What causes mating system shifts in plants? Arabidopsis lyrata as a case study.

The genetic breakdown of self-incompatibility (SI) and subsequent mating system shifts to inbreeding has intrigued evolutionary geneticists for decades. Most of our knowledge is derived from interspecific comparisons between inbreeding species and their outcrossing relatives, where inferences may be confounded by secondary mutations that arose after the initial loss of SI. Here, we study an intraspecific breakdown of SI and its consequences in North American Arabidopsis lyrata to test whether: (1) particular S-locus haplotypes are associated with the loss of SI and/or the shift to inbreeding; (2) a population bottleneck may have played a role in driving the transition to inbreeding; and (3) the mutation(s) underlying the loss of SI are likely to have occurred at the S-locus. Combining multiple approaches for genotyping, we found that outcrossing populations on average harbour 5 to 9 S-locus receptor kinase (SRK) alleles, but only two, S1 and S19, are shared by most inbreeding populations. Self-compatibility (SC) behaved genetically as a recessive trait, as expected from a loss-of-function mutation. Bulked segregant analysis in SC × SI F2 individuals using deep sequencing confirmed that all SC plants were S1 homozygotes but not all S1 homozygotes were SC. This was also revealed in population surveys, where only a few S1 homozygotes were SC. Together with crossing data, this suggests that there is a recessive factor that causes SC that is physically unlinked to the S-locus. Overall, our results emphasise the value of combining classical genetics with advanced sequencing approaches to resolve long outstanding questions in evolutionary biology.

Physical activity and cardiovascular disease risk factors in urban school children.

Although the clinical signs of cardiovascular disease (CVD) are not evident until adulthood, many of the risk factors have their roots in early childhood. The aim of this study was to examine physical activity levels (PA) and the incidence of CVD risk factors in a small population (n=102) of primary school children in Dublin. Risk factors measured included overweight/obesity, blood lipids, blood pressure (BP), physical fitness and PA levels. Over a quarter of the group were overweight/obese (n = 29, 28%). Despite relatively good fitness levels, PA levels were low with less than half the group (n = 44, 46%) participating in the recommended 1 hour/day. Fewer girls reported spending > 1 hour/day at PA compared to boys (n = 14 v n = 30). Six children had elevated cholesterol levels and five children had higher than normal BP values. Sixteen children demonstrated clustering of CVD risk factors and in those who were inactive the risk was greater. Our data suggest that in children as young as 10 years significant risk factors already exist. Furthermore, the low level of PA in girls provides a target for health promotion programmes.

Hematodinium infection seasonality in the Firth of Clyde (Scotland) Nephrops norvegicus population: a re-evaluation.

Hematodinium infections in Norway lobster Nephrops norvegicus from the Clyde Sea area (CSA) population, Scotland, UK, have previously been undetected in summer. This study aimed to establish if the CSA is actually devoid of infected N. norvegicus in this season. Two PCR assays, an ELISA and 2 tests that detect only patent infection (pleopod and body colour methods) were applied in a 21 mo study. Patent infection was seasonal, appearing predominantly in spring, while subpatent infection diagnosed by ELISA and PCR was highly prevalent in all seasons. Generalised linear modelling supported this assertion, as sampling in September and February significantly increased the probability of finding infected N. norvegicus (p < 0.01); infections were predominantly subpatent and patent respectively, at these times. Therefore, Hematodinium seasonality in N. norvegicus populations is likely to have been an artefact of insensitive diagnostic tests. Light Hematodinium infections were found using PCR assays when patent infections were at their most prevalent and intense, suggesting that infection develops at different rates in different N. norvegicus individuals and that only a portion of the total number of infected N. norvegicus die within a single year. These new data were added to a long-term data series for the CSA (1990 to 2008), which showed that after an initial 5 yr epidemic period, prevalence stabilised at 20 to 25%. Comparisons with 'susceptible-infected-recovered/removed' (SIR) models suggest that this high prevalence is maintained through high birth rates of susceptible host N. norvegicus.

Topological selectivity of a hybrid site-specific recombination system with elements from Tn3 res/resolvase and bacteriophage P1 loxP/Cre.

In order to investigate the functions of the parts of the Tn 3 recombination site res, we created hybrid recombination sites by placing the loxP site for Cre recombinase adjacent to the "accessory" resolvase-binding sites II and III of res. The efficiency and product topology of in vitro recombination by Cre between two of these hybrid sites were affected by the addition of Tn 3 resolvase. The effects of resolvase addition were dependent on the relative orientation and spacing of the elements of the hybrid sites. Substrates with sites II and III of res close to loxP gave specific catenated or knotted products (four-noded catenane, three-noded knot) when resolvase and Cre were added together. The product topological complexity increased when the length of the spacer DNA segment between loxP and res site II was increased. Similar resolvase-induced effects on Cre recombination product topology were observed in reactions of substrates with loxP sites adjacent to full res sites. The results demonstrate that the res accessory sites are sufficient to impose topological selectivity on recombination, and imply that intertwining of two sets of accessory sites defines the simple catenane product topology in normal resolvase-mediated recombination. They are also consistent with current models for the mechanism of catalysis by Cre.

A major surface antigen of procyclic stage Trypanosoma congolense.

Five monoclonal antibodies (mAb) were raised that bound to the surface of procyclic stage Trypanosoma congolense with high intensity in immunofluorescence. Immunoblot analysis of trypanosome lysates using 3 of these mAb revealed a diffuse SDS-PAGE band of 36-40 kDa. The purified antigen did not react with Coomassie Blue or silver stains, but did stain blue with Stains-all, indicating acidity. For the one mAb tested, the epitope was periodate-sensitive and therefore probably glycan. Although this antigen shares properties with procyclin/PARP, which forms a surface coat on procyclic Trypanosoma brucei, a search in T. congolense for homologues of a procyclin/PARP gene revealed only non-coding sequence of partial similarity. Using a differential screen, a procyclic stage T. congolense cDNA clone was isolated that encoded a putative 256-amino acid protein containing 2 peptides chemically sequenced independently by Beecroft et al. [36]. The protein, termed glutamate and alanine-rich protein (GARP), has potential hydrophobic leader and tail sequences (the latter with potential for replacement by a glycosyl phosphoinositol anchor) and no potential N-linked glycosylation sites. It has no significant sequence homology with known proteins. Antibodies against a translational fusion of GARP bound specifically in Western blots to a band very similar to that detected by the mAb and also to the purified antigen. Immunogold electron microscopy revealed a dense packing of the antigen on the cell surface. It appears that procyclic T. brucei and T. congolense have major surface proteins with structural analogy, but with no sequence homology.