Cloning and tissue expression of the equine transferrin receptor

Characterization of anemia in horses presents a challenge, as they do not release reticulocytes into peripheral blood. Transferrin receptor (TfR) expression is highest on erythroid cells in people and rats, and measurement of a soluble serum form (sTfR) is used to quantify erythropoiesis in these species. We hypothesized that equine TfR (eTfR) expression is similar in quantity and distribution to that in these other species and thus has potential for characterization of the regenerative response in anemic horses.

This study was conducted to clone and sequence the eTfR gene and measure expression levels using quantitative real-time PCR and immunohistochemical (IHC) staining.

Total RNA from equine bone marrow was used to produce cDNA. The eTfR gene was amplified using pooled gene-specific primers, and PCR products were sequenced. Rapid amplification of cDNA ends was used to obtain the first 22 nucleotides of the coding sequence. Quantitative PCR was performed using eTfR gene-specific primers, and IHC staining was used to localize TfR protein expression.

The deduced amino acid (aa) sequence (767 aa) of the eTfR was 75-83% identical with sequences of the receptor in several other mammals. As in people and rats, eTfR mRNA expression was highest in the bone marrow, and distribution in other tissues was also similar.

The eTfR gene is similar to that of other mammals in structure and expression levels. We hypothesize that it is also similar in function and that, following development of an immunoassay, determining sTfR concentrations will be useful for identifying the regenerative response in anemic horses.