Arguments concerning the basal evolution of the Bryozoa

The number of tentacles per unit of body volume decreases with increasing body size in the Bryozoa. The ranges of zooid sizes and of tentacle numbers of the Phylactolaemata do considerably overlap with those of the Gymnolaemata s. l., but only the phylactolaemes form horseshoe-shaped lophophores. Therefore, the lophophore form in the Bryozoa does not simply depend on body sizes but on differences in the genomes in the two sub-classes. A lining-in of similar or similar seeming external shapes of zooids has no persuasive power unless it is combined with convincing arguments concerning the accompanying emendations of the internal anatomy. Economizations and attained degrees of functional effectivity provide main guide-lines for the argumentation and for testing the probability of discussed cases of evolutionary branching during attempts to reconstruct alterations of the internal anatomy. Recapitulative arrangements may play an important role in this context. Statistics on “phens” cannot help to solve these problems. Comparison of the forms of the body bending, of the modes of ontogenetioal displacement of the polypide, and of the arrangements of the body musculature in combination supports the interpretation that the Stenostomata and the Eurystomata have a common root with primarily erect, uncalcified forms and thus most probably are a monophyletic group of Gymnolaemata s. l. originating in phylactolaeme like ancestors. Omitting the Phylactolaemata (as a linking group with many plesiomorph features) in attempts to reconstruct the bryozoan evolution drastically increases the amount of morphological differences between the Gymnolaemata s. l. and the Phoronidae, which are commonly accepted to have pre-served the most morphological characteristics of the bryozoan ancestors. It must be warned of an overestimation of the possible role of the fossil record for the reconstruction of the bryozoan phylogeny, which strongly demands the aids by investigations also on Recent species.     

The structure of protein evolution and the evolution of protein structure

The observed distribution of protein structures can give us important clues about the underlying evolutionary process, imposing important constraints on possible models. The availability of results from an increasing number of genome projects has made the development of these models an active area of research. Models explaining the observed distribution of structures have focused on the inherent functional capabilities and structural properties of different folds and on the evolutionary dynamics. Increasingly, these elements are being combined.     

Wall structure and bud formation in Rhodotorula glutinis

Summary The first stage in the formation of a bud in Rhodotorula glutinis is the production of a tapered plate of new wall material between the existing wall and the plasmalemma. The parent cell wall is lysed, allowing the bud to emerge enveloped in this new wall. Mucilage is synthesised to surround the developing bud. As the bud grows a septum forms centripetally dividing the two cells. When the daughter cell reaches maximum size the septum cleaves along its axis, producing the bud scar on the parent cell and the birth scar on the daughter cell. The birth scar is obliterated later as the wall of the young cell grows. A system of endoplasmic reticulum and vesicles is found in young buds and is thought to be responsible for the transport of wall material precursors.     

Magmas gene structure and evolution

Magmas is a nuclear encoded protein found in the mitochondria of mammalian cells. It participates in granulocyte-macrophage-colony stimulating factor (GM-CSF) signaling in hematopoietic cells and has an essential role in invertebrate development. In order to characterize the protein structural features and gene evolution of Magmas, a dataset containing 61 Magmas homologs from 52 species distributed among animals, plants and fungi was analyzed. All Magmas members were found to possess three novel sequence motifs in addition to a conserved leader peptide. Phylogenetic tree and dN/dS rate ratios showed that Magmas was evolutionarily conserved. Analysis of Magmas gene organization demonstrated incremental intron acquisition in plants and vertebrates. Significant genetic diversity in Magmas was observed from kingdom specific amino acid signatures, the presence of predicted signal peptides that target the protein to other intracellular locations besides the mitochondria, and the detection of multiple isoforms in higher animals. These studies demonstrate that Magmas members constitute an important family of conserved proteins having multifunctional activities, and provide a basis for future experiments.     

Floral structure and evolution in the Anacardiaceae

WANNAN, B. S. & QUINN, C. J, 1991. Floral structure and evolution in the Anacardiaceae. Carpel morphology and anatomy is investigated in 17 genera and carpellode morphology in 12 genera. There is an evolutionary sequence in the family from poorly differentiated, nearly apocarpous gynoecia towards syncarpous gynoecia with clearly defined stigmata, styles and ovaries. There has also been marked reduction culminating in pseudomonomery. The carpellodes of the male flowers appear more conservative, and provide evidence of affinities between genera with quite different fertile gynoecia. The characters have been polarized using Burseraceae as a sister group. Data from these sources, as well as from pericarp anatomy, wood anatomy and biflavonoid content indicate that the long standing intrafamilial classification into five tribes is artificial, and that the two small satellite families, Blepharocaryaceae and Julianiaceae should be included in the family. A large monophyletic group is recognized comprised of essentially four of the existing tribes (Anacardiëae, Dobineëae, Semecarpeae, Rhoëae), as well as the two satellite families. This group incorporates two subgroups of more closely allied genera. The remaining genera (mostly Spondiadeae) are very diverse, and for the present are placed in an artificial group characterised by a set of plesiomorphs. Relationships within this group must be resolved before a satisfactory taxonomy of the family can be achieved.     

Test structure and evolution in the Foraminifera

For about a decade shell structures have formed the basis of the main taxonomic subdivision of the Foraminifera. Recent investigations have shown that within the monolamellar nodosariaceans no evolution with respect to wall structure has taken place since the Permian. The bilamellar aragonitic forms have remained stable at least since the Jurassic (Triassic?). The bilamellar calcitic forms have remained stable since the Jurassic (Triassic?). The wall structure of the non-lamellar porcellaneous forms has shown no change since the Carboniferous. The non-lamellar monocrystalline forms first occurred in the Upper Carboniferous and appear to have remained stable ever since. The microgranular Foraminifera, first appearing in the Cambrian, disappeared in the Triassic. Their primary structure is not known. The agglutinated forms seem to have started in the Cambrian, if not before. Evolutionary development leading to a higher degree of complexity of shell structure seems to be present (agglutinated—porcellaneous—monocrystalline—monolamellar and bilamellar), and may culminate in a more phylogeny-oriented systematic subdivision than the one we have today.     

Wall structure and bud formation inCryptococcus neoformans

Cells ofCryptococcus neoformans fixed by the TAPO-acrolein-osmium method show a highly electron-dense capsule with fibrillar and granular structures and a wall organized in two main layers. The outer layer is electrontransparent and contains a variable amount of low to medium-density material, especially abundant in actively growing cells. The inner wall layer shows a lamellar aspect and in the majority of the cells may further be divided into two sub-layers mainly on the basis of lamellar compactness. The wall of the bud, since its early appearance, is also formed by an inner dark lamellar layer and an outer, electron-transparent one. While the former is seen as a direct continuation of the corresponding innermost part of the parent wall, the latter orginates from the inside of the lamellar wall and grows out with the emerging bud through a rupture of the lateral parental wall. Capsular material always covers the wall of the bud even if its amount is very reduced in the early stages of the budding.     

苔藓动物的起源与系统发生研究进展—形态学和分子生物学的证据

苔藓动物是后生动物中的一个重要类群。然而,和其它主要后生动物类群相比,长期以来对它的系统学研究却相对滞后。其起源,系统发生地位以及与其它后生物门类之间、其内部各高级分类群间的谱系发生关系一直存在争议。一般认为它是介于原口动物和后口动物之间的过渡类群。但是,近年来的分子系统学研究已经证实了它的原口归属。古生物学资料表明,虽然苔藓动物的大多数类群在奥陶纪已经分化出来,但它在寒武纪却缺乏任何化石记录。另外,苔藓动物起源的时间和方式、其内部各类群间的系统发生关系特别是现生类群和化石类群之间的关系等诸多问题的解决,还有待于大量的形态学和不同的分子数据的进一步积累,并结合其地层分布等各种相关资料进行综合研究。     

Gametogenesis in placental and non-placental ovicellate cheilostome Bryozoa

Oogenesis is compared in two cheilostome bryozoans with contrasting reproductive strategies. from southern Britain: Chartella papyracea (Ellis & Solander) is a non–placental ovicellate brooder, whereas Bugula flabellata (Thompson in Gray) is a placental brooder. The ovarian cycles are similar, and each oocyte develops in tandem with a single nurse cell. Eggs of both species are telolecithal, However, those of B. flabellata are less than 20% the volume of those of the other species, and there are considerable differences in the ultra-structure of oogenesis. In both cases, spermatogenesis has the typical bryozoan pattern. Precocious insemination of the oocyte occurs in both species.     

RNA secondary structure and compensatory evolution

The classic concept of epistatic fitness interactions between genes has been extended to study interactions within gene regions, especially between nucleotides that are important in maintaining pre-mRNA/mRNA secondary structures. It is shown that the majority of linkage disequilibria found within the Drosophila Adh gene are likely to be caused by epistatic selection operating on RNA secondary structures. A recently proposed method of RNA secondary structure prediction based on DNA sequence comparisons is reviewed and applied to several types of RNAs, including tRNA, rRNA, and mRNA. The patterns of covariation in these RNAs are analyzed based on Kimura's compensatory evolution model. The results suggest that this model describes the substitution process in the pairing regions (helices) of RNA secondary structures well when the helices are evolutionarily conserved and thermodynamically stable, but fails in some other cases. Epistatic selection maintaining pre-mRNA/mRNA secondary structures is compared to weak selective forces that determine features such as base composition and synonymous codon usage. The relationships among these forces and their relative strengths are addressed. Finally, our mutagenesis experiments using the Drosophila Adh locus are reviewed. These experiments analyze long-range compensatory interactions between the 5' and 3' ends of Adh mRNA, the different constraints on secondary structures in introns and exons, and the possible role of secondary structures in RNA splicing.     

Molecular evolution and structure of alpha-actinin

The N-terminal actin-binding domain of alpha-actinin is connected to the C-terminal EF-hands by a rod domain. Because of its ability to form dimers, alpha-actinin can cross-link actin filaments in muscle cells as well as in nonmuscle cells. In the prototypic alpha-actinins, the rod domain contains four triple helical bundles, or so-called spectrin repeats. We have found some atypical alpha-actinins in early diverging organisms, such as protozoa and yeast, where the rod domain contains one and two spectrin repeats, respectively. This implies that the four repeats present in modern alpha-actinins arose after two consecutive intragenic duplications from an alpha-actinin with a single repeat. Further, the evolutionary gene tree of alpha-actinins shows that the appearance of four distinct alpha-actinin isoforms may have occurred after the vertebrate-invertebrate split. The topology of the tree lends support to the hypothesis that two rounds (2R) of genome duplication occurred early in the vertebrate radiation. The phylogeny also considers these atypical isoforms as the most basal to alpha-actinins of vertebrates and other eukaryotes. The analysis also positioned alpha-actinin of the fungi Encephalitozoo cuniculi close to the protozoa, supporting the suggestion that microsporidia are early eukaryotes. Because alpha-actinin is considered the basal member of the spectrin family, our studies will improve the understanding of the origin and evolution of this superfamily.     

Seasonal patterns of population structure in a colonial marine invertebrate (Bugula stolonifera, Bryozoa)

For sessile invertebrates, the degree to which dispersal mechanisms transport individuals away from their natal grounds can have significant ecological implications. Even though the larvae of the marine bryozoan Bugula stolonifera have limited dispersal potential, high levels of genetic mixing have been found within their conspecific aggregations. In this study, we investigated whether this high mixing within aggregations of B. stolonifera also resulted in high mixing between aggregations. Adult colonies were collected from five sites within and one site outside of Eel Pond, Woods Hole, Massachusetts, in August 2009 and genotyped at 10 microsatellite loci. Significant genotypic differentiation was found between most sites, suggesting limited connectivity across sites, even those separated by only 100 m. This investigation was extended to determine if low levels of genetic mixing throughout the reproductive season could result in increased homogeneity between sites. Four of the five sites in Eel Pond were sampled early, mid-, and late in the reproductive season in 2010, and again in early 2011. Inter- and intra-annual genotypic differentiation was then assessed within and between sites. Results from these analyses document that low levels of mixing could result in increased homogeneity between some aggregations, but that barriers to genetic exchange prevented mixing between most sites. Further, results from inter-annual comparisons within sites suggest that any potential homogeneity achieved throughout the reproductive season will likely be lost by the beginning of the next reproductive season due to the annual cycle of colony die-back and regrowth experienced by B. stolonifera colonies in Eel Pond.     

Chromatin structure and evolution in the human genome

Background  

Evolutionary rates are not constant across the human genome but genes in close proximity have been shown to experience similar levels of divergence and selection. The higher-order organisation of chromosomes has often been invoked to explain such phenomena but previously there has been insufficient data on chromosome structure to investigate this rigorously. Using the results of a recent genome-wide analysis of open and closed human chromatin structures we have investigated the global association between divergence, selection and chromatin structure for the first time.