TMEM209/NPP-28 partitions PLK-1 between the nuclear envelope and nuclear interior during mitosis
The onset of mitosis in animal cells is marked by nuclear envelope breakdown (NEBD), which requires coordinated disassembly of nuclear pore complexes (NPCs) and the nuclear lamina. Polo-like kinase 1 (Plk1/PLK-1) initiates NEBD through phosphorylation of NPC components, but mechanisms that spatially regulate PLK-1 between NPCs and the nuclear interior are unclear. Here, we identify the Caenorhabditis elegans TMEM209 homolog NPP-28 as a transmembrane nucleoporin that concentrates PLK-1 at the nuclear envelope while limiting its nuclear accumulation to promote NEBD. We identify docking sites within NPP-28 that mediate PLK-1 nuclear envelope-association. NPP-28 is phosphorylated by PLK-1 in vitro, and mutational analysis suggests that NPP-28-mediated docking facilitates NEBD, whereas phosphorylation prevents premature NEBD. Simultaneous loss of npp-28 and the transmembrane nucleoporin npp-12/gp210 exacerbates mitotic NEBD defects in early embryos and causes severe defects in germline development. Together, our findings identify NPP-28 as a spatial regulator of PLK-1 during mitosis with functional relationships with other conserved transmembrane nucleoporins depending on context.