Avian metallothioneins: structure, regulation and evolution

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Metallothioneins (MTs) are cysteine-rich proteins involved in metal homeostasis and detoxification.
• Avian MT gene families are relatively simple, with conserved structures and sequences across species.
• MT gene expression is regulated by various factors, including metal ions, stress, and developmental stages.

Purpose of the Study:

• To review studies on the molecular biology of avian metallothionein (MT) genes.
• To analyze the structure, function, and regulation of MT genes in birds.
• To investigate the cis-acting elements and transcription factors involved in MT gene induction.

Main Methods:

• Analysis of cloned avian MT genes and cDNAs.
• Comparison of nucleotide sequences of turkey and chicken MT genes.
• Structure-function studies using transient transfection assays and transgenic mice.

Main Results:

• Avian MT gene families are simple, with identical major MT protein sequences across species.
• Chicken MT genes are inducible by metal ions (Zn, Cu), LPS, and oxidative stress, and expressed during liver development.
• A conserved metal-responsive enhancer in the proximal promoter region of chicken and turkey MT genes regulates expression via transcription factors and Sp1 binding sites.

Conclusions:

• Avian MT genes exhibit remarkable sequence conservation and a simple gene family structure.
• The identified metal-responsive enhancer plays a key role in regulating MT gene expression in response to metal ions.
• Understanding MT gene regulation provides insights into metal homeostasis and cellular defense mechanisms in birds.