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.     

The structure ofHLA-B35 suggests that it is derived fromHLA-Bw58 by two genetic mechanisms

The primary structure ofHLA-B51 andHLA-Bw52 suggested thatHLA-B51 was derived fromHLA-Bw52 by the combination of a genetic exchange withHLA-B8 and a point mutation. To investigate the evolution of theHLA-B5 cross reactive group, theHLA-B35 gene was cloned and the primary structure was determined.HLA-B35 is identical toHLA-Bw58 except in the α₁ domain. The α₁ domain ofHLA-B35 except Bw4/Bw6-associated amino acids is identical to that ofHLA-B51 ^*, which was suspected to be an intermediate gene betweenHLA-B51 andHLA-Bw52. These data suggest thatHLA-B35 has evolved fromHLA-Bw58 in two steps; an in vivo replacement of the α₁ domain withHLA-B51 and genetic exchange with one of theHLA-Bw6 genes. These three genes andHLA-Bw58 are postulated to share a common ancestor.     

Regional distribution of DNA and RNA in rat brain: A sensitive determination using high-performance liquid chromatography with electrochemical detection

DNA and RNA contents in 20 brain regions or nuclei of the rat were determined by a highly sensitive method using high-performance liquid chromatography with electrochemical detection. The high DNA and RNA contents were found in the hypothalamic nuclei, especially the median eminence-arcuate nucleus. These results may be available for the preparation of nucleic acids as the regional control.     

Some KpnI family members are associated with the Alu family in the human genome

The structures of the termini and their flanking regions of two human KpnI family members were investigated. The two differed in length, but the starting sequence at one terminal (defined as the 5' terminal) was found to be common to both members. The Alu family sequence was found in the 5' flanking regions. The KpnI family sequence started several base-pairs downstream from the 3' end of the Alu family sequence. In both cases, the Alu family sequence was not flanked by the direct repeat sequence common to the Alu family. These two members showed no sequence homology in 3' terminal regions. Interestingly, the Alu family plus the KpnI family unit was found to be flanked by a direct repeat sequence of several base-pair length. Based on these findings, relationship between the Alu family and KpnI family is discussed.     

Carbon-cycling changes during regeneration of a decinduous broadleaf forest after clear-cutting II. Aboveground net production

Growth and death rates of aboveground plant parts were measured in a mature forest and four different-aged deciduous broadleaf forests regeneratede after clear-cutting, with special reference to rates for woody parts (stems and branches) of different diameters (ø) in rerms of the pipe model theory (Shinozaki et al., 1964). The total biomass increment of woody parts of trees higher than 1.3 m varied within a range of 2.1-4.6 ton ha^?1 yr^?1, the increase beingdue largely to the growth of canopy trees exposed to direct sunlight. Biomass increments of small (ø<1 cm) and medium (1≤ø<5 cm) woody parts were negligibly small except in the youngest forest, and changes in aboveground woody biomass with forest age after clear-cutting mainly resulted from accumulation of large (5 cm<ø) woody parts of canopy trees. Biomass loss of trees due to death and grazing increased with forest age from 4.0 to 8.3 ton ha^?1 yr^?1. Recovery of leaf and small wood falls was observed at the early stage of regeneration, while large wood falls increased during regeneration. Flower and fruit fall was markedly higher in the mature forest than in the other four forest types. Mortality of woody parts became higher with forest age and was 20, 5.0 and 0.46% yr^?1 for small, medium and large parts, respectively, at the mature stage. Aboveground net production of the forest was in therange 7.6-13.3 ton ha^?1 yr^?1 with the undergrowth vegetation lower than 1.3 m being 0.4-1.4 ton ha^?1 yr^?1. Production recovered rapidly at an early stage of regeneration and was highest in mature forest.     

Gnawing damage by rodents to the seedlings ofFagus crenata andQuercus mongolica var.grosseserrata in a temperateSasa grassland-deciduous forest series in southwestern Japan

The effects of dwarf bamboo,Sasa, cover on the initial morrality of hardwood seedlings were investigated by transplanting 1-year-old beech (Fagus crenata) and current-year oak (Quercus mongolica var.grosseserrata) seedling to three different stands; old-growth beech and secondary oak forests withSasa undergrowth, and aSasa grassland in a grassland-forest series near the top of Mt Jippo, southwestern Japan. The most frequent cause of seedling morrality was gnawing of the stems by rodents. In the beech forest, the gnawing was more likely to occur underSasa cover, suggesting that it provides a good habitat for rodents on the beech forest floor. TheSasa under growth may thus play an imporrant role in regeneration of beech forest. In the oak floor, mortality of both species was low and only a little gnawing occurred during a year. However, no natural oak seedling were found in the forest even after a mast year. This may be because most of the acorns disappeated before establishment. The early-stage demography of hardwood seedling as oak may thus play an imporrant role in regeneration of oak forest. In theSasa grassland where the seed supply is small, almost all of the seedlings died fromo gnawing regardless of the presence ofSasa cover. These factors prevent the recruitment of a sizable seedling bank. Rodents may thus play an imporrant role in maintenance of theSasa grassland.     

Nitric Oxide Reversibly Suppresses Xanthine Oxidase Activity

The effects of nitric oxide (NO) on xanthine oxidase (XOD) activity and the site(s) of the redox center(s) affected were investigated. XOD activity was determined by superoxide (O₂^-) generation and uric acid formation. NO reversibly and dose-dependently suppressed XOD activity in both determination methods. The suppression interval also disclosed a dose-dependent prolongation. The suppression occurred irrespective of the presence or absence of xanthine; indicating that the reaction product of NO and O₂^-, peroxynitrite, is not responsible for the suppression. Application of synthesized peroxynitrite did not affect XOD activity up to 2 μM. Methylene blue, which is an electron acceptor from Fe/S center, prevented the NO-induced inactivation. The results indicate that NO suppresses XOD activity through reversible alteration of the flavin prosthetic site.