X-interface is not the explanation for the slow disassembly of N-cadherin dimers in the apo state

In spite of structural similarities Epithelial- (E-) and Neural- (N-) cadherins are expressed at two types of synapses and differ significantly in dimer disassembly kinetics. Recent studies suggested that the formation of an X-dimer intermediate in E-cadherin is the key requirement for rapid disassembly of the adhesive dimer (Harrison et al., Nat Struct Mol Biol 2010;17:348-357 and Hong et al., J Cell Biol 2011;192:1073-1083). The X-interface in E-cadherin involves three noncovalent interactions, none of which is conserved in N-cadherin. Dimer disassembly is slow at low calcium concentration in N-cadherin, which may be due to the differences in the X-interface residues. To investigate the origin of the slow disassembly kinetics we introduced three point mutations into N-cadherin to provide the opportunity for the formation of X-interface interactions. Spectroscopic studies showed that the triple mutation did not affect the stability or the calcium-binding affinity of the X-enabled N-cadherin mutant. Analytical size exclusion chromatography was used to assay for the effect of the mutation on the rate of dimer disassembly. Contrary to our expectation, the disassembly of dimers of the X-enabled N-cadherin mutant was as slow as seen for wild-type N-cadherin in the apo-state. Thus, the differences in the X-interface residues are not the origin of slow disassembly kinetics of N-cadherin in the apo-state.     

The use of CrossMAb technology for the generation of bi- and multispecific antibodies

The major challenge in the generation of bispecific IgG antibodies is enforcement of the correct heavy and light chain association. The correct association of generic light chains can be enabled using immunoglobulin domain crossover, known as CrossMAb technology, which can be combined with approaches enabling correct heavy chain association such as knobs-into-holes (KiH) technology or electrostatic steering. Since its development, this technology has proven to be very versatile, allowing the generation of various bispecific antibody formats, not only heterodimeric/asymmetric bivalent 1+1 CrossMAbs, but also tri- (2+1), tetravalent (2+2) bispecific and multispecific antibodies. Numerous CrossMAbs have been evaluated in preclinical studies, and, so far, 4 different tailor-made bispecific antibodies based on the CrossMAb technology have entered clinical studies. Here, we review the properties and activities of bispecific CrossMAbs and give an overview of the variety of CrossMAb-enabled antibody formats that differ from heterodimeric 1+1 bispecific IgG antibodies.     

Spin crossover in a mononuclear compound [Fe(EPPA)(bpym)](ClO4)2 (EPPA = N-(2-aminoethyl)-N-(3-aminopropyl)-2-(aminomethyl)pyridine, bpym = 2,2′-bipyrimidine): Synthesis, structure, and magnetic properties

The synthesis, magnetic properties and single crystal study of a new spin crossover compound [Fe(EPPA)(bpym)](ClO₄)₂ with EPPA = N-(2-aminoethyl)-N-(3-aminopropyl)-2-(aminomethyl)pyridine, bpym = 2,2′-bipyrimidine are reported. Variable-temperature magnetic susceptibility data collected in the temperature range 10-294 K reveal the occurrence of a relatively cooperative spin transition with T_1/2 = 108 K. The crystal structure of [Fe(EPPA)(bpym)](ClO₄)₂ was determined by single-crystal X-ray diffraction method. The structure of the complex consists of mononuclear [Fe(EPPA)(bpym)](ClO₄)₂ units. The potentially bis-bidentate bpym ligand acting as a bidentate one, is coordinated to iron(II) in cis-position by two nitrogen atoms. The four remaining positions in the pseudooctahedral [FeN₆] core are occupied by one pyridinic and three aliphatic nitrogens of the EPPA ligand. The network of cooperative links in the crystal lattice is represented by H-bonding and π stacking interactions.     

基于量子进化算法的RNA序列-结构比对

多序列比对是计算分子生物学的经典问题,也是许多生物学研究的重要基础步骤．RNA作为生物大分子的一种,不同于蛋白质和DNA,其二级结构在进化过程中比初级序列更保守,因此要求在RNA序列比对中不仅要考虑序列信息,更要着重考虑二级结构信息．提出了一种基于量子进化算法的RNA多序列-结构比对程序,对RNA序列进行了量子编码,设计了考虑进结构信息的全交叉算子,提出了适合于进行RNA序列-结构比对的适应度函数,克服了传统进化算法收敛速度慢和早熟问题．在标准数据库上的测试,证实了方法的有效性．     

Recombination and selection in the maintenance of the adaptive value of inversions

A huge amount of data seem to confirm the adaptive value of inversions in Drosophila. The inhibition of recombination in heterokaryotypes mediated by inversions seems fundamental in maintaining their adaptive role. This study shows that recombination is highly suppressed in Drosophila subobscura because of chromosomal inversions, not only inside the inversions but also outside them. It seems that the region outside the inversion where recombination is inhibited is asymmetrical and independent of the inversion length. Despite the difficulty of crossovers taking place near inversion breakpoints, the only two recombination events detected inside inversions were located close to the breakpoint. Thus, selection could be largely responsible for the recombination reduction maintaining sets of adaptive alleles inside the inverted region. Heterokaryotype descendants were always in higher frequency than inbred or outbred homokaryotypes, regardless of the geographical origin of the chromosome, suggesting that chromosomes carrying the same arrangement, although with a different set of alleles for neutral markers, could be submitted to the same selection processes.     

Unequal first cleavage in the Tubifex egg: involvement of a monastral mitotic apparatus

The first cleavage in the freshwater oligochaete Tubifex hattai is unequal and meridional, and produces a smaller cell AB and a larger cell CD. This study traces the process of furrow formation, reorganization of cortical F-actin and the assembly of a mitotic apparatus during this unequal division. Cleavage furrow formation consists of two stages: (i) when eggs are viewed from the animal pole, meridionally running furrows emerge at two points of the egg's equator that are 90° apart from each other and approach the egg axis as they deepen; and (ii) at the midpoint between the equator and the egg center, the bottoms of these furrows link to each other on the animal and vegetal surfaces of the egg and form a continuous ring of constriction in a plane parallel to the egg axis. Egg cortices, isolated during the first step and stained with rhodamine-phalloidin, show that the bottoms of recently formed furrows are underlaid by a belt of tightly packed actin bundles (i.e. a contractile arc). The transition to the second stage of furrow formation coincides with the conversion of these actin belts into a continuous ring of F-actin. Whole-mount immunocytochemistry of microtubules reveals that the first cleavage in Tubifex involves an asymmetric mitotic spindle, which initially possesses an aster at one pole but not the other. This ‘monastral’ spindle is located at the egg's center and orients itself perpendicular to the egg axis. During anaphase, astral rays elongate to reach the cell surface, so that the array of astral microtubules in the plane of the egg's equator covers a sector of 270–300°. In contrast, it is not until the transition to telophase that microtubules emanating from the anastral spindle pole approach the cell margin. If eggs are compressed along the egg axis or forced to elongate, they form monastral spindles and divide unequally. In living compressed eggs, mitotic spindles, which are recognizable as bright streaks at the egg's center, appear not to shift their position along the spindle axis during division, suggesting that without eccentric migration of spindles Tubifex eggs are able to divide unequally. These results suggest that mechanisms that translocate the mitotic spindle eccentrically do not operate in Tubifex eggs during the first cell cycle. The mechanisms that generate asymmetry in spindle organization are discussed in the light of the present results.     

Steady size distributions for cells in one-dimensional plant tissues

We consider a population of cells growing and dividing steadily without mortality, so that the total cell population is increasing, but the proportion of cells in any size class remains constant. The cell division process is non-deterministic in the sense that both the size at which a cell divides, and the proportions into which it divides, are described by probability density functions. We derive expressions for the steady size/birth-size distribution (and the corresponding size/age distribution) in terms of the cell birth-size distribution, in the particular case of one-dimensional growth in plant organs, where the relative growth rate is the same for all cells but may vary with time. This birth-size distribution is shown to be the principal eigenfunction of a Fredholm integral operator. Some special cases of the cell birth-size distribution are then solved using analytical techniques, and in more realistic examples, the eigen-function is found using a simple, generally applicable numerical iteration.     

Centrosome-attracting body: A novel structure closely related to unequal cleavages in the ascidian embryo

The mechanism of unequal cleavage is one of the most intriguing subjects in cell biology. Previous studies of unequal cleavage have focused on a limited number of organisms such as yeasts, nematodes, sea urchins and annelids. The cleavage pattern of the ascidian embryo is invariant. In the ascidian embryo, the posterior-most blastomeres divide unequally in three successive cleavages. In the present study, it was shown that the ascidian embryo provides another good experimental system with which to analyze the mechanism of unequal cleavage. A novel structure, designated as CAB (centrosome-attracting body), which was found specifically in the unequally cleaving blastomeres was described. In the course of unequal cleavages, first, a thick microtubule bundle appeared between CAB and one of the centrosomes. Then with the shortening of the microtubule bundle, the nucleus with the centrosome was drawn toward CAB, situated at the posterior cortex of the blastomere. Finally, a cleavage furrow formed in the middle of the asymmetrically located mitotic apparatus and produced two blastomeres of different size, generating a smaller cell that inherits CAB. The CAB seemed to play an essential role in the unequal cleavages in the ascidian embryo.     

Sex determination system of the rosy bitterling, Rhodeus ocellatus ocellatus

The rosy bitterling, Rhodeus ocellatus ocellatus, is the only fish species known in which artificial triploids are always male, regardless of the kind of polyploidization technique used. In order to elucidate the genetic sex determination system of the rosy bitterling, two kinds of gynogenesis were carried out: retention of the second polar body (GRSPB) and suppression of the first cleavage (GSFC). The sex ratio of progeny was nearly 7:1 (:) for both GRSPB and GSFC, while those of control and parental fish were almost 1:1. In backcrosses of female progeny by GRSPB and normal diploid males, male progeny were observed at low frequency (one or two individuals in each experiment), except in one experiment where the appearance rate of males was about 50%. From results of gynogenesis and backcrosses, the following conclusions can be made. The genetic sex determination system of the rosy bitterling is a heterogametic female system (ZW). Survival rate of superfemales (WW), produced by gynogenesis, is much lower than that of males (ZW).There is a possibility that crossovers between sex determining genes and a centromere occur in the first meiosis. With repect to the mechanism of unisexuality (male) of artificial triploids of the rosy bitterling, only males (ZZZ and ZZW) are presumed viable, while females (ZWW) are probably inviable.     

Life-Cycle Assessment and Temporal Distributions of Emissions: Developing a Fleet-Based Analysis

Although the product-centered focus of life-cycle assessment has been one of its strengths, this analytical perspective embeds assumptions that may conflict with the realities of environmental problems. This article demonstrates, through a series of mathematical derivations, that all the products in use, rather than a single product, frequently should be the appropriate unit of analysis. Such a "fleet-centered" approach supplies a richer perspective on the comparative emissions burdens generated by alternative products, and it eliminates certain simplifying assumptions imposed upon the analysis by a product-centered approach.
A sample numerical case, examining the comparative emissions of steel-intensive and aluminum-intensive automobiles, is presented to contrast the results of the two approaches. The fleet-centered analysis shows that the "crossover time" (i.e., the time required before the fuel economy benefits of the lighter aluminum vehicle offset the energy intensity of the processes used to manufacture the aluminum in the first place) can be dramatically longer than that predicted by a product-centered life-cycle assessment.
The fleet-centered perspective explicitly introduces the notion of time as a critical element of comparative life-cycle assessments and raises important questions about the role of the analyst in selecting the appropriate time horizon for analysis. Moreover, with the introduction of time as an appropriate dimension to life-cycle assessment, the influences of effects distributed over time can be more naturally and consistently treated.