Marcusenius desertus sp. nov. (Teleostei: Mormyridae), a mormyrid fish from the Namib desert

We critically compared Marcusenius specimens from the mouth of the Cunene River on the Namibia/Angola border, a harsh desert environment on the Atlantic Ocean coast virtually devoid of aerial insects with aquatic larvae which are an important food item, with Marcusenius multisquamatus Kramer & Wink, 2013 from the escarpment region of that same river, in a relatively rich and productive subtropical savannah environment. River mouth specimens were differentiated in morphology and electric organ discharges, as determined by ANOVA/MANOVA comparisons, principal component and discriminant analyses on morphological and electrophysiological characters, and genetics, including sequences of the mitochondrial cytochrome b gene, indicating reproductive isolation. Specimens from the river mouth differed from M. multisquamatus, their closest relatives, by having a shorter snout, a smaller eye diameter, and smaller nares separation. River mouth specimens were also differentiated from other, increasingly less-close relatives, such as M. altisambesi Kramer et al., 2007 from the Okavango River, Botswana, and from M. krameri Maake et al., 2014 from the Limpopo System, South Africa. We therefore designate the new species Marcusenius desertus sp. nov. for the Cunene River mouth population.     

Out of America: tracing the genetic footprints of the global diffusion of maize

Maize was first domesticated in a restricted valley in south-central Mexico. It was diffused throughout the Americas over thousands of years, and following the discovery of the New World by Columbus, was introduced into Europe. Trade and colonization introduced it further into all parts of the world to which it could adapt. Repeated introductions, local selection and adaptation, a highly diverse gene pool and outcrossing nature, and global trade in maize led to difficulty understanding exactly where the diversity of many of the local maize landraces originated. This is particularly true in Africa and Asia, where historical accounts are scarce or contradictory. Knowledge of post-domestication movements of maize around the world would assist in germplasm conservation and plant breeding efforts. To this end, we used SSR markers to genotype multiple individuals from hundreds of representative landraces from around the world. Applying a multidisciplinary approach combining genetic, linguistic, and historical data, we reconstructed possible patterns of maize diffusion throughout the world from American “contribution” centers, which we propose reflect the origins of maize worldwide. These results shed new light on introductions of maize into Africa and Asia. By providing a first globally comprehensive genetic characterization of landraces using markers appropriate to this evolutionary time frame, we explore the post-domestication evolutionary history of maize and highlight original diversity sources that may be tapped for plant improvement in different regions of the world.     

Structural basis of siRNA recognition by TRBP double‐stranded RNA binding domains

The accurate cleavage of pre‐micro(mi)RNAs by Dicer and mi/siRNA guide strand selection are important steps in forming the RNA‐induced silencing complex (RISC). The role of Dicer binding partner TRBP in these processes remains poorly understood. Here, we solved the solution structure of the two N‐terminal dsRNA binding domains (dsRBDs) of TRBP in complex with a functionally asymmetric siRNA using NMR, EPR, and single‐molecule spectroscopy. We find that siRNA recognition by the dsRBDs is not sequence‐specific but rather depends on the RNA shape. The two dsRBDs can swap their binding sites, giving rise to two equally populated, pseudo‐symmetrical complexes, showing that TRBP is not a primary sensor of siRNA asymmetry. Using our structure to model a Dicer‐TRBP‐siRNA ternary complex, we show that TRBP's dsRBDs and Dicer's RNase III domains bind a canonical 19 base pair siRNA on opposite sides, supporting a mechanism whereby TRBP influences Dicer‐mediated cleavage accuracy by binding the dsRNA region of the pre‐miRNA during Dicer cleavage.     

Mitochondrial mismatch analysis is insensitive to the mutational process

Mismatch distributions are histograms showing the pattern of nucleotide (or restriction) site differences between pairs of individuals in a sample. They can be used to test hypotheses about the history of population size and subdivision (if selective neutrality is assumed) or about selection (if a constant population size is assumed). Previous work has assumed that mutations never strike the same site twice, an assumption that is called the model of infinite sites. Fortunately, the results are surprisingly robust even when this assumption is violated. We show here that (1) confidence regions inferred using the infinite- sites model differ little from those inferred using a model of finite sites with uniform site-specific mutation rates, and (2) even when site- specific mutation rates follow a gamma distribution, confidence regions are little changed until the gamma shape parameter falls well below its plausible range, to roughly 0.01. In addition, we evaluate and reject the proposition that mismatch waves are produced by pooling data from several subdivisions of a structured population.      

Modifications of Δ5-3-ketosteroid isomerase induced by ultraviolet irradiation in the presence of the solid-phase photoaffinity reagent Δ6-testosterone agarose

The nature of the products formed during the photoinactivation of Δ⁵-3-ketosteroid isomerase in the presence of the solid-phase photoaffinity reagent Δ⁶-testosterone succinyl agarose has been investigated after ultraviolet irradiation. The polypeptide products eluted from the agarose phase by sodium cholate, sodium dodecyl sulfate, and pH 10.5 triethylamine buffer have been characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis, pH 4–6 gel isoelectric focusing, and amino acid analysis. The amino acid compositions of the cholate eluted and SDS eluted products are found to be similar to that of native isomerase, whereas the covalently bound polypeptide eluted by pH 10.5 triethylamine possesses a distinetly different composition. Digestion of the covalently bonded isomerase polypeptide with trypsin yields an agarose-bound peptide fraction that has been characterized by its amino acid composition. This composition is different from that of the undigested covalently bound polypeptide and suggests that the site of covalent attachment lies somewhere between residues 28 and 45 of the isomerase polypeptide.     

Fine-scale spatial distribution of plants and resources on a sandy soil in the Sahel

Three species, wheat, maize and cotton, were grown in pots and subjected to high (85–100% field capacity, _F), medium (65–85% _F) and low (45–65% _F) soil moisture treatments and high (700 l l^–1) and low (350 l l^–1) CO₂ concentrations. Biomass production, photosynthesis, evapotranspiration and crop water use efficiency were investigated. Results showed that the daily photosynthesis rate was increased more in wheat and cotton at high [CO₂] than in maize. In addition, differences were more substantial at low soil water treatment than at high soil water treatment. The daily leaf transpiration was reduced significantly in the three crops at the high CO₂ concentration. The decrease at low soil water was smaller than at high soil water. Crop biomass production responses showed a pattern similar to photosynthesis, but the CO₂-induced increase was more pronounced in root production than shoot production under all soil water treatments. Low soil water treatment led to more root biomass under high [CO₂] than high soil water treatment. CO₂ enrichment caused a higher leaf water use efficiency (WUE) of three crops and the increase was more significant in low than in high soil water treatment. Crop community WUE was also increased by CO₂ enrichment, but the increase in wheat and cotton was much greater than in maize. We conclude that at least in the short-term, C₃ plants such as wheat and cotton may benefit from CO₂ enrichment especially under water shortage condition.     

HeLa细胞端粒酶最适反应条件及活性重建

端粒是真核细胞染色体末端的重复ＤＮＡ序列 ,其生物学功能是防止染色体ＤＮＡ降解、末端融合、非正常重组和染色体的缺失[1] .由于存在“末端复制问题” ,随着老化人体细胞端粒重复序列长度不断缩短 ,但在生殖细胞中由于端粒酶的存在 ,端粒序列并不缩短 .端粒酶是由蛋白质和ＲＮＡ构成的核蛋白 ,是依赖ＲＮＡ的ＤＮＡ聚合酶 ,在ＤＮＡ3’端合成端粒重复序列[2 ] .研究表明 ,在 85 %～ 95 %的人肿瘤细胞中可以检测到端粒酶的活性[3 ,4 ] ,而在正常体细胞中除生殖细胞和造血干细胞等极少数细胞中存在端粒酶活性外 ,均检测不到端粒酶活性 ,这…     

Insemination management for a one-injection prostaglandin F(2)alpha synchronization system. II. One versus two inseminations following detection of estrus

Following detection of estrus in an estrus synchronization system, 216 dairy heifers were inseminated (A.I.) randomly either soon after detected estrus (1X) or soon after detected estrus and again 10 to 12 h later (2X). Average h from detection of estrus to A.I. was 1.8+/-0 for 1X and 1.1+/-0 and 11.1+/-0.4 for 2X. During the regimen, heifers were checked visually for estrus daily for five consecutive days with 16.0 and 17.3% showing estrus and receiving A.I. in the 1X and 2X groups, respectively. Those not seen in estrus were injected with 25 mg PGF(2)alpha with observations for estrus and A.I. continuing for five more days. Response rates as indicated by estrus following prostaglandin F(2)alpha (PGF(2)alpha) were 74.7 and 75.8% for 1X and 2X, respectively. Percentages of heifers in estrus <24, 25 to 48, 49 to 72, 73 to 96 and >96 h after PGF(2)alpha were 3.7, 22.8, 47.1, 15.4 and 11.0, respectively. Based on rectal palpation for pregnancy between 45 and 60 days after A.I., conception rates of 70.2% for 1X and 68.6% for 2X did not differ significantly (P>0.05). Progesterone concentrations at injection for heifers not responding to PGF(2)alpha were lower than was seen in responding heifers (2.7 vs 5.8 ng/ml) (P<0.01). Data from the present experiment supports the conclusion of an earlier experiment that satisfactory conception can be achieved with a single, established daily insemination period.