Short term memory of Caenorhabditis elegans against bacterial pathogens involves CREB transcription factor

Coupled dopamine and insulin signaling mediated transgenerational and multigenerational inheritance of adaptive traits in Caenorhabditis elegans upon parental training with Salmonella enterica Serovar Typhi

The nervous system's ability to perceive and learn about the environment can help organisms evolve and acquire traits, potentially generating adaptive responses. However, its potential to produce heritable modulations is a scientific lacuna, which is under-explored. Here, with the help of Caenorhabditis elegans, which has a well-established neuronal networking, we found that on training the worms on a candidate pathogenic bacterium Salmonella enterica Serovar Typhi, the worms could exhibit a characteristic transgenerational pathogenic avoidance up to three subsequent generations to the otherwise attractive pathogen. Our further analyses suggested that dopamine signaling is essential for the learning and transmission of the learned traits across generations and that inhibiting or mutating the expression of DAT-1 involved in dopamine transportation eliminated the inheritance patterns. Also, the offspring generations showed enhanced survival resistance against S. Typhi, which was coupled with the higher levels of C-type lectins suggesting priming of the offspring's immune system to generate resistance against S. Typhi upon re-exposure. Enhanced DAF-2/DAF-16-mediated insulin signaling pathway was observed, suggesting that the inherited immune response could be mediated through insulin/IGF-1 signaling (IIS). Furthermore, mutigenerational training on S. Typhi for three continuous generations induced preferential adaptation and better survivability toward S. Typhi. Taken together, the present study indicates that S. Typhi infection could generate transgenerational heritable dopaminergic modulations, which could possibly be the key signaling player in determining the decision-making ability of the host and also generate adaptive survival response, which could be mediated by the insulin-signaling pathway.IMPORTANCEAdaptation is a phenomenon by which an organism learns and develops a mechanism to respond to dynamic and challenging conditions. It provides animals with an advantage to exhibit phenotypic as well as genotypic plasticity, enabling better survivability. The current study helps in understanding how animals respond to environmental stresses such as bacterial infections and the possible mechanism by which the information of the experience is being transmitted across future generations. Neuronal signaling promotes the brain's ability to learn and generate memory, thereby reorganizing the response of the organism. The study also tries to understand how neuronal signaling could be essential for transmitting the information of parental experiences transgenerationally. Collectively, the study helps us understand the evolutionary adaptations exhibited across generations, which will also help us understand the long-term effects of pathogenesis.

Regulation of miR-61 and col-19 via TGF-β and Notch signalling in Caenorhabditis elegans against Klebsiella aerogenes infection

Klebsiella aerogenes, previously known as Enterobacter aerogenes, is a gram-negative bacterium typically present in the gastrointestinal tract. While numerous studies reported the pathogenicity and drug resistance of this bacterium there remains a lack of comprehensive research on K. aerogenes induced alterations in the host cellular mechanisms. In this study, we identify a previously uncharacterized C. elegans miR-61 that defines an evolutionarily conserved miRNA important for development and innate immunity regulation through Notch and TGF-β signaling pathway. We employed C. elegans wild-type (N2) as well as mutant strains, such as TGF-β (sma-6) and notch-signaling pathway mutants (adm-4 and mir-61). Our results have demonstrated that the K. aerogenes infected mutants exhibited significantly reduced survival rate, reduced pharyngeal pumping, altered swimming and chemotactic behavior. Moreover, K. aerogenes affects the healthspan by increasing ROS level in the mutants. The gene expression analysis revealed that K. aerogenes upregulated egl-30, tph-1 and sod-1 in adm-4, mir-61 mutants not in sma-6. The in-silico analysis indicated an interaction between mir-61 and col-19, which was confirmed by the upregulation of miR-61 expression and the downregulation of col-19 in sma-6, adm-4, and wild-type strains. These findings suggest that C. elegans activates mir-61 and col-19 regulation through the Notch and TGF-β signaling pathway against K. aerogenes infection.

Transcription Factors That Control Behavior-Lessons From C. elegans

Behavior encompasses the physical and chemical response to external and internal stimuli. Neurons, each with their own specific molecular identities, act in concert to perceive and relay these stimuli to drive behavior. Generating behavioral responses requires neurons that have the correct morphological, synaptic, and molecular identities. Transcription factors drive the specific gene expression patterns that define these identities, controlling almost every phenomenon in a cell from development to homeostasis. Therefore, transcription factors play an important role in generating and regulating behavior. Here, we describe the transcription factors, the pathways they regulate, and the neurons that drive chemosensation, mechanosensation, thermosensation, osmolarity sensing, complex, and sex-specific behaviors in the animal model Caenorhabditis elegans. We also discuss the current limitations in our knowledge, particularly our minimal understanding of how transcription factors contribute to the adaptive behavioral responses that are necessary for organismal survival.

Immunometabolic Crosstalk: An Ancestral Principle of Trained Immunity?

Memory was traditionally considered an exclusive hallmark of adaptive immunity. This dogma was challenged by recent reports that myeloid cells can retain 'memory' of earlier challenges, enabling them to respond strongly to a secondary stimulus. This process, designated 'trained immunity', is initiated by modulation of precursors of myeloid cells in the bone marrow. The ancestral innate immune system of lower organisms (e.g., Caenorhabditis elegans) can build long-lasting memory that modifies responses to secondary pathogen encounters. We posit that changes in cellular metabolism may be a common denominator of innate immune memory from lower animals to mammals. We discuss evidence from C. elegans and murine/human systems supporting the concept of an ancestral principle regulating innate immune memory by controlling cellular metabolism.

Lack of CRH Affects the Behavior but Does Not Affect the Formation of Short-Term Memory

Corticotropin-releasing hormone (CRH) is involved in modification of synaptic transmission and affects spatial discrimination learning, i.e., affects the formation of memory in long-term aspect. Therefore, we have focused on CRH effect on short-term memory. We have used stress task avoidance (maze containing three zones: entrance, aversive, and neutral) and compared the behavior and short-term memory in wild-type mice and mice lacking CRH (CRH KO) experiencing one 120-min session of restraint stress. As control, non-stressed animals were used. As expected, the animals that experienced the stress situation tend to spend less time in the zone in which the restraint chamber was present. The animals spent more time in the neutral zone. There were significant differences in number of freezing bouts in the aversive and entrance zones in CRH KO animals. CRH KO control animals entered the neutral zone much more faster than WT control and spent more time immobile in the neutral zone than WT control. These data give evidence that lacking of CRH itself improves the ability of mice to escape away from potentially dangerous area (i.e., those in which the scent of stressed animal is present).