Repetition costs in sequence chunking

We examined how flexibly we plan sequences of actions when we switch between multiple action sequences. Mastering a sequential skill is assumed to involve integrating successive actions into groups known as chunks that can be efficiently planned and smoothly executed. Chunking is suggested by gains in planning efficiency for long compared to short action sequences following practice and learning associations between actions and perceptual outcomes. Less is understood about how efficiently we plan sequential chunks when we switch between multiple action sequences. Do we plan learned chunks less efficiently when we switch to a different action sequence? We examined this question by comparing the initiation and execution latencies of long versus short action sequences, performed from memory, when sequences switched or repeated across trials. Additionally, each action within the sequences generated predictable perceptual outcomes that were either spatially compatible or spatially incompatible with the action sequences. Results suggested repetition costs (instead of benefits) when performing long sequences. Repetition, as opposed to switching, prolonged initiation and increased the error rate of long compared to short sequences. We attribute these results to the flexible coordination of chunk planning and execution. Repetition may prolong advanced planning of long sequences in order to resolve conflict between multiple chunks, and switching may allow the planning of later chunks to be postponed until execution. We propose that the chunking of action sequences can both facilitate and interfere with action-switching performance.

Evolutionary and functional implications of 3' untranslated region length of mRNAs by comprehensive investigation among four taxonomically diverse metazoan species

Background

In eukaryotic organisms, it has been well acknowledged that 3′ untranslated regions (3′ UTRs) of mRNA are actively involved in post-transcriptional regulations of gene expression. Although both shortening and lengthening of 3′ UTRs of specific candidate genes were explicitly documented to have functional consequences, landscape of 3′ UTR lengths in relation to evolutionary dynamics and biological meanings remains to be elucidated when large-scale data become available.

Objectives

The primary objective of this study was to revealed different inter- and intra-species patterns on length distribution of 3′ UTRs in comparison with 5′ UTRs and coding regions.

Methods

In the present study, we investigated 3′ UTR lengths in a highly curated set of 57,135 mRNA sequences among four well-studied and taxonomically diverse metazoan species (fruit fly, zebrafish, mouse and human).

Results

The average length ratio of 3′–5′ UTRs considerably increased from fruit fly (twofold) to human (fivefold). Moreover, genes can be characterized by the obviously different patterns of evolutionary change on 3′ UTR lengths. By utilizing the Gene Ontology annotations, genes with differential lengths of 3′ UTRs were suggested to have the divergent functional implications. In human, we further revealed that ubiquitously transcribed genes had higher median lengths of 3′ UTRs than the genes of tissue-restricted expressions.

Conclusion

We conducted a comprehensive analysis and provided an overview regarding 3′ UTRs biology of mRNAs in animals, whereas the mechanistic explanations of 3′ UTRs length variation in correlation to regulation of gene expression still remain to be further studied.

Electronic supplementary material

The online version of this article (10.1007/s13258-019-00808-8) contains supplementary material, which is available to authorized users.

Phellinus noxius: molecular diversity among isolates from Taiwan and its phylogenetic relationship with other species of Phellinus based on sequences of the ITS region

BACKGROUND

Analysis of phylogenetic relationship of 91 isolates of Phellinus noxius obtained from 46 plant species in Taiwan did not show distinct grouping based on ITS sequences.

RESULTS

However, the ITS nucleotides showed 20 different kinds of variations including single nucleotide polymorphisms, deletion and insertion in ITS1 and ITS2, but none in 5.8 S. The Taiwanese isolates of P. noxius were dividable into long (type L), median (type M) and short (type S) groups based on ITS sequence length. Two isolates with identical ITS sequence belonged to types L. Type M with 72 isolates was further divided into 33 subtypes, while types S with 17 isolates was further divided into two subtypes.

CONCLUSION

Phylogenetic analysis of ITS sequences among Phellinus species showed that isolates of P. noxius were in the same clade distinctly separated from other Phellinus species.