Nagpal, J. | Search bioRxiv

bioRxiv2022

Optogenetic induction of chronic glucocorticoid exposure in early-life impairs stress-response in larval zebrafish.

Organisms respond to stressors through a coordinated set of physiological and behavioural responses. Zebrafish provides an opportunity to study conserved mechanisms underlying the stress-response that is regulated largely by the neuroendocrine Hypothalamus-Pituitary-Adrenal/Interrenal (HPA) axis, with glucocorticoids (GC) as the final effector. In this study, we evaluated the effect of chronically active GC signalling in early life on the baseline and stress evoked GC(cortisol) levels in larval zebrafish. To this end, we employed an optogenetic actuator, Beggiatoa photoactivated adenylyl cyclase, expressed in the interrenal cells of zebrafish and demonstrate that its chronic activation leads to hypercortisolaemia and dampens the acute-stress evoked cortisol levels, across a variety of stressor modalities during early life. This blunting of stress-response, a phenotype reported by many studies to be observed in human subjects exposed to early-life trauma, was conserved in ontogeny at a later developmental stage. Furthermore, we observe a strong reduction of proopiomelanocortin (POMC)-expressing cells in the pituitary as well as global upregulation of FKBP5 gene expression, impinging on the negative feedback regulation elicited by elevated cortisol levels. Going forward, we propose that this model can be leveraged to tease apart the mechanisms underlying developmental programming of HPA axis by early-life stress and its implications for vulnerability and resilience to stress in adulthood.

neuroscience↗

bioRxiv2018

Robust and sensitive GFP-based cGMP sensor for real time imaging in intact Caenorhabditis elegans

cGMP is a ubiquitous second messenger that plays a role in sensory signaling and plasticity through its regulation of ion channels and kinases. Previous studies that primarily used genetic and biochemical tools suggest that cGMP is spatiotemporally regulated in multiple sensory modalities, including light, heat, gases, salt and odor. FRET- and GFP-based cGMP sensors were developed to visualize cGMP in primary cell culture and Caenorhabditis elegans to corroborate these findings. While a FRET-based sensor has been used in an intact animal to visualize cGMP, the requirement of a multiple emission system limits its ability to be used on its own as well as with other sensors and fluorescent markers. Here, we demonstrate that WincG2, a codon-optimized version of the cpEGFP-based cGMP sensor FlincG3, can be used in C. elegans to visualize rapidly changing cGMP levels in living, behaving animals using a single fluorophore. We coexpressed the sensor with the blue light-activated guanylyl cyclases BeCyclOp and bPGC in body wall muscles and found that the rate of WincG2 fluorescence correlated with the rate of cGMP production by each cyclase. Furthermore, we show that WincG2 responds linearly upon NaCl concentration changes and SDS presentation in the cell bodies of the gustatory neuron ASER and the nociceptive phasmid neuron PHB, respectively. Intriguingly, WincG2 fluorescence in the ASER cell body decreased in response to a NaCl concentration downstep and either stopped decreasing or increased in response to a NaCl concentration upstep, which is opposite in sign to previously published calcium recordings. These results illustrate that WincG2 can be used to report rapidly changing cGMP levels in an intact animal and that the reporter can potentially reveal unexpected spatiotemporal landscapes of cGMP in response to stimuli.\n\nAuthor SummarycGMP is a second messenger that plays an important role in sensory signaling and neural plasticity. Previous genetic and biochemical studies indirectly suggest that cGMP is spatiotemporally regulated in neurons to modulate neural activity. While a FRET-based sensor for cGMP has been used in intact Caenorhabditis elegans to examine its spatiotemporal regulation in neurobiological processes, its use has been limited due to the complicated setup required to image this type of sensor. Here, we describe a GFP-based cGMP sensor that has been codon optimized for use in C. elegans and demonstrate that it responds robustly and reliably to endogenously changing cGMP levels. We show that the sensor responds to cGMP production by coexpressing it with blue light-activated guanylyl cyclases, and we show that it responds to NaCl and sodium dodecyl sulfate when expressed in a gustatory and nociceptive neuron, respectively. We think that this sensor can be used to investigate the spatiotemporal regulation of cGMP in neurons and its relationship to neural activity.

neuroscience↗