The wormsorter is an instrument analogous to a FACS machine that is used in studies of Caenorhabditis elegans, typically to sort worms based on expression of a fluorescent reporter. Here, we highlight an alternative usage of this instrument, for sorting worms according to their degree of colonization by a GFP-expressing pathogen. This new usage allowed us to address the relationship between colonization of the worm intestine and induction of immune responses. While C. elegans immune responses to different pathogens have been documented, it is still unknown what initiates them. The two main possibilities (which are not mutually exclusive) are recognition of pathogen-associated molecular patterns, and detection of damage caused by infection. To differentiate between the two possibilities, exposure to the pathogen must be dissociated from the damage it causes. The wormsorter enabled separation of worms that were extensively-colonized by the Gram-negative pathogen Pseudomonas aeruginosa, with the damage likely caused by pathogen load, from worms that were similarly exposed, but not, or marginally, colonized. These distinct populations were used to assess the relationship between pathogen load and the induction of transcriptional immune responses. The results suggest that the two are dissociated, supporting the possibility of pathogen recognition.
Cancers accumulate mutations over time, each of which brings the potential for recognition by the immune system. We evaluated T-cell recognition of the tumor mutanome in ovarian cancer patients undergoing standard treatment.
Conidiation (asexual sporulation) is a key developmental process in filamentous fungi. We examined the gene regulatory roles of the Aspergillus fumigatus developmental transcription factors StuAp and BrlAp during conidiation. Conidiation was completely abrogated in an A. fumigatus DeltabrlA mutant and was severely impaired in a DeltastuA mutant. We determined the full genome conidiation transcriptomes of wild-type and DeltabrlA and DeltastuA mutant A. fumigatus and found that BrlAp and StuAp governed overlapping but distinct transcriptional programs. Six secondary metabolite biosynthetic clusters were found to be regulated by StuAp, while only one cluster exhibited BrlAp-dependent expression. The DeltabrlA mutant, but not the DeltastuA mutant, had impaired downregulation of genes encoding ribosomal proteins under nitrogen-limiting, but not carbon-limiting, conditions. Interestingly, inhibition of the target of rapamycin (TOR) pathway also caused downregulation of ribosomal protein genes in both the wild-type strain and the DeltabrlA mutant. Downregulation of these genes by TOR inhibition was associated with conidiation in the wild-type strain but not in the DeltabrlA mutant. Therefore, BrlAp-mediated repression of ribosomal protein gene expression is not downstream of the TOR pathway. Furthermore, inhibition of ribosomal protein gene expression is not sufficient to induce conidiation in the absence of BrlAp.
Caenorhabditis elegans has been used for over a decade to characterize signaling cascades controlling innate immune responses. However, what initiates these responses in the worm has remained elusive. To gain a better understanding of the initiating events we delineated genome-wide immune responses to the bacterial pathogen Pseudomonas aeruginosa in worms heavily-colonized by the pathogen versus worms visibly not colonized. We found that infection responses in both groups were identical, suggesting that immune responses were not correlated with colonization and its associated damage. Quantitative RT-PCR measurements further showed that pathogen secreted factors were not able to induce an immune response, but exposure to a non-pathogenic Pseudomonas species was. These findings raise the possibility that the C.elegans immune response is initiated by recognition of microbe-associated molecular patterns. In the absence of orthologs of known pattern recognition receptors, C. elegans may rely on novel mechanisms, thus holding the potential to advance our understanding of evolutionarily conserved strategies for pathogen recognition.
Stress-activated protein kinase (SAPK) pathways are evolutionarily conserved signaling modules that orchestrate protective responses to adverse environmental conditions. However, under certain conditions, their activation can be deleterious. Thus, activation of the c-Jun N-terminal kinase (JNK) SAPK pathway exacerbates a diverse set of pathologies, many of which are typical of old age. The contexts determining whether the outcome of JNK signaling is protective or detrimental are not fully understood. Here, we show that the age of an animal defines such a context. The Caenorhabditis elegans JNK homolog, KGB-1, provides protection from heavy metals and protein folding stress in developing animals. However, we found that with the onset of adulthood, KGB-1 activity becomes detrimental, reducing stress resistance and lifespan. Genetic analyses coupled with fluorescent imaging linked this phenotypic switch to age-dependent antagonistic modulation of DAF-16/FOXO: KGB-1 activation enhanced DAF-16 nuclear localization and transcriptional activity during development but decreased it in adults. Epistasis analyses showed that DAF-16 was necessary and sufficient to explain some of the kgb-1-dependent detrimental phenotypes, but not all. The identification of early adulthood as a point following which the contribution of KGB-1 activity reverses from beneficial to detrimental sheds new light on the involvement of JNK signaling in age-related pathologies. Furthermore, the age-dependent reversal has intriguing implications for our understanding of aging.
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