Insulin from the β-cells of the pancreatic islets of Langerhans controls energy homeostasis in vertebrates, and its deficiency causes diabetes mellitus. During embryonic development, the transcription factor Neurogenin3 initiates the differentiation of the β-cells and other islet cell types from pancreatic endoderm, but the genetic program that subsequently completes this differentiation remains incompletely understood. Here we show that the transcription factor Rfx6 directs islet cell differentiation downstream of Neurogenin3. Mice lacking Rfx6 failed to generate any of the normal islet cell types except for pancreatic-polypeptide-producing cells. In human infants with a similar autosomal recessive syndrome of neonatal diabetes, genetic mapping and subsequent sequencing identified mutations in the human RFX6 gene. These studies demonstrate a unique position for Rfx6 in the hierarchy of factors that coordinate pancreatic islet development in both mice and humans. Rfx6 could prove useful in efforts to generate β-cells for patients with diabetes.

No abstract

Pyrenophora tritici-repentis, the causal agent of tan spot on wheat, is a homothallic loculoascomycete with a complex race structure. The objectives of this study were to confirm the homothallic nature of the pathogen, characterize mating type diversity and toxin production genes in a global collection of strains, and analyze how these traits are associated between each other and with existing races. The pseudothecia production capacity, race identification, mating type locus (MAT), internal transcribed spacer, and glyceraldehyde-3-phosphate dehydrogenase regions were analyzed in a selection of 88 strains originating from Europe, North and South America, North Africa, and Central and South Asia. Some (60%) strains produced pseudothecia containing ascospores, independent of their origin. Race identification obtained using the multiplex polymerase chain reaction targeting host-selective toxin (HST) genes was consistent, overall, with the results based on the inoculation of a set of differential wheat cultivars and confirmed the predominance of race 1/2 strains ( approximately 83%). However, discrepancies in race identification, differences from the reference tester strains, and atypical ToxA profiles suggest the presence of new races and HSTs. The MAT1-1 and MAT1-2 coding regions are consecutively arranged in a single individual, suggesting putative heterothallic origin of P. tritici-repentis. Upstream from the MAT is an open reading frame of unknown function (ORF1) containing a MAT-specific degenerate carboxy-terminus. The phylogenetic analysis of the MAT locus reveals two distinct groups, unlinked to geographical origin or ToxA profile. Group I, the best-represented group, is associated with typical tan spot lesions caused by races 1, 2, 3, and 5 on wheat. It is more homogenous than group II encompassing race 4 strains, as well as isolates associated primarily with small spot lesions on wheat leaves or other hosts. Group II could contain several distinct taxa.

A PCR test based on the 16S rRNA gene was set up that could identify any of the five species of the 'Bacillus subtilis group' (B. subtilis, B. pumilus, B. atrophaeus, B. lichenijormis and B. amyloliquefaciens). The test was directly applicable to single colonies and showed excellent specificity. In the mixed population context of wastewater analysis, direct detection of the target Bacillus species by PCR on either crude or purified DNA extracts had poor sensitivity. When assayed on cell suspensions derived from enriched wastewater samples, sensitivity was increased. Using a simple calibration method, it was possible to estimate the proportion of the target organisms. This method was found suitable for easy monitoring of a wastewater bioaugmentation experiment carried out with a mixture of sporulated Bacillus strains.