title: Expression of the receptor protein-tyrosine kinases Tyro-3, Axl, and mer in the developing rat central nervous system.
abstract: Tyro-3, Axl, and Mer are three related receptor protein-tyrosine kinases (RPTKs) characterized by an extracellular domain exhibiting significant amino acid sequence similarity to neural cell adhesion molecules. The molecule Gas6 (for growth arrest-specific gene-6) has been shown to activate each of these receptors. Gas6 is expressed extensively in the central nervous system (CNS), suggesting that interactions between Gas6 and its receptors are likely to have physiologically relevant functions. To identify and localize the relevant Gas6/RPTK pairs, we have characterized the developmental expression of Tyro-3, Axl, and Mer in rat CNS using blotting and mRNA in situ hybridization analyses. Throughout development, Tyro-3 was the most widely expressed of the three receptors in the CNS, with Axl and Mer detected in only a limited number of sites in the adult. Tyro-3 expression was low in the embryo and increased markedly during early postnatal stages, with a time course paralleling that of synaptogenesis. Axl and Mer were expressed at low but relatively constant levels throughout development. In the cerebellum, all three receptors were found in Purkinje cells, and Tyro-3 was also detected in both granule neurons and Bergmann glia. Insofar as Gas6 has been previously shown to also be expressed by Purkinje cells, it may be engaged in both autocrine and paracrine signaling. The three receptors were also detected in cerebellar white matter, primarily during myelination. In the cortex, Tyro-3 was expressed at high levels during postnatal development and in the adult. Beginning at P6 in the hippocampus, Tyro-3 was expressed at high levels in CA1 pyramidal neurons and at lower levels in CA3 and was not detected in dentate granule neurons. Axl and Mer were found in the molecular layer of the dentate gyrus and were absent from the pyramidal and dentate granule neurons. In that Gas6 is expressed throughout the pyramidal cell layer, it may activate these cells in both an autocrine and a paracrine manner. These studies provide initial clues for elucidating the cellular functions of the Axl subfamily members and suggest potential complex Gas6/RPTK as well as RPTK/RPTK signaling interactions in the mature and developing CNS.
authors.affiliation: Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Prieto
authors.forename: J L
authors.initials: JL
authors.lastname: Weber
authors.forename: C
authors.initials: C
authors.lastname: Lai
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002478:Cells, Cultured; D002490:Central Nervous System / Q000196:embryology* / Q000254:growth & development* / Q000378:metabolism; D002531:Cerebellum / Q000196:embryology / Q000254:growth & development / Q000378:metabolism; D002540:Cerebral Cortex / Q000196:embryology / Q000254:growth & development / Q000378:metabolism; D005333:Fetus; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D006624:Hippocampus / Q000196:embryology / Q000254:growth & development / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D009413:Nerve Fibers, Myelinated / Q000378:metabolism / Q000648:ultrastructure; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism*; D009457:Neuroglia / Q000166:cytology / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009836:Oligodendroglia / Q000166:cytology / Q000378:metabolism; D015513:Oncogene Proteins / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000196:embryology* / Q000254:growth & development* / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D000076202:c-Mer Tyrosine Kinase; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D019006:Neural Cell Adhesion Molecules; D015513:Oncogene Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C490765:Mertk protein, rat; C084944:TYRO3 protein, human