Cloning and characterization of cDNAs for hormones and/or receptors of growth hormone, insulin-like growth factor-I, thyroid hormone, and corticosteroid and the gender-, tissue-, and developmental-specific expression of their mRNA transcripts in fathead m

Growth hormone (GH), insulin-like growth factor-I (IGF-I), thyroid hormones, and corticosteroids play central roles in a wide range of body functions but, in fish, information on their interactions is limited. These axes of the endocrine system are also potential targets for disruption of signaling pathways by hormone-mimicking chemicals, but have received little study. Molecular approaches offer an effective way to help unravel these endocrine interactions but require the appropriate gene-specific assays to do so. In this study, the cDNAs for a suite of hormones and/or receptors involved in signaling for the effects of GH and IGF-I [GH, GH receptor (GHR), IGF-I, IGF-I receptor (IGF-IR)], thyroid hormones [thyroid hormone receptor α (TRα) and β (TRβ)], and corticosteroids [glucocorticoid receptor (GR)] were cloned from the fathead minnow (Pimephales promelas; fhm), and the tissue-, developmental-, and gender-related expression of their mRNA transcripts established. By polymerase chain reaction (PCR) strategy, we obtained full-length 1123-bp GH, 817-bp IGF-I, 1584-bp TRβ, and 2571-bp GR cDNAs, coding for 210 amino acid (aa) GH, 161 aa IGF-I, 378 aa TRβ, and 745 aa GR putative proteins, and partial-length 158-bp GHR, 811-bp IGF-IR, and 446-bp TRα cDNAs. Real-time PCR analyses revealed broad tissue expression for the target mRNAs; all targets were expressed in brain, pituitary, gill, liver, gonad, intestine, and muscle, with the exception of GH that was expressed only in the pituitary and gonad. Expression patterns in both juvenile and adult fhm were complex, with both temporal-, tissue-, and sex-specific characteristics. For example, hepatic expressions of GHR, IGF-I, and IGF-IR were far higher in males than in females, possibly reflecting the sex-related dimorphism in growth that occurs in this species, and TRα and TRβ showed divergent expression patterns during development (where TRβ predominated) and in adult tissues implying some distinct roles for the two TR subtypes.