贺兰山不同生境旱生灌木的解剖学研究

贺兰山荒漠地带三种不同基质生境的２０种旱生灌木的营养器官的比较解剖学研究表明：其共同特点是叶片的表面积／体积的比值小,叶表具厚的角质层、表皮毛,气孔下陷、并具孔下室,叶向中栅栏组织发达;轴器官中木栓层细胞层数多,皮层较厚,机械组织发达,木薄壁组织及髓部细胞的细胞壁术化加厚,根内都具周皮、木质部的导管分子大小不一、频率较高。此外,根、茎、叶中普遍存在粘液细胞和草酸钙结晶,部分植物的根和茎内有异常维管组织。这些结构特征都与早生环境相关,而不同基质生境中生长的植物尚存在一定差异。     

Origin and radiation of the house mouse: clues from nuclear genes

Although quite a lot is known about the genetic structure of the polytypic species Mus musculus at the periphery of its range, the centre of origin and dispersion of the species remains unknown. To investigate the amount of genetic subdivision that occurs in the central parts of its range, we analysed the genetic variation in four new samples of mice coming from Iran, Pakistan, northern and southern India using 35 autosomal protein loci and restriction fragment length polymorphisms of three genes of the Vβ gene complex of the immune system. The variation was then compared with that found in the subspecies occupying the peripheral regions of the species range. The two samples from the northern part of the Indian subcontinent were shown to be more heterozygous than the samples from any of the other regions. They also contain the majority of the alleles that exist in the differentiated subspecies at the periphery of the species range. A neighbour-joining analysis on Nei's genetic distances and a factorial analysis of correspondences on the allelic composition of each sample both place the Pakistani and Indian populations in a phylogenetically and genetically central position compared to the peripheral subspecies. These results suggest that the populations in this geographically central area have retained most of the ancestral polymorphisms, which in turn indicates that the Indian subcontinent is probably the cradle of the species. The nature of the genetic relationships between the various populations throughout the species range and the possibility that they form an incipient ring species are also discussed. Our results are in agreement with the classical model of geographic differentiation where genetic divergence in allopatry is considered to be the prime cause of subspecies formation that may eventually lead to partial reproductive isolation on secondary contact.     

Use of comparative reasoning tools for evaluation of the effect of sterilization conditions on fermentations to produce acidic fibroblast growth factor

The effects of various medium sterilization conditions on fermentations of a recombinant, acidic fibroblast growth factor (aFGF) producing Escherichia coli have been studied. Changes in the medium resulting from sterilization were monitored by pH and absorption spectra. This simple experiment provided excellent data for the demonstration of the usefulness of comparative reasoning tools in order to evaluate the effect of sterilization on fermentation performance. The time profiles of the main parameters (e.g., carbon dioxide evolution rate, dissolved oxygen, pH, and aFGF productivity) were simplified into piecewise contiguous linear segments, each of which was sequentially numbered. The length, position, and slope of each tine were then characterized. Application of the comparative reasoning tools confirmed that separate sterilization of the glucose was necessary for the success of the process, despite adding to the cost and complexity. The comparative data analysis also showed that scaleup with longer sterilization holding and cooling times would not be detrimental to aFGF production. (c) 1995 John Wiley & Sons, Inc.     

Redescription ofDiaphanosoma volzi Stingelin, 1905 (Crustacea: Daphniiformes: Sididae) with remarks on comparative morphology,biology and geographical distribution

The rareDiaphanosoma volzi Stingelin, long confused withD. sarsi Richard andD. celebensis Stingelin, is redescribed, based on extensive material of parthenogenetic and gamogenetic females and males from Thailand. Indonesia, Malaysia, Philippines, India, Australia and Sudan, and a study of intra- and interpopulation morphological variability. Compared with otherDiaphanosoma species, it shows the greatest degree of oligomerization and specialization. It is widely distributed in the tropics and subtropics of the Eastern hemisphere, and mostly occurs in shallow, vegetated habitats.     

Homology modeling of histidine-containing phosphocarrier protein and eosinophil-derived neurotoxin: Construction of models and comparison with experiment

Homology modeling methods have been used to construct models of two proteins—the histidine-containing phosphocarrier protein (HPr) from Mycoplasma capricolum and human eosinophil-derived neurotoxin (EDN). Comparison of the models with the subsequently determined X-ray crystal structures indicates that the core regions of both proteins are reasonably well reproduced, although the template structures are closer to the X-ray structures in these regions—possible enhancements are discussed. The conformations of most of the side chains in the core of HPr are well reproduced in the modeled structure. As expected, the conformations of surface side chains in this protein differ significantly from the X-ray structure. The loop regions of EDN were incorrectly modeled—reasons for this and possible enhancements are discussed. © 1995 Wiley-Liss, Inc.     

Comparative modeling of the three-dimensional structure of type II antifreeze protein.

Type II antifreeze proteins (AFP), which inhibit the growth of seed ice crystals in the blood of certain fishes (sea raven, herring, and smelt), are the largest known fish AFPs and the only class for which detailed structural information is not yet available. However, a sequence homology has been recognized between these proteins and the carbohydrate recognition domain of C-type lectins. The structure of this domain from rat mannose-binding protein (MBP-A) has been solved by X-ray crystallography (Weis WI, Drickamer K, Hendrickson WA, 1992, Nature 360:127-134) and provided the coordinates for constructing the three-dimensional model of the 129-amino acid Type II AFP from sea raven, to which it shows 19% sequence identity. Multiple sequence alignments between Type II AFPs, pancreatic stone protein, MBP-A, and as many as 50 carbohydrate-recognition domain sequences from various lectins were performed to determine reliably aligned sequence regions. Successive molecular dynamics and energy minimization calculations were used to relax bond lengths and angles and to identify flexible regions. The derived structure contains two alpha-helices, two beta-sheets, and a high proportion of amino acids in loops and turns. The model is in good agreement with preliminary NMR spectroscopic analyses. It explains the observed differences in calcium binding between sea raven Type II AFP and MBP-A. Furthermore, the model proposes the formation of five disulfide bridges between Cys 7 and Cys 18, Cys 35 and Cys 125, Cys 69 and Cys 100, Cys 89 and Cys 111, and Cys 101 and Cys 117.(ABSTRACT TRUNCATED AT 250 WORDS)     

A reconsideration of the reptilian relationships of Archaeopteryx

The cladistic relationships of Archaeopteryx , the earliest known bird, are re-examined and previous hypotheses of relationships evaluated. The morphology of Archaeopteryx is redescribed. New interpretations of the fossils are presented, particularly in regard to the morphology of the pectoral girdle, manus, pelvic girdle, tarsus and pes. These new interpretations challenge some of the phylogenetic hypotheses recently presented and a new version of thecodontian relationships is suggested.     

Comparative sensitivities of electrophoretic assays for human enzymes

The sensitivities of 26 starch gel electrophoretic enzyme assays have been compared using HeLa human cells and A9 mouse cells grown in vitro.This research was supported by National Institutes of Health Grant No. USPHS GM 09966.     

Inference of Gene Flow between Species under Misspecified Models

Genomic sequence data provide a rich source of information about the history of species divergence and interspecific hybridization or introgression. Despite recent advances in genomics and statistical methods, it remains challenging to infer gene flow, and as a result, one may have to estimate introgression rates and times under misspecified models. Here we use mathematical analysis and computer simulation to examine estimation bias and issues of interpretation when the model of gene flow is misspecified in analysis of genomic datasets, for example, if introgression is assigned to the wrong lineages. In the case of two species, we establish a correspondence between the migration rate in the continuous migration model and the introgression probability in the introgression model. When gene flow occurs continuously through time but in the analysis is assumed to occur at a fixed time point, common evolutionary parameters such as species divergence times are surprisingly well estimated. However, the time of introgression tends to be estimated towards the recent end of the period of continuous gene flow. When introgression events are assigned incorrectly to the parental or daughter lineages, introgression times tend to collapse onto species divergence times, with introgression probabilities underestimated. Overall, our analyses suggest that the simple introgression model is useful for extracting information concerning between-specific gene flow and divergence even when the model may be misspecified. However, for reliable inference of gene flow it is important to include multiple samples per species, in particular, from hybridizing species.