Metamorphosis-associated immune system maturation in Senegalese sole

The thyroid hormones (THs) are proposed as putative regulators of immune system maturation in developing teleost fish. To gain insight into this process the Senegalese sole (Solea senegalensis) that has a well-characterized TH-driven metamorphosis was used. Differential gene expression analysis was performed across developmental stages (n = 3 per stage): pre-metamorphosis, onset of metamorphosis, metamorphosis, early climax, climax, and post-metamorphic juveniles. Metamorphosis is a massive gene-oriented developmental process, involving the differential expression of 8145 genes. Clustering analysis was used to identify immune-related genes with similar expression patterns to hypothalamus-pituitary-thyroid (HPT) axis-related genes. TH-regulated candidate immune genes were identified (133) and analysis of their promoter region revealed 84 contained putative TH receptor (TR) binding sites (TREs). Two consensus TRE sequences were identified in the candidate genes, 5'-ntgnGntCacan (exclusive to TRα), and 5'-nnntGgtCannn (common to both TRs). TRα-exclusive TREs were less common than those that bound interchangeably TRα and TRβ. In the promoter region, TRα-exclusive TREs were always accompanied by the pan-TRE consensus sequence, never occurring independently.