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Two functionally different protein isoforms are produced from the chicken estrogen receptor-alpha gene
C Griffin1, G Flouriot, V Sonntag-Buck
1European Molecular Biology Laboratory, Heidelberg, Germany.
Molecular Endocrinology (Baltimore, Md.)
|September 9, 1999
Summary
Researchers discovered two chicken estrogen receptor-alpha (ER-alpha) protein forms. One form is truncated, leading to distinct gene expression modulation and ligand-independent activity, suggesting a common feature in egg-laying species.
Area of Science:
- Molecular Biology
- Endocrinology
- Genetics
Background:
- The chicken estrogen receptor-alpha (ER-alpha) protein is crucial for estrogen signaling.
- Previous studies identified a 66 kDa ER-alpha form (form I).
- The functional diversity of ER-alpha isoforms in non-mammalian vertebrates remains incompletely understood.
Purpose of the Study:
- To identify and characterize novel isoforms of chicken ER-alpha (cER-alpha).
- To investigate the differential functional properties of cER-alpha isoforms.
- To explore the evolutionary conservation of ER-alpha isoforms in oviparous species.
Main Methods:
- SI nuclease mapping to analyze mRNA transcripts.
- Western blotting to detect protein isoforms.
- Reporter gene assays to assess functional activity.
Main Results:
- Two cER-alpha protein forms were identified: a 66 kDa form I and a novel 61 kDa form II, lacking N-terminal amino acids.
- Form II is encoded by a distinct mRNA (A2) transcribed from a specific promoter and is liver-enriched.
- The two cER-alpha forms exhibit differential abilities to modulate estrogen target gene expression in a promoter- and cell type-specific manner.
- Form II displays partial ligand-independent transactivating or repressing activity, unlike the strictly ligand-dependent form I.
Conclusions:
- The chicken ER-alpha gene produces two functionally distinct protein isoforms.
- The truncated form II exhibits unique ligand-independent activity.
- The existence of two ER-alpha isoforms is likely a conserved feature in oviparous species, as evidenced by similar findings in Xenopus laevis and rainbow trout.