PP2Acs Are Essential For The Completion Of Meiosis ? In Mouse Oocyte

Mammalians produce gametes by meiosis.In females,it starts from the embryonic stage and end after the fertilization with sperm.Meiosis in mammalian oocytes is a precisely controlled process.Disturbance involved in this process may cause aneuploidy and lead to female subfertility or infertility.The phosphorylation and dephosphorylation of proteins play essential roles in the meiosis process.Protein phosphatase 2A(PP2A)family is the most abundant phosphatases specific for serine/threonine phosphorylation in mammalian cells and mediates various biological processes.Vast of studies have demonstrate PP2A is important for the development and maturation of mammalian oocytes,by using chemical inhibitors or RNA interferes.However,genetically inactivation of PP2A in oocytes of mammalian model has not been achieved,which is necessary for study it's in vivo roles.Here we established a conditional knockout mouse model in which the two genes coding for catalytic subunits of PP2A(PP2Acs),Ppp2ca and Ppp2cb,were deleted in mouse oocytes from the developmental stage.The loss of PP2Acs in oocytes resulted in female infertility.Although the ovarian morphology,the quantity of fully grown oocytes and the induction of ovulation were normal,the eggs produced by the knockout mice could not give rise to 2-cell stage embryos.This indicates the infertility is oocyte-autonomous.Looking into the meiotic maturation process we found loss of PP2Acs did not perturb the meiotic entrance,but disrupted the completion of first meiotic division.Chromosomal alignment was abnormal and homologous chromosomes could not segregate in the knockout oocytes.The self assembly of microtubule organization centers(MTOCs)was disrupted and the activation of APC/C was delayed,along with the defect of chromosomal alignment.The stretching forces exerted on homologous chromosomes in knockout oocytes were lower.Examination of the kinetochore fibers revealed that in knockout oocytes homologous chromosomes lack correct kinetochores-microtubule attachments on their sister kinetochore pairs.We found the phosphorylation status of KMN network,which is controlled by the counteraction of Aurora kinase B(AURKB)and PP2A in mitosis,was increased on the kinetochore of the knockout oocytes.So we test whether the meiotic defects resulted from the PP2Acs deficiency could be restored by the inhibition of AURKB/C in oocytes using AURKB/C inhibitor hesperadin.We found after hesperadin treatment,the stretching forces on homologous chromosomes were restored significantly,and the kinetochore-microtubule attachments partly restored.However,the chromosomal alignment and segregation had no significant change after hesperadin treatment in knockout oocytes.The results indicated the AURKB/C-PP2A counteraction on kinetochores existed in mouse oocyte meiosis I,but was not the primary cause of the meiotic defects in the PP2Acs deficiency oocytes.Taken together,we showed catalytic subunits of PP2A play essential roles in oocytes meiosis I,regulating the chromosomal alignment and segregation.Ablation PP2Acs in the mouse oocytes in vivo would result in female infertility.Moreover,counteractions between AURKB/C and PP2A on homologous chromosomes were involved in meiosis I of mouse oocyte.As PP2A certainly have multiple functions in meiosis process,phosphorylation and microtubule attachment on the kinetochores may be only a portion of the targets that PP2A regulates.What are the main functions of PP2A in chromosome alignment during meiosis I,which are the crucial causes for the defects of PPACs deficiency oocytes,need further investigation.