The lepidopteran mitochondrial control region: structure and evolution

For several species of lepidoptera, most of the approximately 350-bp mitochondrial control-region sequences were determined. Six of these species are in one genus, Jalmenus; are closely related; and are believed to have undergone recent rapid speciation. Recent speciation was supported by the observation of low interspecific sequence divergence. Thus, no useful phylogeny could be constructed for the genus. Despite a surprising conservation of control-region length, there was little conservation of primary sequences either among the three lepidopteran genera or between lepidoptera and Drosophila. Analysis of secondary structure indicated only one possible feature in common--inferred stem loops with higher-than-random folding energies-- although the positions of the structures in different species were unrelated to regions of primary sequence similarity. We suggest that the conserved, short length of control regions is related to the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In addition, determination of flanking sequences for one Jalmenus species indicated (i) only weak support for the available model of insect 12S rRNA structure and (ii) that tRNA translocation is a frequent event in the evolution of insect mitochondrial genomes.      

Topochemical distribution of lignin and hydroxycinnamic acids in sugar-cane cell walls and its correlation with the enzymatic hydrolysis of polysaccharides

Background  

Lignin and hemicelluloses are the major components limiting enzyme infiltration into cell walls. Determination of the topochemical distribution of lignin and aromatics in sugar cane might provide important data on the recalcitrance of specific cells. We used cellular ultraviolet (UV) microspectrophotometry (UMSP) to topochemically detect lignin and hydroxycinnamic acids in individual fiber, vessel and parenchyma cell walls of untreated and chlorite-treated sugar cane. Internodes, presenting typical vascular bundles and sucrose-storing parenchyma cells, were divided into rind and pith fractions.     

Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae)

Individual plants of several Amelanchier taxa contain many polymorphic nucleotide sites in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA). This polymorphism is unusual because it is not recent in origin and thus has resisted homogenization by concerted evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the result of gene flow between two major North American clades resolved by phylogenetic analysis of ITS sequences. Western North American species plus A. humilis and A. sanguinea of eastern North America form one clade (A), and the remaining eastern North American Amelanchier make up clade B. Five eastern North American taxa are polymorphic at many of the nucleotide sites where clades A and B have diverged and are thought to be of hybrid origin, with A. humilis or A. sanguinea as one parent and various members of clade B as the other parent. Morphological evidence suggests that A. humilis is one of the parents of one of the polymorphic taxa, a microspecies that we refer to informally as A. "erecta." Sequences of 21 cloned copies of the ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical to A. humilis sequence or to the clade B consensus sequence, or they are apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier "erecta" and another polymorphic taxon are suspected to be relatively old because both grow several hundred kilometers beyond the range of one of their parents. ITS sequence polymorphisms have apparently persisted in these two taxa perhaps because of polyploidy and/or agamospermy (asexual seed production), which are prevalent in the genus.      

鲤鱼肥胖基因的分子克隆及在大肠杆菌中的表达

为了研究鲤鱼肥胖基因的结构特点和体外表达产物的生物学活性 ,利用RT PCR技术从鲤鱼肠系膜脂肪组织中扩增出鲤鱼肥胖基因的cDNA编码序列 ,分析表明该cDNA序列由 4 38个核苷酸组成 ,编码 14 6个氨基酸组成的多肽 ,鲤鱼肥胖基因与人、猪、鼠的相比 ,核苷酸同源性分别为 :84 %、 86 %、 95 % ;氨基酸的同源性分别为 84 %、 82 %、 96 %。构建了原核表达载体 pET 2 8a li,利用IPTG在大肠杆菌中进行了诱导表达 ,并对表达产物进行了初步纯化和生物活性检测 ,结果表明 ,鲤鱼肥胖基因在大肠杆菌中进行了高效特异性融合表达 ,融合蛋白质分子量约为 2 0kD ,经薄层扫描分析 ,目的蛋白占菌体总蛋白的 2 0 3%。表达产物经过纯化和复性能够明显抑制小鼠的摄食和生长 ,说明表达产物Leptin具有明显的生物学活性     

Glutamine repeats and inherited neurodegenerative diseases: molecular aspects

Several dominantly inherited, late onset, neurodegenerative diseases are due to expansion of CAG repeats, leading to expansion of glutamine repeats in the affected proteins. These proteins are of very different sizes and, with one exception, show no sequence homology to known proteins or to each other; their functions are unknown. In some, the glutamine repeat starts near the N-terminus, in another near the middle and in another near the C-terminus, but regardless of these differences, no disease has been observed in individuals with fewer than 37 repeats, and absence of disease has never been found in those with more than 41 repeats. Protein constructs with more than 41 repeats are toxic to E. coli and to CHO cells in culture, and they elicit ataxia in transgenic mice. These observations argue in favour of a distinct change of structure associated with elongation beyond 37–41 glutamine repeats. The review describes experiments designed to find out what these structures might be and how they could influence the properties of the proteins of which they form part. Poly- -glutamines form pleated sheets of β-strands held together by hydrogen bonds between their amides. Incorporation of glutamine repeats into a small protein of known structure made it associate irreversibly into oligomers. That association took place during the folding of the protein molecules and led to their becoming firmly interlocked by either strand- or domain-swapping. Thermodynamic considerations suggest that elongation of glutamine repeats beyond a certain length may lead to a phase change from random coils to hydrogen-bonded hairpins. Possible mechanisms of expansion of CAG repeats are discussed in the light of looped DNA model structures.     

A multigene phylogeny of the Gelidiales including nuclear large-subunit rRNA sequence data

Partial sequences (1032 bp) of the nuclear-encoded large ribosomal RNA gene (LSU) were determined for 16 gelidialean species, and analyzed separately and in combination with plastid rbcL and nuclear SSU gene sequences. The number of informative characters and levels of sequence divergence among taxa are intermediate in LSU sequences as compared to that for rbcL and SSU. Analyses of the separate LSU, and a combined LSU, SSU, and rbcL data sets have identified early-diverging lineages within the Gelidiales including Gelidiella, Pterocladia, Pterocladiella, and a lineage including Gelidium and species classified in other genera. The relationships among most gelidialean taxa are well-resolved and well-supported by analyses of the combined data; however, the relationships of Ptilophora and Capreolia remain unclear. It is speculated that these two lineages have diverged from a common ancestor over an evolutionarily short period of time. This revised version was published online in June 2006 with corrections to the Cover Date.     

Out of Africa and back again: nested cladistic analysis of human Y chromosome variation

We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544 individuals from Africa, Asia, Europe, Oceania, and the New World. Phylogenetic analyses of these nine sites resulted in a tree for 10 distinct Y haplotypes with a coalescence time of approximately 150,000 years. The 10 haplotypes were unevenly distributed among human populations: 5 were restricted to a particular continent, 2 were shared between Africa and Europe, 1 was present only in the Old World, and 2 were found in all geographic regions surveyed. The ancestral haplotype was limited to African populations. Random permutation procedures revealed statistically significant patterns of geographical structuring of this paternal genetic variation. The results of a nested cladistic analysis indicated that these geographical associations arose through a combination of processes, including restricted, recurrent gene flow (isolation by distance) and range expansions. We inferred that one of the oldest events in the nested cladistic analysis was a range expansion out of Africa which resulted in the complete replacement of Y chromosomes throughout the Old World, a finding consistent with many versions of the Out of Africa Replacement Model. A second and more recent range expansion brought Asian Y chromosomes back to Africa without replacing the indigenous African male gene pool. Thus, the previously observed high levels of Y chromosomal genetic diversity in Africa may be due in part to bidirectional population movements. Finally, a comparison of our results with those from nested cladistic analyses of human mtDNA and beta-globin data revealed different patterns of inferences for males and females concerning the relative roles of population history (range expansions) and population structure (recurrent gene flow), thereby adding a new sex-specific component to models of human evolution.      

Genetic basis and breeding application of clonal diversity and dual reproduction modes in polyploid Carassius auratus gibelio

A unisexual species is generally associated with polyploidy, and reproduced by a unisexual reproduction mode, such as gyno- genesis, hybridogenesis or parthenogenesis. Compared with other unisexual and polyploid species, gibel carp (Carassius au- ratus gibelio) has a higher ploidy level of hexaploid. It has undergone several successive rounds of genome polyploidy, and experienced an additional, more recent genome duplication event. More significantly, the dual reproduction modes, including gynogenesis and s...     

Recent developments in the systematics of the Gigartinaceae (Gigartinales, Rhodophyta) based on rbcL sequence analysis and morphological evidence

The phylogenetic systematics of the Gigartinaceae is discussed for seven genera and three undescribed generic lineages and 65 taxa representing 62 species based on an analysis of rbcL sequences and morphological evidence. An examination of rbcL trees resulting from analyses of these taxa identifies seven lineages: (i) ‘Gigartina’ alveata; (ii) Rhodoglossum/Gigartina; (iii) Chondracanthus; (iv) Ostiophyllum; (v) Sarcothalia; (vi) ‘Gigartina’ skottsbergii; and (vii) a large clade containing Iridaea/‘Sarcothalia’, Mazzaella and Chondrus. These lineages and Chondrus are strongly supported; however, two groups, Iridaea/‘Sarcothalia’ and Mazzaella, receive no bootstrap support. The morphology of the female reproductive system is investigated with the aid of computer-generated, color-coded tracings of photographs of cystocarps seen in cross section at different developmental stages. Seven basic cystocarp types were found which corresponded to species groups seen in rbcL trees. These were: (i) a ‘Gigartina’ alveata group in which the carposporangia-bearing filaments develop apomictically from gametophytic cells; (ii) a Rhodoglossum/Gigartina group in which gonimoblast filaments penetrate the surrounding envelope fusing progessively with envelope cells; (iii) a Chondracanthus group in which gonimoblast filaments penetrate the envelope but fuse with envelope cells only at late developmental stages; (iv) a Sarcothalia group in which the gonimoblast filaments displace an envelope composed mainly of secondary gametophytic filaments and link to envelope cells by terminal tubular gonimoblast cells; (v) an Iridaea group similar to the Sarcothalia group, but with an envelope composed of a mixture of medullary cells and secondary gametophytic filaments; (vi) a Mazzaella group that lacks a true envelope and in which gonimoblast filaments connect to modified gametophytic cells by means of terminal tubular cells; (vii) a Chondrus group in which gonimoblast filaments penetrate the medulla and link to modified medullary cells by means of conjunctor cells forming secondary pit connections. The further separation of these groups into genera is based largely on tetrasporangial characters.