Changing expression and subcellular distribution of karyopherins during murine oogenesis

Mammalian oocyte growth and development is driven bya strictprogramof gene expression that relieson the timely presence of transcriptional regulators via nuclearpores.By targeting specific cargos for nucleo-cytoplasmic transport, karyopherin (KPN)proteins are key to the relocation of essential transcription factors and chromatin-remodelling factors into and out of the nucleus. Using multiple complementary techniques, here we establish that KPNA genes and proteins are dynamically expressed and relocalised throughout mouse oogenesis and folliculogenesis. Of the KPNAs examined (Kpna1, Kpna2, Kpna3, Kpna4, Kpna6, Kpna7, Kpnb1, Ipo5 and Xpo1), allwere expressed in the embryonic ovarywith up-regulation of protein levels concomitant with meiotic entry for KPNA2, accompanied by the redistribution of the cellular localisation of KPNA2 and XPO1. In contrast, postnatal folliculogenesis revealed significant up-regulation of Kpna1, Kpna2, Kpna4, Kpna6 and Ipo5 and down-regulation of Kpnb1, Kpna7 and Xpo1 at the primordial to primary follicle transition. KPNAs exhibited different localisation patterns in both oocytes and granulosa cells during folliculogenesis, with three KPNAs - KPNA1, KPNA2 and IPO5 - displayingmarked enrichment in the nucleus by antral follicle stage. Remarkably, varied subcellular expression profiles were also identified in isolated pre-ovulatory oocytes with KPNAs KPNA2, KPNB1 and IPO5 detected in the cytoplasmand at the nuclear rimand XPO1 in cytoplasmic aggregates. Intriguingly, meiotic spindle stainingwas also observed for KPNB1 and XPO1 inmeiosis II eggs, implying roles for KPNAs outside of nucleo-cytoplasmic transport. Thus, we propose that KPNAs, by targeting specific cargoes, are likely to be key regulators of oocyte development.