Synthesis of peptide substrates for mammalian thioredoxin reductase.

Mammalian thioredoxin reductase (TR) catalyzes the reduction of the redox-active disulfide bond of thioredoxin (Trx) and is similar in structure and mechanism to glutathione reductase except for a C-terminal 16-amino acid extension containing a rare vicinal selenylsulfide bond. This vicinal selenylsulfide bond is essentially a substrate for the enzyme's N-terminal redox center. Here we report the synthesis of peptide substrates for the truncated enzyme missing the C-terminal redox center. We developed a procedure for the synthesis of peptides containing cyclic vicinal disulfide/selenylsulfide bonds as well as their corresponding acyclic heterodimers. Vicinal disulfide bonds form eight-membered ring structures and are difficult to synthesize owing to their propensity to dimerize during oxidation. Our procedure makes use of two key improvements for on-resin disulfide bond formation presented previously by Galande and coworkers (Galande AK, Weissleder R, Tung C-H. An effective method of on-resin disulfide bond formation in peptides. J. Comb. Chem. 2005; 7: 174-177). First, the addition of an amine base to the deprotection solution allows the complete removal of the StBu group, allowing it to be replaced with a 5-Npys group. The second enhancement is the direct use of a Cys(Mob) or Sec(Mob) derivative as the nucleophilic partner instead of utilizing a naked sulfhydryl or selenol. These improvements result in the formation of a vicinal disulfide (or selenylsulfide) bond in high purity and yield. A direct comparison with the Galande procedure is presented. We also present a novel strategy for the formation of an acyclic, interchain selenylsulfide-linked peptide (linking H-PTVTGC-OH and H-UG-OH). Cysteine analogs of the cyclic and acyclic peptides were also synthesized. The results show that the ring structure contributes a factor of 52 to the rate, but the presence of selenium in the peptide is more important to catalysis than the presence of the ring.     

Effect of Entomopathogenic Nematodes on Mesocriconema xenoplax Populations in Peach and Pecan

The effect of Steinernema riobrave and Heterorhabditis bacteriophora on population density of Mesocriconema xenoplax in peach was studied in the greenhouse. Twenty-one days after adding 112 M. xenoplax adults and juveniles/1,500 cm³ soil to the soil surface of each pot, 50 infective juveniles/cm² soil surface of either S. riobrave or H. bacteriophora were applied. Another entomopathogenic nematode application of the same density was administered 3 months later. The experiment was repeated once. Mesocriconema xenoplax populations were not suppressed (P ≤ 0.05) in the presence of either S. riobrave or H. bacteriophora 180 days following ring nematode inoculation. On pecan, 200 S. riobrave infective-stage juveniles/cm² were applied to the soil surface of 2-year-old established M. xenoplax populations in field microplots. Additional applications of S. riobrave were administered 2 and 4 months later. This study was terminated 150 days following the initial application of S. riobrave. Populations of M. xenoplax were not suppressed in the presence of S. riobrave.     

长白山东坡不同海拔长白落叶松径向生长对气候变化的响应

为了解高山林线附近树木生长对气候变化的敏感性, 选取长白山东坡火山喷发后形成的过渡性植物群落长白落叶松(又称黄花落叶松) (Larix olgensis)林为研究对象, 并建立不同海拔高度长白落叶松的3个年轮宽度年表, 研究不同生境长白落叶松径向生长对气候变化的响应, 并利用冗余分析对不同海拔的年轮指数与气候因子的关系做进一步分析。主要结果如下: (1)高海拔年轮年表的统计特征更显著, 比低海拔径向生长对气候因子的响应更加敏感; (2)高海拔径向生长主要受上年生长季前期和生长季气温的限制, 尤其是上年6月和8月气温的限制作用, 低海拔径向生长主要与降水量有关, 受当年9月降水量和当年8月帕尔默干旱指数(PDSI)的共同影响; (3)林线内树木对气候响应的敏感性强于林线外, 林线外小生境的异质性及干扰事件频发可能掩盖了树木对气候因子的敏感性, 林线下方可能是检验林线处树木生长对气候响应平均状态的最佳位置; (4)不同海拔年轮年表与气候因子的冗余分析与响应函数分析的结果基本一致, 进一步证明了冗余分析可以有效地量化树轮指数与气候因子的关系。该研究为全球变暖背景下长白山东坡长白落叶松林的管理及该区域气候重建提供了基础数据。     

雉鸡(Phasianus colchicus)营巢生境的模拟分析研究

将多元统计学方法与地理信息系统结合对动物的栖息地进行适宜性分析,是近年动物栖息地研究者和管理者都十分感兴趣的方面。本研究采用马氏距离法,利用地理信息系统模拟甘肃雉鸡的营巢生境。模拟结果表明,与已知营巢生境相似水平为0.95的区域面积,仅占整个研究区的0.68%,而与已知营巢生境迥然不同（P＜0.05）的区域面积占79.08%。营巢生境与非营巢生境在生境类型组成和地形因素上存在多方差异,营巢生境中农田和草坡占有极大比例,用于营巢的区域总是更接近生境的边缘。特别是接近于农田、草坡和白桦阔叶林等生境,表明倾向于在这几种生境的边缘附近营巢。营巢生境的平均海拔比非营巢生境低,坡度也较缓,坡向则更偏于东南方。在同一生境类型内部,用于营巢的区域和不利用的区域之间也存在很大差别,营巢区域总是更接近生境的边缘。某一生境周围的其它生境类型也会影响雉鸡的营巢选择。     

Effects of begging on growth rates of nestling chicks

We investigated whether an increase in begging levels delaysgrowth of chicks. In experiment 1, we hand-reared nine pairsof ring dove squabs, divided into a control and a begging group.All squabs received similar amounts of food, but those in thebegging group had to beg for a prolonged period in order tobe fed, while squabs in the control group received food withoutbegging. Squabs stopped responding to the treatment after 10days and, at that time, there was no effect of induced beggingon their body mass. In experiment 2, we hand-reared 27 pairsof magpie chicks for 3 days. The design of experiment 2 wassimilar to that of experiment 1. Daily food intake and beggingaffected growth rates. On average, chicks in the begging groupgrew 0.8 g/day less than control chicks, which represents adecrease of 8.15% in growth rate. Because growth is usuallypositively associated with expected fitness, this demonstratesthat begging is a costly behavior, an assumption routinelymade in models of begging behavior.     

Cytokinesis and the contractile ring in fission yeast

The fission yeast Schizosaccharomyces pombe provides a genetic model system for the study of cytokinesis. As in many eukaryotes, cell division in the fission yeast requires an actin-myosin-based contractile ring. Numerous components of the contractile ring that function in ring assembly, positioning and contraction have been characterized. Many of these proteins are evolutionarily conserved, suggesting that common molecular mechanisms may govern aspects of eukaryotic cell division. Recent advances in the assembly and placement of the contractile ring are discussed. In particular, major findings have been made in the characterization of myosins in cytokinesis, and in how the cell division site may be positioned by the nucleus.     

Ensuring a representative sample of earlywood vessels for dendroecological studies: an example from two ring-porous species

The analysis of time series of wood cell anatomical features (such as the earlywood vessels of ring-porous trees) is a successful approach to understand the effect of environmental factors on tree growth and thus constitutes a valuable source of information about past environmental conditions. However, despite the rising interest in analyzing wood anatomical time series, little or no attention has been paid to establish an adequate sample of cells in order to minimize the risk of missing a valuable environmental signal. In order to contribute to such methodological bases, this paper is aimed at (1) identifying a representative sample of earlywood vessels within a tree, which encode the same climatic information, and (2) assessing if it is preferable to obtain the sample of vessels along one or two radii. Four individuals of sessile oak (Quercus petraea (Mattuschka) Liebl.) and sweet chestnut (Castanea sativa Mill.) were harvested and all their earlywood vessel lumina were measured along two 40-mm wide radial strips. Measured vessels were selected stepwise while increasing the tangential width of the wood section from 1 to 40 mm, analyzing at each step (1) the common signal of chronologies and (2) the correlation to the main climatic variables controlling growth. Additionally, both radii in each tree were analyzed together and separately. The results showed that a total tangential width of 10 mm was enough to stabilize the climatic signal with improvement when distributed along two different radii, but a slightly larger tangential width was required to reach an optimal common signal. We suggest that, at least for the case of these two species growing at this specific climatic context, two 5-mm increment cores ensure a representative vessel selection.     

Different responses to photoperiod in non-diapausing colonies of the flesh fly, Boettcherisca peregrina

Abstract.  The effect of photoperiod on pupariation time and the ability to secrete ecdysteroids by the larval ring gland of the flesh fly, Boettcherisca peregrina , are compared among three tropical non-diapausing colonies, Bp (forest), Bp (Luwuk) and Bp (NC) and one temperate diapausing colony of Bp (Tokyo). Non-diapausing colonies do not enter diapause under any photoperiod at 20°C, whereas the Bp (Tokyo) diapausing colony enters diapause at the pupal stage under a short-day photoperiod. The times required for 50% pupariation of Bp (forest), Bp (Luwuk) and Bp (Tokyo) are 34 h, 36 h 20 min and 34 h 40 min under short days (SD), respectively. However, Bp (NC) pupariates in a much shorter time (26 h 10 min) compared with the others. The 50% pupariation times of Bp (NC), Bp (forest) and Bp (Tokyo) under long days (LD) are 27 h, 25 h 50 min and 26 h 40 min, respectively. However, it is much longer in Bp (Luwuk) at 53 h 20 min. The rates of secretion of ecdysteroids by the larval ring glands in vitro in Bp (Tokyo) and Bp (forest) are six- to ten-fold higher under SD (6.00 and 3.69 ng) than under LD (0.60 ng), whereas the ring glands of Bp (Luwuk) and Bp (NC) secrete 3.06 and 8.25 ng ecdysteroids under LD and 5.18 and 10.53 ng under SD, respectively. These results suggest there are at least three different physiological types among non-diapausing colonies of B. peregrina : Bp (forest), Bp (Luwuk) and Bp (NC).     

Cytokinesis of neuroepithelial cells can divide their basal process before anaphase

Neuroepithelial (NE) cells, the primary stem and progenitor cells of the vertebrate central nervous system, are highly polarized and elongated. They retain a basal process extending to the basal lamina, while undergoing mitosis at the apical side of the ventricular zone. By studying NE cells in the embryonic mouse, chick and zebrafish central nervous system using confocal microscopy, electron microscopy and time-lapse imaging, we show here that the basal process of these cells can split during M phase. Splitting occurred in the basal-to-apical direction and was followed by inheritance of the processes by either one or both daughter cells. A cluster of anillin, an essential component of the cytokinesis machinery, appeared at the distal end of the basal process in prophase and was found to colocalize with F-actin at bifurcation sites, in both proliferative and neurogenic NE cells. GFP-anillin in the basal process moved apically to the cell body prior to anaphase onset, followed by basal-to-apical ingression of the cleavage furrow in telophase. The splitting of the basal process of M-phase NE cells has implications for cleavage plane orientation and the relationship between mitosis and cytokinesis.