Transcription dynamics and regulation of heat shock protein genes during stress and development in the estuarine cnidarian Nematostella vectensis

Heat shock proteins (HSPs) are conserved molecular chaperones that function in protecting cells from proteotoxic conditions. Most eukaryotes have multiple HSP genes that encode for proteins localizing in the cytoplasm, endoplasmic reticulum (ER), and mitochondria. In marine invertebrates of the phylum Cnidaria, where HSPs are often used as biomarkers of environmental stress, little is known about how particular HSPs vary in copy number, expression, inducibility, and regulation within a species. In this study, we characterized the diversity of the full repertoire of HSP70 and HSP90 genes in an emerging model cnidarian, Nematostella vectensis . We identified five distinct HSP70 and three HSP90 genes, with at least one homolog from each family belonging to the three primary clades based on subcellular localization. Although transcription of none of these HSPs was significantly induced by a temperature change of 10°C, two cytosolic HSP70s and one cytosolic HSP90 were significantly upregulated with a 20°C increase in temperature. Most HSPs followed a similar pattern of expression across various developmental stages of N. vectensis , with an increase in expression during the early larval stage followed by a decrease during the juvenile stage. HSPs showed evidence for differential expression in particular cell types, where multiple cytosolic and ER HSPs were highly expressed in neuronal and cnidocyte cell types. Moreover, there were differences in the abundance and sequences of regulatory heat shock element motifs in the putative promoters of N. vectensis HSPs, providing a potential mechanistic basis of functional diversification in response to temperature and development. By characterizing the expression of all HSP70 and HSP90 genes in this cnidarian, we reveal distinct roles of these core genes in the proteostasis response, providing a foundation for future functional studies into the diverse contributions of HSPs to cnidarian life cycle and stress resilience.