Cyclin‐dependent kinase‐activating kinases CDKD;1 and CDKD;3 are essential for preserving mitotic activity in Arabidopsis thaliana

For the full activation of cyclin‐dependent kinases (CDKs), not only cyclin binding but also CDK phosphorylation is required. This activating phosphorylation is mediated by CDK‐activating kinases (CAKs). Arabidopsis has four genes showing similarity to vertebrate‐type CAKs, three CDKDs (CDKD;1‐CDKD;3) and one CDKF (CDKF;1). We previously found that the cdkf;1 mutant is defective in post‐embryonic development, even though the kinase activities of core CDKs remain unchanged relative to the wild type. This raised a question about the involvement of CDKDs in CDK activation in planta. Here we report that the cdkd;1 cdkd;3 double mutant showed gametophytic lethality. Most cdkd;1‐1 cdkd;3‐1 pollen grains were defective in pollen mitosis I and II, producing one‐cell or two‐cell pollen grains that lacked fertilization ability. We also found that the double knock‐out of CDKD;1 and CDKD;3 caused arrest and/or delay in the progression of female gametogenesis at multiple steps. Our genetic analyses revealed that the functions of CDKF;1 and CDKD;1 or CDKD;3 do not overlap, either during gametophyte and embryo development or in post‐embryonic development. Consistent with these analyses, CDKF;1 expression in the cdkd;1‐1 cdkd;3‐1 mutant could not rescue the gametophytic lethality. These results suggest that, in Arabidopsis, CDKD;1 and CDKD;3 function as CAKs controlling mitosis, whereas CDKF;1 plays a distinct role, mainly in post‐embryonic development. We propose that CDKD;1 and CDKD;3 phosphorylate and activate all core CDKs, CDKA, CDKB1 and CDKB2, thereby governing cell cycle progression throughout plant development.     

JNK and p38 MAPK are independently involved in tributyltin-mediated cell death in rainbow trout (Oncorhynchus mykiss) RTG-2 cells

Mitogen-activated protein kinases (MAPKs) are a family of Ser/Thr protein kinases that transmit various extracellular signals to the nucleus inducing gene expression, cell proliferation, and apoptosis. Recent studies have revealed that organotin compounds induce apoptosis and MAPK phosphorylation/activation in mammal cells. In this study, we elucidated the cytotoxic mechanism of tributyltin (TBT), a representative organotin compound, in rainbow trout (Oncorhynchus mykiss) RTG-2 cells. TBT treatment resulted in significant caspase activation, characteristic morphological changes, DNA fragmentation, and consequent apoptotic cell death in RTG-2 cells. TBT exposure induced the rapid and sustained accumulation of phosphorylated MAPKs, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38 MAPK). Further analysis using pharmacological inhibitors against caspases and MAPKs showed that TBT also induced cell death in a caspase-independent manner and that p38 MAPK is involved in TBT-induced caspase-independent cell death, whereas JNK is involved in the caspase-dependent apoptotic pathway. Thus, TBT employs at least two independent signaling cascades to mediate cell death in RTG-2 cells. To our knowledge, this is the first study revealing the relationship between MAPK activation and TBT cytotoxicity in RTG-2 cells.     

Evidence for transmission of the zoonotic apicomplexan parasite Babesia duncani by the tick Dermacentor albipictus

Babesiosis is a potentially fatal tick-borne zoonotic disease caused by a species complex of blood parasites that can infect a variety of vertebrates, particularly dogs, cattle, and humans. In the United States, human babesiosis is caused by two distinct parasites, Babesia microti and Babesia duncani. The enzootic cycle of B. microti, endemic in the northeastern and upper midwestern regions, has been well characterised. In the western United States, however, the natural reservoir host and tick vector have not been identified for B. duncani, greatly impeding efforts to understand and manage this zoonotic disease. Two and a half decades after B. duncani was first described in a human patient in Washington State, USA, we provide evidence that the enzootic tick vector is the winter tick, Dermacentor albipictus, and the reservoir host is likely the mule deer, Odocoileus hemionus. The broad, overlapping ranges of these two species covers a large portion of far-western North America, and is consistent with confirmed cases of B. duncani in the far-western United States.     

Stable nitrogen isotopic composition of amino acids reveals food web structure in stream ecosystems

The stable N isotopic composition of individual amino acids (SIAA) has recently been used to estimate trophic positions (TPs) of animals in several simple food chain systems. However, it is unknown whether the SIAA is applicable to more complex food web analysis. In this study we measured the SIAA of stream macroinvertebrates, fishes, and their potential food sources (periphyton and leaf litter of terrestrial C3 plants) collected from upper and lower sites in two streams having contrasting riparian landscapes. The stable N isotope ratios of glutamic acid and phenylalanine confirmed that for primary producers (periphyton and C3 litter) the TP was 1, and for primary consumers (e.g., mayfly and caddisfly larvae) it was 2. We built a two-source mixing model to estimate the relative contributions of aquatic and terrestrial sources to secondary and higher consumers (e.g., stonefly larva and fishes) prior to the TP calculation. The estimated TPs (2.3–3.5) roughly corresponded to their omnivorous and carnivorous feeding habits, respectively. We found that the SIAA method offers substantial advantages over traditional bulk method for food web analysis because it defines the food web structure based on the metabolic pathway of amino groups, and can be used to estimate food web structure under conditions where the bulk method cannot be used. Our result provides evidence that the SIAA method is applicable to the analysis of complex food webs, where heterogeneous resources are mixed.     

Large Scale Spatial Risk and Comparative Prevalence of Borrelia miyamotoi and Borrelia burgdorferi Sensu Lato in Ixodes pacificus

Borrelia miyamotoi is a newly described emerging pathogen transmitted to people by Ixodes species ticks and found in temperate regions of North America, Europe, and Asia. There is limited understanding of large scale entomological risk patterns of B. miyamotoi and of Borreila burgdorferi sensu stricto (ss), the agent of Lyme disease, in western North America. In this study, B. miyamotoi, a relapsing fever spirochete, was detected in adult (n = 70) and nymphal (n = 36) Ixodes pacificus ticks collected from 24 of 48 California counties that were surveyed over a 13 year period. Statewide prevalence of B. burgdorferi sensu lato (sl), which includes B. burgdorferi ss, and B. miyamotoi were similar in adult I. pacificus (0.6% and 0.8%, respectively). In contrast, the prevalence of B. burgdorferi sl was almost 2.5 times higher than B. miyamotoi in nymphal I. pacificus (3.2% versus 1.4%). These results suggest similar risk of exposure to B. burgdorferi sl and B. miyamotoi from adult I. pacificus tick bites in California, but a higher risk of contracting B. burgdorferi sl than B. miyamotoi from nymphal tick bites. While regional risk of exposure to these two spirochetes varies, the highest risk for both species is found in north and central coastal California and the Sierra Nevada foothill region, and the lowest risk is in southern California; nevertheless, tick-bite avoidance measures should be implemented in all regions of California. This is the first study to comprehensively evaluate entomologic risk for B. miyamotoi and B. burgdorferi for both adult and nymphal I. pacificus, an important human biting tick in western North America.     

Using food network unfolding to evaluate food–web complexity in terms of biodiversity: theory and applications

Food–web complexity often hinders disentangling functionally relevant aspects of food–web structure and its relationships to biodiversity. Here, we present a theoretical framework to evaluate food–web complexity in terms of biodiversity. Food network unfolding is a theoretical method to transform a complex food web into a linear food chain based on ecosystem processes. Based on this method, we can define three biodiversity indices, horizontal diversity (D_H), vertical diversity (D_V) and range diversity (D_R), which are associated with the species diversity within each trophic level, diversity of trophic levels, and diversity in resource use, respectively. These indices are related to Shannon's diversity index (H′), where H′ = D_H + D_V ? D_R. Application of the framework to three riverine macroinvertebrate communities revealed that D indices, calculated from biomass and stable isotope features, captured well the anthropogenic, seasonal, or other within‐site changes in food–web structures that could not be captured with H′ alone.     

Compromised intestinal lipid absorption in mice with a liver-specific deficiency of liver receptor homolog 1

Bile acids (BAs) are water-soluble end products from cholesterol metabolism and are essential for efficient absorption of dietary lipids. By using targeted somatic mutagenesis of the nuclear receptor liver receptor homolog 1 (LRH-1) in mouse hepatocytes, we demonstrate here that LRH-1 critically regulates the physicochemical properties of BAs. The absence of LRH-1 and subsequent deficiency of Cyp8b1 eliminate the production of cholic acid and its amino acid conjugate taurocholic acid and increase the relative amounts of less amphipathic BA species. Intriguingly, while the expression of Cyp8b1 is almost extinguished in the livers of mice that lack LRH-1, the expression of the rate-limiting enzyme of BA synthesis, i.e., Cyp7a1, remains unchanged. The profound remodeling of the BA composition significantly reduces the efficacy of intestinal absorption of lipids and reuptake of BAs and facilitates the removal of lipids from the body. Our studies unequivocally demonstrate a pivotal role for LRH-1 in determining the composition of BAs, which, in turn has major consequences on whole-body lipid homeostasis.     

Enhanced propagation of fish nodaviruses in BF-2 cells persistently infected with snakehead retrovirus (SnRV)

Fish nodaviruses are causative agents of viral nervous necrosis causing high mortality in cultured marine fishes around the world. The first successful isolation of fish nodavirus was made with SSN-1 cells, which are persistently infected with snakehead retrovirus (SnRV). In the present study, a BF-2 cell line persistently infected with SnRV (PI-BF-2) was established to evaluate the influence of SnRV on the production of fish nodavirus. The PI-BF-2 cells were slightly more slender than BF-2 cells, but no difference was observed in propagation rate between both cell lines. No difference was observed in production of SnRV between PI-BF-2 and SSN-1 cell lines. Although both PI-BF-2 and BF-2 cell lines showed no cytopathic effect (CPE) after inoculation of striped jack nervous necrosis virus (SJNNV) and redspotted grouper nervous necrosis virus (RGNNV), these fish nodaviruses could be amplified in BF-2 cells, and moreover, production of fish nodaviruses in the PI-BF-2 cell line was more than 40 times higher than in BF-2 cells. Thus, it was concluded that BF-2 cell permissiveness to fish nodaviruses was enhanced by persistent infection with SnRV. Furthermore, homologous cDNA to genomic RNA of SJNNV was detected from both PI-BF-2 and SSN-1 cell lines persistently infected with SnRV. The amount of nodavirus cDNA in SJNNV-inoculated PI-BF-2 cells was clearly lower than that in SJNNV-inoculated SSN-1 cells.