Previous studies have demonstrated that the

Previous studies have demonstrated that the expression of the Aurora B gene is maximally increased at G2/M phage during mitosis (Honda et al., 2003, Fu et al., 2007, Goldenson and Crispino, 2015), and exhibits an extraordinary upregulation in a number of human cancers (Fu et al., 2007, Kollareddy et al., 2008). Intriguingly, we found that BmAurB was highly expressed in testis and ovary of silkworm larvae on the middle of final larval instar. It has been reported that cell proliferation phase of either spermatogenesis in testis or oogenesis in ovary occur at late larval stage in silkworm (Xiang, 1995). Therefore, our results indicate that BmAurB may be involved in the regulation of both spermatogenesis and oogenesis. In addition, DPQ mg and silk gland of silkworm larvae undergo mitotic cycle and endocycle, respectively (Maqbool et al., 2010, Zhang et al., 2012, Zielke et al., 2013). Our data demonstrate that BmAurB expression can be detected in brain but not in silk gland during silkworm larval development, suggesting that BmAurB is essential for mitotic progression in silkworm. Generally, the ablation of Aurora B has no effect on mitotic entry but disrupts the mitotic progression, resulting in an abnormality of chromosomal segregation, the spindle assembly checkpoint, and cytokinesis (Fu et al., 2007, Goldenson and Crispino, 2015). In fact, the suppression of endogenous BmAurB in silkworm BmN4-SID1 cells by RNAi or specific inhibitor also led to similar phenotypes, like chromosome segregation error, G2/M arrest, and accumulation of polyploid cells, confirming that BmAurB is critical for proper cytokinesis in silkworm. In addition, extensive studies have demonstrated that Aurora B is involved in mitotic progression by phosphorylating multiple substrates (Fu et al., 2007, Goldenson and Crispino, 2015), like histone H3 that is required for chromatin condensation and separation during mitosis (Adams et al., 2001, Giet and Glover, 2001, Hirota et al., 2005), and serves as a mitotic marker (Hendzel et al., 1997). Interestingly, our data also showed that the phosphorylation of H3 (pH3) was also decreased after BmAurB RNAi or treatment with AZD1152-HQPA as Aurora B inhibitor, suggesting that the regulation of BmAurB on silkworm cytokinesis might also depend on its phosphorylation on H3. Taken together, our data strongly indicate a functional conservation of Aurora B in mitotic progression in metazoan.
Conclusions In this study, we cloned and characterized full-length cDNA of the Aurora B gene (BmAurB) from silkworm. Phylogenetic analysis suggests that the separation of Aurora kinases may have occurred after separation between mammalian and insect. In addition, BmAurB exhibits a high expression in gonads, moderate expression in brain, and nonexpression in silk gland during silkworm larval development. The inhibition of BmAurB in silkworm BmN4-SID1 cells disturbs proper cytokinesis. Our next goal is to investigate the specific functions of the BmAurB kinase in gonad and silk gland during silkworm development.
Conflicts of interest
Acknowledgments This work was supported by grants from the National Natural Science Foundation of China (no. 31272503 and 31572464).
Histones are subjected to a variety of covalent post-translational modifications, including methylation, acetylation, phosphorylation, ubiquitination, etc. . Two serine residues (S10 and S28) at the N-terminal tail of canonical histone H3 are phosphorylated by Aurora kinase B (AURKB) during mitosis , , . H3.3 is a histone variant exhibiting replication-independent deposition at telomeres, pericentromeric regions, and active genes . H3.3 differs from H3.1 by 5 aa in sequence, including a serine-to-alanine substitution at position 31. Phosphorylation of H3.3S31 appears during mitosis in mammals, from late prometaphase to metaphase at pericentromeric heterochromatin . In human ALT cancer cells, large amounts of histone H3.3 serine 31 phosphorylation (H3.3S31ph) have been observed at chromosome arms, and CHK1 has been reported to be the corresponding kinase . H3.3S31ph enrichment at chromosome arms during anaphase is a signature of lagging or misaligned chromosomes; however, CHK1 inhibitors do not block the enrichment of H3.3S31ph at lagging chromosome arms . Thus, the kinase(s) responsible for H3.3S31 phosphorylation remains to be identified.