Required for small ribosomal subunit biogenesis in neuroblasts (PubMed:24615015). Plays a role in mushroom body development (PubMed:15375215). Nuclear from interphase until early prophase and is then redistributed to the cytoplasm during mitosis when the nucleus is disassembled. Shows widespread expression in third instar larval brain with no apparent difference between males and females (at protein level). Detected at low levels in the mushroom body neuropil and is also expressed in many cells of the brain outside the mushroom body (at protein level). Not detected in third instar larval brain cells in anaphase (at protein level). Detected in male and female third instar larvae with very low levels detected in adults (at protein level). May be phosphorylated in vivo by CkIIalpha. mbm and CkIIalpha colocalize to the nucleolus and mbm is phosphorylated in vitro by CkIIalpha. Lethality around pupal formation with rare escapers with a delayed eclosion time (PubMed:24615015). Reduced size of neuroblasts and ganglion mother cells with no effect on cell size in wing imaginal disks (PubMed:24615015). Grossly reduced mushroom bodies with degeneration of Kenyon cells (PubMed:15375215).