Characterization of the equine glycogen debranching enzyme gene (AGL): Genomic and cDNA structure, localization, polymorphism and expression.

The article explores the characteristics of the glycogen debranching enzyme gene (AGL) in horses. In particular, the research focuses on the structure, location, variation and expression of this gene.

Introduction and Significance of AGL

• The glycogen debranching enzyme (AGL) plays a crucial role in the glycogen degradation pathway. In humans, a deficiency in AGL activity can lead to a type III glycogen storage disease known as Cori-Forbes disease.
• A unique property of AGL gene expression is the occurrence of multiple alternative splicing in its 5′ region, meaning there are variations in the way the gene sequences are arranged.

Equine AGL Features

• The study identified the location of the AGL gene on ECA5q14-q15. Additionally, it determined that the sequence of the equine cDNA was 7.5kb in length with an open reading frame of 4602 base pairs. The gene is 69kb long and includes 35 exons.
• The researchers discovered that the AGL gene is ubiquitously expressed in horses and shows five tissue-dependent cDNA variants arising from alternative splicing of the first exons.

Comparison with Human AGL

• The AGL gene in horses’ skeletal muscles and heart contains four out of the six variants observed in humans, while the equine liver expresses three of these four human variants. The research also uncovered a new alternative splicing variant in equine skeletal and heart muscles.

Protein Isoforms and SNPs

• All mRNA variants of the AGL gene in horses likely encode only two different protein isoforms consisting of 1533 and 1377 amino acids.
• The research identified four single nucleotide polymorphisms (SNPs) in horse AGL mRNA. SNPs are variations at a single point in a DNA sequence.

Promoter Sequence

• The predicted equine promoter sequence revealed its structure to be similar to other mammalian species. However, the arrangement of transcription factor binding sites did not correspond with transcription start sites of tissue-specific variants. This suggests factors other than the original promoter sequence may influence transcription initiation.