The first contiguous estrogen receptor gene from a fish, Oreochromis aureus: evidence for multiple transcripts

Area of Science:

• Molecular Biology
• Genomics
• Endocrinology

Background:

• The estrogen receptor (ER) is crucial for reproductive and metabolic functions.
• Piscine estrogen receptors are vital for understanding fish endocrine systems.
• Characterizing the O. aureus ER gene provides insights into fish-specific adaptations.

Purpose of the Study:

• To clone and characterize the complete O. aureus estrogen receptor (OaER) gene.
• To investigate the structural features and regulatory mechanisms of the OaER gene.
• To explore alternative transcriptional start sites and polyadenylation in estrogen-induced OaER expression.

Main Methods:

• Gene cloning and sequencing of the O. aureus ER gene.
• Intron-exon structure analysis and comparison with human ER.
• Promoter region analysis for regulatory elements.
• RT-PCR and SI nuclease mapping to identify transcriptional start sites and polyadenylation signals.

Main Results:

• The 40.4 kb OaER gene has ten exons with two unique introns (I and V).
• The promoter lacks TATA/CAAT boxes but contains putative regulatory elements, including an imperfect estrogen response element (ERE).
• OaER exhibits conserved C and E domains, a long F domain (77 amino acids), and a long 3' UTR.
• Estrogen induction leads to alternative transcriptional start sites and polyadenylation, generating up to four distinct OaER transcripts.

Conclusions:

• The OaER gene structure presents unique features compared to other vertebrate ER genes.
• Autoregulation of OaER expression is suggested by the ERE location.
• Alternative transcription and polyadenylation contribute to transcript diversity in O. aureus ER, impacting gene regulation.