van Rijn, E. | bioRxiv Science

bioRxiv2021

Do naps benefit novel word learning? Developmental differences and white matter correlates

Behavioural and neuroimaging data suggest that memory representations of newly learned words undergo changes during nocturnal sleep, including improvements in explicit recall and lexical integration (i.e., after sleep, novel words compete with existing words during online word recognition). Some studies have revealed larger sleep-benefits in children relative to adults. However, whether daytime naps play a similar facilitatory role is unclear. We investigated the effect of a daytime nap (relative to wake) on explicit memory (recall/recognition) and lexical integration (lexical competition) of newly learned novel words in young adults and children aged 10-12 years, also exploring white matter correlates of the pre- and post-nap effects of word learning in the child group with diffusion weighted MRI. In both age groups, a nap maintained explicit memory of novel words and wake led to forgetting. However, there was an age group interaction when comparing change in recall over the nap: children showed a slight improvement whereas adults showed a slight decline. There was no evidence of lexical integration at any point. Although children spent proportionally more time in slow-wave sleep (SWS) than adults, neither SWS nor spindle parameters correlated with over-nap changes in word learning. For children, increased fractional anisotropy (FA) in the uncinate fasciculus and arcuate fasciculus were associated with the recognition of novel words immediately after learning, and FA in the right arcuate fasciculus was further associated with changes in recall of novel words over a nap, supporting the importance of these tracts in the word learning and consolidation process. These findings point to a protective role of naps in word learning, and emphasize the need to advance theories of word learning by better understanding both the active and passive roles that sleep plays in supporting vocabulary consolidation over development.

neuroscience↗

bioRxiv2017

Impact of fluorescent protein fusions on the bacterial flagellar motor

Fluorescent fusion proteins open a direct and unique window onto protein function. However, they also introduce the risk of perturbation of the function of the native protein. Successful applications of fluorescent fusions therefore rely on a careful assessment and minimization of the side effects. Such insight, however, is still lacking for many applications of fluorescent fusions. This is particularly relevant in the study of the internal dynamics of motor protein complexes, where both the chemical and mechanical reaction coordinates can be affected. Fluorescent proteins fused to the stator of the bacterial flagellar motor (BFM) complex have previously been used to successfully unveil the internal subunit dynamics of the motor. Here we report the effects of three different fluorescent proteins fused to the stator, all of which altered BFM behavior. The torque generated by individual stators was reduced while their stoichiometry in the complex remained unaffected. MotB fusions decreased the rotation-direction switching frequency of single motors and induced a novel BFM behavior: a bias-dependent asymmetry in the speed attained in the two rotation directions. All these effects could be mitigated by the insertion of a linker at the fusion point. These findings provide a quantitative account of the effects of fluorescent fusions on BFM dynamics and their alleviation--new insights that advance the use of fluorescent fusions to probe the dynamics of protein complexes.\n\nAuthor summaryMuch of what is known about the biology of proteins was discovered by fusing them to fluorescent proteins that allow detection of their location. But the label comes at a cost: the presence of the tag can alter the behavior of the protein of interest in unforeseen, yet biologically relevant ways. These side effects limit the depth to which fluorescent proteins can be used to probe protein function. One of the systems that has been successfully studied with fluorescent fusions for which these effects have not been addressed are dynamic protein complexes that carry out mechanical work. We examined how fluorescent proteins fused to a component of the bacterial flagellar motor complex impacts its function. Our findings show that the fusion proteins altered biologically relevant dynamical properties of the motor, including induction of a novel mechanical behavior, and demonstrate an approach to alleviate this. These results advance our ability to dissect the bacterial flagellar motor, and the internal dynamics of protein complexes in general, with fluorescent fusion proteins while causing minimal perturbation.

biophysics↗