Patterns of intermediate host use and levels of association between two conflicting manipulative parasites.

For many parasites with complex life cycles, manipulation of intermediate host phenotypes is often regarded as an adaptation to increase the probability of successful transmission. This phenomenon creates opportunities for either synergistic or conflicting interests between different parasite species sharing the same intermediate host. When more than one manipulative parasite infect the same intermediate host, but differ in their definitive host, selection should favour the establishment of a negative association between these manipulators. Both Polymorphus minutus and Pomphorhynchus laevis exploit the amphipod Gammarus pulex as intermediate host but differ markedly in their final host, a fish for P. laevis and a bird for P. minutus. The pattern of host use by these two conflicting manipulative parasites was studied. Their incidence and intensity of infection and their distribution among G. pulex were first examined by analysing three large samples of gammarids collected from the river Tille, Eastern France. Both parasites had low prevalence in the host population. However, temporal fluctuation in the level of parasitic infection was observed. Overall, prevalence of both parasite species was higher in male than in female G. pulex. We then assessed the degree of association between the two parasites among their intermediate hosts, using two different methods: a host-centred measure and a parasite-centred measure. Both measures gave similar results; showing random association between the two acanthocephalan species in their intermediate hosts. We discuss our results in relation to the selective forces and ecological constraints that may determine the pattern of association between conflicting manipulative parasites.     

Two naturally occurring variants of TAFI (Thr-325 and Ile-325) differ substantially with respect to thermal stability and antifibrinolytic activity of the enzyme.

Thrombin-activable fibrinolysis inhibitor (TAFI) is a carboxypeptidase B-like zymogen that is activated to TAFIa by plasmin, thrombin, or the thrombin-thrombomodulin complex. The enzyme TAFIa attenuates clot lysis by removing lysine residues from a fibrin clot. Screening of nine human cDNA libraries indicated a common variation in TAFI at position 325 (Ile-325 or Thr-325). This is in addition to the variation at amino acid position 147 (Ala-147 or Thr-147) characterized previously. Thus, four variants of TAFI having either Ala or Thr at position 147 and either Thr or Ile at position 325 were stably expressed in baby hamster kidney cells and purified to homogeneity. The kinetics of activation of TAFI by thrombin/thrombomodulin were identical for all four variants; however, Ile at position 325 extended the half-life of TAFIa from 8 to 15 min at 37 degrees C, regardless of the residue at position 147. In clot lysis assays with thrombomodulin and the TAFI variants, or with pre-activated TAFI variants, the Ile-325 variants exhibited an antifibrinolytic effect that was 60% greater than the Thr-325 variants. Similarly, in the absence of thrombomodulin, the Ile-325 variants exhibited an antifibrinolytic effect that was 30-50% greater than the Thr-325 variants. In contrast, the variation at position 147 had little if any effect on the antifibrinolytic potential of TAFIa. The increased antifibrinolytic potential of the Ile-325-containing TAFI variants reflects the fact that these variants have an increased ability to mediate the release of lysine from partially degraded fibrin and suppress plasminogen activation. These findings imply that individuals homozygous for the Ile-325 variant of TAFI would likely have a longer lived and more potent TAFIa enzyme than those homozygous for the Thr-325 variant.     

Role of nucleotidyl transferase motif V in strand joining by chlorella virus DNA ligase.

ATP-dependent DNA ligases, NAD(+)-dependent DNA ligases, and GTP-dependent RNA capping enzymes are members of a covalent nucleotidyl transferase superfamily defined by a common fold and a set of conserved peptide motifs. Here we examined the role of nucleotidyl transferase motif V ((184)LLKMKQFKDAEAT(196)) in the nick joining reaction of Chlorella virus DNA ligase, an exemplary ATP-dependent enzyme. We found that alanine substitutions at Lys(186), Lys(188), Asp(192), and Glu(194) reduced ligase specific activity by at least an order of magnitude, whereas substitutions at Lys(191) and Thr(196) were benign. The K186A, D192A, and E194A changes had no effect on the rate of single-turnover nick joining by preformed ligase-adenylate but affected subsequent rounds of nick joining at the ligase adenylation step. Conservative substitutions K186R, D192E, and E194D partially restored activity, whereas K186Q, D192N, and E194Q substitutions did not. Alanine mutation of Lys(188) elicited distinctive catalytic defects, whereby single-turnover nick joining by K188A-adenylate was slowed by an order of magnitude, and high levels of the DNA-adenylate intermediate accumulated. The rate of phosphodiester bond formation at a pre-adenylated nick (step 3 of the ligation pathway) was slowed by the K188A change. Replacement of Lys(188) by arginine reversed the step 3 arrest, whereas glutamine substitution was ineffective. Gel-shift analysis showed that the Lys(188) mutants bound stably to DNA-adenylate. We infer that Lys(188) is involved in the chemical step of phosphodiester bond formation.     

Evidence for Fine-Scale Natal Homing Among Island Beach Spawning Sockeye Salmon, Oncorhynchus nerka

Salmonid fishes aggregate for breeding at spatially defined, suitable habitats. These aggregations may evolve into discrete populations when precise natal homing leads to reproductive isolation, and local regimes of selection lead to adaptation. Population structure is often defined by persistent differences in selectively neutral genetic markers and in mean values of morphological and life-history traits between locations. This approach is limited by the spatial scale at which traits diverge; low levels of reproductively successful straying, combined with similar selective pressures on life-history traits resulting from similar habitat features and environmental conditions, can significantly reduce the power of these discriminatory methods. We compared data on three life-history traits and polymorphism of DNA microsatellites for evidence of population subdivision among sockeye salmon spawning on spatially discrete but physically similar beaches on islands in Iliamna Lake, Alaska. We found small but significant differences in average body length, body depth and age composition between sites as well as significant interactions between site and year. These interactions, reflecting random variation in growth or recruitment among sites, are a powerful tool for discriminating populations with similar mean trait values. These results suggest fine-scale homing to natal sites, but the microsatellite data revealed no evidence of restricted gene flow among sites. There seems to be enough straying among the populations to prevent differentiation at neutral traits but enough homing for them to be functionally distinct.     

Antigen-induced airway inflammation in the Brown Norway rat results in airway smooth muscle hyperplasia.

Asthma is characterized by chronic airways inflammation, airway wall remodeling, and airway hyperresponsiveness (AHR). An increase in airway smooth muscle has been proposed to explain a major part of AHR in asthma. We have used unbiased stereological methods to determine whether airway smooth muscle hyperplasia and AHR occurred in sensitized, antigen-challenged Brown Norway (BN) rats. Ovalbumin (OA)-sensitized BN rats chronically exposed to OA aerosol displayed airway inflammation and a modest level of AHR to intravenously administered ACh 24 h after the last antigen challenge. However, these animals did not show an increase in smooth muscle cell (SMC) number in the left main bronchus, suggesting that short-lived inflammatory mechanisms caused the acute AHR. In contrast, 7 days after the last aerosol challenge, there was a modest increase in SMC number, but no AHR to ACh. Addition of FCS to the chronic OA challenge protocol had no effect on the degree of inflammation but resulted in a marked increase in both SMC number and a persistent (7-day) AHR. These results raise the possibility that increases in airway SMC number rather than, or in addition to, chronic inflammation contribute to the persistent AHR detected in this model.     

Homozygous Defects in LMNA, Encoding Lamin A/C Nuclear-Envelope Proteins, Cause Autosomal Recessive Axonal Neuropathy in Human (Charcot-Marie-Tooth Disorder Type 2) and Mouse

The Charcot-Marie-Tooth (CMT) disorders comprise a group of clinically and genetically heterogeneous hereditary motor and sensory neuropathies, which are mainly characterized by muscle weakness and wasting, foot deformities, and electrophysiological, as well as histological, changes. A subtype, CMT2, is defined by a slight or absent reduction of nerve-conduction velocities together with the loss of large myelinated fibers and axonal degeneration. CMT2 phenotypes are also characterized by a large genetic heterogeneity, although only two genes---NF-L and KIF1Bbeta---have been identified to date. Homozygosity mapping in inbred Algerian families with autosomal recessive CMT2 (AR-CMT2) provided evidence of linkage to chromosome 1q21.2-q21.3 in two families (Zmax=4.14). All patients shared a common homozygous ancestral haplotype that was suggestive of a founder mutation as the cause of the phenotype. A unique homozygous mutation in LMNA (which encodes lamin A/C, a component of the nuclear envelope) was identified in all affected members and in additional patients with CMT2 from a third, unrelated family. Ultrastructural exploration of sciatic nerves of LMNA null (i.e., -/-) mice was performed and revealed a strong reduction of axon density, axonal enlargement, and the presence of nonmyelinated axons, all of which were highly similar to the phenotypes of human peripheral axonopathies. The finding of site-specific amino acid substitutions in limb-girdle muscular dystrophy type 1B, autosomal dominant Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy type 1A, autosomal dominant partial lipodystrophy, and, now, AR-CMT2 suggests the existence of distinct functional domains in lamin A/C that are essential for the maintenance and integrity of different cell lineages. To our knowledge, this report constitutes the first evidence of the recessive inheritance of a mutation that causes CMT2; additionally, we suggest that mutations in LMNA may also be the cause of the genetically overlapping disorder CMT2B1.