A novel neuron-enriched homolog of the erythrocyte membrane cytoskeletal protein 4.1

We report the molecular cloning and characterization of 4.1N, a novel neuro nal homolog of the erythrocyte membrane cytoskeletal protein 4.1 (4.1R). Th e 879 amino acid protein shares 70, 36, and 46% identity with 4.1R in the d efined membrane-binding, spectrin-actin-binding, and C-terminal domains, re spectively. 4.1N is expressed in almost all central and peripheral neurons of the body and is detected in embryonic neurons at the earliest stage of p ostmitotic differentiation. Like 4.1R, 4.1N has multiple splice forms as ev idenced by PCR and Western analysis. Whereas the predominant 4.1N isoform i dentified in brain is similar to 135 kDa, a smaller 100 kDa isoform is enri ched in peripheral tissues. Immunohistochemical studies using a polyclonal 4.1N antibody revealed several patterns of neuronal staining, with localiza tions in the neuronal cell body, dendrites, and axons. In certain neuronal locations, including the granule cell layers of the cerebellum and dentate gyrus, a distinct punctate-staining pattern was observed consistent with a synaptic localization. In primary hippocampal cultures, mouse 4.1N is enric hed at the discrete sites of synaptic contact, colocalizing with the postsy naptic density protein of 95 kDa (a postsynaptic marker) and glutamate rece ptor type 1 (an excitatory postsynaptic marker). By analogy with the roles of 4.1R in red blood cells, 4.1N may function to confer stability and plast icity to the neuronal membrane via interactions with multiple binding partn ers, including the spectrin-actin-based cytoskeleton, integral membrane cha nnels and receptors, and membrane-associated guanylate kinases.