Novel Mitotic Functions of Stem Loop-Binding Protein (SLBP)

Abstract

Histone pre-mRNAs are the only animal mRNAs known to lack a polyA tail, instead ending in a conserved 16-nucleotide stem loop. Stem Loop-Binding Protein (SLBP) binds this structure, facilitating the processing into mature mRNA, and functioning in exporting this mRNA from the nucleus for translation. The loss of SLBP in humans results in Wolf-Hirschhorn Syndrome, highlighting the importance of SLBP function in cellular and developmental processes. Previous studies have shown that loss of SLBP in Drosophila leads to pleiotropic effects that have been attributed to DNA damage caused by a lack of histone protein. However, reducing histone levels themselves does not cause DNA damage, suggesting SLBP may have additional cellular functions. We have previously found that Drosophila SLBP localises to the spindle area during mitosis and that it biochemically associates with a large number of proteins involved both in translational control, and in cell cycle regulation. In this study I investigate the possibility that SLBP functions in mitosis in the early Drosophila embryo. Using RNAseq I demonstrate that SLBP does not differentially associate with the mRNAs of the interacting proteins. In contrast, I show that loss of SLBP results in mis-localisation of at least some of these interactors; suggesting that, rather than regulating their translation, SLBP is involved in directly regulating the function of these proteins. I also show that RNAi of SLBP in the embryo results in a wide variety of problems which can be classified as a DNA damage-like response; however, these defects can occur in the absence of DNA damage. I suggest a hypothesis for how SLBP functions to control so many proteins with such a wide variety of functions, through co-ordination with the DNA damage response checkpoint kinase 2 (CHK2).