Human fetuses do not register chromosome damage inflicted by radiation exposure in lymphoid precursor cells except for a small but significant effect at low doses

Human fetuses are thought to be highly sensitive to radiation exposure because diagnostic low-dose X rays have been suggested to increase the risk of childhood leukemia. However, animal studies generally have not demonstrated a high radiosensitivity of fetuses, and the underlying causes for the discrepancy remain unidentified. We examined atomic bomb survivors exposed in utero for translocation frequencies in blood lymphocytes at 40 years of age. Contrary to our expectation of a greater radiosensitivity in fetuses than in adults, the frequency did not increase with dose except for a small increase (less than 1%) at doses below 0.1 Sv, which was statistically significant. We interpret the results as indicating that fetal lymphoid precursor cells comprise two subpopulations. One is small in number, sensitive to the induction of both translocations and cell killing, but rapidly diminishing above 50 mSv. The other is the major fraction but is insensitive to registering damage expressed as chromosome aberrations. Our results provide a biological basis for resolving the long-standing controversy that a substantial risk of childhood leukemia is implicated in human fetuses exposed to low-dose X rays whereas animal studies involving mainly high-dose exposures generally do not confirm it.     

Mmr1p is a mitochondrial factor for Myo2p-dependent inheritance of mitochondria in the budding yeast

Class V myosins play a pivotal role in organelle distribution. In the budding yeast, Myo2p, a class V myosin, is essential for mitochondrial distribution. We identified MMR1 as a high-dose suppressor of the myo2 mitochondrial defect and that Mmr1p resides restrictively on the bud-localizing mitochondria and forms a complex with Myo2p tail. Mmr1p loss delayed mitochondrial transfer to buds and completely abolished mitochondrial distribution in the absence of Ypt11p, which promotes mitochondrial distribution by complex formation with Myo2p tail. The myo2-573 mutation, which causes a mitochondrial distribution defect and inactivates the Mmr1p function, reduced association between Myo2p and Mmr1p and depolarized Mmr1p localization on mitochondria. These strongly suggest that Mmr1p is a key mitochondrial component of the link between Myo2p and mitochondria for Myo2p-dependent mitochondrial distribution. Genetical analysis revealed that the Mmr1p-Myo2p pathway is independent of the Ypt11p-Myo2p pathway, suggesting that an essential system for mitochondrial distribution is composed of two independent Myo2p pathways.     

An association study using AFLP markers and application to a beef cattle breeding population

Using amplified fragment length polymorphism (AFLP) fingerprinting, selective genotyping was performed to determine if this method was effective for selecting superior breeding stock. Forty-eight cows with extreme genetic merit for beef marbling score (BMS) were selected from a population of Japanese Black cattle (n = 4462), including 25 with the highest for predicted breeding value (PBV) and 23 with the lowest. Sixteen AFLP fragments were selected for further analysis based on fragment frequency differences between the high and low groups. A linear discriminant analysis using these AFLP fragments was applied in order to derive a discriminant function that classified the cows into high and low groups. Seven of the 16 fragments were included in the resulting function and the discriminant scores (general genetic values, GGV) of the 48 cows were calculated using the function. These cows were clearly separated into high and low groups by GGV with a correlation ratio of 0.91 (discriminative error of 2.1%). The same function was then applied to 121 additional cows that were randomly selected from the original population. A significant regression coefficient of GGV on BMS-PBV (R2 = 0.45) was obtained, which indicates that the GGV can be used as a selection criterion for BMS in this population. These results suggest that AFLP fingerprinting can be used for animal breeding without identifying the underlying genes affecting the trait of interest.     

The Wnt/beta-catenin pathway directs neuronal differentiation of cortical neural precursor cells

Neural precursor cells (NPCs) have the ability to self-renew and to give rise to neuronal and glial lineages. The fate decision of NPCs between proliferation and differentiation determines the number of differentiated cells and the size of each region of the brain. However, the signals that regulate the timing of neuronal differentiation remain unclear. Here, we show that Wnt signaling inhibits the self-renewal capacity of mouse cortical NPCs, and instructively promotes their neuronal differentiation. Overexpression of Wnt7a or of a stabilized form of beta-catenin in mouse cortical NPC cultures induced neuronal differentiation even in the presence of Fgf2, a self-renewal-promoting factor in this system. Moreover, blockade of Wnt signaling led to inhibition of neuronal differentiation of cortical NPCs in vitro and in the developing mouse neocortex. Furthermore, the beta-catenin/TCF complex appears to directly regulate the promoter of neurogenin 1, a gene implicated in cortical neuronal differentiation. Importantly, stabilized beta-catenin did not induce neuronal differentiation of cortical NPCs at earlier developmental stages, consistent with previous reports indicating self-renewal-promoting functions of Wnts in early NPCs. These findings may reveal broader and stage-specific physiological roles of Wnt signaling during neural development.     

Expression of chlorophyllase is not induced during autumnal yellowing in Ginkgo biloba

Autumnal tints are one of the most fascinating natural phenomena, but the molecular mechanism of chlorophyll (Chl-)degradation in deciduous trees has not been fully understood. In this study, from the leaves of Ginkgo biloba, chlorophyllase-homologous GbCLH was cloned by RT-PCR with degenerated primers. The expression of GbCLH in different yellowing stages was analyzed by Northern hybridization. The expression level of GbCLH was highest in green leaves and significantly declined during the process of leaf yellowing. These results suggested that GbCLH should be involved in chlorophyll-homeostasis in Ginkgo biloba.     

Agonist-induced isometric contraction of smooth muscle cell-populated collagen gel fiber

String-shaped reconstitutedsmooth muscle (SM) fibers were prepared in rectangular wells by thermalgelation of a mixed solution of collagen and cultured SM cells derivedfrom guinea pig stomach. The cells in the fiber exhibited an elongatedspindle shape and were aligned along the long axis. The fibercontracted in response to KCl (140 mM), norepinephrine (NE;10⁷ M), epinephrine (10⁷ M), phenylephrine(10⁶ M), serotonin (10⁶ M), and histamine(10⁵ M), but not acetylcholine (10⁵ M).Phentolamine (10⁷ M) produced a parallel rightward shiftof the NE dose-response curve. Moreover, NE-induced contractionwas partially inhibited by nifedipine and completely abolished by theintracellular Ca²⁺ chelator1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acidacetoxymethyl ester, the myosin light chain kinase inhibitor ML-9, theRho kinase inhibitor Y-27632, and papaverine. A[³H]quinuclidinyl benzilate binding study revealed thatthe loss of response to acetylcholine was due to the loss of muscarinic receptor expression during culture. The expression of contractile proteins in the fibers was similar to that in cultured SM cells. Theseresults suggest that, although the fiber is not a model for fullydifferentiated SM, contractile mechanisms are maintained.

     

Partial Purification and Characterization of Thermostable Acid Phosphatase from Thermoacidophilic Archaeon Sulfolobus acidocaldarius

Thermostable acid phosphatase (APase) from thermoacidophilic archaeon Sulfolobus acidocaldarius was isolated, partially purified, and characterized. The optimum pH and temperature of the enzyme for p-nitrophenylphosphate (pNPP) as a substrate were 5.0 and 70°C, respectively. The apparent K _m value was 1.9 mM. This APase showed a native molecular mass of 20 kDa on a gel filtration chromatography. Of the APase activity, 60% remained after 60 min of heat treatment at 75°C. To confirm whether the APase is active in the monomeric form, we attempted to elute the enzyme from SDS-polyacrylamide gels with Disk electrophoresis apparatus and renature the enzyme. The APase activity was recovered up to 50% in the 14- to 35-kDa range, and maximum around 25 kDa. These results suggest that this APase is monomeric protein. Received: 8 July 1999 / Accepted: 9 August 1999     

Decay-accelerating factor in guinea pig stomachs following ischemia reperfusion stress

A complement regulatory protein, decay-accelerating factor (DAF, CD55), is known to protect host tissues from autologous complement activation. DAF is present on the apical side of human gastric epithelial cells, and its expression increases during gastritis. To develop an animal model for analysis of DAF expression on gastric cells, a mAb to guinea pig DAF was successfully used. Although DAF expression in the mucosal epithelium of the stomach is weak, as judged by immunohistochemical staining with the mAb, it was temporarily up-regulated at 12 and 24 h, and at 3 days after ischemia reperfusion (I/R) (p < 0.05). The DAF mRNA level in gastric tissues was determined by Northern blot analysis and found to be highest at 6 h after I/R, returning to the baseline at 24 h. Strong DAF mRNA expression was observed in the cytoplasm of cells beneath the eroded tissues 6 h after I/R. In guinea pigs, alternative splicing of DAF mRNA generates both GPI-anchored types and transmembrane types of DAF. RT-PCR analysis revealed that mRNAs of the transmembrane types had become significantly dominant by 6 h after I/R, whereas levels for the GPI-anchored types remained unchanged. In guinea pigs depleted of complement by cobra venom factor treatment, the area of erosion and the up-regulation of DAF expression in gastric epithelial cells after I/R were significantly limited compared with the normocomplementemic group, indicating that DAF may be up-regulated by an inflammatory stress.