Summary Mammalian NIMA-like kinase-1 (NEK1) is a dual-specificity kinase highly expressed in mouse germ cells during prophase I of meiosis. Loss of NEK1 induces retention of cohesin on chromosomes at meiotic prophase I. Timely deposition and removal of cohesin is essential for accurate chromosome segregation. Two processes regulate cohesin removal: a non-proteolytic mechanism involving WAPL, Sororin, and PDS5B and direct cleavage by Separase. Herein, we demonstrate a role for NEK1 in the regulation of WAPL loading during meiotic prophase I, via an interaction between NEK1 and PDS5B. This regulation of WAPL by NEK1-PDS5B is mediated by the protein phosphatase PP1γ, which both interacts with, and is a phosphotarget, of NEK1. Taken together, our results reveal that NEK1 phosphorylates PP1γ leading to dephosphorylation of WAPL, which in turn results in its retention on chromosome cores to promote loss of cohesion at the end of prophase I in mammals.

NIMA-related kinase 1 (NEK1) is a serine/threonine and tyrosine kinase that is highly expressed in mammalian germ cells. Mutations in Nek1 induce anemia, polycystic kidney and infertility. In this study we evaluated the role of NEK1 in meiotic spindle formation in both male and female gametes. Our results show that the lack of NEK1 provokes an abnormal organization of the meiosis I spindle characterized by elongated and/or multipolar spindles, and abnormal chromosome congression. The aberrant spindle structure is concomitant with the disruption in localization and protein levels of myosin X (MYO10) and α-adducin (ADD1), both of which are implicated in the regulation of spindle formation during mitosis. Interaction of ADD1 with MYO10 is dependent on phosphorylation, whereby phosphorylation of ADD1 enables its binding to MYO10 on mitotic spindles. Reduction in ADD1 protein in NEK1 mutant mice is associated with hyperphosphorylation of ADD1, thereby preventing the interaction with MYO10 during meiotic spindle formation. Our results reveal a novel regulatory role for NEK1 in the regulation of spindle architecture and function during meiosis.

Telomeres are dynamic nucleoprotein structures capping the physical ends of linear eukaryotic chromosomes. They consist of telomeric DNA repeats (TTAGGG), the shelterin protein complex, and Telomeric Repeat-Containing RNA (TERRA). Proposed TERRA functions are wide-ranging and include telomere maintenance, telomerase inhibition, genomic stability, and alternative lengthening of telomere. However, the role of TERRA in primordial germ cells (PGCs), the embryonic precursors of germ cells, is unknown. Using RNA-fluorescence in situ hybridization (RNA-FISH) we identify TERRA in PGCs soon after these cells have migrated to, and become established in, the developing gonad. RNA-FISH showed the presence of TERRA transcripts in female PGCs at 11.5, 12.5 and 13.5 days post-coitum. In male PGCs, however, TERRA transcripts are observable from 12.5 dpc. Using qPCR we evaluated chromosome-specific TERRA expression, and demonstrated that TERRA levels vary with sex and gestational age, and that transcription of TERRA from specific chromosomes is sexually dimorphic. TERRA interacting proteins were evaluated using Identification of Direct RNA Interacting Proteins (iDRiP) which identified 48 in female and 26 in male protein interactors specifically within nuclear extracts from PGCs at 13.5 dpc. We validated two different proteins the splicing factor, proline- and glutamine-rich (SFPQ) in PGCs and Non-POU domain-containing octamer-binding protein (NONO) in somatic cells. Our results show that, TERRA interacting proteins are determined by sex in both PGCs and somatic cells. Taken together, our data indicate that TERRA expression and interactome during PGC development are regulated in a dynamic fashion that is dependent on gestational age and sex.