The C-terminal tail domain of neurofilament protein-H (NF-H) forms the crossbridges and regulates neurofilament bundle formation.

In order to study the role of NF-H in a neurofilament network formation in neurons, we coexpressed NF-H with neurofilament protein-L (NF-L) in Sf9 cells using the baculovirus expression system. Electron microscopy observations revealed that parallel arrays of 10 nm filaments with frequent crossbridges between adjacent filaments were formed in the cytoplasm of Sf9 cells infected with the recombinant virus that co-expressed NF-L and NF-H. To explore the function of the C-terminal tail domain of NF-H, various deletion mutants lacking portions of the tail domain were constructed, and each of them was coexpressed with NF-L. The results show that the tail domain of NF-H is a structural component of crossbridges and is involved in parallel bundle formation of neurofilaments, as core filaments of the axon. The last 191 amino acids of the C-terminal tail domain of NF-H play a key role in crossbridge formation.