The removal of non‐coding sequences, introns, from the mRNA precursors is an essential step in eukaryotic gene expression. U12‐type introns are a minor subgroup of introns, distinct from the major or U2‐type introns. U12‐type introns are present in most eukaryotes but only account for less than 0.5% of all introns in any given genome. They are processed by a specific U12‐dependent spliceosome, which is similar to, but distinct from, the major spliceosome. U12‐type introns are spliced somewhat less efficiently than the major introns, and it is believed that this limits the expression of the genes containing such introns. Recent findings on the role of U12‐dependent splicing in development and human disease have shown that it can also affect multiple cellular processes not directly related to the functions of the host genes of U12‐type introns. At the same time, advances in understanding the regulation and phylogenetic distribution of the minor spliceosome are starting to shed light on how the U12‐type introns and the minor spliceosome may have evolved. WIREs RNA 2013, 4:61–76. doi: 10.1002/wrna.1141This article is categorized under: RNA Processing > Splicing Mechanisms

Previous studies have reported that chromosome synteny in Lepidoptera has been well conserved, yet the number of haploid chromosomes varies widely from 5 to 223. Here we report the genome (393 Mb) of the Glanville fritillary butterfly (Melitaea cinxia; Nymphalidae), a widely recognized model species in metapopulation biology and eco-evolutionary research, which has the putative ancestral karyotype of n=31. Using a phylogenetic analyses of Nymphalidae and of other Lepidoptera, combined with orthologue-level comparisons of chromosomes, we conclude that the ancestral lepidopteran karyotype has been n=31 for at least 140 My. We show that fusion chromosomes have retained the ancestral chromosome segments and very few rearrangements have occurred across the fusion sites. The same, shortest ancestral chromosomes have independently participated in fusion events in species with smaller karyotypes. The short chromosomes have higher rearrangement rate than long ones. These characteristics highlight distinctive features of the evolutionary dynamics of butterflies and moths.

The full exploration of gene-environment interactions requires model organisms with well-characterized ecological interactions in their natural environment, manipulability in the laboratory and genomic tools. The waterfleaDaphnia magnais an established ecological and toxicological model species, central to the food webs of freshwater lentic habitats and sentinel for water quality. Its tractability and cyclic parthenogenetic life-cycle are ideal to investigate links between genes and the environment. Capitalizing on this unique model system, the STRESSFLEA consortium generated a comprehensive RNA-Seq data set by exposing two inbred genotypes ofD. magnaand a recombinant cross of these genotypes to a range of environmental perturbations. Gene models were constructed from the transcriptome data and mapped onto the draft genome ofD. magnausing EvidentialGene. The transcriptome data generated here, together with the available draft genome sequence ofD. magnaand a high-density genetic map will be a key asset for future investigations in environmental genomics.