Checkpoint kinases are required for oocyte meiotic progression by the maintenance of normal spindle structure and chromosome condensation

Checkpoint Kinase 1 Is a Key Signal Transducer of DNA Damage in the Early Mammalian Cleavage Embryo

After fertilization, remodeling of the oocyte and sperm genome is essential for the successful initiation of mitotic activity in the fertilized oocyte and subsequent proliferative activity of the early embryo. Despite the fact that the molecular mechanisms of cell cycle control in early mammalian embryos are in principle comparable to those in somatic cells, there are differences resulting from the specific nature of the gene totipotency of the blastomeres of early cleavage embryos. In this review, we focus on the Chk1 kinase as a key transduction factor in monitoring the integrity of DNA molecules during early embryogenesis.

Knockdown of Chk1 inhibits proliferation and promotes apoptosis in mouse granulosa cells and its regulation mechanism by miR-15a and miR-16

Checkpoint kinase 1 (Chk1) is a protein kinase which preserves the genome integrity, and works as an evolutionally conserved DNA damage response and cell cycle checkpoint. However, the functional roles and regulatory mechanism of Chk1 in mouse granulosa cells (GCs) have not been fully elucidated. In this study, by RNA interfering, Chk1 gene was knocked down in GCs. Knockdown of Chk1 inhibited proliferation and increased apoptosis of GCs (p < 0.05), respectively; in addition, cell cycle of GCs was arrested at S and G2/M phases. Further qRT-PCR results showed that cell cycle factors (Cyclin B1 and Cyclin D 1) and a marker gene of proliferation (PCNA) were downregulated (p < 0.001), while apoptotic factors (p53b, p21, caspase-3, and Bax) were upregulated (p < 0.01), which suggested that knockdown of Chk1 may inhibit proliferation, regulate cell cycle, and promote apoptosis at the transcriptional level in GCs. In vitro studies showed a negative correlation between Chk1 mRNA and miR-16 expression during follicular development. To elucidate the relationship between Chk1 and miR-15a/16, luciferase reporter plasmids were constructed and luciferase assays revealed that both miR-15a and miR-16 could bind to the 3' UTR of Chk1 mRNA, and significantly downregulate the protein level of Chk1 (p < 0.01), while miR-16, not miR-15a, could significantly decrease the mRNA level of Chk1 (p < 0.05). This result indicated that miR-16 directly induced Chk1 mRNA destabilization, while miR-15a regulated Chk1 expression through translational repression. Taken together, this study uncovered the roles of Chk1 in mouse granulosa cells and its regulation by miR-15a and miR-16 through different mechanisms.