Developmental expression in the mouse nervous system of the p493F12 SAP kinase.

Mitogen-activated protein (MAP) kinases are proline-directed, serine/threonine kinases that respond to a variety of extracellular signals. A subgroup of these kinases, stress-activated protein (SAP) kinases, phosphorylate c-jun in response to cellular stress. Using monoclonal antibody (MAb) 3F12, we have cloned and partially characterized p493F12 kinase, a mouse homologue of the rat SAP beta kinase and described its expression in the adult and developing mouse. Unlike previously reported MAP and SAP kinases, it is primarily expressed as a 2.7 kb transcript in neurons in the nervous system of the adult mouse. A 2.4 kb transcript is also expressed in the testis. Immunocytochemically, MAb 3F12 decorates a loop-like structure encircling the nucleus in the cytoplasm of neurons in the adult brain, and distinct perinuclear dots in the embryos. In situ hybridization first reveals expression in post-mitotic neurons, on embryonic day 11. The mRNA is also expressed in the Neuro-2A neuroblastoma cell line and is not upregulated in response to differentiating agents. The neuronal specificity of this kinase suggests the presence of a signal transduction cascade unique to neurons. As the amino acid sequence is highly conserved in the human and mouse, the latter may serve as a model for regulation and expression of this kinase.