Structure/cytoskeletal
There was a moderate difference in expression (two-fold to 10-fold) of genes involved in cytoskeletal structure and organization in the 25° group. CCT4 and CCT5 are genes required for the production of actin and tubulin, and TBCB is a cofactor that ensures proper folding of tubulin during production (Lopez-Fanarraga et al. 2001; Brackley and Grantham 2009). Several upregulated genes modulate the interactions between various cytoskeletal components but have no known association with the stress response. AIF1L cross-links actin filaments and is involved in actin bundling (Schulze et al. 2008). SYNPO organizes actin filaments in response to RHOA signaling (Asanuma et al. 2006). CNN2 (calponin 2) binds actin and is thought to aid in the regulation of cytoskeletal organization (Tang et al. 2006). PDLIM1 encodes an adaptor protein that binds to cytoskeletal proteins (Sharma et al. 2011). These upregulated genes have not been previously associated with the stress response, but may play a role in stress-related structural changes in thermally stressed juvenile Chinook.
Certain upregulated cytoskeletal genes, such as MMP13, TAGLN, and CDC42SE1, have known associations with the cellular stress response. MMP13 codes for the protein collagenase 3, which is involved in connective tissue degradation and cytoskeletal component turnover (Knauper et al. 1996). Several other MMP family members were notably downregulated (Table S1); therefore, the roles of other family members in this process are likely more complex than the upregulation of a single gene. TAGLN codes for a calponin family protein, transgelin, which gels actin filaments and is overexpressed in senescent cells (Thweatt et al. 1992; Assinder et al. 2009). CDC42SE1 mediates cytoskeletal scaffold changes in response to immune signaling through CDC42 (Pirone et al. 2000). The upregulation of these genes indicates that some degree of cellular restructuring may take place in response to thermal stress.