Unique structure of the M loop region of β1-tubulin may contribute to size variability of platelets in the family Felidae

Background: Platelet size is relatively uniform in mammals except for domestic cats. Uniform platelet production by megakaryocytes can be disrupted if microtubule assembly or dynamics is impaired. Mutations in the gene encoding β1-tubulin have been documented in dogs and people, and the resulting microtubule effects have been associated with production of large platelets. Objectives: The objectives of this study were to evaluate morphology of platelets on feline blood smears, determine the gene sequences encoding β1-tubulin in members of the family Felidae, and compare the findings with those in other mammalian species to determine whether predicted structural differences in β1-tubulin that might affect microtubule stability or assembly were present. Methods: At least 100 platelets/smear on blood smears from 15 domestic cats and 88 big cats were evaluated to assess platelet size variability. Platelet-derived cDNA obtained from a domestic cat and genomic DNA isolated from blood samples of domestic cats and other members of the family Felidae were analyzed by PCR using primers specific for β1-tubulin. Gene sequences obtained were compared with those of other common mammals. Results: Two differences in gene sequence were found in a highly conserved region encoding the M loop of β1-tubulin in members of the family Felidae compared with sequences from other species. Platelet size variation was present in big cats and domestic cats. In addition, a rare amino acid change was documented in the C-terminal region encoding the H11 helix in domestic cats. Conclusion: Members of the family Felidae have an altered M loop region in β1-tubulin compared with other mammals. This variation may contribute to the observed platelet size variability.