YPEL5 is a member of the YPEL gene family that is highly conserved in the eukaryotic species and apparently involved in a certain cell division-related function. In this study, we examined the functional and phylogenetic aspects of YPEL5 protein in more detail. During cell cycle, YPEL5 protein was detected at different subcellular localizations; at interphase, it was located in the nucleus and centrosome, then it changed location sequentially to spindle poles, mitotic spindle, and spindle midzone during mitosis, and finally transferred to midbody at cytokinesis. Knockdown of YPEL5 function by siRNA or anti-sense morpholino oligonucleotide inhibited the growth of cultured COS-7 cells and early development of medaka fish embryos, indicating its involvement in cell cycle progression. Interestingly, RanBPM (Ran Binding Protein in the Microtubule organizing center, encoded by RANBP9) was identified as a YPEL5-binding protein by yeast two-hybrid method. A paralog of RanBPM, namely RanBP10 (encoded by RANBP10), was found to be another YPEL5-binding protein, and these two protein genes are highly conserved each other. Comparative genomic analysis allowed us to define a new gene family consisting of RanBPM and RanBP10, named Scorpin, providing a basis to better understand how they interact with YPEL5.
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