Establishment and validation of an endoplasmic reticulum stress reporter to monitor zebrafish ATF6 activity in development and disease

Abstract

Induction of endoplasmic reticulum (ER) stress is associated with diverse developmental and degenerative diseases. Modified ER homeostasis causes activation of conserved stress pathways at the ER called the unfolded protein response (UPR). ATF6 is a transcription factor activated during ER stress as part of a coordinated UPR. ATF6 resides at the ER and, upon activation, is transported to the Golgi apparatus, where it is cleaved by proteases to create an amino-terminal cytoplasmic fragment (ATF6f). ATF6f translocates to the nucleus to activate transcriptional targets. Here, we describe the establishment and validation of zebrafish reporter lines for ATF6 activity. These transgenic lines are based on a defined and multimerized ATF6 consensus site, which drives either eGFP or destabilized eGFP, enabling dynamic study of ATF6 activity during development and disease. The results show that the reporter is specific for the ATF6 pathway, active during development and induced in disease models known to engage UPR. Specifically, during development, ATF6 activity is highest in the lens, skeletal muscle, fins and gills. The reporter is also activated by common chemical inducers of ER stress, including tunicamycin, thapsigargin and brefeldin A, as well as by heat shock. In models for amyotrophic lateral sclerosis and cone dystrophy, ATF6 reporter expression is induced in spinal cord interneurons or photoreceptors, respectively, suggesting a role for ATF6 response in multiple neurodegenerative diseases. Collectively our results show that these ATF6 reporters can be used to monitor ATF6 activity changes throughout development and in zebrafish models of disease. This article has an associated First Person interview with the first author of the paper.

Permissive epigenetic landscape facilitates distinct transcriptional signatures of activating transcription factor 6 in the liver

“…In contrast, GO terms related to developmental processes are populated by unique set of genes, indicating these are not redundant. This is in line with studies that have uncovered a role for Atf6 in development and tissue homeostasis [25,54,55]. Taken together, the curated list of CPATs extend the role of Atf6 in cellular processes beyond proteostasis, namely xenobiotic metabolism and nuclear organization.…”

Endoplasmic Reticulum Stress and Unfolded Protein Response in Neurodegenerative Diseases

“…ATF4 ablation in mutant SOD1 G85R mice led to the protection against ALS, these mice appeared more resistant to ALS than mutant mice expressing normal levels of ATF4, possibly because of the reduced levels of apoptosis components, such as CHOP [ 127 ]. The role of IRE1 in ALS was shown by studying the homeodomain interacting protein kinase 2 (HIPK2), an essential component of the IRE1-ASK1 apoptotic cascade activating JNK under ER stress [ 128 ]. In SOD1 G93A mice, loss of HIPK2 was associated with delayed disease onset, reduced cell death in spinal motor neurons, and improved survival [ 128 ].…”

“…The role of IRE1 in ALS was shown by studying the homeodomain interacting protein kinase 2 (HIPK2), an essential component of the IRE1-ASK1 apoptotic cascade activating JNK under ER stress [ 128 ]. In SOD1 G93A mice, loss of HIPK2 was associated with delayed disease onset, reduced cell death in spinal motor neurons, and improved survival [ 128 ]. Furthermore, the ablation of XBP1 led to reduced motor neuron death and aggregation of mutant SOD1, mainly due to a homeostatic link between the UPR and the autophagy pathway [ 114 ].…”

The Current Understanding of Autophagy in Nanomaterial Toxicity and Its Implementation in Safety Assessment-Related Alternative Testing Strategies

“…It is worth mentioning that the zebrafish model can help us quickly and efficiently understand cellular and molecular mechanisms. Due to the advancement of genetic tools, mechanisms, such as those of ROS and autophagy triggered by toxicants, can be easily observed via fluorescent reporters and transgenic lines [85][86][87][88].…”