Expression and localization of receptor tyrosine kinase Tyro3 in rat brain.

Objective: To detect the expression patterns and localization of the Tyro3, Axl, and Mer (TAM) receptor tyrosine kinases in the rat brain, and to understand the significance of this receptor family in the brain.

Methods: Sprague Dawley rats aged P3 (day 3 of postnatal development), P9, P15, P30 and P52 were anesthetized and their brains removed. Real time quantitative PCR was used to determine mRNA expression levels of TAM. Western blotting was applied to analyze protein expression levels of TAM peptides. The immunohistochemical stainings of Tyro3 protein in adult rat brains were detected by the avidin-biotin-peroxidase complex method.

Results: Tyro3 was the most highly expressed and widely distributed receptor among TAM family. Its mRNA level increased dramatically during the second postnatal week, reached at the highest level by P30, and remained at that level in the adult. The relative expression quantitative of Tyro3 mRNA in the adult rat brain increased about 3.2-fold than that at P15 stage. The expression of Tyro3 protein was detected faintly at early stage, gradually increased from P15, and reached maximal levels at adult stage. The relative density of immunoreactive product of Tyro3 peptide in the rat brain was up-regulated 1.3-fold from P15 to adult (P52). Immunohistochemical stainings demonstrated that Tyro3 protein was detected in the majority of cells of all the cortical layers. Strong signals were observed in the piriform cortex and the hippocampus. At the subcellular level, Tyro3 was detected both in the soma and dendrites of pyramidal neurons.

Conclusion: The results imply that Tyro3 is the main TAM receptor tyrosine kinase expressed in adult rat brain that modulates signaling cascades influencing synaptic function in the brain.