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Attention regulates visual working memory (VWM) performance by determining how its resources are distributed among encoded information. During encoding, this process is both flexible and strategic: Resources are unequally allocated to items based on the probability that each will be probed for memory recall. Here we assessed whether VWM resources can be strategically re-distributed among encoded items during maintenance. Across three experiments, participants encoded the colours of various shapes and were given information about the probability that each remembered item would be probed for recall via a retro-cue prompting the prioritization of two (E1 and E2) or one (E3) representation(s). We observe a reliable benefit of the retro-cues in all three experiments such that cued items were recalled with greater precision than non-cued items; however, we observed no evidence that the magnitude of this benefit was affected by the probability assigned to the cues when two items were prioritized, and only marginal evidence for an effect when a single item was prioritized. We argue that, although resources can be re-distributed post-encoding, the mechanism underlying this capability lacks the flexibility of that which underlies resource distribution during encoding, highlighting an important limitation in how attention regulates VWM performance.

Although recent evidence suggests that visual short-term memory is a continuous resource, little is known about how flexibly this resource can be allocated. The current study used a continuous report procedure and attentional prioritization via probabilistic spatial cues to address three unknown properties of a flexible continuous resource. The first experiment measured multiple responses from each trial to assess whether multiple items could simultaneously be prioritized. Second, since past work has shown that participants could prioritize VSTM representations according to two states of attentional priority, we examined whether participants could maintain three levels of priority. Lastly, we examined whether flexible allocation is possible when the prioritization cues are provided after initial encoding (i.e. a retro-cue). The results demonstrated that when participants had to recall multiple items on each trial, there were clear differences in response precision between cued and uncued items; however, two items of the same category were not always stored with equal precision. When three attentional priority levels were provided, participants’ precision was no different between high- and medium-priority, but significantly improved over low priority items, suggesting participants did not assign different memory weights to the two higher-priority conditions. When prioritization was performed via retro-cues, participants could re-allocate memory resources, but not when more than one item was to be prioritized, suggesting limitations in the flexible allocation of resources after initial encoding. Together, the results provide evidence of a VSTM resource that is flexibly, but variably, allocated using up to two attentionally guided priority goals, primarily during encoding.

The Gene Promoter Expression Prediction challenge consisted of predicting gene expression from promoter sequences in a previously unknown experimentally generated data set. The challenge was presented to the community in the framework of the sixth Dialogue for Reverse Engineering Assessments and Methods (DREAM6), a community effort to evaluate the status of systems biology modeling methodologies. Nucleotide-specific promoter activity was obtained by measuring fluorescence from promoter sequences fused upstream of a gene for yellow fluorescence protein and inserted in the same genomic site of yeast Saccharomyces cerevisiae. Twenty-one teams submitted results predicting the expression levels of 53 different promoters from yeast ribosomal protein genes. Analysis of participant predictions shows that accurate values for low-expressed and mutated promoters were difficult to obtain, although in the latter case, only when the mutation induced a large change in promoter activity compared to the wild-type sequence. As in previous DREAM challenges, we found that aggregation of participant predictions provided robust results, but did not fare better than the three best algorithms. Finally, this study not only provides a benchmark for the assessment of methods predicting activity of a specific set of promoters from their sequence, but it also shows that the top performing algorithm, which used machine-learning approaches, can be improved by the addition of biological features such as transcription factor binding sites.

Background: Alternative arrangements of chromosome 2 inversions in Anopheles gambiae are important sources of population structure, and are associated with adaptation to environmental heterogeneity. The forces responsible for their origin and maintenance are incompletely understood. Molecular characterization of inversion breakpoints provides insight into how they arose, and provides the basis for development of molecular karyotyping methods useful in future studies. Methods: Sequence comparison of regions near the cytological breakpoints of 2Rb allowed the molecular delineation of breakpoint boundaries. Comparisons were made between the standard 2R+(b) arrangement in the An. gambiae PEST reference genome and the inverted 2Rb arrangements in the An. gambiae M and S genome assemblies. Sequence differences between alternative 2Rb arrangements were exploited in the design of a PCR diagnostic assay, which was evaluated against the known chromosomal banding pattern of laboratory colonies and field-collected samples from Mali and Cameroon. Results: The breakpoints of the 7.55 Mb 2Rb inversion are flanked by extensive runs of the same short 72 bp) tandemly organized sequence, which was likely responsible for chromosomal breakage and rearrangement. Application of the molecular diagnostic assay suggested that 2Rb has a single common origin in An. gambiae and its sibling species, Anopheles arabiensis, and also that the standard arrangement 2R+(b)) may have arisen twice through breakpoint reuse. The molecular diagnostic was reliable when applied to laboratory colonies, but its accuracy was lower in natural populations. Conclusions: The complex repetitive sequence flanking the 2Rb breakpoint region may be prone to structural and sequence-level instability. The 2Rb molecular diagnostic has immediate application in studies based on laboratory colonies, but its usefulness in natural populations awaits development of complementary molecular tools.