the alpha-Arp1 mRNA corresponding to the longer cDNA is transcribed not only in various non-muscle tissues but also in muscle tissues, while the transcript corresponding to the shorter one becomes expressed only in skeletal muscle as development progresses. It is suggested that alpha-Arp1 may play some role in muscle, as judged by the significant level of its expression.

Low molecular-weight G-actin binding proteins involved in the regulation of actin assembly during myofibrillogenesis

We previously demonstrated that small G-actin binding proteins, cofilin, ADF and profilin, are involved in the actin dynamics during myofibrillogenesis (OBINATA, T. (1993). Int. Rev. Cytol., 143: 153-189.). To better understand how they are responsible for the regulation of actin assembly, the amounts of the actin-binding proteins were quantified by means of quantitative immunoblotting and compared with that of G-actin pool. The sum of the amounts of cofilin, ADF and profilin was insufficient at early developmental stages but sufficient at later stages to account for the pool of G-actin in muscle cells. We detected expression of thymosin beta 4 at a considerable level in young embryonic but not in adult skeletal muscles. We, therefore, conclude that the G-actin pool in young embryonic skeletal muscle is mainly due to cofilin, ADF, profilin and thymosin beta 4. Switching from a non-muscle-type (NM-) cofilin to a muscle-type (M-) cofilin was observed during muscle development of mammals. In order to clarify cofilin-dependent regulation of actin assembly in muscle cells, cofilin tagged with fluorescence dyes was introduced into C2 myoblasts by a micro injection method. The exogeneous cofilin, but not ADF, caused quick disassembly of actin filaments and accumulated in furrow region of dividing cells. The analogs of the unphosphorylated form (A3-cofilin) and the phosphorylated form (D3-cofilin) were prepared by converting Ser3, a regulatory phosphorylation site, to Ala or Asp. When A3-cofilin and D3-cofilin were injected into living cells, the former was concentrated at the membrane ruffles and cleavage furrow, while the latter showed only diffuse distribution in the cytoplasm. These results suggest that the subcellular distribution of cofilin as well as its interaction with actin in vivo is regulated by its phosphorylation and dephosphorylation.