The inchworm episode: Reconstituting the phenomenon of kinesin motility

New Mechanist philosophical models of "phenomenon reconstitution" understand the process to be driven by explanatory considerations. Here I discuss an episode of phenomenon reconstitution that occurred entirely within an experimental program dedicated to characterizing (rather than explaining) the phenomenon of kinesin motility. Rather than being driven by explanatory considerations, as standard mechanist views maintain, I argue that the phenomenon of kinesin motility was reconstituted to enhance researchers’ primary experimental tool—the single molecule motility assay.

In Vitro Anthelmintic Activity of Ethanol Stem Bark Extract of Albizia ferruginea (Guill. & Perr.) Benth

Albizia ferruginea (Guill. & Perr.) Benth bark is used in the traditional medicine as a vermifuge. This study sought to determine the anthelmintic activity of the stem bark extract of Albizia ferruginea. The powdered A. ferruginea stem bark was extracted with ethanol. Phytochemical screening was carried out on A. ferruginea ethanol extract (AFE) and then screened for its anthelmintic property against Pheretima posthuma and Haemonchus contortus using the adult motility assay. The effect of AFE and its fractions on the anthelminthic activity of mebendazole and albendazole were also determined using the adult worm (P. posthuma) motility assay. AFE showed a dose-dependent anthelmintic activity against P. posthuma and H. contortus. The least concentration of AFE (0.5 mg/mL) paralyzed and killed P. posthuma within 272.50 ± 12.42 min and 354.50 ± 5.06 min of exposure, respectively. AFE at the least test concentration (0.14 mg/mL) caused paralysis and induced death of H. contortus, after at 63.50 ± 2.98 and 254.96 ± 2.44 min of exposure, respectively. AFE extract at 0.25 and 0.125 mg/mL increased the paralytic and helminthicidal activities of albendazole. The paralytic and helminthicidal activities of mebendazole were reduced when combined with AFE (0.25 and 0.125 mg/mL). Among the three fractions obtained from AFE, the methanol fraction showed the highest anthelmintic activity. The methanol fraction at 0.5 mg/mL caused paralysis after 69.90 ± 0.15 min and death of worm after 92.53 ± 0.74 min of exposure. The petroleum ether and ethyl acetate fractions showed relatively low anthelmintic activity. Phytochemical screening of AFE revealed the presence of tannins, saponins, glycosides, alkaloids, and coumarins. The results from this study show that A. ferruginea possesses anthelmintic activity which gives credence to its folkloric use.

Impact of regulatory light chain mutation K104E on the ATPase and motor properties of cardiac myosin

Mutations in the cardiac myosin regulatory light chain (RLC, MYL2 gene) are known to cause inherited cardiomyopathies with variable phenotypes. In this study, we investigated the impact of a mutation in the RLC (K104E) that is associated with hypertrophic cardiomyopathy (HCM). Previously in a mouse model of K104E, older animals were found to develop cardiac hypertrophy, fibrosis, and diastolic dysfunction, suggesting a slow development of HCM. However, variable penetrance of the mutation in human populations suggests that the impact of K104E may be subtle. Therefore, we generated human cardiac myosin subfragment-1 (M2β-S1) and exchanged on either the wild type (WT) or K104E human ventricular RLC in order to assess the impact of the mutation on the mechanochemical properties of cardiac myosin. The maximum actin-activated ATPase activity and actin sliding velocities in the in vitro motility assay were similar in M2β-S1 WT and K104E, as were the detachment kinetic parameters, including the rate of ATP-induced dissociation and the ADP release rate constant. We also examined the mechanical performance of α-cardiac myosin extracted from transgenic (Tg) mice expressing human wild type RLC (Tg WT) or mutant RLC (Tg K104E). We found that α-cardiac myosin from Tg K104E animals demonstrated enhanced actin sliding velocities in the motility assay compared with its Tg WT counterpart. Furthermore, the degree of incorporation of the mutant RLC into α-cardiac myosin in the transgenic animals was significantly reduced compared with wild type. Therefore, we conclude that the impact of the K104E mutation depends on either the length or the isoform of the myosin heavy chain backbone and that the mutation may disrupt RLC interactions with the myosin lever arm domain.

Essential oil of Rosmarinus officinalis induces in vitro anthelmintic and anticoccidial effects against Haemonchus contortus and Eimeria spp. in small ruminants

This work aimed to evaluate the valorisation of the volatile oil of “Rosmarinus officinalis L.”, a spontaneously growing medicinal plant in Tunisia, by studying its chemical composition, anthelmintic and anticoccidial potentials against Eimeria spp. and Haemonchus contortus at different essential oil concentrations. The main compounds of the R. officinalis essential oil identified by GC/MS were three monoterpenes: 1,8-cineole (52.06%), α-pinene (15.35%) and camphor (7.69%). The anticoccidial activity was estimated by the inhibition percentage of the oocyte sporulation in addition to the unsporulated and degenerated Eimeria oocysts using a haemocytometer after exposure to different essential oil concentrations. The essential oil was active against Eimeria spp. oocysts of sheep at IC₅₀ = 1.82 ug/ml. Therefore, the IC₅₀ values of the anticoccidial activity of this oil examined was 1.82 mg/ml. The anthelmintic efficacy of the rosemary volatile oil against Haemonchus contortus was realised by two in vitro tests: the egg hatch assay (EHA) and the adult worm’s motility assay (AWMA), by comparing this efficacy with albendazole (anthelmintic, of reference). In the egg hatch assay, the percentage of inhibition was observed at 16 mg/ml and was 73.76% after 2 days of incubation (IC₅₀ = 11.41 mg/ml) and for the adult worm’s motility assay, it was 100% inhibition.

Nematocidal Effects of a Coriander Essential Oil and Five Pure Principles on the Infective Larvae of Major Ovine Gastrointestinal Nematodes In Vitro

The anthelmintic effects of extracted coriander oil and five pure essential oil constituents (geraniol, geranyl acetate, eugenol, methyl iso-eugenol, and linalool) were tested, using larval motility assay, on the third-stage larvae (L3s) of Haemonchus contortus, Trichostrongylus axei, Teladorsagia circumcincta, Trichostrongylus colubriformis, Trichostrongylus vitrinus and Cooperia oncophora. Coriander oil and linalool, a major component of tested coriander oil, showed a strong inhibitory efficacy against all species, except C. oncophora with a half maximal inhibitory concentration (IC50) that ranged from 0.56 to 1.41% for the coriander oil and 0.51 to 1.76% for linalool. The coriander oil and linalool combinations conferred a synergistic anthelmintic effect (combination index [CI] <1) on larval motility comparable to positive control (20 mg/mL levamisole) within 24 h (p < 0.05), reduced IC50 values to 0.11–0.49% and induced a considerable structural damage to L3s. Results of the combined treatment were validated by quantitative fluorometric microplate-based assays using Sytox green, propidium iodide and C12-resazurin, which successfully discriminated live/dead larvae. Only Sytox green staining achieved IC50 values comparable to that of the larval motility assay. The cytotoxicity of the combined coriander oil and linalool on Madin–Darby Canine Kidney cells was evaluated using sulforhodamine-B (SRB) assay and showed no significant cytotoxic effect at concentrations < 1%. These results indicate that testing essential oils and their main components may help to find new potential anthelmintic compounds, while at the same time reducing the reliance on synthetic anthelmintics.

Collective and contractile filament motions in the myosin motility assay

In this computational study of the myosin motility assay, we demonstrated that volume-exclusion effects lead to distinct collective behaviors of actin filaments, whereas actin cross-linking proteins induce contractile behaviors of actin filaments.