Abstract
The primary function of cyclin‐dependent kinases (CDKs) in complex with their activating cyclin partners is to promote mitotic division in somatic cells. This canonical cell cycle‐associated activity is also crucial for fertility as it allows the proliferation and differentiation of stem cells within the reproductive organs to generate meiotically competent cells. Intriguingly, several CDKs exhibit meiosis‐specific functions and are essential for the completion of the two reductional meiotic divisions required to generate haploid gametes. These meiosis‐specific functions are mediated by both known CDK/cyclin complexes and meiosis‐specific CDK‐regulators and are important for a variety of processes during meiotic prophase. The majority of meiotic defects observed upon deletion of these proteins occur during the extended prophase I of the first meiotic division. Importantly a lack of redundancy is seen within the meiotic arrest phenotypes described for many of these proteins, suggesting intricate layers of cell cycle control are required for normal meiotic progression. Using the process of male germ cell development (spermatogenesis) as a reference, this review seeks to highlight the diverse roles of selected CDKs their activators, and their regulators during gametogenesis.
Highlights
Despite extensive research delineating the various roles of the cyclin-dependent kinases (CDKs), cyclins, and Speedy proteins during gametogenesis, pertinent questions remain even surrounding the best-characterized members of these protein families, CDK2, CDK4, the Eand D-type cyclins, and Speedy A
Aal chains of spermatogonia in these mice were observed to inappropriately retain GFRA1 expression, which is downregulated in wild-type spermatogonia of the same stage. These results suggest that regulation of CDK2 activity is required to appropriately complete the developmental switch between gonocytes and spermatogonia, and the resultant differentiation status of abnormal spermatogonial stem cells (SSCs) is not sufficient to support their further differentiation [168]
The small number of Cdkn2cÀ/À mice that survive until adulthood exhibits immaturity of germinal tissues including testis and ovaries, which suggests that this gene might be necessary for the normal differentiation of germ cells [185]
Summary
The primary function of cyclin-dependent kinases (CDKs) in complex with their activating cyclin partners is to promote mitotic division in somatic cells. The synaptonemal complex lateral and central elements are disassembled, a process which is completed by diakinesis Throughout these stages, sister chromatid arms remain closely connected via cohesins [74], but paired homologous chromosomes remain linked solely at meiotic crossover sites. Successful crossover resolution allows the segregation of homologs into two daughter cells and completes the reciprocal exchange of maternal and paternal DNA at the resolved crossover site Achieving this genetic exchange of information during meiotic prophase I is a hallmark of meiotic division and is the major determinant of heterogeneity within the genome of developing germ cells [55,83,84,85,86,87]
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