Consequences of HSF knockdown on gene expression during the heat shock response in Tigriopus californicus

Although the existence of a cellular heat shock response is nearlyuniversal, its relationship to organismal thermal tolerance is notcompletely understood. Many of the genes involved are known to beregulated by the highly conserved heat shock transcription factor-1(HSF-1), yet the regulatory network is not fully characterized. Here,we investigated the role of HSF-1 in gene expression followingthermal stress using knockdown of HSF-1 by RNA interference in theintertidal copepod Tigriopus californicus. We observed someevidence for decreased transcription of heat shock protein genesfollowing knockdown, supporting the widely acknowledged role ofHSF-1 in the heat shock response. However, the majority ofdifferentially expressed genes between the control and HSF-1knockdown groups were upregulated, suggesting that HSF-1normally functions to repress their expression. Differentialexpression observed in genes related to chitin and cuticle formationlends support to previous findings that these processes are highlyregulated following heat stress. We performed a genome scan andidentified a set of 396 genes associated with canonical heat shockelements. RNA-seq data did not find those genes to be more highlyrepresented in our HSF-1 knockdown treatment, indicating thatrequirements for binding and interaction of HSF-1 with a given geneare not simply predicted by the presence of HSF-1 binding sites.Further study of the pathways implicated by these results and futurecomparisons among populations of T. californicus may help usunderstand the role and importance of HSF-1 in the heat shockresponse and, more broadly, in organismal thermal tolerance.