Topoisomerases of kinetoplastid parasites: why so fascinating?

DNA topoisomerases are the key enzymes involved in carrying out high precision DNA transactions inside the cells. However, they are detrimental to the cell when a wide variety of topoisomerase-targeted drugs generate cytotoxic lesions by trapping the enzymes in covalent complexes on the DNA. The discovery of unusual heterodimeric topoisomerase I in kinetoplastid family added a new twist in topoisomerase research related to evolution, functional conservation and their preferential sensitivity to Camptothecin. On the other hand, structural and mechanistic studies on kinetoplastid topoisomerase II delineate some distinguishing features that differentiate the parasitic enzyme from its prokaryotic and eukaryotic counterparts. This review summarizes the recent advances in research in kinetoplastid topoisomerases, their evolutionary significance and the death of the unicellular parasite Leishmania donovani induced by topoisomerase I inhibitor camptothecin.     

2n/4n嵌合体胚胎的发育特点及其应用

2n/4n嵌合体是指用二倍体的胚胎细胞和四倍体的胚胎细胞聚合所形成的嵌合体。这种嵌合体在胚胎的发育过程中。四倍体来源的细胞在分布上具有一定的倾向性,即倾向于分布在胚外组织,如胎盘;而在胎儿本身的组织中,很少能找到四倍体细胞的存在,就2n/4n嵌合体胚胎的制作、嵌合体胚胎的发育特点及该技术的可能应用进行了综述。     

Microsolvation and hydration enthalpies of CaC2O4(H2O) n (n = 0-16) and C2O4 2-(H2O) n (n = 0-14): an ab initio study

We studied hydrated calcium oxalate and its ions at the restricted Hartree–Fock RHF/6-31G* level of theory. Performing a configurational search seems to improve the fit of the HF/6-31G* level to experimental data. The first solvation shell of calcium oxalate contains 13 water molecules, while the first solvation shell of oxalate ion is formed by 14 water molecules. The first solvation shell of Ca(II) is formed by six water molecules, while the second shell contains five. At 298.15 K, we estimate the asymptotic limits (infinite dilution) of the total standard enthalpies of hydration for Ca(II), oxalate ion and calcium oxalate as ?480.78, –302.78 and –312.73 kcal mol^?1, resp. The dissociation of hydrated calcium oxalate is an endothermic process with an asymptotic limit of +470.84 kcal mol^?1.

太谷发现2n=4毛足雕翅摇蚊

毛足雕翅摇蚊Glyptotendipes barbipes (Staeger)最早由H. Bauer引人细胞遗传学 研究。H. Bauer发现,该物种唾腺染色体具深 染色的呈鼓形的异染色质区,这种异染色质区 代表着丝粒位置;染色体组由三对长的中着丝 粒染色体和一对端着丝粒染色体组成［[31。此 后,人们对分布于欧洲、苏联和北美的·G. barbi pe,不同种群唾腺染色体斑带模式进行了分 析,证明该物种为一具高度倒位多态性的物 种[4-810但是,上述研究中并未发现染色体数目 的变异,即该物种具有摇蚊科典型的染色体数 目,2。～ 8-     

小鼠遗传背景对4n胚胎及2n-4n聚合胚制作效率的影响

不同品系小鼠的 2 细胞期胚胎 (二倍体 ,2n) ,经电融合后 ,获得发育的 4 细胞期四倍体胚胎 (4n)的能力上存在着差异。将不同品系小鼠的 2n、 4n胚胎分别配对作聚合 ,所获 2n 4n聚合胚的发育结果表明 :在着床前 ,2n 4n聚合胚的获得率因胚胎品系组合的不同而异 ;胚胎移植后 ,聚合胚在与 4n胚胎相同或相近品系的移植受体中 ,其着床率较高 ;在着床后胎儿及出生仔鼠的获得率上 ,采用遗传杂合性的 2n胚胎所组成的 2n 4n聚合组合较高。上述结果提示 :小鼠的遗传背景可影响到 4n胚胎及相应 2n 4n聚合胚的制作效率。以GFP标记跟踪2n 4n聚合胚 4n细胞着床后的发育命运 ,发现 :妊娠中后期的孕体中 ,4n细胞限制性地分布至胚外组织     

Four-wave mixing signals from β-carotene and its n = 15 homologue

The third-order nonlinear optical responses of β-carotene and its homologue having a conjugation-double bond n = 15 have been investigated using sub-20 fs ultra-short optical pulses in order to clarify the dissipation processes of excess energy. Using the four-wave mixing spectroscopy, we observed a clear coherent oscillation with a period of a few tens of femtoseconds. The spectral density of these molecules was estimated that allowed the theoretical linear and nonlinear optical signals to be directly compared with the experimental data. Calculations based on the Brownian oscillator model were performed under the impulsive excitation limit. We show that the memory of the vibronic coherence generated upon the excitation into the S₂ state is lost via the relaxation process including the S₁ state. The vibronic decoherence lifetime of the system was estimated to be 1 ps, which is about 5 times larger than the life time of the S₂ state (∼150 fs) determined in previous studies. The role of coherence and the efficient energy transfer in the light-harvesting antenna complexes are discussed.     

A sponge diversity centre within a marine ‘island’

The exposed and gulf-stream warmed south-west coast of Ireland has a Lusitanean fauna composed of elements of the colder waters to the north and east, and others from the warmer Mediterranean Sea. Lough Hyne, a small marine body, is unusual on this coast in being very sheltered, but also in being characterised by many different niches within a small space (1 km²). Sponges are particularly abundant, morphologically varied and more than 100 species have been described. Species diversity was measured at 6 m intervals on vertical and inclined profiles (to a maximum of 30 m) at six sites, spanning a range of flow rate and sedimentation regimes. Diversity, richness, evenness and density varied significantly with both flow regime and depth, but was much lower on the surrounding Atlantic coast. Four different sponge communities were differentiated on the basis of sponge species assemblages which correlated with different environmental conditions. At sites of turbulent and fast flow conditions, sponge diversity and richness were lowest, with the highest values being found at the sites of moderate and high sedimentation. Significant differences were observed in all four ecological variables with respect to substratum angle with the exception of the site experiencing the most turbulent flow conditions. Lough Hyne was found to possess the second highest sponge species diversity (H=3.626) and richness (77 species) of all available figures from temperate, polar and tropical areas (of similar sized sampling area). The uniqueness, diversity and species composition of the sponge community at this location suggests Lough Hyne is, biologically, a marine island within the island of Ireland.     

New Caledonia: a very old Darwinian island?

New Caledonia has generally been considered a continental island, the biota of which largely dates back to Gondwanan times owing to its geological origin and the presence of phylogenetic relicts. This view is contradicted by geological evidence indicating long Palaeocene and Eocene submersions and by recent biogeographic and phylogenetic studies, with molecular or geophysical dating placing the biota no older than the Oligocene. Phylogenetic relicts do not provide conclusive information in this respect, as their presence cannot be explained by simple hypotheses but requires assumption of many ad hoc extinction events. The implication of this new scenario is that all the New Caledonian biota colonized the island since 37 Ma Local richness can be explained by local radiation and adaptation after colonization but also by many dispersal events, often repeated within the same groups of organisms. Local microendemism is another remarkable feature of the biota. It seems to be related to recent speciation mediated by climate, orography, soil type and perhaps unbalanced biotic interactions created by colonization disharmonies. New Caledonia must be considered as a very old Darwinian island, a concept that offers many more fascinating opportunities of study.     

The island rule: made to be broken?

The island rule is a hypothesis whereby small mammals evolve larger size on islands while large insular mammals dwarf. The rule is believed to emanate from small mammals growing larger to control more resources and enhance metabolic efficiency, while large mammals evolve smaller size to reduce resource requirements and increase reproductive output. We show that there is no evidence for the existence of the island rule when phylogenetic comparative methods are applied to a large, high-quality dataset. Rather, there are just a few clade-specific patterns: carnivores; heteromyid rodents; and artiodactyls typically evolve smaller size on islands whereas murid rodents usually grow larger. The island rule is probably an artefact of comparing distantly related groups showing clade-specific responses to insularity. Instead of a rule, size evolution on islands is likely to be governed by the biotic and abiotic characteristics of different islands, the biology of the species in question and contingency.     

Thermal stability of carbon [n,5] prismanes (n = 2–4): a molecular dynamics study

Tight-binding molecular dynamics simulations are carried out to analyse the thermal stability of the carbon [n,5] prismanes with n = 2–4 over a wide temperature range. The results obtained demonstrate that the isomerisation activation energy as well as the frequency factor in the Arrhenius equation of these metastable nanostructures rapidly decreases with an increase of n. Therefore, the increase in the effective length of [n,5] prismane leads to the decrease in its lifetime up to the moment of its isomerisation. Nevertheless, the stability of [n,5] prismanes is confirmed to be sufficient for their existence at the liquid-nitrogen temperature. The main identified mechanism of [n,5] prismanes isomerisation is the interlayer C–C bond breaking leading to their transformation to the hypostrophene-based molecular systems.     

用2n作母本,用4n作父本也能产生3n西瓜种子吗?

高中《生物》课本 P150上,谈到三倍体西瓜的培育过程。其中有这样一段话:“……用四倍体植株作母本,用二倍体植株作父本,进行交配,就能在四倍体植株上结出三倍体西瓜的种子。”对此,不少师生提出另一种设想:如果反过来,用二倍体(2n)植株作母本,用四倍体     

The chromosome banding pattern in two cytotypes (2n = 36 and 38) of blind mole rats from Turkey (Mammalia: Spalaxidae)

Two cytotypes (2n = 36 and 38) of blind mole rats, Nannospalax xanthodon (Nordmann, 1840), from the Ayd?n and Manisa provinces in Turkey were investigated. Conventional chromosome staining, Ag-NOR staining and C-banding analysis were carried out. From the cytogenetic point of view, the particular phylogenetic position of these populations is supported by their low diploid numbers only, and the Cbanding pattern and the NORs distribution seem generally similar to populations with higher chromosome numbers. Several autosomal pairs with centromeric dark Cbands were observed in the 2n=36 cytotype. One autosomal pair possessed an interstitial dark C-band on the short arm; another pair possessed an interstitial dark Cband on the long arm. Whole C-heterochromatic short arms were observed in three subtelocentric autosomal pairs in the 2n=38 cytotype. Most of the other autosomal pairs possessed centromeric dark C-bands. Distinct dark C-bands were observed also in the presumed X chromosomes of both the cytotypes. The Ag-NOR regions were found on three autosomal pairs of both the cytotypes. These sites were located in telomeric areas of the short arms of two subtelocentric and one submetacentric pair.     

Synaptotagmin 4: A New Antiobesity Target?

In this issue of Neuron, Zhang et?al. show that Synaptotagmin 4 (Syt4) is specifically induced in adult hypothalamic oxytocin neurons by high-fat diet. Evidence is provided to support a critical role for Syt4 in negative regulation of oxytocin release, which in turn is responsible for diet-induced obesity, raising the possibility of using Syt4 as a new antiobesity target.     

A global analysis of avian island diversity–area relationships in the Anthropocene

Research on island species–area relationships (ISAR) has expanded to incorporate functional (IFDAR) and phylogenetic (IPDAR) diversity. However, relative to the ISAR, we know little about IFDARs and IPDARs, and lack synthetic global analyses of variation in form of these three categories of island diversity–area relationship (IDAR). Here, we undertake the first comparative evaluation of IDARs at the global scale using 51 avian archipelagic data sets representing true and habitat islands. Using null models, we explore how richness-corrected functional and phylogenetic diversity scale with island area. We also provide the largest global assessment of the impacts of species introductions and extinctions on the IDAR. Results show that increasing richness with area is the primary driver of the (non-richness corrected) IPDAR and IFDAR for many data sets. However, for several archipelagos, richness-corrected functional and phylogenetic diversity changes linearly with island area, suggesting that the dominant community assembly processes shift along the island area gradient. We also find that archipelagos with the steepest ISARs exhibit the biggest differences in slope between IDARs, indicating increased functional and phylogenetic redundancy on larger islands in these archipelagos. In several cases introduced species seem to have ‘re-calibrated’ the IDARs such that they resemble the historic period prior to recent extinctions.