Specialized roles of the two pathways for the synthesis of mannosylglycerate in osmoadaptation and thermoadaptation of Rhodothermus marinus

Rhodothermus marinus responds to fluctuations in the growth temperature and/or salinity by accumulating mannosylglycerate (MG). Two alternative pathways for the synthesis of MG have been identified in this bacterium: a single-step pathway and a two-step pathway. In this work, the genetic and biochemical characterization of the two-step pathway was carried out with the goal of understanding the function of the two pathways and their regulatory mechanisms. Mannosyl-3-phosphoglycerate synthase (MPGS) of the two-step pathway was purified from R. marinus. Sequence information led to the isolation of two contiguous genes, mpgs (encoding MPGS) and mpgp (encoding mannosyl-3-phosphoglycerate phosphatase). The recombinant MPGS had a low specific activity compared with other homologous MPGSs and contained approximately 30 additional residues at the C terminus. Truncation of this extension produced a protein with a 10-fold higher specific activity. Moreover, the activity of the complete MPGS was enhanced upon incubation with R. marinus cell extracts, and protease inhibitors abolished activation. Therefore, the C-terminal peptide of MPGS was identified as a regulatory site for short term control of MG synthesis in R. marinus. The control of gene expression by heat and osmotic stress was also studied; the level of mannosylglycerate synthase involved in the single-step pathway was selectively enhanced by heat stress, whereas MPGS was overproduced in response to osmotic stress. The concomitant changes in the level of MG were assessed as well. We conclude that the two alternative pathways for the synthesis of MG are differently regulated at the level of expression to play specific roles in the adaptation of R. marinus to two different types of aggression. This is the only example of pathway multiplicity being rationalized in terms of the need to respond efficiently to distinct environmental stresses.     

Distinct neural activity associated with focused-attention meditation and loving-kindness meditation

This study examined the dissociable neural effects of ānāpānasati (focused-attention meditation, FAM) and mettā (loving-kindness meditation, LKM) on BOLD signals during cognitive (continuous performance test, CPT) and affective (emotion-processing task, EPT, in which participants viewed affective pictures) processing. Twenty-two male Chinese expert meditators (11 FAM experts, 11 LKM experts) and 22 male Chinese novice meditators (11 FAM novices, 11 LKM novices) had their brain activity monitored by a 3T MRI scanner while performing the cognitive and affective tasks in both meditation and baseline states. We examined the interaction between state (meditation vs. baseline) and expertise (expert vs. novice) separately during LKM and FAM, using a conjunction approach to reveal common regions sensitive to the expert meditative state. Additionally, exclusive masking techniques revealed distinct interactions between state and group during LKM and FAM. Specifically, we demonstrated that the practice of FAM was associated with expertise-related behavioral improvements and neural activation differences in attention task performance. However, the effect of state LKM meditation did not carry over to attention task performance. On the other hand, both FAM and LKM practice appeared to affect the neural responses to affective pictures. For viewing sad faces, the regions activated for FAM practitioners were consistent with attention-related processing; whereas responses of LKM experts to sad pictures were more in line with differentiating emotional contagion from compassion/emotional regulation processes. Our findings provide the first report of distinct neural activity associated with forms of meditation during sustained attention and emotion processing.     

Genetic homogeneity among breeding grounds and nursery areas of an exploited Lake Malawi cichlid fish

1. Nursery areas are commonly recognized as important habitats for the management and conservation of fish stocks. Here we report the use of nursery areas by an exploited offshore cichlid in Lake Malawi, Rhamphochromis longiceps .
2. Like all haplochromine cichlids that have been studied, the species is a maternal mouthbrooder that broods eggs for several weeks following spawning. We found evidence that during this brooding period females migrate from open water to release juveniles in three shallow peripheral waterbodies (Chia Lagoon, Unaka Lagoon, Lake Malombe). However, it was unclear whether there is geographical population structuring within the species, which could indicate stock differences in their use of these nursery habitats, or if the lake contains a genetically panmictic population that employs nursery habitats opportunistically.
3. To investigate spatial and temporal population structuring within the lake we genotyped populations at seven microsatellite DNA loci. Overall, we found no significant spatial structuring among juveniles from the peripheral lagoons or among breeding males within the main lake body. Moreover, we found no evidence of temporal structuring among males on the breeding grounds within Lake Malawi or females entering Chia lagoon. Together, these results suggest that Lake Malawi contains a genetically homogeneous population of R. longiceps .
4. At present we know little of the distribution of juvenile R. longiceps elsewhere in the Lake Malawi basin, but their absence from surveyed rocky and sandy littoral habitats makes it possible that the species is dependent upon a small number of nearshore nursery areas, including these lagoons. As such, conservation of lagoon habitats and monitoring of exploited fish stocks within them may be important for effective preservation of biodiversity within the catchment.     

Development and cross-species testing of western bluebird (Sialia mexicana) microsatellite primers

Western and eastern bluebirds (Sialia mexicana and S. sialis) are socially monogamous passerines that engage in extra‐pair copulations. We obtained microsatellites from S. mexicana and optimized and characterized 15 microsatellite DNA loci in 60 individuals of this species. Primer pairs yielded an average of 13 alleles per locus in western bluebirds (range 3–35 alleles) with an average observed heterozygosity of 0.68 (range 0.27–0.88). All 15 loci also successfully amplified in S. sialis (n = 24), with an average of 11.5 alleles per locus (range 4–26) and an average observed heterozygosity of 0.59 (range 0.22–0.90).