Abstract
Maternal factors are required for oocyte maturation and embryo development. To better understand the role of DNA methyltransferase 1 (Dnmt1) in oocyte maturation and embryo development, small interfering RNA (siRNA) was conducted in porcine oocytes. In this study, our results showed that Dnmt1 localized in oocyte cytoplasm and its expression displayed no obvious change during oocyte maturation. When siRNAs targeting Dnmt1 were injected into germinal vesicle (GV) stage oocytes, Dnmt1 transcripts significantly decreased in matured oocytes (P<0.05). After Dnmt1 knockdown in GV stage oocytes, the significant reduction of glutathione content, mitochondrial DNA copy number, glucose-6-phosphate dehydrogenase activity and expression profiles of maternal factors and the severely disrupted distribution of cortical granules were observed in MII stage oocytes (P<0.05), leading to the impaired oocyte cytoplasm. Further study displayed that Dnmt1 knockdown in GV stage oocytes significantly reduced the development of early embryos generated through parthenogenetic activation, in vitro fertilization and somatic cell nuclear transfer (P<0.05). In conclusion, Dnmt1 was indispensable for oocyte cytoplasmic maturation, providing a novel role for Dnmt1 in the regulation of oocyte maturation.
Highlights
The ability of oocytes to support the subsequent embryonic development involves nuclear and cytoplasmic maturation [1, 2]
The quality of oocyte cytoplasmic maturation is closely correlated with glutathione (GSH) content, mitochondrial DNA copy number and cortical granule (CG) distribution, etc. [2, 5, 6], and the stored maternal factors take a key role in oocyte cytoplasmic maturation [2, 7]
When small interfering RNA (siRNA) were injected into germinal vesicle (GV) stage oocytes, siRNA-replication foci domain (RFD), siRNA-bromo adjacent homology domain (BAH) or siRNA-DCM resulted in a 66%, 74% or 79% reduction of DNA methyltransferase 1 (Dnmt1) transcripts in matured oocytes, respectively, significantly lower than those in the controls noninjected or injected with water or negative siRNAs (Fig 2, P
Summary
The ability of oocytes to support the subsequent embryonic development involves nuclear and cytoplasmic maturation [1, 2]. Oocyte nuclear maturation refers to the dynamics of chromosome separation, while cytoplasmic maturation involves the redistribution of cytoplasmic organelles and the storage and progressing of mRNA and proteins, and is the core factor for achieving the subsequent embryonic development [3, 4]. Oocyte cytoplasmic maturation is a complex progress and affected by multiple factors [1]. The quality of oocyte cytoplasmic maturation is closely correlated with glutathione (GSH) content, mitochondrial DNA (mtDNA) copy number and cortical granule (CG) distribution, etc. [2, 5, 6], and the stored maternal factors take a key role in oocyte cytoplasmic maturation [2, 7]. The quality of oocyte cytoplasmic maturation is closely correlated with glutathione (GSH) content, mitochondrial DNA (mtDNA) copy number and cortical granule (CG) distribution, etc. [2, 5, 6], and the stored maternal factors take a key role in oocyte cytoplasmic maturation [2, 7].
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