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Comment |
Histone methyltransferase SMYD3 regulates the expression of transcriptional factors during bovine oocyte maturation and early embryonic development. Bai H et al. (2015) Mammalian early embryonic development is controlled by a unique program of gene expression, and involves epigenetic reprogramming of histone modifications and DNA methylation. SET and MYND domain-containing protein 3 (SMYD3) is a histone H3 lysine 4 methyltransferase that plays important roles in transcription regulation. The expression of SMYD3 has been studied in some cancer cell lines. However, its expression in oocytes and embryos has not previously been reported. Here, we detected the SMYD3 mRNA and found that it was expressed throughout bovine oocyte in vitro maturation and early embryonic development. Microinjection of SMYD3 siRNA at germinal vesicle stage decreased the transcription level of NANOG, and blocked the development of in vitro fertilization embryos at 4-8 cell stage. Conversely, Microinjection of SMYD3 siRNA at pronuclear stage did not affect early embryonic development. Our findings suggest that SMYD3 regulates the expression of NANOG, and plays an essential role in bovine early embryonic development.//////////////////
Modifications of SMYD3 Occurred During Oocyte Maturation,
Instead of after Fertilization, with Subsequent Effects on Early EmbryoDevelopment. Yan Li, Xia Wu, Haidong Bai, Penghui Xin, Yongli Yue, Xudong Ao,
and Haiquan Yu. Inner Mongolia University, Hohhot, China
SMYD3 (SET and MYND domain-containing protein 3), a histone H3K4-
specific dimethyltransferase and trimethyltransferase, contains two conserved SET
and MYND domains. The SET domain acts as methyltransferase; the MYND domain
is a zinc finger motif which is involved in protein-protein interaction and recognizes
specific sequence of DNA. SMYD3 regulate downstream genes activity and
expression by maintaining H3K4 trimethylation; the trimethylated H3K4 tends to be
associated with gene-active transcription. It has been reported that SMYD3 and
Meisetz are H3K4-specific trimethyltransferases. During bovine oocyte maturation
H3K4 is trimethylated from pre-meiotic to pachytene stages. However, the transcript
of Meisetz is only detected in germ cells from pre-meiotic stage to pachytene stage. It
is implied that there might exist other methyltransferases for the maintenance of
H3K4me3 trimethylation after pachytene, and SMYD3 is probably a potential
candidate. In the present study, two experiments were designed to test this hypothesis.
In Experiment 1, SMYD3-siRNAs were injected into bovine GV oocytes and
zygotes; then SMYD3 mRNA were detected after oocyte maturation and embryo
development. In the injection group, the relative expression of SMYD3 mRNA
decreased to 18% of that in the non-injection group. However, there was no
significant difference in maturation rate between SMYD3-siRNA injection group and
Non-siRNA (nonsense siRNA) injection group (67.14% vs. 66.06%, P.0.05); these
results indicated that the mRNA level of SMYD3 had no effect on oocyte maturation
in vitro. After maturation and fertilization of the SMYD3-siRNA injected GV
oocytes, the cleavage rates of SMYD3-siRNA injection group, no injection group
DOs (denuded oocytes) and non-siRNA injection group were 44.07%, 42.8%, and
42.95% respectively. However, the 8-cell and blastocyst development were
significantly lower in SMYD3-siRNA injection group than in no injection group
DOs and non-siRNA injection group (3.29% vs. 17.51%, 12.82%; 0% vs. 10.89%,
8.33%; P,0.01), respectively. These results suggested that SMYD3 may activate
some important genes which play key roles in embryo development from 2-cell stage
to blastocyst. In Experiment 2, zygotes derived from IVM and IVDF were injected
with SMYD3-siRNA. After culture of these injected zygotes, no statistical differences
were observed in the cleavage rates (55.88% vs. 56.88% vs. 58.43%), 8-cell
development (32.35% vs. 34.94% vs. 31.9%), and blastocyst development (23.83%
vs. 29.0% vs. 24.01%) among the SMYD3-siRNA, non-siRNA injection group and
normal fertilized oocytes. These results suggest that the modifications of SMYD3
occurred during oocyte maturation, instead of after fertilization, and had subsequent
effects on early embryo development. (SSR 2010)
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