title: Deletion of Mylk1 in oocytes causes delayed morula-to-blastocyst transition and reduced fertility without affecting folliculogenesis and oocyte maturation in mice.
abstract: The mammalian oocyte undergoes two rounds of asymmetric cell divisions during meiotic maturation and fertilization. Acentric spindle positioning and cortical polarity are two major factors involved in asymmetric cell division, both of which are thought to depend on the dynamic interaction between myosin II and actin filaments. Myosin light chain kinase (MLCK), encoded by the Mylk1 gene, could directly phosphorylate and activate myosin II. To determine whether MLCK was required for oocyte asymmetric division, we specifically disrupted the Mylk1 gene in oocytes by Cre-loxP conditional knockout system. We found that Mylk1 mutant female mice showed severe subfertility. Unexpectedly, contrary to previously reported in vitro findings, our data showed that oocyte meiotic maturation including spindle organization, polarity establishment, homologous chromosomes separation, and polar body extrusion were not affected in Mylk1(fl/fl);GCre(+) females. Follicular development, ovulation, and early embryonic development up to compact morula occurred normally in Mylk1(fl/fl);GCre(+) females, but deletion of MLCK caused delayed morula-to-blastocyst transition. More than a third of embryos were at morula stage at 3.5 Days Postcoitum in vivo. The delayed embryos could develop further to early blastocyst stage in vitro on Day 4 when most control embryos reached expanded blastocysts. Our findings provide evidence that MLCK is linked to timely blastocyst formation, though it is dispensable for oocyte meiotic maturation.
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Qiu-Xia
authors.initials: QX
authors.lastname: Liang
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Qing-Hua
authors.initials: QH
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Shu-Tao
authors.initials: ST
authors.lastname: Qi
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Zhong-Wei
authors.initials: ZW
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Meng-Wen
authors.initials: MW
authors.lastname: Hu
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Xue-Shan
authors.initials: XS
authors.lastname: Ma
authors.affiliation: Model Animal Research Center and MOE Key Laboratory of Animal Models of Disease, Nanjing University, Nanjing, China.
authors.forename: Min-Sheng
authors.initials: MS
authors.lastname: Zhu
authors.affiliation: Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri.
authors.forename: Heide
authors.initials: H
authors.lastname: Schatten
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China wangzb@ioz.ac.cn.
authors.forename: Zhen-Bo
authors.initials: ZB
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China sunqy@ioz.ac.cn.
authors.forename: Qing-Yuan
authors.initials: QY
authors.lastname: Sun
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D033481:Chromosomes, Mammalian / Q000235:genetics; D005260:Female; D005298:Fertility / Q000235:genetics* / Q000502:physiology; D005306:Fertilization / Q000235:genetics; D017353:Gene Deletion; D007246:Infertility / Q000235:genetics / Q000503:physiopathology; D008540:Meiosis / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D009028:Morula / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000235:genetics* / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D006080:Ovarian Follicle / Q000502:physiology*; D059705:Polar Bodies / Q000502:physiology; D011247:Pregnancy; D008941:Spindle Apparatus / Q000235:genetics / Q000502:physiology
chemical_list: D009219:Myosin-Light-Chain Kinase
keywords: meiosis; morula-to-blastocyst transition; mouse oocyte; myosin II; myosin light chain kinase (MLCK)