EXPRESSION AND DEVELOPMENTAL REGULATION OF EHK-1, A NEURONAL ELK-LIKERECEPTOR TYROSINE KINASE IN BRAIN

Protein tyrosine kinases are pivotal in central nervous tissue develop ment and maintenance. Here we focus on the expression of Ehk-1, a nove l Elk-related receptor tyrosine kinase. Ehk-1 gene expression is obser ved in the developing and adult central nervous system and is highly r egulated throughout development at both the messenger RNA and protein levels. Three messenger RNA transcripts of 8.5, 5.9 and 5.1 kb are det ectable in the rat brain and a variety of splice possibilities have be en identified. However, a major protein species of around M(r) 120,000 predominates throughout development. Ehk-1 messenger RNA and protein levels are highest in the first postnatal week. By in situ messenger R NA hybridization the gene is expressed by all neurons of the adult bra in, but mostly in the hippocampus, cerebral cortex and large neurons o f the deep cerebellar nuclei, as well as the Purkinje and granular cel ls of the cerebellum. At earlier stages of development, transcripts ar e most prominent in the periventricular germinal layers of the brain. Immunohistochemistry reveals a pronounced membrane associated protein expression in immature neurons. In the adult animal, peak reactivity w as found in the neuropil with sparing of most perikarya. The spatial a nd temporal pattern of ehk-1 gene expression suggests a role in both t he development and maintenance of differentiated neurons of the centra l nervous system.