Branchpoint translocation by fork remodelers as a general mechanism of R-loop removal

Co-transcriptional R loops arise from stalling of RNA polymerase, leading to the formation of stable DNA:RNA hybrids. Unresolved R loops promote genome instability but are counteracted by helicases and nucleases. Here, we show that branchpoint translocases are a third class of R-loop-displacing enzyme in vitro. In cells, deficiency in the Fanconi-anemia-associated branchpoint translocase FANCM causes R-loop accumulation, particularly after treatment with DNA:RNA-hybrid-stabilizing agents. This correlates with FANCM localization at R-loop-prone regions of the genome. Moreover, other branchpoint translocases associated with human disease, such as SMARCAL1 and ZRANB3, and those from lower organisms can also remove R loops in vitro. Branchpoint translocases are more potent than helicases in resolving R loops, indicating their evolutionary important role in R-loop suppression. In human cells, FANCM, SMARCAL1, and ZRANB3 depletion causes additive effects on R-loop accumulation and DNA damage. Our work reveals a mechanistic basis for R-loop displacement that is linked to genome stability.

SMG8/SMG9 Heterodimer Loss Modulates SMG1 Kinase to Drive ATR Inhibitor Resistance

Gastric cancer represents the third leading cause of global cancer mortality and an area of unmet clinical need. Drugs that target the DNA damage response, including ATR inhibitors (ATRi), have been proposed as novel targeted agents in gastric cancer. Here, we sought to evaluate the efficacy of ATRi in preclinical models of gastric cancer and to understand how ATRi resistance might emerge as a means to identify predictors of ATRi response. A positive selection genome-wide CRISPR-Cas9 screen identified candidate regulators of ATRi resistance in gastric cancer. Loss-of-function mutations in either SMG8 or SMG9 caused ATRi resistance by an SMG1-mediated mechanism. Although ATRi still impaired ATR/CHK1 signaling in SMG8/9-defective cells, other characteristic responses to ATRi exposure were not seen, such as changes in ATM/CHK2, γH2AX, phospho-RPA, or 53BP1 status or changes in the proportions of cells in S- or G2-M-phases of the cell cycle. Transcription/replication conflicts (TRC) elicited by ATRi exposure are a likely cause of ATRi sensitivity, and SMG8/9-defective cells exhibited a reduced level of ATRi-induced TRCs, which could contribute to ATRi resistance. These observations suggest ATRi elicits antitumor efficacy in gastric cancer but that drug resistance could emerge via alterations in the SMG8/9/1 pathway.

SIGNIFICANCE

These findings reveal how cancer cells acquire resistance to ATRi and identify pathways that could be targeted to enhance the overall effectiveness of these inhibitors.

Caseous Lymphadenitis in Sheep in the Falkland Islands

Caseous lymphadenitis (CLA), also called pseudotuberculosis, is a chronic and highly infectious disease of sheep and goats, subject to obligatory registration in the European Union. The EU law also applies to special territories, which include the Falkland Islands. On the Falkland Islands 99% of sheep and goats are slaughtered in one slaughterhouse, overseen by veterinary authorities, and approved for export to EU countries (mainly the UK). The export season begins about the middle of January and usually lasts 3-4 months. In the years 2013-2015 were examined 162 317 sheep, including 39 971 lambs, 35 357 yearlings and 86 989 mature rams. During the study lung tissue clippings were collected. During the 2013 season lesions were observed in 8 025 of animals (13.9% CLA). In 2014 lesions were noted in 7716 with CLA accounting for 13.91% and in 2015 lesions were noted in 5743 with CLA accounting for 11.7%. Further analysis of cases of CLA on the Falkland Islands seems interesting, as they are British overseas territories and therefore part of the European Union.

Parthenogenesis as a life strategy among mites of the suborder Uropodina (Acari: Mesostigmata)

This paper presents the results of observations concerning the phenomenon of parthenogenesis among European mites of the suborder Uropodina. An analysis of the sex ratios of 66 Polish species revealed that 18 of them (more than one fourth of the examined species) consisted only of females. The authors observed no significant relationship between geographical distribution and the lack of males in the population. Populations consisting entirely of females were observed among widely distributed species as well as among species characterized by narrow geographical ranges. Nonetheless, an increase in the number of parthenogenetic species, especially as a percentage of Middle European and Scandinavian fauna, was also discernible. Species that reproduced without males were associated with forest litter and soil, whereas bisexual species "eagerly" inhabited various relatively unstable and temporary micro environ ments (for instance, dead wood, birds' or small mammals' nests). The authors aim to define the biological role of occasionally appearing males for the species consisting almost entirely of females and discuss ecological and evolutionary aspects of parthenogenesis in mites of the suborder Uropodina.