Phylogeography and genetic diversity of the commercially-collected Caribbean blue-legged hermit crab (Clibanarius tricolor)

Shifts from ornamental fish tanks to functional reef ecosystem aquaria has led to unprecedented pressure on marine invertebrate fisheries. The Caribbean blue-legged hermit crab (Clibanarius tricolor) is among the species targeted for functional reef tanks, valued for its role as an aquarium cleaner. Little is known about the biology of the species or the genetic landscape in which the increased collecting is happening. Here, we investigate the phylogeographic history and genetic diversity of C. tricolor through analysis of mitochondrial (CO1, 16S) and nuclear (H3) DNA. We test whether phylogeographic breaks for other invertebrates structure the genetic diversity of C. tricolor and explore additional factors that may govern structure, such as reproductive strategy, life history, habitat preference, adult mobility, demographic history, and vicariance events. Based on these three markers, we find high genetic diversity and connectivity and find no evidence to support the tested barriers as relevant to gene flow for C. tricolor. Rather, mitochondrial and nuclear markers infer high genetic diversity, panmixia, and demographic expansion during the Pleistocene. Our finding of panmixia makes it difficult to identify source or sink populations, but the absence of hierarchical structure inferred from mtDNA and nuDNA markers we use, high levels of genetic diversity and homogeneity for these same markers, and advantageous life history traits suggest C. tricolor is not currently at special risk; however, geographically restricted haplotypes and limitations within our study prevent us from making a strong conclusion about the sustainability of the fishery. Our work on the Caribbean blue-legged hermit crab highlights the importance of acquiring basic information on exploited species and reiterates that common regional forces may not equally impact connectivity among co-distributed species.

     

Genetic dissection of Al tolerance QTLs in the maize genome by high density SNP scan

Background

Aluminum (Al) toxicity is an important limitation to food security in tropical and subtropical regions. High Al saturation on acid soils limits root development, reducing water and nutrient uptake. In addition to naturally occurring acid soils, agricultural practices may decrease soil pH, leading to yield losses due to Al toxicity. Elucidating the genetic and molecular mechanisms underlying maize Al tolerance is expected to accelerate the development of Al-tolerant cultivars.

Results

Five genomic regions were significantly associated with Al tolerance, using 54,455 SNP markers in a recombinant inbred line population derived from Cateto Al237. Candidate genes co-localized with Al tolerance QTLs were further investigated. Near-isogenic lines (NILs) developed for ZmMATE2 were as Al-sensitive as the recurrent line, indicating that this candidate gene was not responsible for the Al tolerance QTL on chromosome 5, qALT5. However, ZmNrat1, a maize homolog to OsNrat1, which encodes an Al³⁺ specific transporter previously implicated in rice Al tolerance, was mapped at ~40 Mbp from qALT5. We demonstrate for the first time that ZmNrat1 is preferentially expressed in maize root tips and is up-regulated by Al, similarly to OsNrat1 in rice, suggesting a role of this gene in maize Al tolerance. The strongest-effect QTL was mapped on chromosome 6 (qALT6), within a 0.5 Mbp region where three copies of the Al tolerance gene, ZmMATE1, were found in tandem configuration. qALT6 was shown to increase Al tolerance in maize; the qALT6-NILs carrying three copies of ZmMATE1 exhibited a two-fold increase in Al tolerance, and higher expression of ZmMATE1 compared to the Al sensitive recurrent parent. Interestingly, a new source of Al tolerance via ZmMATE1 was identified in a Brazilian elite line that showed high expression of ZmMATE1 but carries a single copy of ZmMATE1.

Conclusions

High ZmMATE1 expression, controlled either by three copies of the target gene or by an unknown molecular mechanism, is responsible for Al tolerance mediated by qALT6. As Al tolerant alleles at qALT6 are rare in maize, marker-assisted introgression of this QTL is an important strategy to improve maize adaptation to acid soils worldwide.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-153) contains supplementary material, which is available to authorized users.     

Immunoprophylaxis of respiratory syncytial virus: global experience

In sarcoidosis, host genetic factors are discussed as contributing to disease susceptibility and course. Since tumor necrosis factor (TNF)-α is a central mediator of granuloma formation and since elevated TNF-α levels are found during active phases of sarcoidosis, genetic polymorphisms correlating with influences on TNF-α levels are of special interest. The complete sequencing of the MHC region and the increase in the number of identified gene polymorphisms in this locus associated with TNF-α production offer the opportunity of detecting new genes associated with sarcoidosis and perhaps of defining disease-associated haplotypes that bear the potential of serving as predictive markers for this disease.     

Gender Stereotype Susceptibility

Gender affects performance on a variety of cognitive tasks, and this impact may stem from socio-cultural factors such as gender stereotyping. Here we systematically manipulated gender stereotype messages on a social cognition task on which no initial gender gap has been documented. The outcome reveals: (i) Stereotyping affects both females and males, with a more pronounced impact on females. Yet an explicit negative message for males elicits a striking paradoxical deterioration in performance of females. (ii) Irrespective of gender and directness of message, valence of stereotype message affects performance: negative messages have stronger influence than positive ones. (iii) Directness of stereotype message differentially impacts performance of females and males: females tend to be stronger affected by implicit than explicit negative messages, whereas in males this relationship is opposite. The data are discussed in the light of neural networks underlying gender stereotyping. The findings provide novel insights into the sources of gender related fluctuations in cognition and behavior.     

Gene delivery mediated by cationic liposomes: from biophysical aspects to enhancement of transfection

Cationic liposomes complexed with DNA have been used extensively as non-viral vectors for the intracellular delivery of reporter or therapeutic genes in culture and in vivo. However, the relationship between the features of the lipid-DNA complexes (`lipoplexes') and their mode of interaction with cells, the efficiency of gene transfer and gene expression remain to be clarified. To gain insights into these aspects, the size and zeta potential of cationic liposomes (composed of 1,2-dioleoyl-3- (trimethylammonium) propane (DOTAP) and its mixture with phosphatidylethanolamine (PE)), and their complexes with DNA at different (+/-) charge ratios were determined. A lipid mixing assay was used to assess the interaction of liposomes and lipoplexes with monocytic leukaemia cells. The use of inhibitors of endocytosis indicated that fusion of the cationic liposomes with cells occurred mainly at the plasma membrane level. However, very limited transfection of these cells was achieved using the above complexes. It is possible that the topology of the cationic liposome-DNA complexes does not allow the entry of DNA into cells through a fusion process at the plasma membrane. In an attempt to enhance transfection mediated by lipoplexes composed of DOTAP and its equimolar mixture with dioleoylphosphatidylethanolamine (DOPE) two different strategies were explored: (i) association of a targeting ligand (transferrin) to the complexes to promote their internalization, presumably by receptor-mediated endocytosis; and (ii) association of synthetic fusogenic peptides (GALA or the influenza haemagglutinin Nterminal peptide HA-2) to the complexes to promote endosomal destabilization and release of the genetic material into the cytoplasm. These strategies were effective in enhancing transfection in a large variety of cells, including epithelial and lymphoid cell lines, as well as human macrophages, especially with the use of optimized lipid/ DNA (+/-) charge ratios. Besides leading to high levels of transfection, the ternary complexes of cationic liposomes, DNA, and protein or peptide, have the advantages of being active in the presence of serum and being non-toxic. Moreover, such ternary complexes present a net negative charge and, thus, are likely to alleviate the problems associated with the use of highly positively charged complexes in vivo, such as avid complexation with serum proteins. Overall, the results indicate that these complexes, and their future derivatives, may constitute viable alternatives to viral vectors for gene delivery in vivo.     

Outer pore topology of the ECaC-TRPV5 channel by cysteine scan mutagenesis

The substituted cysteine accessibility method (SCAM) was used to map the external vestibule and the pore region of the ECaC-TRPV5 calcium-selective channel. Cysteine residues were introduced at 44 positions from the end of S5 (Glu515) to the beginning of S6 (Ala560). Covalent modification by positively charged MTSET applied from the external medium significantly inhibited whole cell currents at 15/44 positions. Strongest inhibition was observed in the S5-linker to pore region (L520C, G521C, and E522C) with either MTSET or MTSES suggesting that these residues were accessible from the external medium. In contrast, the pattern of covalent modification by MTSET for residues between Pro527 and Ile541 was compatible with the presence of a alpha-helix. The absence of modification by the negatively charged MTSES in that region suggests that the pore region has been optimized to favor the entrance of positively charged ions. Cysteine mutants at positions -1, 0, +1, +2 around Asp542 (high Ca2+ affinity site) were non-functional. Whole cell currents of cysteine mutants at +4 and +5 positions were however covalently inhibited by external MTSET and MTSES. Altogether, the pattern of covalent modification by MTS reagents globally supports a KcsA homology-based three-dimensional model whereby the external vestibule in ECaC-TRPV5 encompasses three structural domains consisting of a coiled structure (Glu515 to Tyr526) connected to a small helical segment of 15 amino acids (527PTALFSTFELFLT539) followed by two distinct coiled structures Ile540-Pro544 (selectivity filter) and Ala545-Ile557 before the beginning of S6.     

Exosomes: a common pathway for a specialized function

Exosomes are membrane vesicles that are released by cells upon fusion of multivesicular bodies with the plasma membrane. Their molecular composition reflects their origin in endosomes as intraluminal vesicles. In addition to a common set of membrane and cytosolic molecules, exosomes harbor unique subsets of proteins linked to cell type-associated functions. Exosome secretion participates in the eradication of obsolete proteins but several findings, essentially in the immune system, indicate that exosomes constitute a potential mode of intercellular communication. Release of exosomes by tumor cells and their implication in the propagation of unconventional pathogens such as prions suggests their participation in pathological situations. These findings open up new therapeutic and diagnostic strategies.