Depletion of maternal SMC2 impaired pronuclear activity
Since the pronuclear morphology was altered, we hypothesized that the
pronuclear function in SMC2 depleted zygotes might be affected. We
performed BrdU staining to show DNA replication.
SMC2-/+ zygotes underwent the DNA replication process,
however, the activity decreased by more than half compared with the
control (Fig. 4D and E).
To assess whether the transcription activity was affected by the lack of
maternal SMC2, we selected several embryo development related genes that
should be transcription-activated in zygotes. After fertilization, new
transcripts need to be generated along with protein synthesis
corresponding to minor ZGA (Yu et al., 2016). This progress appears in
the late zygote and two-cell stage. Therefore, we chose fertilized PN5
zygotes to detect the transcription levels.
First, we investigated the expression of transcription-related genes
(pre-rRNA, FBL, and B23 ) (Liu et al., 2019). We found that
all of the selected gene expressions decreased at the late zygote stage
in SMC2 depleted embryos compared to the control group (Fig. 4F).
Then, we selected several translation-related genes (Rpl26,
Rps13, and Rps20 ), and the results showed that these gene
expressions were also significantly lower in the SMC2−/ + group, while they were activated normally in the
control along with embryonic development (Fig. 4G).
The major aim for transcription in zygotes is the preparation for
successful ZGA (Li et al., 2013). Further, we detected several
representative genes that were highly transcribed during minor ZGA in
late zygotes (MuERV-L , Dppa4, Sertad1 ) (Kigami et al.,
2003). Notably, expressions of all these genes was down-regulated in
SMC2 −/ + embryos (Fig. 4H). The disorganized zygotic
genome activation may lead to the zygote arrest in SMC2-deficient
embryos.