Cloning and sequencing of an equine insulin-like growth factor I cDNA and its expression in fetal and adult tissues.

This research isolated and sequenced an equine insulin-like growth factor I (IGF I) cDNA, comparing it with its human counterpart and studying its expression in both adult and fetal horse tissues.

Isolation and Sequencing of Equine IGF I cDNA

• The researchers successfully isolated a cDNA for the equine insulin-like growth factor I (IGF I) by using reverse transcriptase-polymerase chain reaction, a method to generate specific DNA sequences from RNA templates.
• This cDNA was then sequenced, revealing a fragment containing 465 base pairs (bp).

Characteristics of the Sequenced cDNA

• The sequenced fragment included the coding regions for the signal peptide, the entirety of the mature protein, as well as 4 amino acids into the E-peptide. In proteins, the signal peptide guides the protein to specific destinations in a cell, while the E-peptide has been associated with enhancing growth factor activity.
• The mature equine IGF I peptide, akin to its human equivalent, contains 70 amino acids and showed 100% homology between the horse and human, meaning it has identical amino acid sequences in both species.
• The 49-amino-acid signal peptide had a small difference: whereas the human signal peptide possesses a threonine at position 26, the equine one has an isoleucine instead.

Nucleotide Homology Across the Entire Clone

• Upon examining the nucleotide homology across the entire cDNA clone, there was a 96.3% similarity between horse and human, and 91.6% similarity between horse and rat.
• The nucleotide homology refers to the percentage of identical nucleotide sequences (the building blocks of DNA) in a given genomic region of two or more species, suggesting a common evolutionary origin.

cDNA Hybridization in Fetal and Adult Tissues

• The study also found that the isolated cDNA hybridized to the same transcripts in both fetal and adult tissues. This shows a conservation of function and sequence in both developmental stages, meaning that the gene’s function is maintained throughout the development of the horse.