The evolutionary history of the white-rayed species of Melampodium (Asteraceae) involved multiple cycles of hybridization and polyploidization

? Premise of the study: Polyploidy plays an important role in race differentiation and eventually speciation. Underlying mechanisms include chromosomal and genomic changes facilitating reproductive isolation and/or stabilization of hybrids. A prerequisite for studying these processes is a sound knowledge on the origin of polyploids. A well-suited group for studying polyploid evolution consists of the three species of Melampodium ser. Leucantha (Asteraceae): M. argophyllum, M. cinereum, and M. leucanthum. ? Methods: The origin of polyploids was inferred using network and tree-based phylogenetic analyses of several plastid and nuclear DNA sequences and of fingerprint data (AFLP). Genome evolution was assessed via genome size measurements, karyotype analysis, and in situ hybridization of ribosomal DNA. ? Key results: Tetraploid cytotypes of the phylogenetically distinct M. cinereum and M. leucanthum had, compared to the diploid cytotypes, doubled genome sizes and no evidence of gross chromosomal rearrangements. Hexaploid M. argophyllum constituted a separate lineage with limited intermixing with the other species, except in analyses from nuclear ITS. Its genome size was lower than expected if M. cinereum and/or M. leucanthum were involved in its origin, and no chromosomal rearrangements were evident. ? Conclusions: Polyploids in M. cinereum and M. leucanthum are of recent autopolyploid origin in line with the lack of significant genomic changes. Hexaploid M. argophyllum also appears to be of autopolyploid origin against the previous hypothesis of an allopolyploid origin involving the other two species, but some gene flow with the other species in early phases of differentiation cannot be excluded.     

Inhibition of long myosin light-chain kinase activation alleviates intestinal damage after binge ethanol exposure and burn injury

Laboratory evidence suggests that intestinal permeability is elevated following either binge ethanol exposure or burn injury alone, and this barrier dysfunction is further perturbed when these insults are combined. We and others have previously reported a rise in both systemic and local proinflammatory cytokine production in mice after the combined insult. Knowing that long myosin light-chain kinase (MLCK) is important for epithelial barrier maintenance and can be activated by proinflammatory cytokines, we examined whether inhibition of MLCK alleviated detrimental intestinal responses seen after ethanol exposure and burn injury. To accomplish this, mice were given vehicle or a single binge ethanol exposure followed by a sham or dorsal scald burn injury. Following injury, one group of mice received membrane permeant inhibitor of MLCK (PIK). At 6 and 24 h postinjury, bacterial translocation and intestinal levels of proinflammatory cytokines were measured, and changes in tight junction protein localization and total intestinal morphology were analyzed. Elevated morphological damage, ileal IL-1β and IL-6 levels, and bacterial translocation were seen in mice exposed to ethanol and burn injury relative to either insult alone. This increase was not seen in mice receiving PIK after injury. Ethanol-exposed and burn-injured mice had reduced zonula occludens protein-1 and occludin localization to the tight junction relative to sham-injured mice. However, the observed changes in junctional complexes were not seen in our PIK-treated mice following the combined insult. These data suggest that MLCK activity may promote morphological and inflammatory responses in the ileum following ethanol exposure and burn injury.     

The Arabidopsis RING-type E3 ligase XBAT32 mediates the proteasomal degradation of the ethylene biosynthetic enzyme, 1-aminocyclopropane-1-carboxylate synthase 7

E3 ubiquitin ligases select specific proteins for ubiquitin conjugation, and the modified proteins are commonly degraded through the 26S proteasome. XBAT32 is a RING-type E3 ligase involved in maintaining appropriate levels of ethylene. Previous work has suggested that XBAT32 modulates ethylene production by ubiquitinating two ethylene biosynthesis enzymes, ACS4 (type-II isoform) and ACS7 (type-III isoform). In Arabidopsis, conserved sequences within the C-terminal tail of type-I and -II 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) isoforms influence ubiquitin-dependent proteolysis. ACS7, the sole Arabidopsis type-III ACS, contains a truncated C-terminal tail that lacks all known regulatory sequences, which suggests that this isoform may not be subject to ubiquitin-mediated proteasomal degradation. Here we demonstrate in planta that ACS7 is turned over in a 26S proteasome-dependent manner and that degradation of ACS7 requires the E3 ligase XBAT32. Furthermore, the ethylene-related phenotypes that result from overexpression of ACS7 in wild-type plants are greatly exaggerated in xbat32-1, suggesting that XBAT32 is required to attenuate the effect of overexpression of ACS7. This observation is consistent with a role for XBAT32 in the ubiquitin-mediated degradation of ACS7. The dark-grown phenotype of xbat32-1 seedlings overexpressing ACS7 can be effectively rescued by aminoethoxyvinylglycine, an inhibitor of ACS activity. The degradation rate of ACS4 is also significantly slower in the absence of XBAT32, further implicating XBAT32 in the ubiquitin-mediated degradation of ACS4. Altogether, these results demonstrate that XBAT32 targets ethylene biosynthetic enzymes for proteasomal degradation to maintain appropriate levels of hormone production.     

Changes to the N cycle following bark beetle outbreaks in two contrasting conifer forest types

Outbreaks of Dendroctonus beetles are causing extensive mortality in conifer forests throughout North America. However, nitrogen (N) cycling impacts among forest types are not well known. We quantified beetle-induced changes in forest structure, soil temperature, and N cycling in Douglas-fir (Pseudotsuga menziesii) forests of Greater Yellowstone (WY, USA), and compared them to published lodgepole pine (Pinus contorta var. latifolia) data. Five undisturbed stands were compared to five beetle-killed stands (4–5 years post-outbreak). We hypothesized greater N cycling responses in Douglas-fir due to higher overall N stocks. Undisturbed Douglas-fir stands had greater litter N pools, soil N, and net N mineralization than lodgepole pine. Several responses to disturbance were similar between forest types, including a pulse of N-enriched litter, doubling of soil N availability, 30–50 % increase in understory cover, and 20 % increase in foliar N concentration of unattacked trees. However, the response of some ecosystem properties notably varied by host forest type. Soil temperature was unaffected in Douglas-fir, but lowered in lodgepole pine. Fresh foliar %N was uncorrelated with net N mineralization in Douglas-fir, but positively correlated in lodgepole pine. Though soil ammonium and nitrate, net N mineralization, and net nitrification all doubled, they remained low in both forest types (<6 μg N g soil^?1 NH₄ ⁺or NO₃ ^?; <25 μg N g soil^?1 year^?1 net N mineralization; <8 μg N g soil^?1 year^?1 net nitrification). Results suggest that beetle disturbance affected litter and soil N cycling similarly in each forest type, despite substantial differences in pre-disturbance biogeochemistry. In contrast, soil temperature and soil N–foliar N linkages differed between host forest types. This result suggests that disturbance type may be a better predictor of litter and soil N responses than forest type due to similar disturbance mechanisms and disturbance legacies across both host–beetle systems.     

Clinical and pathological heterogeneity of cervical intraepithelial neoplasia grade 3

Objective

Cervical intraepithelial neoplasia grade 3 (CIN3), the immediate cervical cancer precursor, is a target of cervical cancer prevention. However, less than half of CIN3s will progress to cancer. Routine treatment of all CIN3s and the majority of CIN2s may lead to overtreatment of many lesions that would not progress. To improve our understanding of CIN3 natural history, we performed a detailed characterization of CIN3 heterogeneity in a large referral population in the US.

Methods

We examined 309 CIN3 cases in the SUCCEED, a large population-based study of women with abnormal cervical cancer screening results. Histology information for 12 individual loop electrosurgical excision procedure (LEEP) segments was evaluated for each woman. We performed case-case comparisons of CIN3s to analyze determinants of heterogeneity and screening test performance.

Results

CIN3 cases varied substantially by size (1–10 LEEP segments) and by presentation with concomitant CIN2 and CIN1. All grades of CINs were equally distributed over the cervical surface. In half of the women, CIN3 lesions were found as multiple distinct lesions on the cervix. Women with large and solitary CIN3 lesions were more likely to be older, have longer sexual activity span, and have fewer multiple high risk HPV infections. Screening frequency, but not HPV16 positivity, was an important predictor of CIN3 size. Large CIN3 lesions were also characterized by high-grade clinical test results.

Conclusions

We demonstrate substantial heterogeneity in clinical and pathological presentation of CIN3 in a US population. Time since sexual debut and participation in screening were predictors of CIN3 size. We did not observe a preferential site of CIN3 on the cervical surface that could serve as a target for cervical biopsy. Cervical cancer screening procedures were more likely to detect larger CIN3s, suggesting that CIN3s detected by multiple independent diagnostic tests may represent cases with increased risk of invasion.