Inversion, duplication, and changes in gene context are associated with human chromosome 18 evolution

Human chromosome 18 differs from its homologues in the great apes by a pericentric inversion. We have identified a chimpanzee bacterial artificial chromosome that spans a region where a break is likely to have occurred in a human progenitor and have characterized the corresponding regions in both chimpanzees and humans. Interspecies sequence comparisons indicate that the ancestral break occurred between the genes ROCK1 and USP14. In humans, the inversion places ROCK1 near centromeric heterochromatin and USP14 adjacent to highly repetitive subtelomeric repeats. In addition, we provide evidence for a human segmental duplication that may have provided a mechanism for the inversion.     

YplA is exported by the Ysc, Ysa, and flagellar type III secretion systems of Yersinia enterocolitica

Yersinia enterocolitica maintains three different pathways for type III protein secretion. Each pathway requires the activity of a specific multicomponent apparatus or type III secretion system (TTSS). Two of the TTSSs are categorized as contact-dependent systems which have been shown in a number of different symbiotic and pathogenic bacteria to influence interactions with host organisms by targeting effector proteins into the cytosol of eukaryotic cells. The third TTSS is required for the assembly of flagella and the secretion of the phospholipase YplA, which has been implicated in Y. enterocolitica virulence. In this study, YplA was expressed from a constitutive promoter in strains that contained only a single TTSS. It was determined that each of the three TTSSs is individually sufficient for YplA secretion. Environmental factors such as temperature, calcium availability, and sodium chloride concentration affected the contribution of each system to extracellular protein secretion and, under some conditions, more than one TTSS appeared to operate simultaneously. This suggests that some proteins might normally be exported by more than one TTSS in Y. enterocolitca.     

Novel carbazole and acyl-indole antimitotics

In the course of our Heat Shock 90 program, certain carbazole compounds were identified which had an off-target antiproliferative activity. To understand the off-target activity, we studied one analog with strong activity. We discovered that it had an effect on tubulin polymerization kinetics and was competitive with colchicine. Additional analogs were made, and a number of potent compounds were identified.     

MADS-box out of the black box

The compelling elegance of using genome‐wide scans to detect the signature of selection is difficult to resist, but is countered by the low demonstrated efficacy of pinpointing the actual genes and traits that are the targets of selection in nonmodel species. While the difficulty of going from a suggestive signature to a functional nucleotide polymorphism should not prevent researchers from using genome scans, it does lessen their long‐term utility within and across study systems. In a new study published in this issue of Molecular Ecology ( Mariac et al. 2011 ), researchers have gone a long way towards increasing the relevance of genome‐wide scans for selection via two approaches: (i) they tailored the markers used in the scan to target a family of developmental genes that were good candidates for controlling a trait of interest and (ii) they used an independent mapping population to confirm the association of the gene with polymorphism in the trait of interest. All of this was completed in the nonmodel system of pearl millet (Pennisetum glaucum) and may provide a road map for other researchers hoping to pin down solid candidate genes for selected traits in natural or cultivated systems. Outside of these broad methodological innovations, the paper specifically focuses on a trait (flowering time) that varies across an environmental gradient (rainfall). This environmental gradient potentially serves as a model for environmental change over time, and allele frequencies at the gene can therefore be used to track how populations of pearl millet will adapt to future climate shifts at the genetic level.     

Hybridization and the colonization of novel habitats by annual sunflowers

Although invasive plant species often have a hybrid ancestry, unambiguous evidence that hybridization has stimulated the evolution of invasive behaviors has been difficult to come by. Here, we briefly review how hybridization might contribute to the colonization of novel habitats, range expansions, and invasiveness and then describe work on hybrid sunflowers that forges a direct link between hybridization and ecological divergence. We first discuss the invasion of Texas by the common sunflower and show that the introgression of chromosomal segments from a locally adapted species may have facilitated range expansion. We then present evidence that the colonization of sand dune, desert floor, and salt marsh habitats by three hybrid sunflower species was made possible by selection on extreme or “transgressive” phenotypes generated by hybridization. This body of work corroborates earlier claims regarding the role of hybridization in adaptive evolution and provides an experimental and conceptual framework for ongoing studies in this area.