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Temporal patterns of gene expression of G1-S cyclins and cdks during the first and second mitotic cell cycles in
1Department of Obstetrics and Gynecology, University of Pennsylvania, Philadelphia 19104-6018, USA.
Abstract:
Cell-cycle progression in somatic cells is regulated by a family of cyclins and cyclindependent kinases (cdks) that form specific complexes as a function of cell-cycle progression. However, the transcript abundance of G1-S cyclins and cdks during the meiotic and mitotic cell cycles of mammalian embryos has not been previously reported. Using a reverse transcription-polymerase chain reaction (PCR) assay that detects changes in either mRNA abundance or polyadenylation state, we examined the relative levels of gene expression for the G1-S cyclins and cdks, as well as for p21, p27, and the retinoblastoma (Rb) gene in mouse oocytes, metaphase II-arrested eggs, and 1-2-cell embryos. The PCR products for cyclins D1, D3, and A, as well as cdk4, p21, and Rb, displayed similar levels in meiotically incompetent and competent oocytes, as well as in metaphase II-arrested eggs. The levels of PCR products for cyclin D2, p27, and two forms of cdk2 were similar in meiotically incompetent and competent oocytes but decreased during oocyte maturation. Finally, the level of PCR products for cyclin E and cdk2 gradually decreased during the progression from meiotically incompetent oocytes to metaphase II-arrested eggs. When the levels of PCR products for the G1-S regulatory genes were evaluated during the first and second mitotic cell cycles, four main patterns were found: 1) steady levels for cyclin A; 2) steady levels followed by a 2-3-fold increase during the G2 phase of the second mitotic cell cycle for cyclins D1, E, cdk2, and p21; 3) a transient increase during the S and/or G2 phases of the first mitotic cell cycle for p27, cyclin D3, and the two forms of cdk2; and 4) higher levels during the first cell cycle and then a decrease with lower levels during the second mitotic cell cycle for cyclin D2 and Rb. cdk4 expression displayed a combination of patterns 2 and 3. The increase in the amount of PCR product for the cdk4 gene during the first mitotic cell cycle was due to polyadenylation, whereas the increase in the amount of PCR product for cdk4, cdk2, and cyclins D1 and E in the second mitotic cell cycle was a product of activation of the embryonic genome.
Insights
This study reveals distinct patterns in G1-S cyclins and cyclin-dependent kinases (cdks) during mouse embryonic development. Gene expression changes during meiosis and early mitosis are crucial for cell cycle regulation.
Area of Science:
- Developmental Biology
- Molecular Biology
- Genetics
Background:
- Cell-cycle progression relies on cyclins and cyclin-dependent kinases (cdks).
- The expression patterns of G1-S cyclins and cdks in mammalian embryonic development are largely unknown.
- Understanding these patterns is vital for comprehending embryonic cell division.
Purpose of the Study:
- To investigate the transcript abundance of G1-S cyclins and cdks during mouse oocyte maturation and early embryonic cell cycles.
- To analyze the expression of key cell cycle regulators including p21, p27, and the retinoblastoma (Rb) gene.
- To identify distinct expression patterns during meiotic and mitotic phases of early development.
Main Methods:
- Utilized reverse transcription-polymerase chain reaction (RT-PCR) to assess mRNA abundance and polyadenylation states.
- Examined gene expression in mouse oocytes (meiotically incompetent and competent), metaphase II-arrested eggs, and 1-2-cell embryos.
- Analyzed expression profiles during the first and second mitotic cell cycles.
Main Results:
- Cyclins D1, D3, A, cdk4, p21, and Rb showed stable levels during oocyte maturation.
- Cyclin D2, p27, and cdk2 levels decreased during oocyte maturation.
- Cyclin E and cdk2 levels gradually decreased from immature oocytes to metaphase II-arrested eggs.
- Four distinct expression patterns were observed for G1-S regulatory genes during mitotic cell cycles, including steady, increasing, transient, and decreasing levels.
- Specific genes like cyclin D1, E, cdk2, and p21 increased during the G2 phase of the second mitotic cycle due to embryonic genome activation.
Conclusions:
- Mouse embryonic development involves dynamic regulation of G1-S cyclins and cdks.
- Expression patterns differ significantly between meiotic and mitotic cell cycles.
- Embryonic genome activation plays a role in regulating key cell cycle genes during early mitotic divisions.