Regulatory protein of the MTREX-exosome complex involved in the synthesis of the 60S ribosomal subunit. Participates in an early cleavage of the pre-rRNA processing pathway in cooperation with NVL (By similarity). Required for blastocyst formation, is necessary for RNA transcription, processing and/or stability during preimplantation development (PubMed:21799883). Isoform 1 interacts (through WDR repeats) with NVL; the interaction is independent of RNA or pre-60S ribosome particles. Isoform 2 does not interact with NVL. Interacts with MTREX; the interaction dissociation in a late stage of rRNA synthesis is required for appropriate maturation of pre-60S particles and depends on the ATPase activity of NVL. Nucleolar location depends on active PolI transcription of pre-rRNA. Expressed at low levels in MII oocytes and 1-cell embryos and increases through subsequent cleavage stage divisions. The peak of mRNA expression occurs at the morula stage, with a slight decrease in blastocyst embryos.