A subtilisin-like serine protease is required for epidermal surface formation inArabidopsisembryos and juvenile plants

The surfaces of land plants are covered with a cuticle that is essential for retention of water. Epidermal surfaces of Arabidopsis thaliana embryos and juvenile plants that were homozygous for abnormal leaf shape1 (ale1) mutations were defective, resulting in excessive water loss and organ fusion in young plants. In ale1 embryos, the cuticle was rudimentary and remnants of the endosperm remained attached to developing embryos. Juvenile plants had a similar abnormal cuticle. The ALE1 gene was isolated using a transposon-tagged allele ale1-1. The predicted ALE1 amino acid sequence was homologous to those of subtilisin-like serine proteases. The ALE1 gene was found to be expressed within certain endosperm cells adjacent to the embryo and within the young embryo. Expression was not detected after germination. Our results suggest that the putative protease ALE1 affects the formation of cuticle on embryos and juvenile plants and that an appropriate cuticle is required for separation of the endosperm from the embryo and for prevention of organ fusion.

Increased inactivation of nitric oxide is involved in impaired coronary flow reserve in heart failure

Recent evidence suggests that increased inactivation of endothelium-derived nitric oxide (NO) by oxygen free radical (OFR) formation is involved in the pathogenesis of endothelial dysfunction in heart failure (HF). However, it is unclear whether increased OFR limits coronary flow reserve in HF. To test this hypothesis, we examined the effects of antioxidant therapy on coronary flow reserve in a canine model of tachycardia-induced HF. The flow reserve (percent increase in coronary blood flow) to adenosine or to 20-s ischemia was less and OFR formation (electron-spin resonance spectroscopy) in myocardial tissues was greater in HF dogs than in controls. Immunohistochemical staining of 4-hydroxy-2-nonenal, an OFR-induced lipid peroxide, was detected in coronary microvessels of HF dogs. Intracoronary infusion of a cell-permeable OFR scavenger, tiron, suppressed OFR formation and improved the vasodilating capacity to adenosine or brief ischemia in HF dogs but not in controls. A NO synthesis inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), diminished the beneficial effects of tiron in HF dogs. Vasodilation to sodium nitroprusside was similar between control and HF dogs, and no change in its response was noted with tiron or tiron + L-NMMA in either group. In summary, antioxidant treatment with tiron improved coronary flow reserve by increasing NO bioactivity in HF dogs. Thus increased OFR formation may impair coronary flow reserve in HF by reducing NO bioactivity.

Expansion of the phragmoplast during plant cytokinesis: a MAPK pathway may MAP it out

Plant cytokinesis involves the formation of a cell plate. This is accomplished with the help of the phragmoplast, a plant-specific cytokinetic apparatus that consists of microtubules and microfilaments. During centrifugal growth of the cell plate, the phragmoplast expands to keep its microtubules at the leading edge of the cell plate. Recent studies have revealed potential regulators of phragmoplast microtubule dynamics and the involvement of a mitogen-activated protein kinase cascade in the control of phragmoplast expansion. These studies provide new insights into the molecular mechanisms of plant cytokinesis.

UV absorption method should not be applied for determining amoxycillin in acidic dissolution test medium

In order to clarify the suitability of assay method, the stability of amoxycillin (AMX) in the acidic solution at pH 1.2 was determined by two different methods, ultraviolet absorption (UV) and HPLC methods. The determination was simultaneously performed for the same sample solutions. The data from HPLC method indicated that AMX degraded and the concentration of AMX in the acidic solution was decreased. The apparent first-order rate constant (k(obs)) for the degradation was 9.83x10(-2) h(-1), and the half-life was calculated to be 7.04 h. On the other hand, the data obtained from UV method apparently represented that the concentration of AMX increased with time-course. This phenomena was brought about by the increase of UV absorption at 272 nm, which accompanied with the degradation of AMX. These results clearly indicate that UV method can not be used for determining the samples accompanying the degradation of AMX. In general, the dissolution test (drug release test) has been used for the evaluation of a sustained-release dosage form of AMX. It is impossible to avoid the degradation of AMX in the test under acidic conditions. The results indicated that the UV method should not be used for the determination of AMX in the test.

The effect of soybean oil refuse powder used as vehicle on the absorption of oxolinic acid in chickens under fasting and nonfasting conditions and the correlation with in vitro dissolution

The effect of soybean oil refuse powder (SOR) when used as a vehicle on the absorption of oxolinic acid (OXA) powder in chicken, the dissolution profile of OXA and the correlation between in vivo and in vitro study were examined. To examine in vivo bioavailability, chickens fed or fasted were studied using a 2 x 2 crossover design. The OXA was administered OXA or OXA-SOR (1 : 9) mixture 20 mg OXA/kg. In vitro dissolution rates for OXA and OXA-SOR were measured using the paddle (PD) and the rotatory dialysis cell dissolution (PTSW) methods. Maximum plasma concentration (Cmax) and area under the curve (AUC) were significantly increased by the addition of SOR to OXA. Differences between OXA and OXA-SOR were more remarkable under fasted as compared with fed condition. In vitro dissolution rates of OXA-SOR pH 1.2, 6.5 and 7.2 as determined by the PD and the PTSW methods were increased in the presence of SOR vehicle. Differences between OXA and OXA-SOR in vitro dissolution rates were greater than in vivo bioavailability. Correlation between in vitro release (%) and in vivo absorption (%) showed good linearity (gamma=0.8805-0.9999).

Lactosaminated and intact N-succinyl-chitosans as drug carriers in liver metastasis

The biodistributions of fluorescently labeled N-succinyl-chitosan (Suc-FTC) and lactosaminated N-succinyl-chitosan (Lac-Suc-FTC) after i.v. administration to mice intravenously inoculated with M5076 cells were investigated at 3 and 12 days post-inoculation. At both time points, Lac-Suc-FTC was specifically localized to the liver. However, the area under the concentration-time curve in the liver decreased gradually by progress of the liver metastasis. At 3 days post-inoculation, Suc-FTC showed good retention in the systemic circulation and was little distributed to the liver. However, at 12 days post-inoculation, Suc-FTC was eliminated relatively fast from the systemic circulation and gradually accumulated in the liver. The antitumor effects of mitomycin C (MMC), Lac-Suc-MMC conjugate (Lac-Suc-MMC) and highly succinylated Suc (Suc(II))-MMC conjugate (Suc(II)-MMC) were examined on single i.v. administration for both metastatic stages. For administration at 3 days post-inoculation, Lac-Suc-MMC alone tended to elongate significantly the lifespan at a lower dose (0.4 mg eq. MMC/kg), and MMC, Suc(II)-MMC and Lac-Suc-MMC increased significantly the lifespan at a higher dose (10 mg eq. MMC/kg). However, at 12 days post-inoculation (late stage of metastasis), neither MMC nor the conjugates were effective even at the higher dose (10 mg eq. MMC/kg). Both carriers, Suc showing systemic long-circulation and Lac-Suc with an ability of liver-specific localization, are thought to be drug carriers with potentialities for therapeutics at early stage of metastasis.

Bifurcation, birooted primary canines: a case report

A rare case of birooted primary canines is reported. A male patient aged 6 years 4 months of age presented with pain and swelling related to the upper right first primary molar. Radiographic examination revealed an incidental finding of bifurcation of the roots of all four primary canines. This represents a rare finding. The prevalence of birooted permanent canines in the Japanese population has been reported, but the prevalence of this abnormality of primary canines in other populations is unknown. This report discusses the findings in the context of the available literature. The possible aetiology, possible inferences for the developing dentition, and the need for careful assessment prior to root canal therapy or extraction are highlighted.

Sustained release ketoprofen microparticles with ethylcellulose and carboxymethylethylcellulose

Microparticulate systems for sustained release of ketoprofen were prepared and evaluated by monitoring drug release in the JP XIII second fluid, pH 6.8. All the microparticulate dosage forms were prepared using ketoprofen in the form of calcium salt (KP-Ca). Simple ethylcellulose microparticles of KP-Ca (EC-MP) exhibited the fairly rapid release in the first phase with slower release in the late period. Most of the drug was released from EC-MP showing high drug content. For polymer-coated microparticles of ketoprofen, Eudragit microparticles of KP-Ca (ER-MP) were first prepared, and then coated with ethylcellulose or with a mixture of carboxymethylethylcellulose and ethylcellulose to produce ethylcellulose-coated (EC-coat) and the mixture-coated microparticles (CMEC/EC-coat), respectively. Some polymer-coated microparticles showed drug release at nearly zero-order rate. Especially, CMEC/EC-coat prepared at a CMEC:EC ratio of 1:1 (w/w), named formation I, could supply the drug constantly and efficiently for about half a day except for an initial rapid release. When formation I was administered intraduodenally to rats, the plasma concentration of ketoprofen could be maintained at a nearly constant level. Kinetic analysis demonstrated that formation I showed a nearly zero-order release rate in vivo consistent with that observed in vitro.

Replication from oriP of Epstein-Barr virus requires human ORC and is inhibited by geminin

A hypomorphic mutation made in the ORC2 gene of a human cancer cell line through homologous recombination decreased Orc2 protein levels by 90%. The G1 phase of the cell cycle was prolonged, but there was no effect on the utilization of either the c-Myc or beta-globin cellular origins of replication. Cells carrying this mutation failed to support the replication of a plasmid bearing the oriP replicator of Epstein Barr virus (EBV), and this defect was rescued by reintroduction of Orc2. Orc2 specifically associates with oriP in cells, most likely through its interaction with EBNA1. Geminin, an inhibitor of the mammalian replication initiation complex, inhibits replication from oriP. Therefore, ORC and the human replication initiation apparatus is required for replication from a viral origin of replication.

G2/M-phase-specific transcription during the plant cell cycle is mediated by c-Myb-like transcription factors

Plant B-type cyclin genes are expressed specifically in late G2- and M-phases during the cell cycle. Their promoters contain a common cis-acting element, called the MSA (M-specific activator) element, that is necessary and sufficient for periodic promoter activation. This motif also is present in the tobacco kinesin-like protein gene NACK1, which is expressed with timing similar to that of B-type cyclin genes. In this study, we show that G2/M-phase-specific activation of the NACK1 promoter also is regulated by the MSA element, suggesting that a defined set of G2/M-phase-specific genes are coregulated by an MSA-mediated mechanism. In a search for MSA binding factors by yeast one-hybrid screening, we identified three different Myb-like proteins that interact specifically with the MSA sequence. Unlike the majority of plant Myb-like proteins, these Myb proteins, NtmybA1, NtmybA2, and NtmybB, have three imperfect repeats in the DNA binding domain, as in animal c-Myb proteins. During the cell cycle, the level of NtmybB mRNA did not change significantly, whereas the levels of NtmybA1 and A2 mRNAs fluctuated and peaked at M-phase, when B-type cyclin genes were maximally induced. In transient expression assays, NtmybA1 and A2 activated the MSA-containing promoters, whereas NtmybB repressed them. Furthermore, expression of NtmybB repressed the transcriptional activation mediated by NtmybA2. Our data show that a group of plant Myb proteins that are structurally similar to animal c-Myb proteins have unexpected roles in G2/M-phase by modulating the expression of B-type cyclin genes and may regulate a suite of coexpressed genes.

Preparation and in vitro properties of N-succinylchitosan- or carboxymethylchitin-mitomycin C conjugate microparticles with specified size

The preparation of cross-linked conjugate microparticles of N-succinyl-chitosan (Suc) or 6-O-carboxymethylchitin (CM) with mitomycin C (MMC), which showed an adequate si-e for liver targeting (0.2-3 microm), was attempted by a combination of water-soluble carbodiimide (EDC) coupling and emulsification technique. As for Suc, microparticles with a diameter less than a few micrometers could be obtained easily, while the preparation of CM microparticles (CM-MPs) of the same diameter was not necessarily easy. First, preparation conditions were compared for CM-MPs, and some conditions gave CM-MPs with a diameter less than a few micrometers. As to CM-MMC conjugate microparticles, the method by addition of EDC after emulsification using CM with low molecular weight (CML) gave more appropriate microparticles with a mean diameter of 0.97microm (CM1-MP-MMC). Suc-MMC conjugate microparticles adequate for liver targeting could be produced by the addition of EDC both before and after emulsification, especially, the conjugate microparticles with a mean diameter of 0.45 microm (Suc-MP-MMC) were derived by the addition of EDC before emulsification. Suc-MP-MMC exhibited a higher drug content than CML-MP-MMC. CML-MP-MMC and Suc-MP-MMC exhibited 50% drug release times of 2.87h and 42.1 h, respectively.

G2/M-phase-specific transcription during the plant cell cycle is mediated by c-Myb-like transcription factors

Plant B-type cyclin genes are expressed specifically in late G2- and M-phases during the cell cycle. Their promoters contain a common cis-acting element, called the MSA (M-specific activator) element, that is necessary and sufficient for periodic promoter activation. This motif also is present in the tobacco kinesin-like protein gene NACK1, which is expressed with timing similar to that of B-type cyclin genes. In this study, we show that G2/M-phase-specific activation of the NACK1 promoter also is regulated by the MSA element, suggesting that a defined set of G2/M-phase-specific genes are coregulated by an MSA-mediated mechanism. In a search for MSA binding factors by yeast one-hybrid screening, we identified three different Myb-like proteins that interact specifically with the MSA sequence. Unlike the majority of plant Myb-like proteins, these Myb proteins, NtmybA1, NtmybA2, and NtmybB, have three imperfect repeats in the DNA binding domain, as in animal c-Myb proteins. During the cell cycle, the level of NtmybB mRNA did not change significantly, whereas the levels of NtmybA1 and A2 mRNAs fluctuated and peaked at M-phase, when B-type cyclin genes were maximally induced. In transient expression assays, NtmybA1 and A2 activated the MSA-containing promoters, whereas NtmybB repressed them. Furthermore, expression of NtmybB repressed the transcriptional activation mediated by NtmybA2. Our data show that a group of plant Myb proteins that are structurally similar to animal c-Myb proteins have unexpected roles in G2/M-phase by modulating the expression of B-type cyclin genes and may regulate a suite of coexpressed genes.

Bioadhesive characteristics of chitosan microspheres to the mucosa of rat small intestine

Chitosan (Chi) microspheres were examined in vitro and in vivo in terms of their bioadhesive characteristics to the mucosa of rat small intestine. Chi was labeled with fluorescein isothiocyanate (FITC), and the microspheres (FTC-MS) were prepared by the dry-in-oil method using the obtained fluorescein thiocarbamyl-chitosan (FTC-Chi). FTC-MS with a mean diameter of 27 microm and size distribution of a few micrometers to several tens of micrometers was used for the bioadhesion experiment. FTC-MS exhibited a tendency to adhere to each part of the small intestine to a greater extent than dissolved FTC-Chi, and the ratio of adhering FTC-MS increased as the amount of added FTC-MS decreased. FTC-MS showed slower transit following intraduodenal injection than oral administration. Following the intraduodenal injection of FTC-MS, more than half remained in the upper or middle part of the small intestine for over 8 h. Further, insulin-containing chitosan microspheres with a mean diameter of 20 microm and size distribution of 5 microm to 45 microm were checked in situ for drug absorption, but intraduodenal or intraileal application hardly gave any decrease in plasma glucose level at a very high dose. The present chitosan microsphere system showed good adhesion to the intestinal mucosa, but scarcely facilitated absorption of insulin.

Identification of a monofunctional aspartate kinase gene of Arabidopsis thaliana with spatially and temporally regulated expression

We screened a gene trap library of Arabidopsis thaliana and isolated a line in which a gene encoding a homologue of monofunctional aspartate kinase was trapped by the reporter gene. Aspartate kinase (AK) is a key enzyme in the biosynthsis of aspartate family amino acids such as lysine, threonine, isoleucine, and methionine. In plants, two types of AK are known: one is AK which is sensitive to feedback inhibition by threonine and carries both AK and homoserine dehydrogenase (HSD) activities. The other one is monofunctional, sensitive to lysine and synergistically S-adenosylmethionine, and has only AK activity. We concluded that the trapped gene encoded a monofunctional aspartate kinase and designated as AK-lys3, because it lacked the HSD domain and had an amino acid sequence highly similar to those of the monofunctional aspartate kinases ofA. thaliana. AK-lys3 was highly expressed in xylem of leaves and hypocotyls and stele of roots. Significant expression of this gene was also observed in trichomes after bolting. Slight expression of AK-lys3 was detected in vascular bundles and mesophyll cells of cauline leaves, inflorescence stems, sepals, petals, and stigmas. These results indicated that this aspartate kinase gene was not expressed uniformly but in a spatially specific manner.

[Atypical Fisher syndrome with optic nerve involvement]

We report a 38-year-old woman who developed what appeared to be Fisher syndrome associated with optic nerve involvement. One week after a common cold, she developed double vision and left facial palsy. Four days after the onset, she developed bilateral blurred vision, painful total ophthalmoplegia, and ataxic gait. Brain CT and MRI findings were normal. Her vision worsened but the optic fundi were normal. Serum anti-GQ 1 b antibody was elevated. She received steroid therapy at another hospital, and her vision, facial palsy and ocular pain improved. She was transferred to our hospital and we treated her by plasma exchange. She showed near complete recovery. Human optic and ocular nerves contain high amount of GQ 1 b. This may be a underlying mechanism for optic nerve involvement in Fisher syndrome. We thought that she had an atypical Fisher syndrome associated with optic nerve involvement.

The ASYMMETRIC LEAVES2 gene of Arabidopsis thaliana regulates formation of a symmetric lamina, establishment of venation and repression of meristem-related homeobox genes in leaves

The asymmetric leaves2 (as2) mutant of Arabidopsis thaliana generated leaf lobes and leaflet-like structures from the petioles of leaves in a bilaterally asymmetric manner. Both the delayed formation of the primary vein and the asymmetric formation of secondary veins were apparent in leaf primordia of as2 plants. A distinct midvein, which is the thickest vein and is located in the longitudinal center of the leaf lamina of wild-type plants, was often rudimentary even in mature as2 leaves. However, several parallel veins of very similar thickness were evident in such leaves. The complexity of venation patterns in all leaf-like organs of as2 plants was reduced. The malformed veins were visible before the development of asymmetry of the leaf lamina and were maintained in mature as2 leaves. In vitro culture on phytohormone-free medium of leaf sections from as2 mutants and from the asymmetric leaves1 (as1) mutant, which has a phenotype similar to that of as2, revealed an elevated potential in both cases for regeneration of shoots from leaf cells. Analysis by the reverse transcription-polymerase chain reaction showed that transcripts of the KNAT1, KNAT2 and KNAT6 (a recently identified member of the class 1 knox family) genes accumulated in the leaves of both as2 and as1 plants but not of wild type. Transcripts of the STM gene also accumulated in as1 leaves. These findings suggest that, in leaves, the AS2 and AS1 genes repress the expression of these homeobox genes, which are thought to maintain the indeterminate cell state in the shoot apical meristem. Taken together, our results suggest that AS2 and AS1 might be involved in establishment of a prominent midvein and of networks of other veins as well as in the formation of the symmetric leaf lamina, which might be related to repression of class 1 knox homeobox genes in leaves.

The transposition pattern of the Ac element in tobacco cultured cells

We investigated physical distances and directions of transposition of the maize transposable element Ac in tobacco cultured cells. We introduced a T-DNA construct that carried a non-autonomous derivative of Ac (designated dAc-I-RS) that included sites for cleavage by restriction endonuclease MluI. Another cleavage site was also introduced into the T-DNA region outside of the dAc-I-RS transposable element. The tobacco cultured cell line BY-2 was transformed with the T-DNA and several transformed lines that had a single copy of the T-DNA at a different chromosomal location were isolated. These lines were co-cultured with Agrobacterium tumefaciens cells that carried a cDNA for the Ac transposase gene under the control of various promoters. Sublines of cultured cells in which dAc-I-RS had been transposed, were isolated. The genomic DNAs of these sublines were isolated and digested with MluI. Sizes of DNA segments generated by digestion were determined by pulse-field gel electrophoresis. Our results showed that 20 to 70% of transposition events had occurred within several hundreds kilo-base pairs (kb) on the same chromosome. These results demonstrate that the Ac-Ds element preferentially transposed to regions near the original site in a tobacco chromosome. In addition, the present results are an example of asymmetric transposition as demonstrated by the distance of transposition on the chromosome.

In vitro and in vivo evaluation of sustained release chitosan-coated ketoprofen microparticles

Simple ketoprofen microspheres (MS) were prepared by the dry-in-oil method using ethylcellulose (EC) as a matrix polymer. Further, the microspheres modified by addition of polyethylene glycol (PEG) and hydroxypropyl cellulose (HPC), called MS-P and MS-H, respectively, were prepared. The in vitro release from MS, MS-P and MS-H was examined in the JP XIII second fluid, pH 6.8, at 37 degrees C and 60 rpm. Chitosan-coated ketoprofen microparticles (Chi-MP) were prepared by the precipitation of droplets of chitosan solution containing MS, and their adhesion to the rat small intestinal mucosa was tested. The plasma concentrations after duodenal administration were investigated for ketoprofen powder suspension, MS and Chi-MP. The particle size was raised with the increase in amount of ketoprofen added. The drug content and addition of PEG or HPC affected the drug release rate. The microspheres with moderate drug content, prepared by addition of modest amount of PEG, exhibited better gradual drug release. Chi-MP showed a good mucoadhesion. The maximum plasma concentration of ketoprofen for Chi-MP was less than one-third of that for ketoprofen powder suspension. Chi-MP tended to show the higher and steadier plasma level than MS.

Biological characteristics of lactosaminated N-succinyl-chitosan as a liver-specific drug carrier in mice

Lactosaminated N-succinyl-chitosan (Lac-Suc) was prepared by reductive amination of N-succinyl-chitosan (Suc) and lactose using sodium cyanoborohydride. Six-day reaction using lactose (12.8-fold (w/w)) yielded Lac-Suc with lactosamination degree of 30% (mol/sugar unit). Fluorescein thiocarbamyl-Lac-Suc (Lac-Suc-FTC) was prepared by labeling Lac-Suc with fluorescein isothiocyanate. Lac-Suc-FTC was injected intravenously at a dose of either 1 (high dose) or 0.2 (low dose) mg/mouse. At both doses, Lac-Suc-FTC initially underwent fast hepatic clearance, showed maximum liver localization at 8 h, and the amounts localized there were maintained even at 48 h post-injection. Very slow excretion into feces and urine was observed. The ratio of liver AUC(0--48 h) to plasma AUC(0--48 h) at low dose was three times higher than that at high dose. On the other hand, the Suc derivative, Gal-Suc, obtained by reductive amination of Suc/galactose showed very little distribution to the liver similarly to Suc itself. Further, since the liver uptake of Lac-Suc-FTC was inhibited by asialofetuin, it was suggested that the liver distribution of Lac-Suc should be concerned with asialoglycoprotein receptor. Thus, Lac-Suc was found available as a carrier exhibiting a high affinity to and long retention in the liver.

[Enhancing effect of switching iontophoresis on transdermal absorption of glibenclamide]

Glibenclamide(GLI) is widely used as an oral hypoglycemic drug in the treatment of non-insulin dependent diabetes mellitus (NIDDM). We investigated The enhancing effect of switching iontophoresis on the transdermal absorption and reduction of skin irritation to develop a transdermal dosage form of GLI. The 0.1% of Gli suspensions in 0.2 M tris-HCl buffer of pH 7.4, 8.0 and 8.5 were prepared as donor solutions. We examined drug permeation through the excised rat abdominal skin, drug absorption in rats and reduction of skin irritation after application of switching iontophoresis for 1 h using DC 10 V. The solubility of GLI in 0.2 M tris-HCl buffer increased with a rise in pH. In the permeation study, GLI was permeated continuously and the cumulative amount of permeated GLI increased using an alkaline donor solution. In the drug absorption study, the application group of pH 8.5 gave higher plasma concentration levels than those of pH 7.4 and 8.0 groups. The skin irritation evoked by the application of iontophoresis was pathologically studied. A total irritation score (TIS) was estimated as a judging standard for the skin damage. The TIS value increased dependently with a rise in pH. However, it was considered that the skin irritations were not serious and small matters. The results demonstrate the possibility of iontophoretic transdermal administration of GLI and the effect of drug solubility in the donor solution on the absorption of GLI.

A case of amelogenesis imperfecta of deciduous and all permanent teeth

We experienced a case with severe enamel defects of both the deciduous teeth and all the permanent teeth. In order to clarify the etiology of enamel defects in this patient, we performed a DNA analysis in addition to conventional examinations. Although we suspected a variety of systemic factors causing enamel defects, there was no evidence suggesting disturbances of amelogenesis. In the present case, we suspected a mutation in the amelogenin gene and performed nucleotide sequencing of the exons of the amelogenin gene, but we could not find any evidence of mutation. We suggest that a mutation of some other gene related to enamel formation or the adventitious factors contributed to the amelogenesis imperfecta in this case.

The NPK1 mitogen-activated protein kinase kinase kinase is a regulator of cell-plate formation in plant cytokinesis

Mitogen-activated protein kinase (MAPK) cascades play important roles not only in the transduction of extracellular signals but in the progression of the cell cycle. However, evidence for their role in cytokinesis is limited. Here, we show that a tobacco MAPK kinase kinase (MAPKKK), designated NPK1, is required for cytokinesis. The activity of NPK1 increases in the late M phase of the tobacco cell cycle. During expansion of a new cross-wall (cell plate) toward the cell cortex, NPK1 is consistently localized to the equatorial zone of the phragmoplast, the cytokinetic apparatus where the cell plate is formed. Expression of a kinase-negative mutant of NPK1 results in the generation of multinucleate cells with incomplete cell plates. Phragmoplasts can be formed, but its expansion toward the cell cortex is also blocked. Thus, our results indicate that the NPK1 MAPKKK is essential for the formation of the cell plate, especially for its lateral growth.

Generation of periventricular leukomalacia by repeated umbilical cord occlusion in near-term fetal sheep and its possible pathogenetical mechanisms

Periventricular leukomalacia (PVL) is a major cause of cerebral palsy. However, pathogenetic mechanisms of PVL have not been fully understood. Although it has been postulated that umbilical cord compression is related to the development of PVL, no animal experiments clearly demonstrated an association of umbilical cord occlusion with 'periventricular' white matter lesions. The purpose of this study is to determine whether umbilical cord occlusions could produce periventricular white matter lesions in fetal sheep and to examine how changes in fetal cardiovascular and metabolic variables are related to the induction of brain damage. Fourteen near-term fetal sheep underwent umbilical cord occlusion (3-min total cord occlusions 5 times at 5-min intervals). Dissections performed 24 h after cord occlusion revealed that periventricular white matter lesions were produced in 7 out of 14 sheep fetuses. According to the pattern of brain damage, we classified the fetal sheep into three groups: 5 fetuses with dominant lesions in the periventricular white matter (group I), 4 fetuses with brain lesions in the cerebral cortex and thalamus (group II) and 5 fetuses with no or minimal brain lesions (group III). Group I showed higher blood pressure and higher plasma lipid peroxide levels before cord occlusion compared to the other groups, while group II showed systemic hypotension during cord occlusion. No significant differences in changes in pH, PaCO2, PaO2 and heart rate were found between the three groups. It is speculated that PVL might be produced by an association of preexisting chronic circulatory instability with an acute episode of severe repetitive cord occlusion.

Expression of chromatin remodeling factors during neural differentiation

The yeast SWI/SNF complex is involved in remodeling of chromatin structure during transcriptional modulation. One of the key subunits of this complex, called SWI2/SNF2, has a DNA-dependent ATPase activity. Two different types of mammalian homolog of yeast SWI2/SNF2, called BRM and BRG1, were recently identified. They are closely similar in structure but have distinct functions. We investigated the expression of BRM and BRG1 during differentiation of neural precursor cells (NPCs) cultured in vitro. The expression of BRM was very low in NPCs and was induced to a high level during differentiation to neurons and astrocytes. In contrast, BRG1 was constantly expressed throughout differentiation. These phenomena were also observed in differentiation of P19 embryonal carcinoma cells to neural cells. Immunocytochemical analyses revealed that the expression of BRM started even in the undifferentiated nestin-positive cells. These results indicate that BRM may have an important role in neural cell differentiation.

Biological fate of highly-succinylated N-succinyl-chitosan and antitumor characteristics of its water-soluble conjugate with mitomycin C at i.v. and i.p. administration into tumor-bearing mice

Highly-succinylated N-succinyl-chitosan (Suc) was fluorescein-labeled, and the labeled product (Suc-FTC) was examined for biodisposition in Sarcoma 180-bearing mice after i.v. and i.p. administration. Suc-FTC injected intravenously was sustained at a high level in the blood circulation and showed little distribution to tissues other than tumor. On the other hand, it took a few hours for Suc-FTC to be transferred to the blood circulation after i.p. administration. There were no marked differences in the distribution of Suc-FTC between i.v. and i.p. administration routes except in the early stage. The urinary excretion of Suc-FTC following both i.v. and i.p. administration was small, but the excretion tended to be suppressed after i.p. administration. Water-soluble Sucmitomycin C conjugate (Suc-MMC) prepared using water-soluble carbodiimide exhibited marked effect at a high dose and suppressed the acute toxic side effect of MMC. Suc-MMC tended to be more toxic at i.p. administration than at i.v. administration. The difference in biodisposition between the two administrations was thought to affect the toxic side effect. The plasma levels of conjugated and free MMCs at 8 h after i.v. administration were higher than those at 8 h after i.p. administration. These suggested more localization of the conjugate in peripheral tissues and less excretion at i.p. administration, which might result in greater toxicity.