Danionella cerebrum as a transparent vertebrate adult model for studying immune-related biological processes and diseases

An optically accessible adult vertebrate model is needed to study dynamic cellular processes in vivo. We aim to develop

and characterize Danionella cerebrum, a teleost related to zebrafish that remains transparent into adulthood, for studying

immune-related biological processes and their impact on disease progression in multiple organs. A transparent adult model is particularly important for live imaging studies of immune related processes due to the dynamic and complex nature of

immune cell heterogeneity and plasticity, the involvement of infiltrating immune cells during disease progression, as well as confounding factors related to aging. D. cerebrum, previously named as D. translucida, was first described by the Judkewitz group in 2018 for brain-related studies. This genetically tractable model is small, adults reach a length of

approximately 12 mm in length, and is optical transparency even into adulthood. Established transgenesis and genome editing methods used in zebrafish have showed to be effective in D. cerebrum. These characteristics make D. cerebrum an

attractive model for noninvasive in vivo visualization of dynamic and complex cellular events in a physiologically relevant

setting. This study aims to build the infrastructure required to use D. cerebrum as a systems biology model organism for

studying immune-related biological processes and their impact on disease progression. Our proof of principle experiments have successfully generated transgenic lines with fluorescently labelled innate immune cells such as neutrophils and

macrophages, and the endothelial cells of the vasculature. We propose to expand our collection of transgenic D. cerebrum

lines by fluorescently labeling multiple organs such as the brain, heart, liver, and kidney. In combination, these transgenic lines will allow us to visualize the complex interplay between immune cells and various organs throughout development,

injury and disease. We will also develop a macrophage/microglia fluorescent activity reporter line which will allow us to observe and measure dynamic state changes displayed by immune cells in a physiologically relevant environment using non-invasive in vivo imaging. To facilitate our studies, we will develop methods and equipment for longitudinal live

imaging of awake adult D. cerebrum. Immune cell functions play important roles in wound healing and regeneration.

Zebrafish are known to have great regeneration capacity in different organs, however, it is not known if D. cerebrum can

regenerate. Our preliminary work suggests that adult D. cerebrum can regenerate its tail fin but this regenerative capacity

decreased in aged animal. Our proposed study will investigate if D. cerebrum regenerates its central nervous system during different developmental stages, its corresponding immune cell response and the transcriptomic changes that accompany these events. We will also perform interspecies comparative analysis using available data from zebrafish regeneration

studies to explore key players in modulating regeneration capacity. This proposal describes strategies that will build the infrastructure required to use D. cerebrum for immunology related studies in vivo. The tools, techniques and knowledge

built for the D. cerebrum immune model will provide an important springboard for carrying out future focused analyses on

immune-related processes that include, but by no means are limited to, inflammaging, wound healing/regeneration, cancer, and neurodegenerative diseases.