Molecular cloning and characterization of chicken neuronal intermediate filament protein α-internexin.

α-Internexin is one of the neuronal intermediate filament (IF) proteins, which also include low-, middle-, and high-molecular-weight neurofilament (NF) triplet proteins, designated NFL, NFM, and NFH, respectively. The expression of α-internexin occurs in most neurons as they begin differentiation and precedes the expression of the NF triplet proteins in mammals. However, little is known about the gene sequence and physiological function of α-internexin in avians. In this study we describe the molecular cloning of the mRNA sequence encoding the chicken α-internexin (chkINA) protein from embryonic brains. The gene structure and predicted amino acid sequence of chkINA exhibited high similarity to those of its zebrafish, mouse, rat, bovine, and human homologs. Data from transient-transfection experiments show that the filamentous pattern of chkINA was found in transfected cells and colocalized with other endogenous IFs, as demonstrated via immunocytochemistry using a chicken-specific antibody. The expression of chkINA was detected at the early stage of development and increased during the developmental process of the chicken. chkINA was expressed widely in chicken brains and colocalized with NF triplet proteins in neuronal processes, as assessed using immunohistochemistry. We also found that chkINA was expressed abundantly in the developing cerebellum and was the major IF protein in the parallel processes of granule neurons. Thus, we suggest that chkINA is a neuron-specific IF protein that may be a useful marker for studies of chicken brain development.