Extensive growth is followed by neurodegenerative pathology in the continuously expanding adult zebrafish retina.

The development of effective treatments for age-related neurodegenerative diseases remains one of the biggest medical challenges today, underscoring the high need for suitable animal model systems to improve our understanding of aging and age-associated neuropathology. Zebrafish have become an indispensable complementary model organism in gerontology research, yet their growth-control properties significantly differ from those in mammals. Here, we took advantage of the clearly defined and highly conserved structure of the fish retina to study the relationship between the processes of growth and aging in the adult zebrafish central nervous system (CNS). Detailed morphological measurements reveal an early phase of extensive retinal growth, where both the addition of new cells and stretching of existent tissue drive the increase in retinal surface. Thereafter, and coinciding with a significant decline in retinal growth rate, a neurodegenerative phenotype becomes apparent,-characterized by a loss of synaptic integrity, an age-related decrease in cell density and the onset of cellular senescence. Altogether, these findings support the adult zebrafish retina as a valuable model for gerontology research and CNS disease modeling and will hopefully stimulate further research into the mechanisms of aging and age-related pathology.