In vivo dissection of the chromosome condensation machinery: reversibility of condensation distinguishes contributions of condensin and cohesin

The machinery mediating chromosome condensation is poorly understood. To begin to dissect the in vivo function(s) of individual components, we monitored mitotic chromosome structure in mutants of condensin, cohesin, histone H3, and topoisomerase II (topo II). In budding yeast, both condensation establishment and maintenance require all of the condensin subunits, but not topo II activity or phospho-histone H3. Structural maintenance of chromosome (SMC) protein 2, as well as each of the three non-SMC proteins (Ycg1p, Ycs4p, and Brn1p), was required for chromatin binding of the condensin complex in vivo. Using reversible condensin alleles, we show that chromosome condensation does not involve an irreversible modification of condensin or chromosomes. Finally, we provide the first evidence of a mechanistic link between condensin and cohesin function. A model discussing the functional interplay between cohesin and condensin is presented.     

Activity of rubidium and cesium in soybean looper (Lepidoptera: Noctuidae): insect feeding on cotton and soybean measured by elemental markers

Uptake and translocation of the elemental markers rubidium (Rb) and cesium (Cs) within adult soybean looper, Pseudoplusia includens (Walker), were determined using atomic absorption spectrophotometry in the laboratory in various feeding and mating treatments. Neonates were tested to determine marker transfer from male and female adults fed rubidium chloride (RbCl)-treated artificial nectar, cesium chloride (CsCI)-treated artificial nectar, or both. All females contained detectable levels of Rb, Cs, or both, which were obtained either through direct feeding or via spermatophores. Rubidium was present in females at significantly greater levels than Cs. No significant differences in Rb levels were observed between feeding or spermatophore acquisitions. Most neonates had significantly higher levels of Rb than Cs. In a field cage study to evaluate adult feeding and oviposition behavior on blooming cotton and blooming soybean treated with RbCl and CsCl, respectively, more eggs contained Rb than Cs, indicating greater feeding on cotton nectar than soybean nectar, regardless of the host plant upon which eggs were laid. Females laid more eggs on blooming soybean than on blooming cotton. Higher levels of Rb in cotton than Cs in soybean were recorded and may be attributed to initial elemental marker quantities available to the insects. This study provides the support for the generalized observations that soybean looper infestations in soybean can be related to feeding activities by adults in cotton.     

Soybean looper (Lepidoptera: Noctuidae) oviposition on cotton and soybean of different growth stages: influence of olfactory stimuli

Soybean looper, Pseudoplusia includens (Walker), oviposition in cotton, Gossypium hirsutum L., and soybean, Glycine max (L.) Merr., of various stages of plant phenological development was evaluated in field cages in 1994, 1995, and 1996. Overall, females preferred to oviposit on soybean over cotton when both crops were compared in vegetative or prebloom stages, when both crops were blooming, and when soybean was blooming or in early pod stage compared with prebloom cotton. Females preferred to deposit eggs on the lower leaf surface in the upper two-thirds of the plant canopy in cotton and soybean. Oviposition in upper and middle canopy levels varied with plant growth stage. Females tended to lay more eggs in the upper canopy compared with the middle canopy in prebloom cotton and vegetative soybean; more eggs were laid in the middle canopy of blooming cotton and reproductive stages of soybean. Females responded to both cotton and soybean volatiles in an olfactometer. There was no significant difference in response to the two sources of volatiles.     

A difference in optomotor behaviour of two Antarctic nototheniid fishes is correlated with the presence of a choroid<Emphasis Type="Italic"> rete mirabile</Emphasis> and Root effect

The hypothesis that fish vision is influenced by the presence of a choroid rete mirabile (an oxygen-concentrating apparatus in the eye) and the Root effect was tested using the optomotor response in two nototheniid species from Antarctica. Pagothenia borchgrevinki, an active cryopelagic zooplanktivore, does not exhibit a major Root effect and the rete is absent. In contrast, the sluggish, benthic nototheniid, Trematomus bernacchii, possesses both a rete and a significant Root effect. Whole-eye ocular PO2 was higher in T. bernacchii (18.6 kPa) than in P. borchgrevinki (18.1 kPa) and the optomotor response of T. bernacchii was positively influenced by subtended angle on a moving background whereas P. borchgrevinki did not respond to any subtended angle (0–600 min of arc). The optomotor response of T. bernacchii may therefore have been facilitated by elevated ocular PO2 due to the presence of the choroid rete and the Root effect.     

The potential of antibody-based immunosuppressive agents for corneal transplantation

Corneal transplantation is a sight-restorative procedure but its success is limited by irreversible graft rejection, which accounts for up to 50 per cent of failures. The normal eye is an immune-privileged site. Multiple mechanisms maintain ocular privilege, including the blood-eye barrier, the lack of blood vessels and lymphatics in the normal cornea, the relative paucity of mature antigen-presenting cells in the central cornea, the presence of immunomodulatory factors in ocular fluids, and the constitutive expressive of CD95L (Fas ligand) within the eye. However, privilege can be eroded by the sequelae of inflammation and neovascularization. Corneal graft rejection in humans is currently suppressed with topical glucocorticosteroids, which are moderately effective. Systemically administered immunosuppressive therapy is of limited efficacy and may be accompanied by unacceptable morbidity. Alternative therapies are needed to improve outcomes. Corneal graft rejection is primarily a cell-mediated response controlled by the CD4+ T cell, and thus CD4 and costimulatory molecule blockade are appealing targets for new therapeutic interventions. A number of monoclonal antibodies have shown promise as immunosuppressants to prolong corneal graft survival in experimental animal models, and may eventually prove to be useful adjuncts to corticosteroids.     

Insertional inactivation of the methionine s-methyltransferase gene eliminates the s-methylmethionine cycle and increases the methylation ratio

Methionine (Met) S-methyltransferase (MMT) catalyzes the synthesis of S-methyl-Met (SMM) from Met and S-adenosyl-Met (Ado-Met). SMM can be reconverted to Met by donating a methyl group to homocysteine (homo-Cys), and concurrent operation of this reaction and that mediated by MMT sets up the SMM cycle. SMM has been hypothesized to be essential as a methyl donor or as a transport form of sulfur, and the SMM cycle has been hypothesized to guard against depletion of the free Met pool by excess Ado-Met synthesis or to regulate Ado-Met level and hence the Ado-Met to S-adenosylhomo-Cys ratio (the methylation ratio). To test these hypotheses, we isolated insertional mmt mutants of Arabidopsis and maize (Zea mays). Both mutants lacked the capacity to produce SMM and thus had no SMM cycle. They nevertheless grew and reproduced normally, and the seeds of the Arabidopsis mutant had normal sulfur contents. These findings rule out an indispensable role for SMM as a methyl donor or in sulfur transport. The Arabidopsis mutant had significantly higher Ado-Met and lower S-adenosylhomo-Cys levels than the wild type and consequently had a higher methylation ratio (13.8 versus 9.5). Free Met and thiol pools were unaltered in this mutant, although there were moderate decreases (of 30%-60%) in free serine, threonine, proline, and other amino acids. These data indicate that the SMM cycle contributes to regulation of Ado-Met levels rather than preventing depletion of free Met.     

Natural variation for seed oil composition in Arabidopsis thaliana

The biochemical pathways involved in the biosynthesis and accumulation of storage lipids in seeds have been extensively studied. However, the regulatory mechanisms of those pathways, their environmental interactions and the ecological implications of variation are poorly understood. We have initiated a new approach: the analysis of natural variation in Arabidopsis thaliana. Three hundred and sixty accessions were surveyed for content of oil, very long chain fatty acids (VLCFAs) and polyunsaturated fatty acids (PUFAs) in their seeds. The results revealed extensive natural variation. A core set of accessions, the seeds of which reproducibly contain extreme amounts of oil, VLCFAs and PUFAs have been identified. Reproducible oil content ranged from 34.6 to 46.0% of seed dry weight. VLCFA content ranged from 13.0 to 21.2% of total fatty acids. PUFA content, ranged from 53.3 to 66.1% of total fatty acids. Interactions were also identified for PUFA and VLCFA content of seeds with vernalisation of plants. Mapping of the regions of the genome involved in controlling the traits was conducted in an F(2) population and indicated that natural variation at the loci FAE1 and FAD3 might be involved in the regulation of VLCFA and PUFA content, respectively. A set of accessions, which capture a broad range of the natural variation for these traits available in A. thaliana, has been selected to form a core set which can be used to further dissect the genetics of the regulation of seed lipid traits and to identify the genes involved.     

Syntenic relationships between Medicago truncatula and Arabidopsis reveal extensive divergence of genome organization

Arabidopsis and Medicago truncatula represent sister clades within the dicot subclass Rosidae. We used genetic map-based and bacterial artificial chromosome sequence-based approaches to estimate the level of synteny between the genomes of these model plant species. Mapping of 82 tentative orthologous gene pairs reveals a lack of extended macrosynteny between the two genomes, although marker collinearity is frequently observed over small genetic intervals. Divergence estimates based on non-synonymous nucleotide substitutions suggest that a majority of the genes under analysis have experienced duplication in Arabidopsis subsequent to divergence of the two genomes, potentially confounding synteny analysis. Moreover, in cases of localized synteny, genetically linked loci in M. truncatula often share multiple points of synteny with Arabidopsis; this latter observation is consistent with the large number of segmental duplications that compose the Arabidopsis genome. More detailed analysis, based on complete sequencing and annotation of three M. truncatula bacterial artificial chromosome contigs suggests that the two genomes are related by networks of microsynteny that are often highly degenerate. In some cases, the erosion of microsynteny could be ascribed to the selective gene loss from duplicated loci, whereas in other cases, it is due to the absence of close homologs of M. truncatula genes in Arabidopsis.