Mechanical Properties of a Single-Headed Processive Motor, Inner-Arm Dynein Subspecies-c of ChlamydomonasStudied at the Single Molecule Level

Dynein from inner arms of Chlamydomonasflagella contains sevendistinct subspecies, a through g. Several lines of evidence suggest thesesubspecies play important roles in generating flagellar beating and thatthe different subspecies are functionally diverse. To evaluate theirroles and diversity, the mechanical properties of subspecies-c, which isa single-headed motor, were examined using optical trap nanometry. Apolystyrene bead coated with a small number of subspecies-c moleculeswas captured with the optical trap and brought into contact with amicrotubule fixed to a coverslip. Movements of the bead were measured bya quadrant photodiode sensor with sub-nanometer- and millisecond-resolution.Beads carrying a single active subspecies-c molecule moved processivelyalong the microtubules in 8-nm steps but slipped backwards under highloads. Force-velocity relationships of single subspecies-c molecules werealmost linear and the shapes of the normalized curves at 5 μM and 100μM ATP were similar. These results indicate that dynein subspecies-cfunctions in a very different way from conventional motor proteins, suchas myosin and kinesin, and has properties that could produceself-oscillation in vivo.

Performance of the Neutral Red uptake assay in the COLIPA international validation study on alternatives to the rabbit eye irritation test

The neutral red uptake (NRU) assay was included as part of the COLIPA international validation trial of in vitro alternatives to the Draize eye irritation test. In a blind trial, 55 substances were tested at four laboratories. Following testing, a prediction of the in vivo Draize modified maximum average score (MMAS) for each substance was made by each laboratory using a prediction model relating mean NR(50) value (concentration causing 50% reduction in NRU from that of untreated control cells) to MMAS. Following statistical analysis of the results and breaking of the code, assessment of the results and further analysis was carried out by the participating laboratories. This paper presents the conclusions with regard to the NRU assay. The initial trial analysis indicated that the interlaboratory reproducibility of results of the NRU assay was good. However, there was a poor correlation between observed and predicted MMAS (using the proposed prediction model) when all the test substances were analysed together (r=0.246). Data analysis of subsets of substances indicated that the best predictions were for pure surfactants only (r=0.843) although this data did not fit within the limits of the prediction model. The NRU assay therefore appears to have limited use as a complete Draize replacement. A further examination of the COLIPA trial data may identify combinations of assays which may be more useful than the individual assays which, like NRU, have been shown to be poor predictors of eye irritation.

Mutations in the NOG gene are commonly found in congenital stapes ankylosis with symphalangism, but not in otosclerosis

Human noggin (NOG) is a responsible gene for multiple synostosis syndrome (SYNS1) and proximal symphalangism (SYM1), two conditions that are recently known to be within a wider range of clinical manifestations of stapes ankylosis with symphalangism. This study was performed to determine the range of phenotype caused by NOG mutations, using Japanese patients with various phenotypes including sporadic inherited SYM1, dominantly inherited SYM1, stapes ankylosis with broad thumb and toes (Teunissen and Cremer syndrome). In addition, 33 patients with typical otosclerosis (without symphalangism) were studied. Direct sequencing analysis disclosed three novel mutations of the NOG gene in three SYM1 families. None of the otosclerosis patients without symphalangism had NOG mutations, indicating that NOG mutations may be restrictively found within patients with various skeletal abnormalities. These results together with the literature review indicated that there are no clear genotype–phenotype correlations for NOG mutations. With regard to surgical outcome, most of the patients in these three families with NOG mutations showed remarkable air–bone gap recovery after stapes surgery. Molecular genetic testing is useful to differentiate syndromic stapes ankylosis from otosclerosis, and even mild skeletal anomalies can be a diagnostic indicator of NOG-associated disease.

The effects of cell adhesion on the growth and protein productivity of animal cells

We investigated the effect of cell adhesion on cellgrowth and productivity of recombinant protein inChinese hamster ovary (CHO) cells. Cells cultured innormal tissue culture dishes attached to the dishsurfaces and grew as a monolayer, while cells culturedin non-treated dishes proliferated in suspension assingle cells without adhering to the dish surfaces. On an agarose-coated dish surface, cell aggregatesformed without attaching to the dish. Growth rates inboth suspension cultures were slightly lower thanthose in monolayer culture. Cell cycle analysisindicated that the duration of the G(1) phase insuspension cultures was longer than that in monolayerculture, suggesting that attachment to the substratummainly affected the transition from the G(1) to theS phase. Consistent with this, CDK inhibitor p27,that inhibits the G(1)S transition, was induced inthe cells cultured in suspension.To assess the productivity of recombinant proteins,CHO cells were transfected with a plasmid containingmurine interferon gamma (mIFN-gamma) under thecontrol of the cytomegalovirus promoter. Insuspension culture, mIFN-gamma productivity wasslightly lower than that in the monolayer culture. When protein kinase C was activated by phorbol ester,mIFN-gamma production was enhanced in both themonolayer and suspension cultures. However, theproductivity in the suspension culture was lower thanthat in the adherent culture even in the presence ofhigh concentrations of phorbol ester. These resultssuggested that cell adhesion to the substratum affectsvarious features of CHO cells.