Allelic Negative Complementation at the Abruptex Locus of DROSOPHILA MELANOGASTER

The mutations of the Abruptex locus in Drosophila melanogaster fall into three categories. There are recessive lethal alleles and viable alleles. The latter can be divided into suppressors and nonsuppressors of Notch mutations. The recessive lethals are lethal in heterozygous combination with Notch. As a rule the recessive lethals are lethal also in heterozygous combination with the viable alleles. Heterozygous combinations of certain viable alleles are also lethal. In such heterozygotes, one heteroallele is a suppressor of Notch and the other is a nonsuppressor. Other heterozygous combinations of viable alleles are viable and have an Abruptex phenotype. The insertion of the wild allele of the Abruptex locus as an extra dose (carried by a duplication) into the chromosomal complement of the fly fully restores the viability of the otherwise lethal heterozygotes if two viable alleles are involved. The extra wild allele also restores the viability of heterozygotes in which a lethal and a suppressor allele are present. If, however, a lethal and a nonsuppressor are involved, the wild allele only partly restores the viability, and the effect of the wild allele is weakest if two lethal alleles are involved. It seems likely that of the viable alleles the suppressors of Notch are hypermorphic and the nonsuppressors are hypomorphic. The lethal alleles share properties of both types, and are possibly antimorphic mutations. It is suggested that the locus is responsible for a single function which, however, consists of two components. The hypermorphic mutations are defects of the one component and the hypomorphic mutations of the other. In heterozygotes their cumulative action leads to decreased viability. The lethal alleles are supposed to be defects of the function as a whole. The function controlled by the locus might be a regulative function.     

Graphs, random sums, and sojourn time distributions, with application to ion-channel modeling.

This paper considers the distribution of a sojourn time in a class of states of a stochastic process having finite discrete state space where sojourn times in any individual state are independent and identically distributed, and transitions between states follow a Markov chain. The state space and possible transitions of the process are represented by a graph. Class sojourn time distributions are derived by modifying this graph using 'composition' of states, defining a new Markov chain on the modified graph, and expressing the sojourn time in a composition state as a random sum. Appropriate compositions are chosen according to the possible "cores" of sojourns in the particular class, where a core describes the structure of a sojourn in terms of a single state or a chain in the original graph. Graph methods provide an algorithmic basis for the derivation, which can be simplified by using symmetry results. Models of ion-channel kinetics are used throughout for illustration; class sojourn time distributions are important in such models because individual states are often indistinguishable experimentally. Markov processes are the special case where sojourn times in individual states are exponentially distributed. In this case kinetic parameter estimation based on the observed class sojourn time distribution is briefly discussed; explicit estimating equations applicable to sequential models of nicotinic receptor kinetics are given.     

高迁移率族蛋白成员HMG20a/b的研究进展

高迁移率族(HMG)蛋白是一类广泛存在的非组蛋白型染色体蛋白,能通过诱导染色质结构的变化影响DNA表达。HMG20a和HMG20b是一对高度同源的HMG家族蛋白,均含有一个结构保守的HMG-box结构域和一个coiled-coil结构域,在生物体内广泛表达。HMG20a/b在细胞核内参与组蛋白去甲基酶复合物LSD1-Co REST的形成及一系列与细胞分裂分化相关的生理进程,如神经细胞核红细胞的分化、细胞质分裂以及EMT过程。研究发现,HMG20a/b一些功能的发挥是通过LSD1-Co REST复合物来实现的;在神经分化过程中,HMG20a、HMG20b具有相互拮抗的作用;而HMG20a促进EMT过程反映它很可能是一个促癌因子。本文对HMG20a/b的结构和体内分布及生物学功能进行综述。     

A search for conceptual congruence between individuals and species

A new argument that species are individuals has recently been presented based on the way species names are used and systemic logic. The alternate idea that species are a categorical item, i.e., collections of individuals, was rejected. We wanted to evaluate this approach by establishing concepts that apply to individuals in order to examine if they are also applicable to a species viewed as a categorical item. It is our thinking that if species are not such, then concepts applicable to individuals will not be applicable to species so viewed. Individuals and species are similar in the presence of conceptual boundaries, unidirectional change and the presence of past and future time. These are all central, and salient, biological phenomena. But, these are concepts that apply also to populations which, for the most part, are not the same as species. Thus, these considerations infer that species, when viewed as a collection of individuals, do not share relevant concepts with individuals. Our conclusion is that a species is a 'unity' rather than an 'individual'.     

Cladistic Analysis of A Problematic Ammonite Group: the Hamitidae (Cretaceous, Albian–turonian) and Proposals for New Cladistic Terms

The Hamitidae are a family of mid–Cretaceous heteromorph ammonites including lineages leading to four other families. Problems are outlined in trying to describe the phylogeny of completely extinct groups such as these heteromorph ammonites using the existing cladistic terminology, which is largely concerned with extant taxa and their ancestors. To solve these problems, two new terms are proposed: †crown groups and †stem groups, which are equivalent to crown and stem groups in terms of the evolutionary history of a clade, but are not defined on the basis of extant taxa. Instead they are defined by the topology of the phylogenetic tree, the †crown group being a clade defined by synapomorphies but which gave rise to no descendants. A †stem group is a branch of a phylogenetic tree which comprises the immediate sister groups of a given †crown group but is not itself a clade. Examples of these terms are described here with reference to the phylogeny of the Hamitidae and their descendants. The Hamitidae are paraphyletic and form †stem groups to a number of †crown groups, namely the Anisoceratidae, Baculitidae, Scaphitidae, and Turrilitidae. The definitions of the genera and subgenera are refined with respect to the type species and the clades within which they occur, and four new genera are described: Eohamites , Helicohamites , Sziveshamites , and Planohamites .     

Cytochemical and fine structural analysis of oogenesis in the gastropod, Ilyanassa obsoleta

An analysis of differentiating oocytes of the gastropod, Ilyanassa obsoleta, has been made by techniques of light and electron microscopy. Early previtellogenic oocytes are limited by a smooth surfaced oolemma and are associated with each other by maculae adhaerentes. Previtellogenic oocytes are also distinguished by a large nucleus containing randomly dispersed aggregates of chromatin. Within the ooplasm are Golgi complexes, mitochondria and a few cisternae of the rough endoplasmic reticulum. When vitellogenesis begins, the oolemma becomes morphologically specialized by the formation of microvilli. One also notices an increase in the number of organelles and inclusions such as lipid droplets. During vitellogenesis there is a dilation of the saccules of the Golgi complexes and cisternae of the endoplasmic reticulum. Associated with the Golgi complexes are small protein-carbohydrate yolk precursors encompassed by a membrane. These increase in size by fusing with each other. The “mature” yolk body is a membrane-bounded structure with a central striated core and a granular periphery. At maturity a major portion of the ooplasmic constituents such as as mitochondria and lipid droplets occupy the animal region while the bulk of the population of yolk bodies are situated in the vegetal hemisphere. The follicle cells incompletely encompass the developing oocyte. In addition to the regularly occurring organelles, follicle cells are characterized by the presence of large quantities of rough endoplasmic reticulum and Golgi complexes whose saccules are filled with a dense substance. Associated with the Golgi saccules are secretory droplets of varied size. Amongst the differentiating oocytes and follicle cells are Leydig cells. These cells are characterized by a large vacuole containing glycogen. A possible function for the follicle and Leydig cells is discussed.     

Modeling capsid self-assembly: design and analysis

A series of simulations aimed at elucidating the self-assembly dynamics of spherical virus capsids is described. This little-understood phenomenon is a fascinating example of the complex processes that occur in the simplest of organisms. The fact that different viruses adopt similar structural forms is an indication of a common underlying design, motivating the use of simplified, low-resolution models in exploring the assembly process. Several versions of a molecular dynamics approach are described. Polyhedral shells of different sizes are involved, the assembly pathways are either irreversible or reversible and an explicit solvent is optionally included. Model design, simulation methodology and analysis techniques are discussed. The analysis focuses on the growth pathways and the nature of the intermediate states, properties that are hard to access experimentally. Among the key observations are that efficient growth proceeds by means of a cascade of highly reversible stages, and that while there are a large variety of possible partial assemblies, only a relatively small number of strongly bonded configurations are actually encountered.     

北京地区蕨类植物区系分析

对北京地区蕨类植物区系进行了初步分析,研究表明,北京共有蕨类植物77种,隶属于19科34属,以蹄盖蕨科、岩蕨科、鳞毛蕨科、卷柏科等为优势科,以岩蕨属、卷柏属、铁角蕨属等为优势属,科内及属内分化程度较低,种类组成贫乏;地理成分以温带成分占优势,有11属为温带分布属,占非世界分布属总数的61．11％,除世界种和中国特有种外,全为温带性质的种;生境特点以石生为主,大多数种类分布在北京西部和北部的山区;与河北的关系最为密切,其次为山西、内蒙、辽宁、山东,与秦岭也有一定的联系,与西藏的关系疏远。     

The genome of Hyperthermus butylicus: a sulfur-reducing, peptide fermenting, neutrophilic Crenarchaeote growing up to 108 degrees C

Hyperthermus butylicus, a hyperthermophilic neutrophile and anaerobe, is a member of the archaeal kingdom Crenarchaeota. Its genome consists of a single circular chromosome of 1,667,163 bp with a 53.7% G+C content. A total of 1672 genes were annotated, of which 1602 are protein-coding, and up to a third are specific to H. butylicus. In contrast to some other crenarchaeal genomes, a high level of GUG and UUG start codons are predicted. Two cdc6 genes are present, but neither could be linked unambiguously to an origin of replication. Many of the predicted metabolic gene products are associated with the fermentation of peptide mixtures including several peptidases with diverse specificities, and there are many encoded transporters. Most of the sulfur-reducing enzymes, hydrogenases and electron-transfer proteins were identified which are associated with energy production by reducing sulfur to H(2)S. Two large clusters of regularly interspaced repeats (CRISPRs) are present, one of which is associated with a crenarchaeal-type cas gene superoperon; none of the spacer sequences yielded good sequence matches with known archaeal chromosomal elements. The genome carries no detectable transposable or integrated elements, no inteins, and introns are exclusive to tRNA genes. This suggests that the genome structure is quite stable, possibly reflecting a constant, and relatively uncompetitive, natural environment.     

Nonlinear theory of ion-acoustic waves in an ideal plasma with degenerate electrons

A nonlinear theory is constructed that describes steady-state ion-acoustic waves in an ideal plasma in which the electron component is a degenerate Fermi gas and the ion component is a classical gas. The parameter ranges in which such a plasma can exist are determined, and dispersion relations for ion-acoustic waves are obtained that make it possible to find the linear ion-acoustic velocity. Analytic gas-dynamic models of ion sound are developed for a plasma with the ion component as a cold, an isothermal, or an adiabatic gas, and moreover, the solutions to the equations of all the models are brought to a quadrature form. Profiles of a subsonic periodic and a supersonic solitary wave are calculated, and the upper critical Mach numbers of a solitary wave are determined. For a plasma with cold ions, the critical Mach number is expressed by an explicit exact formula.     

The cercal receptor system of the praying mantid,Archimantis brunneriana Sauss.

Summary The cerci of the praying mantid, Archimantis brunneriana Sauss., are paired segmented sensory organs located at the tip of the abdomen. Basally the cercal segments are slightly flattened dorso-ventrally and are fused to such a degree that it is difficult to distinguish them. Distally the segments become progressively more flattened laterally and their boundaries become more obvious.Two types of sensilla are present on the cerci, trichoid sensilla and filiform sensilla. Trichoid hairs are longest on the medial side of the cerci and toward the cercal base. On the proximal cercal segments they are grouped toward the middle of each segment while they are more uniformly distributed on the distal segments. Filiform sensilla are found at the distal end of each segment except the last and are most abundant on the middle segments of the cercus. Both the number of cercal segments and the number of sensilla are variable. Trichoid hairs are highly variable in appearance from short and stout to long and thin. They arise from a raised base, have a fluted shaft, and some have a pore at the tip. They are innervated by from one to five dendrites, one of which is always considerably larger than the others. Some of the dendrites continue out into the shaft of the hair.Filiform hairs have fluted shafts and are mounted in a flexible membrane within a cuticular ring in a depression. They are innervated by a single large sensory neuron, the dendrite of which passes across a flattened area on the inner wall of the lumen of the hair. The dendritic sheath forms the lining of the ecdysial canal and is therefore firmly attached to the hair. The dendrite is attached to the sheath by desmosomes distally and is penetrated by projections of the sheath more proximally. A fibrous cap surrounds the dendrite and may hold it in place relative to the hair.The cercal receptor system of Archimantis is compared to those of cockroaches and crickets.     

Similar and divergent features in mammalian and yeast prions

Mammalian transmissible spongiform encephalopathies are likely due to the propagation of an abnormal form of a constitutive protein instead of traditional genetic material (nucleic acids). Such infectious proteins, which are termed prions, exist in yeast. They are at the origin of a number of phenotypes that are inherited in a non-Mendelian manner. These prions are very useful to dissect the molecular events at the origin of this structure-based inheritance. The properties of mammalian and yeast prions are presented and compared. This review highlights a number of similarities and differences.     

Coding of visual objects in the ventral stream

How are objects represented in the brain? Two facets of this question are currently under investigation. First, are objects represented by activity in a relatively small number of neurons that are each selective for the shape or identity of a specific object (a 'sparse code'), or are they represented by a pattern of activity across a large number of less selective neurons (a 'population code')? Second, how are the neurons that code for an object distributed across the cortex: are they clustered together in patches, or are they scattered widely across the cortex? The results from neurophysiology and functional magnetic resonance imaging studies are beginning to provide preliminary answers to both questions.     

Evaluating “Hot Spots” of Soil Contamination (Redux)

Every day, thousands of soil samples are collected from properties suspected of being contaminated. The samples are sent to laboratories where the chemical constituents are quantified. Frequently, one or more samples are identified as constituting a “hot spot” of soil contamination. The consequences of such a determination—more sampling, more remediation, more reporting—are often quite expensive. Yet despite the often costly consequences of identifying a “hot spot,” there appears no supportable methodology for objectively deciding which spots are “hot” and which are “not.” This can lead to situations where sampling episodes are required to demonstrate that there is not a problem, even though just exactly what would comprise a “problem” is not particularly clear and sometimes is not stated. The authors provide a review and analysis of common and published information concerning “hot spots.” They then present a different point of view about “hot spots” from those in common practice, a point of view that will challenge many environmental professionals to reconsider how they evaluate sampling results.     

Development of cell wall appendages inAcanthosphaera zachariasi (Chlorococcales): Kinetics,site of cellulose synthesis and of microfibril assembly,and barb formation

Summary The investigation of the formation of cell wall appendages inAcanthosphaera by means of light and electron microscopy and by the use of dyes which interfere with microfibril assembly resulted in several observations which are helpful to an understanding of the formation of normal cell walls. The barbs are built up in the ER, pass through the Golgi apparatus, and are extruded exocytotically after cytokinesis, a remarkable example of the secretion of a structured product. Each cellulose microfibril in a spike develops in a distinct pit of the plasmalemma. The pits are aggregated in a pit field, generating one spike, and are closely adjacent to a basal vesicle which might have morphogenetic and/or regulatory functions. The pits are the site of cellulose synthesis; here the plasmalemma is conspicuously thickened. As shown directly and by the application of Calcofluor white and Congo red, the microfibrils assemble at a certain distance from the plasma membrane,i.e. cellulose synthesis and microfibril assembly are separated by a gap. It is discussed whether single glucan chains or small bundles of them are released from the plasmalemma. The elongation rate of the spikes indicates that about 1000 glycosidic linkages per glucan chain per minute are formed.     

红褐斑腿蝗血细胞的形态与分类

利用光学显微镜和显微数码拍照系统,对红褐斑腿蝗Catantops pinguis(Stal)血细胞的形态进行观察和分类。结果在红褐斑腿蝗血淋巴中观察到5种血细胞,分别是原血胞、浆血胞、粒血胞、珠血胞和囊血胞。原血胞为小型圆形细胞,边缘圆滑、清晰,核质比例很大。粒血胞多为中型,形状不规则,边缘凹突不平,内含较大的异质性溶酶体颗粒。浆血胞多为中型,刚离体时形状较规则,常呈圆形、卵圆形。浆血胞内缺乏大的颗粒,细胞核大而圆形,细胞质内具许多小型颗粒状物质。浆血胞离体后形状变化较多,常发展出伪足,呈丝状、短芒状、钩状或片状伪足。珠血胞多为大、中型,外形大体呈圆形,但边缘由于大小不等的珠形内含物突出,呈花瓣状。囊血胞多为中型,圆形或椭圆形,细胞质内具有大小不一的带有折光性的颗粒或块状物,细胞边缘比较光滑。     

Dynamics of a quantitative character subject only to stabilising selection

The implications of stabilising selection on a quantitative trait, in the absence of other evolutionary forces, are theoretically investigated in a randomly mating population. The dynamics of various statistics that describe the alleles contributing to the trait are determined and used to infer the behaviour of the trait. Dynamical solutions of the distribution of allelic effects and the distribution of the trait are found when all initial distributions of allelic effects are Gaussian and linkage disequilibria are neglected. Some results for the behaviour of the mean and the variance of genotypic effects of the population, when subject to a moving optimum, are derived. When the initial distributions of allelic effects are not Gaussian, but possess a small asymmetry, the mean and the variance of the allelic effects differ only slightly from the Gaussian results. By contrast, the third central moments of allelic effects, are, at all loci, strictly zero in the Gaussian case but are generally non-zero for non-symmetric initial distributions. To leading order in a quantitative measure of the asymmetry of the distribution, we determine the third central moment of allelic effects.     

Mollicutes-wall-less bacteria with internal cytoskeletons

The structure and motility of the Mollicutes (Spiroplasma, Mycoplasma, and Acholeplasma) are briefly reviewed. The data are presented from the perspective of prokaryotic and eukaryotic motors, cytoskeletons, and cell motility. The Mollicutes are eubacteria derived from Clostridia by regressive evolution and genome reduction to produce the smallest and simplest free-living and self-replicating cells. Structurally, the Mollicutes are characterized by a complete lack of a cell wall and the presence of an internal cytoskeleton. Spiroplasma, which are helical cells with a flat, ribbon-like cytoskeleton, are amenable to structural and geometrical analysis. Motility and shape changes can be explained and modeled by the cytoskeleton acting as a linear motor.