Phylogenetic relationships of Italian Bellevalia species (Asparagaceae), inferred from morphology,karyology and molecular systematics

The seven Bellevalia species and subspecies known from Italy, representing about 10% of the genus and three out of six sections, were studied. An integrated morphological, karyological and molecular approach was used to infer phylogenetic and systematic relationships among them. B. romana (the generitype) is the most distinctive species on karyotype asymmetry grounds. B. boissieri and B.dubia, usually considered as subspecies of one species (the latter endemic to Sicily), deserve specific status based on biparental nrDNA markers (internal transcribed spacer, ITS), since they do not form a single clade. The allotetraploid endemic B. pelagica, morphologically similar to B. romana, is sister to the latter under parsimony, both in morphological and ITS trees; it is also related with B. dubia, based on karyotype asymmetry and a uniparental cpDNA marker (trnL^(UAA)–trnF^(GAA) IGS (intergenic spacer)). A second allotetraploid endemic, B. webbiana, is closely related, on morphological, karyological and molecular grounds, with B. boissieri and B. ciliata, and also with B. trifoliata, three species that might all involved in its origin. B. sect. Conicae Feinbr. and sect. Nutantes Feinbr. are here typified, the former (type: B. ciliata) is most likely a synonym of the latter (type: B. trifoliata).     

CDC25B Overexpression Stabilises Centrin 2 and Promotes the Formation of Excess Centriolar Foci

CDK-cyclin complexes regulate centriole duplication and microtubule nucleation at specific cell cycle stages, although their exact roles in these processes remain unclear. As the activities of CDK-cyclins are themselves positively regulated by CDC25 phosphatases, we investigated the role of centrosomal CDC25B during interphase. We report that overexpression of CDC25B, as is commonly found in human cancer, results in a significant increase in centrin 2 at the centrosomes of interphase cells. Conversely, CDC25B depletion causes a loss of centrin 2 from the centrosome, which can be rescued by treatment with the proteasome inhibitor MG132. CDC25B overexpression also promotes the formation of excess centrin 2 “foci”. These foci can accumulate other centrosome proteins, including γ-tubulin and PCM-1, and can function as microtubule organising centres, indicating that these represent functional centrosomes. Formation of centrin 2 foci can be blocked by specific inhibition of CDK2 but not CDK1. CDK2-mediated phosphorylation of Monopolar spindle 1 (Mps1) at the G1/S transition is essential for the initiation of centrosome duplication, and Mps1 is reported to phosphorylate centrin 2. Overexpression of wild-type or non-degradable Mps1 exacerbated the formation of excess centrin 2 foci induced by CDC25B overexpression, while kinase-dead Mps1 has a protective effect. Together, our data suggest that CDC25B, through activation of a centrosomal pool of CDK2, stabilises the local pool of Mps1 which in turn regulates the level of centrin 2 at the centrosome. Overexpression of CDC25B may therefore contribute to tumourigenesis by perturbing the natural turnover of centrosome proteins such as Mps1 and centrin 2, thus resulting in the de novo assembly of extra-numerary centrosomes and potentiating chromosome instability.     

Nitric oxide signaling in yeast

As a cellular signaling molecule, nitric oxide (NO) is widely conserved from microorganisms, such as bacteria, yeasts, and fungi, to higher eukaryotes including plants and mammals. NO is mainly produced by NO synthase (NOS) or nitrite reductase (NIR) activity. There are several NO detoxification systems, including NO dioxygenase (NOD) and S-nitrosoglutathione reductase (GSNOR). NO homeostasis based on the balance between NO synthesis and degradation is important for the regulation of its physiological functions because an excess level of NO causes nitrosative stress due to the high reactivity of NO and NO-derived compounds. In yeast, NO may be involved in stress responses, but NO and its signaling have been poorly understood due to the lack of mammalian NOS orthologs in the genome. Even though the activities of NOS and NIR have been observed in yeast cells, the gene encoding NOS and the NO production mechanism catalyzed by NIR remain unclear. On the other hand, yeast cells employ NOD and GSNOR to maintain an intracellular redox balance following endogenous NO production, exogenous NO treatment, or environmental stresses. This article reviews NO metabolism (synthesis, degradation) and its regulation in yeast. The physiological roles of NO in yeast, including the oxidative stress response, are also discussed here. Such investigations into NO signaling are essential for understanding the NO-dependent genetic and physiological modulations. In addition to being responsible for the pathology and pharmacology of various degenerative diseases, NO signaling may be a potential target for the construction and engineering of industrial yeast strains.     

Male flowers in Tulipa pumila Moench (Liliaceae) potentially originate from gender diphasy

We found functionally male individuals in an otherwise hermaphroditic population of Tulipa pumila (Liliaceae) located in Tuscany (central Italy). We investigated the sex ratio of this population, followed by morphometric analyses of the scape, leaves and flowers, and tests on pollen germinability and seed number and mass, in order to infer which sexual strategy produced the observed co-occurrence of male and hermaphrodite individuals. We found that sex ratio deviated from 1:1, and functionally male individuals showed a smaller plant size and a reduced pollen fitness (germinability and siring ability) compared to hermaphrodites. These findings point to a resource-dependent sexual allocation strategy, probably associated with gender diphasy.     

Trilobites Calmoniidae de l'Ordovicien supérieur du Maroc et les origines de la Province Malvino-Cafre

A re-examination of the trilobite Baniaspis globosa Destombes (Phacopina) from the Ashgill of the Anti-Atlas (Morocco) shows that it has several derived characters which allow us to classify it in the family Calmoniidae. Calmoniids were characteristic members of the Malvino-Kaffric province during the Lower Devonian. Hence we regard the origins of this palaeogeographic province as located on the northern Gondwanan margin as early as Ashgill, or even Caradoc, times. We agree with those authors who have suggested that the trilobite associations present in the Anti-Atlas, the Montagne Noire (France) and Bohemia during the earlier Ordovician argue against the existence of a 'proto-Tethys' ocean.     

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.      

Un biofacies à Trilobites Homalonotidae dans I'Ordovicien de la marge nord-gondwanienne: implications paléobiologiques et paléogéographiques

During the Llandeilo, the sandy lithological units which develop locally in the Armorican Massif, Spain and Morocco, are all characterized by similar trilobite associations in which endobenthic homalonotids. well adapted to shallow water and sandy substrate, are predominant. During the Llandeilo, on the northern Gondwanan margin, the wide geographical distribution of most of the trilobites, controlled by environmental factors, shows that the existence of a 'Proto-Tethys' ocean is unlikely. □ North Gondwana, Trilobita, Homalonotidae, Ordovician, Llandeilo. palaeoenvironment.     

High local substrate availability stabilizes a cooperative trait

Cooperative behavior is widely spread in microbial populations. An example is the expression of an extracellular protease by the lactic acid bacterium Lactococcus lactis, which degrades milk proteins into free utilizable peptides that are essential to allow growth to high cell densities in milk. Cheating, protease-negative strains can invade the population and drive the protease-positive strain to extinction. By using multiple experimental approaches, as well as modeling population dynamics, we demonstrate that the persistence of the proteolytic trait is determined by the fraction of the generated peptides that can be captured by the cell before diffusing away from it. The mechanism described is likely to be relevant for the evolutionary stability of many extracellular substrate-degrading enzymes.     

蓖麻蚕卵受精的研究

我们从细胞形态上的研究, 证明:蓖麻蚕卵在成熟期分裂的中期(同一横剖面), 基组数染色体是14;分作两圈, 内层4个, 外层10个。成熟卵停止在第一次中期分裂, 纺锤体与卵膜垂直, 待精子入卵后继续向前分裂, 并发现有染色质消散的现象。第二次成熟期分裂结果获得3个极体和1个雌性原核。正常的卵平均能接受2-3条精子, 它们入卵后起收缩、囊化成雄性原核;其中一个与雌性原核合并为“双组核”。剩余的过数精核分裂缓慢, 终于中心体离纺锤体作异形的分裂。