Conserved HSP60 structure with lineage- and context-specific regulation in cnidarians

Heat shock proteins safeguard proteostasis under stress. We examined mitochondrial chaperonin HSP60 in three cnidarians to assess stress responses. We evaluated HSP60 expression in Pocillopora acuta (hard coral), Exaiptasia diaphana (sea anemone), and Cassiopea xamachana (upside-down jellyfish) using immunoblotting. In P. acuta, HSP60 was not detected at the fragment level under either control (25°C) or heat-stress (30°C). In contrast, isolated cells showed transient HSP60 expression under both temperature conditions, indicating context-dependent regulation in coral. E. diaphana and C. xamachana showed elevated HSP60 expression over 24 h when stressed (+5°C above laboratory optima). These patterns indicate lineage-specific regulatory mechanisms underlying chaperone-mediated stress response pathways. Thus, thermal sensitivity varies among species and across biological contexts. Consistent antibody cross-reactivity prompted evolutionary analysis. Phylogenetic analyses confirmed cnidarian HSP60 proteins are orthologous to vertebrate HSP60, demonstrating deep conservation across Metazoa. Although HSP60 is ancient and highly conserved, its role in regulating mitochondrial proteostasis varies across early-diverging metazoans. This study underlines the role of chaperone plasticity in cnidarian thermotolerance and diverging bleaching susceptibility of symbiotic cnidarians.