Two distinct isoforms of cDNA encoding rainbow trout androgen receptors

Area of Science:

• Molecular Endocrinology
• Comparative Genomics
• Fish Biology

Background:

• Androgens are crucial for male sexual development, with their effects mediated by the androgen receptor (AR).
• Understanding AR function in non-mammalian vertebrates like rainbow trout provides insights into receptor evolution and function.

Purpose of the Study:

• To isolate and characterize novel rainbow trout androgen receptor cDNA clones.
• To investigate the functional differences between distinct rainbow trout AR isoforms.

Main Methods:

• Isolation of two rainbow trout AR cDNA clones (rtAR-alpha and rtAR-beta).
• Co-transfection assays to assess transcriptional activity using an androgen-responsive reporter gene.
• Chimera analysis involving rtAR-alpha, rtAR-beta, and rtGR-I (glucocorticoid receptor).
• Hormone-binding assays using [3H]mibolerone.

Main Results:

• Two distinct rainbow trout AR clones, rtAR-alpha and rtAR-beta, were identified with 85% amino acid sequence identity.
• rtAR-alpha activated transcription, while rtAR-beta did not, despite high sequence homology.
• The ligand-binding domain of rtAR-beta was identified as the region responsible for its inactivity.
• rtAR-alpha exhibited specific [3H]mibolerone binding, whereas rtAR-beta showed no detectable binding.

Conclusions:

• Rainbow trout possess at least two functional AR isoforms with differing activities.
• The inability of rtAR-beta to bind androgens explains its lack of transactivation activity.
• These findings highlight functional specialization within ARs in fish, impacting androgen signaling pathways.