Microsatellite-based molecular diversity of bread wheat germplasm and association mapping of wheat resistance to the Russian wheat aphid

Genetic diversity of a set of 71 wheat accessions, including 53 biotype 2 Russian wheat aphid (RWA2)-resistant landraces and 18 RWA2 susceptible accessions, was assessed by examining molecular variation at multiple microsatellite (SSR) loci. Fifty-one wheat SSR primer pairs were used, 81 SSR loci were determined, and 545 SSR alleles were detected. These SSR loci covered all the three genomes, 21 chromosomes, and at least 41 of the 42 chromosome arms. Diversity values averaged over SSR loci were high with mean number of SSR alleles/locus = 6.7, mean Shannon’s index (H) = 1.291, and mean Nei’s gene diversity (He) = 0.609. The three wheat genomes ranked as A > D > B and the homoeologous groups ranked as 7 > 3  > 1 > 2 > 6 > 5 > 4 based on the number of alleles per locus. Xgwm136 on chromosome arm 1AS is the most polymorphic SSR locus with the largest number of observed and effective alleles and the highest H and He. Among all 2485 pairs of wheat accessions, genetic distance (GD) ranged from 0.054 to 1.933 and averaged 0.9832. A dendrogram based on GD matrix showed that all the wheat accessions could be grouped into distinct clusters. Most of the susceptible cultivars (13/18) were clustered into groups that contains all or mostly susceptible accessions. Most of the U.S. cultivars belong to a group that is distinguishable from all the different RWA2 resistant groups. Diversity analysis was also conducted separately for subgroups containing 53 RWA2-resistant accessions and 18 RWA2-susceptible accessions. Association mapping revealed 28 SSR loci significantly associated with leaf chlorosis, and 8 with leaf rolling. New chromosome regions associated with RWA2 resistance were detected, and indicated existence of new RWA resistance genes located on chromosomes of all other homoeologous groups in addition to the groups 1 and 7 in bread wheat. This information is helpful for development of mapping populations for RWA2 resistance genes from different phylogenetic groups, and for wise utilization of the RWA-resistant germplasm in wheat breeding programs.     

Modeling the effects of a Staphylococcal Enterotoxin B (SEB) on the apoptosis pathway

Background  

The lack of detailed understanding of the mechanism of action of many biowarfare agents poses an immediate challenge to biodefense efforts. Many potential bioweapons have been shown to affect the cellular pathways controlling apoptosis [1–4]. For example, pathogen-produced exotoxins such as Staphylococcal Enterotoxin B (SEB) and Anthrax Lethal Factor (LF) have been shown to disrupt the Fas-mediated apoptotic pathway [2, 4]. To evaluate how these agents affect these pathways it is first necessary to understand the dynamics of a normally functioning apoptosis network. This can then serve as a baseline against which a pathogen perturbed system can be compared. Such comparisons can expose both the proteins most susceptible to alteration by the agent as well as the most critical reaction rates to better instill control on a biological network.     

Circularly permuted monomeric red fluorescent proteins with new termini in the ��-sheet

Circularly permuted fluorescent proteins (FPs) have a growing number of uses in live cell fluorescence biosensing applications. Most notably, they enable the construction of single fluorescent protein‐based biosensors for Ca²⁺ and other analytes of interest. Circularly permuted FPs are also of great utility in the optimization of fluorescence resonance energy transfer (FRET)‐based biosensors by providing a means for varying the critical dipole–dipole orientation. We have previously reported on our efforts to create circularly permuted variants of a monomeric red FP (RFP) known as mCherry. In our previous work, we had identified six distinct locations within mCherry that tolerated the insertion of a short peptide sequence. Creation of circularly permuted variants with new termini at the locations corresponding to the sites of insertion led to the discovery of three permuted variants that retained no more than 18% of the brightness of mCherry. We now report the extensive directed evolution of the variant with new termini at position 193 of the protein sequence for improved fluorescent brightness. The resulting variant, known as cp193g7, has 61% of the intrinsic brightness of mCherry and was found to be highly tolerant of circular permutation at other locations within the sequence. We have exploited this property to engineer an expanded series of circularly permuted variants with new termini located along the length of the 10th β‐strand of mCherry. These new variants may ultimately prove useful for the creation of single FP‐based Ca²⁺ biosensors.     

Are males with more attractive resources more selective in their mate preferences? A test in a polygynous species

In many polygynous species, males typically direct more intensecourtship toward more fecund females. Here we examined thisbehavior in relation to the attractiveness of a male's resource.We used the territorial polygynous beaugregory damselfish (Stegastesleucostictus) and manipulated the quality of male breeding territorieswith two types of artificial sites. We also investigated variablenatural breeding territories. Previous studies have shown thatthese different breeding sites were of different qualities,as judged by the number of eggs accrued by the defending male.Males on all three types of breeding sites did court females,and males using the highest quality sites exhibited significantlyhigher courtship intensity. However, only the group of maleson the highest quality site-type modulated their courtship intensityto female quality (i.e., female size). This indicates that males requiredsome minimal level of resource attractiveness (i.e., a threshold) beforethey exhibited mate preferences based on female quality. Further differencesin the resource attractiveness for males defending the high-qualityartificial sites were not related to differences in courtship behavior.     

Territorial boundaries of the male beaugregory damselfish

On six separate occasions during a two month period, there were no significant differences in mean attack distances by territorial male beaugregory damselfish Stregastes leucostictus against male conspecifics, bluehead wrasse Thalassoma bifasciatus and striped parrotfish Scarus iserti . Feeding areas and patrolling areas were typically smaller than attack distances. The presence or absence of eggs, or the quantity of eggs within the male's territory also was not significantly correlated with attack distances. © 2000 The Fisheries Society of the British Isles     

Fine mapping of trypanosomiasis resistance loci in murine advanced intercross lines

We have previously reported the results of genome-wide searches in two murine F₂ populations for QTLs that influence survival following Trypanosoma congolense infection. Three loci, Tir1, Tir2, and Tir3, were identified and mapped to mouse Chromosomes (Chrs) 17, 5, and 1 respectively, with confidence intervals (CIs) in the range 10–40 cM. The size of these CIs is to a large degree the consequence of limited numbers of recombination events in small chromosomal regions in F₂ populations. A number of population designs have been proposed to increase recombination levels in crosses, one of which is the advanced intercross line (AIL). Here we report fine mapping of Tir1, Tir2, and Tir3 in G6 populations of two independent murine AILs created by crossing the C57BL/6J strain with the A/J and BALB/cJ strains, respectively. Data were analyzed by two methods that gave equally informative and similar results. The three QTLs were confirmed in the A/J × C57BL/6J AIL and in the combined data set, but Tir2 was apparently lost from the BALB/cJ × C57BL/6J AIL. The reduction in CIs for the Tir loci ranged from 2.5 to more than ten-fold in G6 populations by comparison with CIs obtained previously in the equivalent F₂ generations. Mapping in the AILs also resolved the Tir3 locus into three trypanosomiasis resistance QTLs, revealing a degree of complexity not evident in extensive studies at the F₂ level. Received: 16 December 1999 / Accepted: 24 March 2000     

Bovine oocyte cytoplasm supports development of embryos produced by nuclear transfer of somatic cell nuclei from various mammalian species.

The transfer of nuclei from one cell to another provides a powerful tool for studying the interactions between the cytoplasm of one cell and the nucleus of another. This study was designed to examine the ability of the bovine metaphase oocyte cytoplasm to support mitotic cell cycles under the direction of differentiated somatic cell nuclei of various mammalian species. Skin fibroblast cells from cows, sheep, pigs, monkeys, and rats were used as sources of donor nuclei. Nuclear transfer units produced by fusion of enucleated bovine oocytes and individual fibroblasts from all species examined underwent transition to interphase accompanied by nuclear swelling, further progression through the cell cycle, and completion of the first mitosis. Regardless of the species of donor fibroblasts used, some cleaving units progressed further and developed to advanced stages, as evidenced by continuation of cell proliferation and formation of a blastocoele cavity at the time appropriate for the donor fibroblast species. Although no pregnancies have been carried to term after transfer of embryos into surrogate animals, these observations suggest that mechanisms regulating early embryonic development may be conserved among mammalian species and that bovine oocyte cytoplasm can support the introduced differentiated nucleus regardless of chromosome number, species, or age of the donor fibroblast.     

Motor neuron disease in Nova Scotia

Fifty-two cases of motor neuron disease seen in two Halifax hospitals were reviewed.Thirty-three (63.5%) had amyotrophic lateral sclerosis, 14 (26.9%) had primary muscular atrophy, four (7.7%) had bulbar palsy and one (1.9%) had primary lateral sclerosis. There were no unusual features in this series when compared with a similar series from the United States. These cases were used to illustrate the features of this disorder and to comment on recent research observations.     

Synthesis of 2',3'-O-(2,4,6-trinitrocyclohexadienylidine)guanosine 5'-triphosphate and a study of its inhibitory properties with adenylate cyclase

A fluorescent GTP analog 2',3'-O-(2,4,6-trinitrocyclohexadienylidine) guanosine 5'-triphosphate (TNP-GTP) has been prepared and some of its physical properties characterized. TNP-GTP was found to be a potent inhibitor of chick embryo heart adenylate cyclase as activated by guanyl 5'-(beta,gamma-imido)triphosphate (GppNHp), F-, and forskolin with Ki values in the 8-15 microM range. It also appeared to inhibit substantially basal adenylate cyclase in this system. TNP-GTP demonstrated an effective competition with [3H]GppNHp, binding to membranes equivalently to GppNHp and about three times better than GTP. 8-Azidoguanosine 5'-triphosphate (8N3GTP) mimics GTP activation of chick embryo heart adenylate cyclase and [gamma-32P]8N3GTP is effectively photoincorporated into a 42,000- to 44,000-Mr doublet when proteins are separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. TNP-GTP effectively prevents this photoincorporation, as does GTP, at concentrations that agree with their respective apparent inhibition and activation binding constants. The data suggest that TNP-GTP could prove to be a valuable tool for studying the mechanisms of GTP regulation of adenylate cyclase and other GTP-regulated systems.