Pum3 is dispensable for mouse oocyte maturation and embryo development in vitro

Pumilio3 (Pum3), an evolutionarily distant homologue of the classical RNA-binding protein PUF (PUMILIO and FBF) family member, is also involved in the process of RNA metabolism through post-transcriptional regulation. However, the functions of Pum3 in mouse oocyte maturation and preimplantation embryonic development have not been elucidated. By comparing RNA levels in different tissues, we found that Pum3 was widely expressed in multiple tissues, but moderately predominant in the ovary. Histochemical staining suggested that the PUM3 protein exhibits positive signals in oocytes, granulosa cells and theca cells of different follicle stages. Oocyte immunofluorescence results showed a slightly higher level of PUM3 protein in metaphase II compared with the germinal vesicle (GV) stage. After knockdown of Pum3 in GV oocytes using siRNA injection (siPUM3), no obvious defect was observed in the processes of GV breakdown and polar body extrusion during in vitro maturation (IVM) for the siPum3 oocytes. Compared with the control group, the siPUM3 group displayed no significant abnormality in the cleavage and blastocyst formation rate of these fertilized oocytes. Therefore, we can conclude that depletion of Pum3 does not affect mouse oocyte maturation and early embryonic development in vitro.

Ribosomal stress induces 2-cell embryo-like state transition of the mouse ESCs through p53 activation

Embryonic stem cells (ESCs) maintain a pluripotent state and genome integrity in long-term culture. A rare population of ESCs showing 2-cell embryo-specific gene expression is believed to play critical roles in sustainable pluripotency and genome stability. However, the molecular mechanism controlling this transition to a 2-cell embryo-like (2CL) state remains unclear. We carried out screening to search for the factors involved in 2CL state induction and found a ribosomal RNA processing factor, Pum3 to be a candidate. Increased 2CL state population accompanied with an accumulation of pre-ribosomal RNA and activated p53 in the Pum3-KO ESC. Furthermore, the increase of 2CL state cells in the Pum3-KO ESCs was completely abrogated by the deletion of p53. The DNA damage induced by the Ultraviolet light (UV) irradiation and Zeocin promoted the transition to a 2CL state in a p53-dependent manner. Thus, our study provides new insights into a 2CL state transition mechanism through stress-dependent p53 activation of ESCs.