Biology

Chromosome biorientation is established by the four-member chromosomal passenger complex (CPC) through phosphorylation of incorrect kinetochore-microtubule attachments. During chromosome alignment, the CPC localizes to the inner centromere, the inner kinetochore and spindle microtubules. Here we show that a small region of the CPC subunit INCENP/Sli15 is required to target the complex to all three of these locations in budding yeast. This region, the SAH, is essential for phosphorylation of outer kinetochore substrates, chromosome segregation, and viability. By restoring the CPC to each of these three locations individually, we found that inner centromere localization is sufficient to establish chromosome biorientation and viability independently of the other two targeting mechanisms. Remarkably, although neither the inner kinetochore nor microtubule binding activities was able to rescue viability individually, they were able to do so when combined. We have therefore identified two ...

Large-scale expansion of (GAA)n repeats in the first intron of the FXN gene is responsible for the severe neurodegenerative disease, Friedreich’s ataxia in humans. We have previously conducted an unbiased genetic screen for GAA repeat instability in a yeast experimental system. The majority of genes that came from this screen encoded the components of DNA replication machinery, strongly implying that replication irregularities are at the heart of GAA repeat expansions. This screen, however, also produced two unexpected hits: members of the CST complex, CDC13 and TEN1 genes, which are required for telomere maintenance. To understand how the CST complex could affect intra-chromosomal GAA repeats, we studied the well-characterized temperature-sensitive cdc13-1 mutation and its effects on GAA repeat instability in yeast. We found that in-line with the screen results, this mutation leads to ∼10-fold increase in the rate of large-scale expansions of the (GAA)100 repeat at semi-permissive ...

The inner kinetochore and microtubule binding activities of the Chromosomal Passenger Complex are sufficient to promote accurate chromosome segregation. In addition, two distinct pathways target the CPC to different attachment states, as an inner centromere-targeting pathway is primarily responsible for complex enrichment at unattached kinetochores

ABSTRACTCANVAS is a recently characterized repeat expansion disease, most commonly caused by homozygous expansions of an intronic (A2G3)nrepeat in theRFC1gene. There are a multitude of repeat motifs found in the human population at this locus, some of which are pathogenic and others benign. In this study, we conducted structure-functional analyses of the main pathogenic (A2G3)nand the main nonpathogenic (A4G)nrepeats. We found that the pathogenic, but not the nonpathogenic, repeat presents a potent, orientation-dependent impediment to DNA polymerizationin vitro. The pattern of the polymerization blockage is consistent with triplex or quadruplex formation in the presence of magnesium or potassium ions, respectively. Chemical probing of both repeats in supercoiled DNA reveals triplex H-DNA formation by the pathogenic repeat. Consistently, bioinformatic analysis of the S1-END-seq data from human cell lines shows preferential H-DNA formation genome-wide by (A2G3)nmotifs over (A4G)nmotif...

Post-settlement metamorphosis and early juvenile development of an advanced balanid was studied on the example of Megabalanus californicus (Pilsbry). A twelve hour period starting with the moult of the cyprid carapace was observed in detail. Developmental changes of living specimens were studied by means of dissecting microscopes and recorded on video tape for further analysis. The successive ontogenetic stages were fixed and studied with scanning electron microscopy.
When shedding the cyprid carapace the juvenile is composed of a „capitulum“ with primordial carina and primordial opercular plates as well as a vestigial peduncle, both being about the same size. The peduncle vestige differs from the „capitulum“ in the structure of its surface and the lack of cuticular hairs. The „capitulum“ consists of the developing wall, which is surrounded by two circles of cuticular hairs, and the operculum holding two additional rows of such hairs. In scanning electron microscopic images the five primordial plates (scuta, terga and carina) are distinguished by their dented appearance.
In the course of development the shape of the juvenile barnacle is changing rapidly. As the body is getting flatter and broader the surface of the rudimentary peduncle approaches the substratum. About four hours after ecdysis the juvenile has achieved the typical cone shape of adult barnacles. The peduncle vestige has become the basis and is getting fixed to the ground by juvenile cement. Cuticular knobs are densely covering most of the surface of the wall and the operculum. The beginning deposition of calcite hardens their plates. About 12 hours after ecdysis the basis is completely fixed to the substratum.

Post-settlement metamorphosis and early juvenile development of an advanced balanid was studied on the example of Megabalanus californicus (Pilsbry). A twelve hour period starting with the moult of the cyprid carapace was observed in detail. Developmental changes of living specimens were studied by means of dissecting microscopes and recorded on video tape for further analysis. The successive ontogenetic stages were fixed and studied with scanning electron microscopy. When shedding the cyprid carapace the juvenile is composed of a "capitulum" with primordial carina and primordial opercular plates as well as a vestigial peduncle, both being about the same size. The peduncle vestige differs from the "capitulum" in the structure of its surface and the lack of cuticular hairs. The "capitulum" consists of the developing wall, which is surrounded by two circles of cuticular hairs, and the operculum holding two additional rows of such hairs. In scanning electr...

Many recent studies have addressed the mechanisms operating during the early stages of speciation, but surprisingly few studies have tested theoretical predictions on the evolution of strong reproductive isolation (RI). To help address this gap, we first undertook a quantitative review of the hybrid zone literature for flowering plants in relation to reproductive barriers. Then, usingPopulusas an exemplary model group, we analysed genome-wide variation for phylogenetic tree topologies in both early- and late-stage speciation taxa to determine how these patterns may be related to the genomic architecture of RI. Our plant literature survey revealed variation in barrier complexity and an association between barrier number and introgressive gene flow. Focusing onPopulus,our genome-wide analysis of tree topologies in speciating poplar taxa points to unusually complex genomic architectures of RI, consistent with earlier genome-wide association studies. These architectures appear to facili...

Speciation, the continuous process by which new species form, is often investigated by looking at the variation of nucleotide diversity and differentiation across the genome (hereafter genomic landscapes). A key challenge lies in how to determine the main evolutionary forces at play shaping these patterns. One promising strategy, albeit little used to date, is to comparatively investigate these genomic landscapes as a progression through time by using a series of species pairs along a divergence gradient. Here, we resequenced 201 whole-genomes from eight closely relatedPopulusspecies, with pairs of species at different stages along the divergence gradient to learn more about speciation processes. Using population structure and ancestry analyses, we document extensive introgression between some species pairs, especially those with parapatric distributions. We further investigate genomic landscapes, focusing on within-species (nucleotide diversity and recombination rate) and among-spe...

Many recent studies have addressed the mechanisms operating during the early stages of speciation, but surprisingly few studies have tested theoretical predictions on the evolution of strong reproductive isolation (RI). To help address this gap, we first undertook a quantitative review of the hybrid zone literature for flowering plants in relation to reproductive barriers. Then, using <i>Populus</i> as an exemplary model group, we analysed genome-wide variation for phylogenetic tree topologies in both early- and late-stage speciation taxa to determine how these patterns may be related to the genomic architecture of RI. Our plant literature survey revealed variation in barrier complexity and an association between barrier number and introgressive gene flow. Focusing on <i>Populus,</i> our genome-wide analysis of tree topologies in speciating poplar taxa points to unusually complex genomic architectures of RI, consistent with earlier genome-wide association stu...

Bactrocera dorsalis is considered among the most destructive and economically important invasive fruit flies worldwide. Native to Southeast Asia, in just a few years, it has spread almost throughout all of sub-Saharan Africa, causing fruit loss in several commercially grown crops. In Europe, it is frequently intercepted as larva on imported fruits during phytosanitary inspections. In recent years, adult specimens have been caught in traps in Austria, Italy, and France, increasing the level of attention to this species. Rapid and unambiguous identification by European plant health laboratories is important to effectively prevent its introduction and establishment in Europe. The harmonized use of validated diagnostic protocols is essential. However, in entomology, unlike other disciplines, diagnostic protocols often lack validation data to support their suitability as adequate identification tools. In this study, tests from two international diagnostic protocols for the identification...