Comparison of the spectra of genetic damage in formaldehyde-induced ad-3 mutations between DNA repair-proficient and -deficient heterokaryons of Neurospora crassa

Repeat-induced point mutation in Neurospora crassa causes the highest known mutation rate and mutational burden of any cellular life

BACKGROUND

Repeat-induced point (RIP) mutation in Neurospora crassa degrades transposable elements by targeting repeats with C→T mutations. Whether RIP affects core genomic sequence in important ways is unknown.

RESULTS

By parent-offspring whole genome sequencing, we estimate a mutation rate (3.38 ×  10-6 per bp per generation) that is two orders of magnitude higher than reported for any non-viral organism, with 93-98% of mutations being RIP-associated. RIP mutations are, however, relatively rare in coding sequence, in part because RIP preferentially attacks GC-poor long duplicates that interact in three dimensional space, while coding sequence duplicates are rare, GC-rich, short, and tend not to interact. Despite this, with over 5 coding sequence mutations per genome per generation, the mutational burden is an order of magnitude higher than the previously highest observed. Unexpectedly, the majority of these coding sequence mutations appear not to be the direct product of RIP being mostly in non-duplicate sequence and predominantly not C→T mutations. Nonetheless, RIP-deficient strains have over an order of magnitude fewer coding sequence mutations outside of duplicated domains than RIP-proficient strains.

CONCLUSIONS

Neurospora crassa has the highest mutation rate and mutational burden of any non-viral life. While the high rate is largely due to the action of RIP, the mutational burden appears to be RIP-associated but not directly caused by RIP.

Diverse data supports the transition of filamentous fungal model organisms into the post-genomics era

Filamentous fungi have been important as model organisms since the beginning of modern biological inquiry and have benefitted from open data since the earliest genetic maps were shared. From early origins in simple Mendelian genetics of mating types, parasexual genetics of colony colour, and the foundational demonstration of the segregation of a nutritional requirement, the contribution of research systems utilising filamentous fungi has spanned the biochemical genetics era, through the molecular genetics era, and now are at the very foundation of diverse omics approaches to research and development. Fungal model organisms have come from most major taxonomic groups although Ascomycete filamentous fungi have seen the most major sustained effort. In addition to the published material about filamentous fungi, shared molecular tools have found application in every area of fungal biology. Similarly, shared data has contributed to the success of model systems. The scale of data supporting research with filamentous fungi has grown by 10 to 12 orders of magnitude. From genetic to molecular maps, expression databases, and finally genome resources, the open and collaborative nature of the research communities has assured that the rising tide of data has lifted all of the research systems together.

An in vitro approach to assess the toxicity of inhaled tobacco smoke components: nicotine, cadmium, formaldehyde and urethane

One of the first lines of defence to inhaled toxins is the barrier formed by the tracheobronchial epithelium, making this the ideal region for studying the toxicity of inhaled substances. This study utilises a highly differentiated, three-dimensional, in vitro model of human upper respiratory tract epithelium (EpiAirway-100) to measure the acute toxicological responses to well-characterised tobacco smoke components. To determine the suitability of this model for screening inhaled toxicants, the EpiAirway tissue model (ETM) was treated apically with tobacco smoke components (nicotine, formaldehyde, cadmium, urethane) which are known to induce a variety of toxic effects (e.g. cytotoxic, thrombogenic, carcinogenic). A range of concentrations were used to model different mechanisms and severity of toxicity which were then compared to known in vivo responses. Similar trends in stress response occurred, with distinct alterations to the tissue in response to all four toxins. At high concentrations, cell viability decreased and tight junctions were degraded, but at sub-toxic concentrations epithelial resistance (indicating tissue integrity) increased 20-60% from control. This peak in resistance coincided with an increase in secreted protein levels, elevated cytokine release and goblet cell hyperplasia and hypertrophy. In conclusion, acute exposure to tobacco smoke components induces measurable toxic responses within human respiratory epithelium. Sub-toxic concentrations appear to illicit a protective response by increasing mucus secretion and mediating immune responses via cytokine release. These responses are comparable to human in vivo responses, indicating potential for the ETM as a tool for screening the toxicity of inhaled compounds.