First Steps in Eukaryogenesis: Physical Phenomena in the Origin and Evolution of Chromosome Structure

Our present understanding of the origin and evolution of chromosomes differs considerably from current understanding of the origin and evolution of the cell itself. Chromosome origins have been less prominent in research, as the emphasis has not shifted so far appreciably from the phenomenon of primeval nucleic acid encapsulation to that of the origin of gene organization, expression, and regulation. In this work we discuss some reasons why preliminary steps in this direction are being taken. We have been led to examine properties that have contributed to raise the ancestral prokaryotic programmes to a level where we can appreciate in eukaryotes a clear departure from earlier themes in the evolution of the cell from the last common ancestor. We shift our point of view from evolution of cell morphology to the point of view of the genes. In particular, we focus attention on possible physical bases for the way transmission of information has evolved in eukaryotes, namely, the inactivation of whole chromosomes. The special case of the inactivation of the X chromosome in mammals is discussed, paying particular attention to the physical process of the spread of X inactivation in monotremes (platypus and echidna). When experimental data is unavailable some theoretical analysis is possible based on the idea that in certain cases collective phenomena in genetics, rather than chemical detail, are better correlates of complex chemical processes.     

Timeline: the march of structural biology

One hundred years ago, we knew very little about biological macromolecules and had no tools available to study their structure. Structural biology is now a mature science. New structures are being solved at an ever-increasing rate and there are important new initiatives to determine all the protein folds that are used by biological systems (structural genomics). This article traces some of the key developments in the field.     

Climatic limits of pink bollworm in Arizona and California: effects of climate warming

The distribution and abundance of pink bollworm (Pectinophora gossypiella Saunders (PBW)) in cotton in Arizona and California was examined using a validated weather-driven, physiologically based demographic model of cotton and PBW integrated into a geographic information system (GIS). Survival of diapause larvae during winter as affected by low temperatures is a key factor determining the range of PBW. Winter survival was estimated using data from Gutierrez et al. (Can. Entomol. 109 (1977) 1457) and Venette et al. (Environ. Entomol. 29 (5) (2000) 1018). The model was run continuously over the period 1 January 1995 to 31 December 2003 using observed weather data from 121 locations. Three output variables were mapped as measures of PBW persistence: over-winter survival of diapause PBW larvae, cumulative daily PBW larval densities over the season, and the number of diapause larvae produced during the season. The distribution of pink bollworm is predicted to be restricted to the relatively frost-free cotton growing areas of Arizona and Southern California where it currently reaches pest status. The model predicts that extension of PBW's range into the Central Valley of California is unlikely. The analysis questions the efficacy of an ongoing area-wide effort to prevent the establishment of PBW in the Central Valley of California. Four global warming scenarios were examined to estimate the effects on the potential geographic range of PBW. Average observed daily temperatures were increased 1.0, 1.5, 2.0 or 2.5 °C, respectively, in the four scenarios. Scenarios with average increases of 1.5–2.5 °C predicted that the range of PBW would expand into the Central Valley of California and the severity of the pest would greatly increase in areas of current infestation.     

Reconstructing the Evolution of Brachypodium Genomes Using Comparative Chromosome Painting

Brachypodium distachyon is a model for the temperate cereals and grasses and has a biology, genomics infrastructure and cytogenetic platform fit for purpose. It is a member of a genus with fewer than 20 species, which have different genome sizes, basic chromosome numbers and ploidy levels. The phylogeny and interspecific relationships of this group have not to date been resolved by sequence comparisons and karyotypical studies. The aims of this study are not only to reconstruct the evolution of Brachypodium karyotypes to resolve the phylogeny, but also to highlight the mechanisms that shape the evolution of grass genomes. This was achieved through the use of comparative chromosome painting (CCP) which hybridises fluorescent, chromosome-specific probes derived from B. distachyon to homoeologous meiotic chromosomes of its close relatives. The study included five diploids (B. distachyon 2n = 10, B. sylvaticum 2n = 18, B. pinnatum 2n = 16; 2n = 18, B. arbuscula 2n = 18 and B. stacei 2n = 20) three allotetraploids (B. pinnatum 2n = 28, B. phoenicoides 2n = 28 and B. hybridum 2n = 30), and two species of unknown ploidy (B. retusum 2n = 38 and B. mexicanum 2n = 40). On the basis of the patterns of hybridisation and incorporating published data, we propose two alternative, but similar, models of karyotype evolution in the genus Brachypodium. According to the first model, the extant genome of B. distachyon derives from B. mexicanum or B. stacei by several rounds of descending dysploidy, and the other diploids evolve from B. distachyon via ascending dysploidy. The allotetraploids arise by interspecific hybridisation and chromosome doubling between B. distachyon and other diploids. The second model differs from the first insofar as it incorporates an intermediate 2n = 18 species between the B. mexicanum or B. stacei progenitors and the dysploidic B. distachyon.     

Ecological and biogeographical analyses of Mediterranean forests of northern Morocco

Mediterranean forests in northern Morocco have been studied. Tree species composition and abundance were investigated in 84 forest sites, distributed throughout the sandstone formation of the Tangier region. The relative abundance of 15 tree and arborescent shrub species was related, by ordination analysis, to altitude, disturbance by fire, and soil fertility. High-elevation forests were dominated by Cedrus atlantica, Quercus pyrenaica and Pinus pinaster. Sacred forests (protected as holy burial places) had a distinct stand structure, and were considered as refuges, for maintaining biodiversity at landscape scale. The evergreen oak Quercus suber and the semideciduous Quercus canariensis co-dominated the lowland forests. The mean basal area of the studied forests was 34 m² ha^–1. The mean trunk size (dbh) for Q. suber was 24 cm and for Q. canariensis 36.5 cm; in both cases there were indications of declining regeneration at population level. A comparative biogeographical analysis with the equivalent region in southern Spain (separated by the Strait of Gibraltar; 14 km wide), indicated a possible biodiversity loss in the Moroccan forests.     

Trafficking of the IKs‐Complex in MDCK Cells: Site of Subunit Assembly and Determinants of Polarized Localization

The voltage‐gated potassium channel K_V7.1 is regulated by non‐pore forming regulatory KCNE β‐subunits. Together with KCNE1, it forms the slowly activating delayed rectifier potassium current I_Ks. However, where the subunits assemble and which of the subunits determines localization of the I_Ks‐complex has not been unequivocally resolved yet. We employed trafficking‐deficient K_V7.1 and KCNE1 mutants to investigate I_Ks trafficking using the polarized Madin‐Darby Canine Kidney cell line. We find that the assembly happens early in the secretory pathway but provide three lines of evidence that it takes place in a post‐endoplasmic reticulum compartment. We demonstrate that K_V7.1 targets the I_Ks‐complex to the basolateral membrane, but that KCNE1 can redirect the complex to the apical membrane upon mutation of critical K_V7.1 basolateral targeting signals. Our data provide a possible explanation to the fact that K_V7.1 can be localized apically or basolaterally in different epithelial tissues and offer a solution to divergent literature results regarding the effect of KCNE subunits on the subcellular localization of K_V7.1/KCNE complexes .     

Silybum marianum: non‐medical exploitation of the species

Silybum marianum (milk thistle) is currently utilised as a medicinal plant which provides raw material for the production of silymarin. Silymarin is composed of a group of flavonolignans that are well known and studied for their medicinal properties. However, the biomass yield potential and the chemical composition of its biomass suggest opportunities for much broader utilisation of S. marianum. This paper reviews the available literature about S. marianum biomass productivity and composition and about properties of products and byproducts of silymarin extraction. Alternative uses of whole plant biomass include fodder, bioenergy production and phytoremediation. Byproducts of silymarin extraction such as oil and flour have possible applications in food, feed and cosmetics. Moreover, the review explores potential alternative applications of silymarin. We conclude that a pivotal issue for further utilisation of S. marianum is the development of improved cultivars suited for the different possible utilisations.