ABSTRACT
Growth factors and their receptors function in the nervous system to induce proliferation and differentiation of neuronal precursor cells and to support survival of mature neurons. We have isolated a murine growth factor receptor tyrosine kinase using an anti-phosphotyrosine antibody screening procedure and studied the pattern of expression. The deduced amino acid sequence of the kinase has all the characteristics of a growth factor receptor and consists of a putative extracellular domain, a transmembrane domain, and a tyrosine kinase domain. Sequence comparison with known receptor tyrosine kinases indicated that the murine kinase is a mouse homolog of tyro3. tyro3 belongs to the Axl/Ufo growth factor receptor family. In the putative extracellular domain, there are two Ig-like domains and two fibronectin type III repeats which are conserved in other members of the Axl/Ufo family receptors. Northern blot hybridization analysis showed that tyro3 is expressed at high levels in the brain of adult mice, although considerable expression was also observed in the testis. In situ hybridization analysis revealed that high levels of tyro3 are expressed in the cerebral cortex, the lateral septum, the hippocampus, the olfactory bulb, and in the cerebellum. The highest levels of tyro3 expression in the brain are associated with neurons. The preferential expression of tyro3 in specific regions of the adult mouse brain suggests that tyro3 may function as a novel neurotrophic factor receptor.
Subject(s)
Brain/physiology , Protein-Tyrosine Kinases/genetics , Receptors, Nerve Growth Factor/genetics , Amino Acid Sequence , Animals , Cerebellum/physiology , Cerebral Cortex/physiology , DNA, Complementary , Gene Expression , Hippocampus/physiology , In Situ Hybridization , Mice , Molecular Sequence Data , Protein-Tyrosine Kinases/isolation & purification , Protein-Tyrosine Kinases/physiology , Receptors, Nerve Growth Factor/physiology , Sequence AnalysisABSTRACT
Chemical synthesis of peptides, though feasible, is hindered by considerations of cost, purity, and efficiency of synthesizing longer chains. Here we describe a transgenic system for producing peptides of therapeutic interest as fusion proteins at low cost and high purity. Transgenic hemoglobin expression technology using the locus control region was employed to produce fusion hemoglobins in the erythrocytes of mice. The fusion hemoglobin contains the desired peptides as an extension at the C end of human alpha-globin. A protein cleavage site is inserted between the C end of the alpha-globin chain and the N-terminal residue of the desired peptide. The peptide is recovered after cleavage of the fusion protein with enzymes that recognize this cleavage signal as their substrate. Due to the selective compartmentalization of hemoglobin in the erythrocytes, purification of the fusion hemoglobin is easy and efficient. Because of its compact and highly ordered structure, the internal sites of hemoglobin are resistant to protease digestion and the desired peptide is efficiently released and recovered. The applicability of this approach was established by producing a 16-mer alpha-endorphin peptide and a 26-mer magainin peptide in transgenic mice. Transgenic animals and their progeny expressing these fusion proteins remain health, even when the fusion protein is expressed at > 25% of the total hemoglobin in the erythrocytes. Additional applications and potential improvements of this methodology are discussed.
