THE CA2-PROTEIN, FREQUENIN IS A NERVOUS SYSTEM-SPECIFIC PROTEIN IN MOUSE PREFERENTIALLY LOCALIZED IN NEURITES( BINDING)

Frequenin is a Ca2+-binding protein that has been implicated in the re gulation of neurotransmitter release at the neuromuscular junction [15 ,16]. However, its cellular and subcellular localization in brain have not been determined. Therefore, we cloned mouse frequenin (Mfreq) and investigated its expression both in vivo and in vitro. The amino acid sequence of Mfreq is homologous to that of frequenins from other spec ies. Northern and Western blot analyses indicated that the Mfreq mRNA is a single species of 4.2 kb, and that the protein has a mass of 24 k Da protein on SDS gel, respectively. Expression of Mfreq is nervous sy stem specific. However, Mfreq mRNA and protein are widely distributed in the brain, spinal cord, and dorsal root ganglia. Mfreq is expressed in early embryonic brain and the levels of Mfreq remain high througho ut development. In situ hybridization and immunocytochemistry demonstr ated that Mfreq is expressed primarily in neurons and presumptive astr ocytes. The Mfreq protein was preferentially localized in neurites (de ndrites and axons). Double immunofluorescence microscopy established t hat Mfreq was co-localized with the dendritic marker, MAP-2 and the sy napse marker, SV2 in cultured hippocampal neurons. The distribution an d subcellular localization of Mfreq may help understand its cellular f unction.