Identification and dynamic transcription of KIF3A homologue gene in spermiogenesis of Octopus tankahkeei

KIF3A is a subunit of the heterotrimeric Kinesin-II motor which achieves fame for its pivotal roles in the assembly and maintenance of cilia and flagella and in intracellular transport of membrane bound organelles and protein complexes in various tissues. Its intimacy to the cell's antenna, namely the primary cilia, makes it also involved in some signaling transduction pathways. To test the idea that KIF3A functions during spermiogenesis of the octopod Octopus tankahkeei, we hereby identified a gene (designated as ot-kif3a) encoding a protein apparently homologous to a group of KIF3As, from the testis of this organism. The full-length ot-kif3a comprised a 344 bp 5' untranslated region, a 2241 bp open reading frame and a 147 bp 3' untranslated region. The putative protein consisted of 746 amino acid residues with a calculated molecular weight of 85 kDa and a predicted isoelectric point of 6.36. It shared an overall sequence identity of 69%, 69%, 69% and 67% to KIF3A from Homo sapiens, Rattus norvegicus, Mus musculus and Danio rerio, respectively. Tissue distribution profile analysis unraveled its presence in all the tissues examined. In situ hybridization of mRNA in spermionenic cells demonstrated that ot-kif3a was expressed moderately at the beginning of spermiogenesis. The abundance of transcripts increased in intermediate spermatid and peaked in drastically remodeling and final spermatids. In mature sperm, the message was still visible in the head and tail. The temporal and spatial expression dynamics of ot-kif3a during spermiogenesis supports the possibility that the putative motor protein, OtKIF3A, participates in the major cytological events during this differentiation program and is vital for the acquisition of the final cellular phenotype.