Spatial Analysis of Slowly Oscillating Electric Activity in the Gut of Mice Using Low Impedance Arrayed Microelectrodes

Smooth and elaborate gut motility is based on cellular cooperation, including smooth muscle, enteric neurons and special interstitial cells acting as pacemaker cells. Therefore, spatial characterization of electric activity in tissues containing these electric excitable cells is required for a precise understanding of gut motility. Furthermore, tools to evaluate spatial electric activity in a small area would be useful for the investigation of model animals. We thus employed a microelectrode array (MEA) system to simultaneously measure a set of 8×8 field potentials in a square area of ∼1 mm². The size of each recording electrode was 50×50 µm², however the surface area was increased by fixing platinum black particles. The impedance of microelectrode was sufficiently low to apply a high-pass filter of 0.1 Hz. Mapping of spectral power, and auto-correlation and cross-correlation parameters characterized the spatial properties of spontaneous electric activity in the ileum of wild-type (WT) and W/W^v mice, the latter serving as a model of impaired network of pacemaking interstitial cells. Namely, electric activities measured varied in both size and cooperativity in W/W^v mice, despite the small area. In the ileum of WT mice, procedures suppressing the excitability of smooth muscle and neurons altered the propagation of spontaneous electric activity, but had little change in the period of oscillations. In conclusion, MEA with low impedance electrodes enables to measure slowly oscillating electric activity, and is useful to evaluate both histological and functional changes in the spatio-temporal property of gut electric activity.     

A 5-bp Insertion in Mip Causes Recessive Congenital Cataract in KFRS4/Kyo Rats

We discovered a new cataract mutation, kfrs4, in the Kyoto Fancy Rat Stock (KFRS) background. Within 1 month of birth, all kfrs4/kfrs4 homozygotes developed cataracts, with severe opacity in the nuclei of the lens. In contrast, no opacity was observed in the kfrs4/+ heterozygotes. We continued to observe these rats until they reached 1 year of age and found that cataractogenesis did not occur in kfrs4/+ rats. To define the histological defects in the lenses of kfrs4 rats, sections of the eyes of these rats were prepared. Although the lenses of kfrs4/kfrs4 homozygotes showed severely disorganised fibres and vacuolation, the lenses of kfrs4/+ heterozygotes appeared normal and similar to those of wild-type rats. We used positional cloning to identify the kfrs4 mutation. The mutation was mapped to an approximately 9.7-Mb region on chromosome 7, which contains the Mip gene. This gene is responsible for a dominant form of cataract in humans and mice. Sequence analysis of the mutant-derived Mip gene identified a 5-bp insertion. This insertion is predicted to inactivate the MIP protein, as it produces a frameshift that results in the synthesis of 6 novel amino acid residues and a truncated protein that lacks 136 amino acids in the C-terminal region, and no MIP immunoreactivity was observed in the lens fibre cells of kfrs4/kfrs4 homozygous rats using an antibody that recognises the C- and N-terminus of MIP. In addition, the kfrs4/+ heterozygotes showed reduced expression of Mip mRNA and MIP protein and the kfrs4/kfrs4 homozygotes showed no expression in the lens. These results indicate that the kfrs4 mutation conveys a loss-of-function, which leads to functional inactivation though the degradation of Mip mRNA by an mRNA decay mechanism. Therefore, the kfrs4 rat represents the first characterised rat model with a recessive mutation in the Mip gene.     

The APC/C activator Cdh1 regulates the G2/M transition during differentiation of placental trophoblast stem cells

Differentiation of placental trophoblast stem (TS) cells to trophoblast giant (TG) cells is accompanied by transition from a mitotic cell cycle to an endocycle. Here, we report that Cdh1, a regulator of the anaphase-promoting complex/cyclosome (APC/C), negatively regulates mitotic entry upon the mitotic/endocycle transition. TS cells derived from homozygous Cdh1 gene-trapped (Cdh1^GT/GT) murine embryos accumulated mitotic cyclins and precociously entered mitosis after induction of TS cell differentiation, indicating that Cdh1 is required for the switch from mitosis to the endocycle. Furthermore, the Cdh1^GT/GT TS cells and placenta showed aberrant expression of placental differentiation markers. These data highlight an important role of Cdh1 in the G2/M transition during placental differentiation.     

Acquisition of a sucrose utilization system in Escherichia coli K-12 derivatives and its application to industry.

An Escherichia coli strain, B-62, that was isolated from a clinical source and was epidemiologically unrelated to E. coli K-12 was the source of chromosomal DNA for a sucrose utilization system (Scr+) in the construction of a plasmid, pST621. The cloned insert of a gene encoding Scr+ in pST621 conferred a sucrose-positive phenotype onto transformed cells of E. coli K-12 derivatives. Sucrase activity of the transformants was as high as that which would correspond to a "gene dosage effect" of a vector plasmid pBR322, whereas the transformants' sucrose uptake activity was always lower than that of E. coli B-62. A region within an XhoI-SacI fragment (3.2 kb) of pBR322-glyA was replaced in the construction of another plasmid, pST5R7, by a fragment (about 2.6 kb) of pST622 containing the gene encoding Scr+. A genetically stable Scr+ derivative of E. coli K-12 was obtained by introducing the gene encoding Scr+ onto E. coli chromosome via homologous recombination between pST5R7 and the chromosome and subsequent plasmid segregation. The use of low-copy-number plasmid RP4 as a cloning vector was also effective for enhancing the stability of Scr+. Tryptophan producers E. coli SGIII1032S, in which the gene encoding Scr+ was cloned onto the chromosome, and E. coli SGIII1032, which carried Scr+ plasmid RP4.5R7, produced from 6% sucrose in shake flasks (33 degrees C, 96 h) 2.3 and 5.7 g of tryptophan per liter, respectively.     

Cloning of the macrolide antibiotic biosynthesis gene acyA, which encodes 3-O-acyltransferase, from Streptomyces thermotolerans and its use for direct fermentative production of a hybrid macrolide antibiotic.

A gene encoding the macrolide modification enzyme 3-O-acyltransferase (acyA) was cloned by chromosome walking onto the carbomycin biosynthetic region in Streptomyces thermotolerans TH475, with the 3' region of the gene encoding the macrolide modification enzyme 4"-O-acyltransferase (acyB1) as a probe. A shortened fragment (1.8 kb) containing acyA was subcloned with pIJ350. A high-level tylosin producer, Streptomyces fradiae MBBF, transformed with the plasmid could produce a hybrid macrolide, 3-O-acetyltylosin, most efficiently.     

A new snailfish of the genus Careproctus (Cottoidei: Liparidae) from the Pacific coast of southern Japan

Ichthyological Research - A new snailfish, Careproctus tomiyamai, is described on the basis of four specimens collected from Suruga Bay, Tosa Bay, and the Hyuga-nada Sea, southern Japan...     

Effect of gravity stress on fidelity of DNA double-strand break repair.

DNA double strand break (DSB) causes many cytotoxic effects such as cellular lethality, somatic mutation, and carcinogenesis. Fidelity of DSB repair is a important factor that determines the quality of genomic stability. It is known that the most of DSBs are properly repaired on the earth, however, little is known whether those are rejoined at the same fidelity even under the space environment. One of the DSB repair pathway, homologous recombination (HR), allows the cells to repair their DSBs with error free. Therefore, the efficiency of HR is a good index to assess the fidelity of DSB repair. In order to clarify the effect of gravity stress on HR pathway, we established a cell line that can detect a site-specific DNA repair via HR. The cells carrying a reporter construct for HR were incubated under hypergravity condition after induction of site specific DSB. Our preliminary results suggest that the gravity stress may affect the HR efficiency.     

Enhancement of tryptophan production by Escherichia coli as an application of genetic engineering

Summary A feedback resistant trp operon plasmid that transformed a multiple mutant (trpR tnaA) of Escherichia coli was found to enhance remarkably the production of tryptophan in a bench-scale fermentor. 5.5 g of tryptophan was accumulated per litre of culture medium at 24th hr in batch. The productivity was 0.229 g/l/hr. This productivity is the highest among those ever reported by other workers. The recombinant plasmid (Tc^r Trp⁺ I^-) used was completely stable in each run when tetracycline was added by 10 g/l into the medium.     

TnA-directed deletion of the trp operon from RSF2124-trp in Escherichia coli

Plasmid pMT-trp was constructed by digestion of RSF2124-trp with restriction endonuclease PstI and ligation with T4 ligase. In pMT-trp about 78% of the DNA of transposon TnA from RSF2124-trp was deleted, and hence the gene for ampicillin resistance was lost. All Trp- segregants from pMT-trp carriers in Escherichia coli W3110 and its derivatives were found to have lost the entire plasmid. On the other hand, deletion plasmids which had lost the trp operon were found among Trp- segregants from RSF2124-trp carriers, particularly from the mutant strain trpAE1 trpR tnaA. The experimental fact that deletion occurred exclusively in RSF2124-trp suggests that the presence of TnA in the plasmid (RSF2124-trp) was responsible for the deletion.