Echinoderm Microtubule Associated Protein Like 1 Is Indispensable for Oocyte Spindle Assembly and Meiotic Progression in Mice

Abstract

Completion of the first meiosis is an essential prerequisite for producing a functionally normal egg for fertilization and embryogenesis, but the precise mechanisms governing oocyte meiotic progression remains largely unclear. Here, we report that echinoderm microtubule associated protein (EMAP) like 1 (EML1), a member of the conserved EMAP family proteins, plays a crucial role in the control of oocyte meiotic progression in the mouse. Female mice carrying an ENU-induced nonsense mutation (c.1956T > A; p.Tyr652∗) of Eml1 are infertile, and the majority of their ovulated oocytes contain abnormal spindles and misaligned chromosomes. In accordance with the mutant oocyte phenotype, we find that EML1 is colocalized with spindle microtubules during the process of normal oocyte meiotic maturation, and knockdown (KD) of EML1 by specific morpholinos in the fully grown oocytes (FGOs) disrupts the integrity of spindles, and delays meiotic progression. Moreover, EML1-KD oocytes fail to progress to metaphase II (MII) stage after extrusion of the first polar body, but enter into interphase and form a pronucleus containing decondensed chromatins. Further analysis shows that EML1-KD impairs the recruitment of γ-tubulin and pericentrin to the spindle poles, as well as the attachment of kinetochores to microtubules and the proper inactivation of spindle assembly checkpoint at metaphase I (MI). The loss of EML1 also compromises the activation of maturation promoting factor around the time of oocyte resumption and completion of the first meiosis, which, when corrected by WEE1/2 inhibitor PD166285, efficiently rescues the phenotype of oocyte delay of meiotic resumption and inability of reaching MII. Through IP- mass spectrometry analysis, we identified that EML1 interacts with nuclear distribution gene C (NUDC), a critical mitotic regulator in somatic cells, and EML1-KD disrupts the specific localization of NUDC at oocyte spindles. Taken together, these data suggest that EML1 regulates acentrosomal spindle formation and the progression of meiosis to MII in mammalian oocytes, which is likely mediated by distinct mechanisms.

Azoxystrobin exposure impairs meiotic maturation by disturbing spindle formation in mouse oocytes

“…Indeed, we observed that MTOC integrity was reduced after AZO treatment. Similar to our observation, it has been reported that a partial decrease in MTOC integrity caused severe spindle abnormalities, but partly disturbed PBE (Wang et al, 2017;Yin et al, 2021).…”

LSM14B controls oocyte mRNA storage and stability to ensure female fertility

“…Our results suggest that significantly increased levels of p-CDK1 (Y15) are probably the causes of the meiotic defects in Lsm14b KO oocytes. Previous studies have shown that PD166285, a specific inhibitor of WEE1/2 kinases, could be able to activate MPF by reduced levels of CDK1 (Y15) phosphorylation in mouse oocytes [ 44 , 45 ]. Western blot analysis showed that PD166285 treatment dramatically reduced the levels of CDK1 (Y15) phosphorylation in Lsm14b KO GV oocytes at the end of 20 h IVM (Fig.…”

“…Low levels of MPF activity are one of the causes of PN formation and meiotic defects [ 45 ]. Our observation that the Lsm14b KO oocytes failed to assemble the MII spindle after extrusion the PB1, but instead entered the interphase and formed PN.…”

“…Furthermore, WB analysis of the p-CDK1 revealed that the levels of p-CDK1 are significantly reduced in Lsm14b KO MII oocytes. Likewise, Eml1 knockdown (KD) impairs MPF activity around the time of oocyte resumption, ultimately leading to the formation of PN [ 45 ]. Similarly, Mastl is required for the rapid rise of CDK1 activity that is needed for the entry into MII stage, and Mastl -null oocytes reassembled a nuclear structure containing decondensed chromatin and failed to enter MII because they maintain high levels of p-CDK1 [ 44 ].…”

The transcriptome landscapes of allantochorion and vitelline-chorion in equine day 30 conceptus

“…Here we mainly revealed that between AC and VC of day 30 equine embryos, there are 484 differential expressed genes. Among these, 305 genes are shown specifically up-regulated in enlarging AC, and it is not surprising that these genes are mainly related to cell mitosis regulation, for example, NDC80 , NUF2 , SPC24 , and SPC25 , which compose the nuclear division cycle 80 (Ndc80) complex to influence mitosis ( Gao et al, 2020 ) and CCNB1 , EML1 , AURKB , AURKA , SPC25 , which are primarily involved in mitotic spindle organization ( Villegas et al, 2014 ; Cheng et al, 2021 ; Yin et al, 2021 ). These results could benefit our understanding of the physiological state of preimplantation AC, and the key genes and pathways controlling the AC enlargement.…”