Intraflagellar transport (IFT) proteins are evolutionarily conserved throughout all ciliated organisms and are essential for the assembly and maintenance of cilia. IFT80, a component of the IF complex, was linked recently to a human developmental disorder, Jeune asphyxiating thoracic dystrophy. We report here identification and characterization of a human IFT80 long isoform (namely IFT80-L), the carboxyl terminus of which shares the protein sequence of IFT80. Sequence analysis indicates that IFT80-L is likely an evolutionarily merged product of genes IFT80 and TRIM59, a RING finger gene we reported previously. Expression analysis of IFT80-L demonstrates that IFT80-L is ubiquitously expressed in humans. By using the nerve growth factor-induced cell differentiation assays, we reveal that IFT80-L is highly expressed in the rapidly proliferating cells but not in differentiated cells, which withdraw from the cell cycle. Our findings suggest that IFT80-L, like other IFT proteins, plays an important role in cell proliferation and differentiation. (c) 2008 Published by Elsevier Inc.