Molecular cloning and expression of equine calcitonin, calcitonin gene-related peptide-I, and calcitonin gene-related peptide-II.

This study involves the successful cloning and tissue expression testing of horse (equine) versions of calcitonin (CT), and two versions of calcitonin-gene-related peptide (CGRP-I and CGRP-II). The findings include a new variant of CGRP (CGRP-I), and showed that these peptides have varying degrees of similarity with versions found in other animals.

Cloning and Tissue Expression of CT and CGRP in Horses

• The researchers successfully cloned different types of calcitonin gene-related peptides (CGRPs) and calcitonin (CT) from horses.
• The DNA sequence of the horse version of CT was found to have over 85% similarity with human, rat and mouse versions, and the DNA of horse CGRP-II showed over 80% similarity with chickens, humans, rats, sheep, pigs, and cows.
• The DNA sequence of the horse version of CGRP-I, however, was not similar to CGRPs from any other species, showing less than 59% similarity. A new, different form of CGRP-I was discovered during this search for similarities.
• The researchers learned that the genes for horse CT and CGRP-I result in the creation of identical signal and N-terminal peptides. This indicated that these two peptides are created from a gene that is similar to the human CALC-I gene.

Expression Patterns of CT and CGRP in Different Tissues

• The researchers used Northern blot analysis to understand where these genes are expressed in horse tissue.
• The expression of CT gene was mainly found in the thyroid gland. However, using another testing method (RT-PCR), the researchers found that the CT gene was also expressed in the pituitary gland and the liver.
• Both CGRP-I and CGRP-II genes were found in various parts of the nervous system and other tissues of neuroectodermal origin. An unexpected finding was the discovery of CGRP-I gene expression in the kidney. This was confirmed by both Northern analysis and RT-PCR testing.

Implications of the Findings

• The researchers believe that CT might play an important role in regulating cell function in the pituitary gland because its mRNA was found in the gland.
• Both versions of CGRP were widely expressed in the central and peripheral nervous system. This shows that those genes are likely crucial to the function of these systems.
• The novel form of CGRP-I and its presence in the kidney raise new lines of inquiry for the role this peptide may be playing in equine health and disease.
• The data from this study is useful for further investigation into the roles of CT, CGRP-I, and CGRP-II play in horses, which will help in understanding and treating equine health issues.