No abstract

In vitro selection of single-stranded nucleic acid aptamers from large random sequence libraries is now a straightforward process particularly when screening with a single target molecule. These libraries contain considerable shape diversity as evident by the successful isolation of aptamers that bind with high affinity and specificity to chemically diverse targets. We propose that aptamer libraries contain sufficient shape diversity to allow deconvolution of a complex mixture of targets. Using unfractionated human plasma as our experimental model, we aim to develop methods to obtain aptamers against as many proteins as possible. To begin, it is critical that we understand how aptamer populations change with increasing rounds of in vitro selection when using complex mixtures. Our results show that sequence representation in the selected population changes dramatically with increasing rounds of selection. Certain aptamer families were apparent after only three selection rounds. Two additional cycles saw a decline in the relative abundance of these families and the emergence of yet another family that accounted for more than 60% of sequences in the pool. To overcome this population convergence, an aptamer-based target depletion method was developed, and the library screen was repeated. The previous dominant family effectively disappeared from the selected populations but was replaced by other aptamer families. Insights gained from these initial experiments are now being applied in the creation of second generation plasma protein screens and also to the analysis of other complex biological targets.

To evaluate the effect of concurrent augmented feedback on isometric force output during familiar and unfamiliar muscle movements, 18 men and 21 women, 18 to 23 years of age, completed two isometric exercises: flexion of the thumb (a familiar muscle movement) and abduction of the fifth digit (an unfamiliar movement). The exercises consisted of 10 maximum voluntary isometric contractions lasting 10 s each and separated by 10-s intertrial rest intervals. Concurrent visual feedback was provided during alternate contractions. The order of exercises and trials for feedback was randomly assigned and balanced over subjects. Peak force output during abduction of the fifth digit was significantly (p less than or equal to .01) greater with (4.4 +/- 0.29 kg) than without feedback (4.1 +/- 0.26 kg). Feedback did not influence (p greater than .05) peak force output during thumb flexion (23.2 +/- 1.09 kg vs 22.5 +/- 1.05 kg). Muscular fatigue was more pronounced during thumb flexion without feedback (18.4 +/- 1.17%) than when feedback was provided (11.8 +/- 1.36%). These data suggest that fatigue may increase the effect of feedback on force generation during familiar muscular movements. To obtain maximal isometric force measures during strength testing, augmented feedback should be provided.